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Analysis of the sawmilling practices in the state of Durango, Mexico Zavala Zavala, David 1981

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ANALYSIS OF THE SAWMILLING PRACTICES IN THE STATE OF DURANGO, MEXICO by DAVID ZAVALA ZAVALA B.Sc. Escuela Nacional de Ag r i c u l t u r a Chapingo, Mexico, 1972 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of Forestry We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1981 © David Zavala Zavala, 1981 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by h i s or her representatives. I t i s understood that copying or p u b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of PAXtTs T 2y The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date April /?f/ DE-6 (2/79) i ABSTRACT Control of sawmilling operations, including log bucking practices and sawing processes, i s one reasonable solution to the Mexican lumber shortage problem. This i s p a r t i c u l a r l y so i f a v a i l a b l e techniques to improve sawmill e f f i c i e n c y can be included i n normal manufacturing processes. Sawmilling analyses were c a r r i e d out to assess the r e l a t i o n s h i p of log volume input to lumber volume recovery, evaluated i n actual and nominal dimensions. Six sawmills were selected, based on the most frequent type of band headrig i n the State of Durango. A s t a t i s t i c a l l y representative sample size of sawlogs was used in each sawmill, amounting to a t o t a l of 870 logs. The proportion of log volume breakdown into lumber and byproduct volumes was analyzed. I t was found that the proportion of chippable residue accounted for 26 per cent of the t o t a l log volume throughput. This suggests the p o s s i b i l i t y of a l l o c a t i n g a large amount of this volume to pulp m i l l s , rather than continuing present practice of burning as waste with no economic return. Sawlog types and lumber recovery c h a r a c t e r i s t i c s under normal manufacturing processes were included in the study. A s i g n i f i c a n t difference of 10.32 per cent was found between the two expressions of lumber recovery percentages based on actual and on nominal dimensions. Major emphasis, however, was given to the analysis of log bucking p r a c t i c e s , lumber dimensions, and sawing v a r i a t i o n , i n respect to th e i r i i e ffect on both potential lumber recovery percentage and potential revenue to the sawmill industry. I t was found that excessive log trim allowance resulted i n a 4.34 per cent wastage of the t o t a l log volume input at the trim saw. Over allowance i n lumber thickness dimension resulted i n a 3.55 per cent loss of the t o t a l lumber volume recovered, and sawing variation accounted for a 2.76 per cent loss. I t was concluded that closer control of sawmilling operations to minimize poor bucking practices and sawing variation has s i g n i f i c a n t potential for lumber recovery increment. I t was also concluded from this study, that future sawmill analysis would require inclusion of log length and sawing variation i n an assessment of sawmill performance. i i i TABLE OF CONTENTS Page ABSTRACT i TABLE OF CONTENTS i i i LIST OF TABLES v i LIST OF FIGURES v i i i ACKNOWLEDGEMENTS i x 1. INTRODUCTION 1 2. LITERATURE SURVEY 4 2.1 Lumber Recovery 4 2.1.1 D e f i n i t i o n 4 2.1.2 Log C h a r a c t e r i s t i c s 5 2.1.2.1 Sweepy Logs 7 2.1.2.2 Taper Logs 7 2.1.2.3 Infested Logs 8 2.1.2.4 Logs from Dead Trees 9 2.1.2.5 C u l l Logs 9 2.1.2.6 Log Diameter 10 2.1.3 Type of Sawmill 10 2.1.4 Cutting Patterns 13 2.1.5 Log Scaling 14 2.1.6 Log Sample Size 16 2.2 Log-Lumber and Byproduct Proportion 18 2.2.1 Volume and Weight Method 19 2.2.2 Saw Kerf and Cutting Patterns Method 21 i v Page 2.3 Quality Control 25 2.3.1 Log Length Allowance 25 2.3.2 Lumber Dimension Allowance 26 3. MATERIALS AND METHODS 33 3.1 Lumber Recovery 33 3.1.1 Sawmill Selection 33 3.1.2 Log Sample Size 34 3.1.3 Log Scaling 34 3.1.4 Log and Lumber Grading 35 3.1.5 Sawmilling Procedure 36 3.1.6 Lumber Y i e l d Evaluation 36 3.2 Log-Lumber and Byproduct Proportion 37 3.3. Quality Control 38 3.3.1 Log-Length Allowance 38 3.3.2 Lumber Dimension Allowance 38 3.3.2.1 Board Thickness Selection 38 3.3.2.2 Sample Size and Board Measurements ... 39 3.3.2.3 Board Sawing. V a r i a t i o n 40 3.3.2.4 Target Size Determination 40 4. RESULTS AND DISCUSSIONS 42 4.1 Raw Material C h a r a c t e r i s t i c s 42 4.1.1 Raw Ma t e r i a l 42 4.1.2 Log Sample Size 43 V Page 4.2 Characteristics of Lumber Recovery 44 4.2.1 Lumber Thickness 44 4.2.2 Lumber Grades 44 4.3 Log Volume and Lumber Volume Relationship 45 4.3.1 Lumber Recovery Percentage 45 4.3.2 Lumber Volume Allowance 46 4.3.3 Log-Lumber and Byproduct Proportion 47 4.4 Quality Control 49 4.4.1 Log Length 49 4.4.2 Sawing Variation 50 4.4.3 Potential Lumber Recovery Increment by Cutting to Target Thickness 50 4.4.4 Potential Lumber Recovery Increment by Reducing Sawing Variation 52 4.5 Economic Analysis 53 5. CONCLUSIONS AND RECOMMENDATIONS 55 5.1 Conclusions 55 5.2 Recommendations 57 BIBLIOGRAPHY 58 TABLES 67 FIGURES 87 v i LIST OF TABLES Table Page 1 Proportion of lumber, chippable residue and sawdust by log diameter range and sawmill type (18, 29, 35, 37, 39, 41) 67 2 Summary of references i n log-lumber and byproduct r e l a t i o n s h i p 68 3 Type and number of sawmills i n the State of Durango .. 69 4 Log grades 70 5 Sawlog d i s t r i b u t i o n by length and diameter categories 71 6 Number of logs and volumes by grading classes 72 7 Number of logs sampled to give 95 per cent confidence i n t e r v a l about the population mean 73 8 Volume and percentage of pieces of lumber recovered by thickness classes 74 9 Lumber volume recovery by grade categories (based on log volume) 75 10 D i s t r i b u t i o n of lumber y i e l d by nominal and actual dimension of thickness, width, length and volume 76 11 Allowance and over-allowance i n volume for d i f f e r e n t board thickness 77 12 Nominal, actual, and allowance volumes related to lumber recovery based on actual and nominal dimension 79 13 Log-lumber and byproducts proportions 80 14 Over-length allowance volume by log length categories 81 15 Log volume l o s t by over length with 4 and 6 inches nominal allowance 82 16 Thickness v a r i a t i o n d i s t r i b u t i o n for nominal 3/4-inch boards 83 17 Mean thickness - sawing v a r i a t i o n and target thickness for nominal 3/4 inch boards 84 v i i Table Page 18 Potential lumber volume recovery in 3/4 inch nominal lumber by cutting to target thickness and by reducing sawing variation 85 19 Potential lumber recovery in different nominal thickness by cutting to target thickness and by reducing sawing variation 86 v i i i LIST OF FIGURES Page 1 D i s t r i b u t i o n of logs by diameter classes 87 2 D i s t r i b u t i o n of logs by length classes 88 3 D i s t r i b u t i o n of logs by grades and volumes 89 4 Proportion of d i f f e r e n t lumber thicknesses produced under nominal manufacturing conditions 90 5 Thickness v a r i a t i o n i n 3/4 inch nominal lumber 91 i x ACKNOWLEDGEMENT I am greatly i n debt to the Consejo Nacional de Ciencia y Tecnologia (CONACYT) for the scholarship granted during the study period at the Uni v e r s i t y of B r i t i s h Columbia. G r a t e f u l l y acknowledged i s the support of the I n s t i t u t o Nacional de Investigaciones Forestales (INIF), which allowed working time to c o l l e c t and analyze the data used i n th i s thesis. Special thanks are due to Dr. N.C. Franz for d i r e c t i n g the write-up, for his constant assistance and encouragement during the most d i f f i c u l t part of my task. Thanks are also due to Dr. R.W. Kennedy for his valuable comments and to Dr. L. Paszner for his advice and comments. Appreciated also i s the help of Mr. J . Rocha i n c o l l e c t i n g and analyzing the data. Special thanks are due to Tom and Dobriela, for the i r constant encouragement. 1 1. INTRODUCTION The sawmill industry i n the State of Durango, with 124 m i l l s , represents approximately 12 per cent of the t o t a l number of sawmills in Mexico (16, 103). Some of the most outstanding c h a r a c t e r i s t i c s of the sawmill industry are: (1) the large number of small sized m i l l s with nearly 70 per cent of them processing less than 20,000 board feet of mixed pine species per s h i f t ; (2) high manpower requirements, with almost 2 men per 1000 board feet of lumber produced, or with an average of 28 workers per m i l l ; (3) low l e v e l of automation, which i s r e f l e c t e d i n the high number of employees and in the equipment c h a r a c t e r i s t i c s ; (4) low c a p i t a l investment with most of the m i l l s having just the required equipment to breakdown the logs i n the simplest way, i . e . a single headrig, an edger with three c i r c u l a r saws and a single trim saw (114, 115). These c h a r a c t e r i s t i c s have a d i r e c t e f f e c t on lumber volume produced per unit of time and on sawmill e f f i c i e n c y . Sawmill u t i l i z a t i o n e f f i c i e n c y i s measured as the percentage of sawn lumber volume produced from the log volume throughput. Many factors a f f e c t i n g sawmill e f f i c i e n c y are not taken into account i n most sawmill assessments, although they have a d e f i n i t e influence on lumber volume recovered from log volume input, and thus, on the net revenue to the enterprises. 2 Some of these factors are: (1) the characteristics and working conditions of the equipment, particularly the headrig; (2) characteristics of raw material, such as log grade and log size; (3) characteristics of the output defined by lumber grades and lumber dimensions; (4) log length allowance practices and log volume lost by bucking errors; (5) lumber dimension allowance and excessive oversizing to avoid skip during dressing due to sawing variation (2, 4, 12, 14, 29, 30, 41, 43, 95, 101). Log length variation and over-thickness allowance analyses generally are not included in evaluating sawmill efficiency. It has been pointed out by some researchers that these two factors are of great importance due to their effect on lumber volume recovery, and thus, on the revenue to the enterprises. However, lumber recovery analyses have shown the benefits from adaption of quality control programs to monitor log length and sawing variation (2, 4, 11, 13, 30, 56, 68, 76, 102, 106, 107, 115). The main purpose of this study was to determine the dimensions and volume of lumber that is produced under current industrial manufacturing practices from the various grades and sizes of logs available to sawmills in the State of Durango. A major emphasis was given to evaluate log bucking practices and their effect on lumber wasted at the trim saw. To cope with the lack of information on lumber thickness variation and lumber over-dimension effects on lumber recovery variation, analysis of 3 these factors was also Included as the main objective. With the results of the analysis i t i s expected to identify the main sources of errors under normal sawmilling practices and suggest the correcting actions to increase lumber y i e l d . 4 2. LITERATURE SURVEY 2.1 Lumber Recovery 2.1.1 D e f i n i t i o n The e v a l u a t i o n of a sawmi l l ope ra t i on , con s i de r i ng equipment, raw m a t e r i a l c h a r a c t e r i s t i c s and lumber y i e l d , i n terms of lumber- log r e l a t i o n s h i p , u s u a l l y has been expressed i n three d i f f e r e n t ways: Lumber Recovery Fac to r (LRF), Overrun, and Lumber Recovery Ra t i o (LRR). Lumber Recovery Factor i s def ined as the nominal board fee t of lumber recovered per cub i c foot of log input to a sawmi l l (22, 105). Thus, LRF i s the r a t i o of nominal lumber recovery (N) to the cub ic sca le of a l o g (V) . Anything that e f f e c t s N or V w i l l i n f l u e n c e LRF (43) . Overrun i s de f ined as the d i f f e r e n c e between board foot volume, est imated by va r i ou s l og s c a l i n g r u l e s , and the a c t u a l lumber recovery (51, 55, 59 ) . Overrun i s u s u a l l y expressed as a percentage determined from the equat ion (61, 110): Lumber Recovery Ra t i o (LRR) i s def ined as the r a t i o of cub ic volume of lumber recovered to the cub i c volume of logs sawn. I t may, f o r convenience, be based on l og and lumber weights which prov ide an i n d i r e c t i n d i c a t i o n of volume subject to e r r o r s due to dens i t y v a r i a t i o n s (51). I t i s sometimes expressed as Per Cent Recovery (84) . I r r e s p e c t i v e of the way expressed, the lumber recovery or the lumber- log r e l a t i o n s h i p va lues obtained w i l l change accord ing to the Overrun % = Lumber t a l l y - n e t s ca l e Net s ca le x 100 [1] 5 following factors: log diameter, log length, log taper, type and number of defects, sawmill types, sawmill recovery practices or product mix, dimension of lumber produced, saw kerf, sawing variation, condition and maintenace of m i l l equipment, and the a b i l i t y , conscientiousness and fatigue level of the sawyer or other m i l l personnel (43, 101). Many studies have been carried out to determine lumber recovery associated with some of the variables l i s t e d . The selection of the variables mostly depend on the study objectives. Type and number of defects in logs, combined with log diameters, log length, and taper have been used in lumber recovery studies to formulate log grading rules. Analysis of sawmilling processes associated with equipment, cutting patterns and log characterisics, has become increasingly important in the last 15 years. Small logs in particular have received much attention recently in lumber recovery evaluations. 2.1.2 Log Characteristics The size and volume of lumber that is produced under current manufacturing practices has a direct relationship with the various grades and sizes of logs (75). The relationship between log surface character-i s t i c s and the lumber yield produced, usually has been used to develop log grading and tree evaluation systems (113). In some instances, i f log grading rules have already been developed, the lumber grade yields and recovery ratios obtained from various log types are used to update grade and volume recovery when ut i l i z a t i o n standards, manufacturing practices, quality or marketing requirements have changed (89, 93). Lane et a l . (75) determined the relationship between the size and volume of lumber that would be produced from various grades and sizes of Sitka spruce with 6 the purpose of developing a tree grading system. The sample size of long merchantable logs was not intended to be representative of a t y p i c a l log mix; rather, the objective was to obtain adequate saw log recovery i n f o r -mation for the f u l l range of size and q u a l i t y of timber a v a i l a b l e . Woodfin ej: a l . (113) used lumber y i e l d values and log surface character-i s t i c s to develop a log grading and tree evaluation system for western hemlock. The sample of 1165 sawn logs yielded a cubic lumber recovery of 48 per cent of the gross cubic volume. Kerbes and Mcintosh (70) developed a log and tree c l a s s i f i c a t i o n system as a guideline i n predicting optimum end-use values from spruce, based on exterior log c h a r a c t e r i s t i c s and end-product values. The most important character-i s t i c s i n the samples examined were top diameter, the number of clear sides and the percentage of defect due to rot and sweep. Bailey and Dobie (6) concluded a lumber quality study of 1086 trembling aspen logs and 428 balsam poplar logs, and developed a four grade q u a l i t y system for both species according to log top diameter, percentage of decay and log sweep. The LRF increased with diameter at breast height (dbh), and the net e f f e c t was increasing value per cubic foot of tree as tree size increased. To evaluate a log grading system already established, Dickinson and Prestemon (22) estimated the y i e l d of hardwood factory lumber grades which were expected from tanoak logs. Dickinson et^ a l . (23), and Prestemon et a l . (94) with si m i l a r objectives as the former analysis, predicted the y i e l d s of factory lumber grades from P a c i f i c madrone and chinkapin logs. The three studies concluded that, because hidden c h a r a c t e r i s t i c s may influence the r e l a t i v e y i e l d of the several grades of lumber from a log, log grades should be applied only when a 7 large number of logs are being c l a s s i f i e d ; otherwise, widely varying re s u l t s may be obtained. The e f f e c t of log grades on lumber q u a l i t y y i e l d has been evaluated for d i f f e r e n t tree species and log c h a r a c t e r i s t i c s . Some of these studies have considered a very large sample of trees and logs to covering the f u l l range of size and q u a l i t y of sawn timber a v a i l a b l e (73, 90, 93). It has been found that in general the trend of lumber q u a l i t y decreases with log q u a l i t y (62, 90, 93) and that conversion returns diminish as log defects increase (33). 2.1.2.1 Sweepy Logs The e f f e c t of a s p e c i f i c log defect on lumber recovery has also been evaluated through some lumber recovery studies. Brown and M i l l e r (12), Dobie (24), and Dobie and Middleton (38) analyzed the e f f e c t of sweepy logs on lumber grade and volume recovered. In general, they found that sweepy logs yielded less lumber than straight logs of the same top diameter and length. The dimensions of lumber from sweepy logs were shorter and narrower. Sawing time was almost 40 per cent longer at the headsaw. As a general r u l e of thumb, Dobie and Middleton (38) established that each 0.1 increase i n sweep/diameter r a t i o led to a reduction i n lumber y i e l d of about 7 per cent as compared to straight logs. 2.1.2.2 Taper Logs Y i e l d of lumber per cubic foot of log, as stated by Dobie (25), decreased as log taper increased. In addition, sawing time at the headsaw per thousand board feet of lumber increased with log taper. Large-taper logs require 12 per cent more time and y i e l d 5.7 per cent 8 l e s s lumber than more c y l i n d r i c a l logs. Hallock (55) and Hallock et a l . (59) established that, within reasonable l i m i t s , when logs are scaled by board foot r u l e s , the greater the taper the more lumber the sawmill operator w i l l get from his log investment. On the other hand, i f cubic scale i s used, his lumber y i e l d decreases per d o l l a r of investment as taper increases. 2.1.2.3 Infested Logs The lumber y i e l d from beetle-infested logs was analyzed by Dobie and Wright (45). In t h e i r study, the s e l e c t i o n of trees to be evaluated was based on tree appearance, which i n turn was a r e f l e c t i o n of time since beetle attack. Grade 1 trees had a green top, grade 2 trees had a red top, grade 3 had grey t i g h t bark and grade 4 had grey loose bark. Trees with green and red f o l i a g e yielded s i m i l a r values per 100 cubic feet of logs, with p o s i t i v e conversion returns. Those with no f o l i a g e but t i g h t bark also yielded p o s i t i v e returns but at a lower l e v e l . For trees sloughing bark the returns were negative. Similar r e s u l t s were found by S i n c l a i r et^ a l . (97), who reported lower lumber y i e l d for beetle-infested timber, as well as a decrease i n the grade of lumber recovered. An analysis of lumber recovery from mist l e t o e - i n f e s t e d trees i s reported by Dobie and B r i t n e f f (32), but the r e s u l t s showed a d i f f e r e n t trend from the former studies. On the average, no important differences between sound logs and infested logs were found, nor was any p a r t i c u l a r difference associated with tree s i z e . Differences i n lumber grade y i e l d s and recovery factors between lodgepole pine with severe crown inf e c t i o n s of dwarf mistletoe and non-infested lodgepole pine trees were not evident. 9 2.1.2.4 Logs from Dead Trees The e f f e c t on lumber y i e l d from dead trees i s quite evident according to Snellgrove (98). His analysis showed that the longer a dead tree stands the greater the wood l o s s ; the t o t a l loss ranged from 28 per cent for trees dead from 0-2 years, to 71 per cent for older dead material. This statement i s also confirmed by Woodfin (111) who found that approximately 28 per cent of the tree value was l o s t i n the f i r s t two years a f t e r m o r t a l i t y . According to Dobie and Wright (46), only the largest diameter classes of the better log q u a l i t y group i s l i k e l y to y i e l d p o s i t i v e conversion returns. Thus, unless there i s a r e a l s c a r c i t y of f i b e r , t h i s p o t e n t i a l source of a d d i t i o n a l supply would not appear, on the average, to be economically recoverable. Plank (88) also reported a very high percentage of low q u a l i t y lumber from dead trees as compared to that obtained from l i v e trees. 2.1.2.5 C u l l Logs With the objective to evaluate the p o s s i b i l i t y of processing c u l l logs into sawn lumber, Snellgrove and Darr (99), and Woodfin and Plank (112) studied the e f f e c t of c u l l logs on lumber y i e l d . Although 47 per cent of the gross cubic volume of c u l l logs could be manufactured into lumber, the lumber produced would be of low grades. Both analyses indicate that chips and lumber values recovered from c u l l logs would not exceed an estimate of the average cost of logging and processing merchantable logs. The economic f e a s i b i l i t y of using c u l l logs for lumber manufacture i s marginal except i n times of extremely high lumber p r i c e s , according to these two studies. 10 2.1.2.6 Log Diameter Log diameter has a d e f i n i t e r e l a t i o n s h i p with q u a l i t y and quantity of lumber. Thus, i t appears i n most grading s p e c i f i c a t i o n s (72). As log diameter increases defects generally decrease with a consequent improvement i n grade recovery of lumber (5, 62, 82). However, i n some cases (65) the reverse i s true, since for any given grade of log, the larger logs may be more defective and lumber q u a l i t y recovered i s diminished. I t has been found that the volumetric lumber y i e l d commonly increases with log diameter, ranging from 40 to 43 per cent i n 10 to 12-inch logs, and 58 to 65 per cent from 24 to 28-inch logs (19, 21, 85, 86, 87). A general concept that would work for both cases would be that, for logs of the same grade, there i s an increase i n per cent recovery with an increase i n diameter and for logs of the same diameter there i s a decrease i n recovery with a decrease i n log grade (69, 92). 2.1.3 Type of Sawmill In sawing large-diameter logs with t r a d i t i o n a l headsaws, l i t t l e change has occurred with respect to recovery and product d i s t r i b u t i o n as lumber, sawdust or chippable residue (105). On the other hand, due to the tendency of diminishing supplies of high q u a l i t y logs, a great deal of innovation has taken place i n processing small-diameter logs, r e s u l t i n g i n e f f e c t s on both recovery and product d i s t r i b u t i o n . The most important single factor i n successful small-log m i l l i n g i s high speed processing (35). Logs are processed as quickly as possible with emphasis on speed rather than on recovery, r e s u l t i n g i n low lumber recovery for small logs (80). When combining the lumber y i e l d and log throughput estimates i n the c a l c u l a t i o n of volume productivity, 11 the throughput has far greater impact than lumber y i e l d (4). Changes i n small-log sawing methods which have taken place i n the l a s t decade have not resulted i n increased lumber y i e l d s from small logs. Rather, they have resulted i n increased productivity and increased y i e l d s of pulp chips (29). The percentage of lumber y i e l d increases with the log top diameter c l a s s , at least f o r chipper headrigs and scrag m i l l s (31, 41). The log quad-band system achieved the greatest lumber y i e l d i n 9 to 12-inch top diameter range, whereas the chipper canter was most e f f e c t i v e i n the 6 to 8-inch range (4). Chip y i e l d s vary with sawmill type, log size and m i l l cutting practices (39). Comparing band-headsaws, c i r c u l a r round-log gang, scrag m i l l and chipper headrig, the chipper headrig yielded a much lower percentage of sawdust and a correspondingly higher percentage of pulp chips (29, 35). The average volume of sawdust obtained with a chipper headrig was seven per cent of the log volume, or about half of the normal sawdust volume from a band m i l l , and less than one t h i r d of that from a scrag stud m i l l . The data reported i n Table No. 1 shows the re l a t i o n s h i p between sawmill type and the proportion of lumber, sawdust and chips, from small logs ranging from 4 to 14 inches top diameter (29, 35, 41). The big differences i n y i e l d s are of course i n sawdust and pulp chips, with chipper headrigs y i e l d i n g a much lower percentage of sawdust and higher percentage of pulp chips. The e f f e c t of log length on lumber recovery with d i f f e r e n t types of m i l l s was analyzed by Dobie and Parry (39). They established that the ra t i o of board feet of lumber recovered per cubic foot of log does not 12 change appreciably i n logs of 12, 16 and 20 feet. Thus, the same percentage of lumber, sawdust and s o l i d residue could be expected from these length classes. On the other hand, i t was pointed out by Dobie and McBride (35), that the LRF decreases as log length increases, whereas the percentage of chip volume increases with log length. A common explana-t i o n i s that the r a t i o of board feet to cubic feet of log decreases with log length because taper i n logs under 40 feet i s not considered i n board foot scale r u l e s . The p o t e n t i a l lumber volume, which i s normally cut out of long tapered logs i n conventional m i l l s , i s recovered instead, as chips by the chip-and-saw m i l l . Thus, the r a t i o of board feet of lumber per cubic foot of large logs would be higher i n conventional m i l l s . Apparently no s i g n i f i c a n t difference i n the percentage of log volume made into sawdust from large logs was found among various types of sawmills (81). Without taking into account the LRF, the p o t e n t i a l advantage of a double-cutting over a s i n g l e - c u t t i n g band headsaw i s an increase i n pr o d u c t i v i t y , which r e s u l t s i n increased gross revenue per s h i f t and reduced cost per unit of output (90). Sawing i n single pass units l i k e chipper headrigs, scrags and log-gangs suggests that throughput should increase with log s i z e . It was pointed out by Dobie (27) and by Dobie et a l . (41) that i n chipper headrigs, sweep or heavily f l a r e d butts had a tendency to become jammed and i n scrag m i l l s feed rate decreased as top diameter increased. In chipper headrigs and scrag m i l l s , however, the cubic feet of log processed per unit of time increased as log size increased. In log-gang m i l l s , productive capacity increased and processing cost per unit of time diminished with increasing diameter to a c e r t a i n optimum, whereafter, the trend in both reversed. 13 In general, for any type of sawmill, considerable processing time can be saved at the headsaw by processing the longest logs. However, lumber lengths are c o n t r o l l e d by market demand (37). 2.1.4 Cutting Patterns A large number of factors a f f e c t the volume of lumber obtained from any given log by the sawing process. These factors are of two types. The f i r s t , such as kerf width, lumber roughness, target s i z e , smallest lumber saved, and slabbing and edging practices are commonly recognized. The second include log breakdown procedures (56, 60). I t i s apparent that no large difference i n LRF e x i s t s between grade sawing and l i v e sawing (78). For s i m i l a r q u a l i t y logs, LRF from l i v e sawing s l i g h t l y exceeds that from grade sawing (1). The same r e l a t i o n i s true for long logs; l i v e sawing r e s u l t s i n a s l i g h t l y higher per cent recovery and value recovery (4). I t has also been established that l i v e sawing on the headsaw takes 18 to 32 per cent le s s time on the average than grade sawing, and y i e l d s considerably higher pro d u c t i v i t y (9, 52). According to Hallock et a l . (60), b a s i c a l l y eight log breakdown systems may be used for converting small softwood logs from 5 to 20-inch diameter to dimension lumber. Short logs, less than 16 feet, with a taper of 3 inches or le s s per 16 feet are best cant sawn, using f u l l -taper on the log and f u l l - t a p e r on the cant. Logs longer than 16 feet, with taper over 3 inches, are best cant sawn using s p l i t - t a p e r on the log and f u l l - t a p e r on the cant. The margin of these advantages can vary from 0.5 per cent to 6.6 per cent, depending on the log mix. In attempting to optimize the conversion of each log, the sawyer faces the d i f f i c u l t task of choosing the best of many d i f f e r e n t sawing 14 patterns i n a l i m i t e d length of time. Since LRF i s inherently lower for smaller logs, the choice of the r i g h t pattern i s even more d i f f i c u l t and c r i t i c a l f o r small logs (77). Because of pressure for high production the sawyer may run varying sizes of logs through the unit without changing to the appropriate patterns. Recovery could be cut in half by sele c t i n g the wrong pattern, as frequently happens for 7-inch diameter logs (3). The v a r i a b l e opening-face live-sawing method i s shown to be the best, increasing the volume recovered by approximately 10 to 14 per cent over that of the poorest opening-face (57, 63). To select the best a l t e r n a t i v e cutting patterns, the use of computer in the sawing process has been useful to obtain high production and the best recovery with small logs. This trend w i l l continue i n the future due to the increasing s c a r c i t y of large q u a l i t y logs and the con t i n u a l l y r i s i n g cost of roundwood. The investment to cover the cost of purchasing computer c o n t r o l l e d equipment may be recovered i n a r e l a t i v e l y short time (63). 2.1.5 Log Scaling Log volume i s expressed in two common ways: by board foot r u l e s , and by cubic scaling procedures. Log rules are one of the oldest means of estimating lumber recovery from logs. They have been used by the lumber industry i n log transactions by both buyers and s e l l e r s to epxress the volume of a log i n terms of the board feet of lumber i t i s expected to y i e l d . There are more than 100 log rules and for most of them allowance must be made for shrinkage and waste i n estimating the volume of boards that could be recovered (15, 65). Most of the board foot scale r u l e s estimate volume somewhat lower than the actual t a l l y of lumber r e s u l t i n g from sawing the log, even i n the most i n e f f i c i e n t m i l l s (59). The difference i s commonly referred to as overrun. A method expected to replace the board foot r u l e s , as a mean of s c a l i n g logs, i s that based on log volume, usually expressed in cubic feet or cubic meters. The most widely used cubic scaling method for c a l c u l a t i n g the volume of logs i s the Smalian formula (55, 59). This formula assumes the cubic volume of a log can be c l o s e l y estimated by multiplying the average area of the two ends of the log, by the length of the log i n the same un i t s . There i s a fundamental difference between the two systems of volume measurement. B a s i c a l l y , any differences i n taper of logs are ignored when board foot rules are used, as the small end diameter of the log and i t s length are the only v a r i a b l es considered. When logs are c u b i c a l l y scaled, both end diameters are considered and the taper i s accounted for i n c a l c u l a t i n g the volume of logs. When logs are scaled by log r u l e s , the lumber y i e l d increases as the taper increases. If cubic scale i s used the lumber y i e l d decreases as taper increases. It i s also common to express the log volume by both systems i n studies where the p r e c i s i o n of estimators i s desired. Hanks and B r i s b i n (62) used the International 1/4-inch and the Scribner log r u l e s , as well as cubic s c a l i n g by the Smalian formula. Henley and Plank (65), Lane ejt a l . (73), and Snellgrove et a l . (100) used the Scribner Decimal C log r u l e , and for gross cubic volume the equation: 2 2 V = 0.00181 L (D + D XD 2 + D 2> [2] Where D^ i s the log s c a l i n g diameter, small end; D 2 i s the diameter, 16 large end, and L i s the log length. Woodfin (110), and Fahey and Martin (48), used the Scribner log rule and the cubic volume equation l i s t e d (65, 73, 100). Dobie and Wright (43) compared two cubic scales used i n B r i t i s h Columbia: the lumber cubic scale, and the firmwood cubic scale, using the Smalian formula and the lumber recovery f a c t o r . Inadequate deductions for b u t t - f l a r e , d i f f i c u l t i e s i n assessing the degree of defect, and inaccuracy i n measurement were the main l i m i t a t i o n s found. For defective logs estimates of volume w i l l vary with the scale used, and consequently the LRF w i l l vary between scales. Over-generous allowances for sweep, f l a r e , and defects w i l l tend to decrease volume and increase LRF, whereas conservative deductions w i l l have the opposite e f f e c t . In general i t was concluded by Dobie and Wright (43), that there could be as many d i f f e r e n t estimates of volume for a given log as there are s c a l e r s , so that the LRF for the same log could vary accordingly. 2.1.6 Log Sample Size The sample size required for analysis of LRF depends on the p r e c i s i o n desired, cost l i m i t a t i o n s , and the type of information needed to s a t i s f y the requirements of the study objectives. Commonly, to evaluate the LRF i n a sawing process, a sample of 100 logs selected at random from the log yard has been used. These logs are processed i n batches i n a normal manner (17, 105). When more precise information i s needed and more variables are analyzed for the required data the sample size usually i s increased. Plank and Henley (89), i n t h e i r study to r e l a t e timber c h a r a c t e r i s t i c s to end product y i e l d values, used a sample size of 1009 merchantable logs to cover the f u l l range of log size a v a i l a b l e even when samples were not representative of a t y p i c a l log mix. 17 With s i m i l a r purpose Henley and Plank (65) selected a sample size of 428 logs that were representative of the a v a i l a b l e tree c h a r a c t e r i s t i c s . Pong and Fahey (93) used a sample size of 1126 logs which was representative of the f u l l range of size and quality of the logs. Bailey (5), with a sample size of 609 logs, ranging from 7 to 17 inches i n diameter, obtained a representative sample size of s t r a i g h t trembling aspen logs, while Mueller and Bager (82), for merchantable logs ranging i n diameter from 7 to 24 inches, needed 675 logs. Dobie et a l . (34), with a sample size of 2585, representative of the major commercial species, compared the difference between the lumber cubic scale and the firmwood cubic scale. Lane et: a l . (73), to determine the lumber y i e l d and recovery r a t i o s for old-growth Douglas-fir, using two log s c a l i n g and grading p r a c t i c e s , processed 2980 woods-length logs and 4974 sawn-length logs. With d i f f e r e n t objectives Lane and Woodfin (74) selected a sample size of 4009 commercial sawlogs to evaluate lumber y i e l d by grade. To s a t i s f y s t a t i s t i c a l requirements, the sample size should be selected according to the v a r i a t i o n of the quantity estimated (26, 54). The required number of logs i s determined by the formula: 2 2 N - [3] E o Where N i s the sample size, s i s the population variance, t i s the appropriate value of Student's t, and E i s the allowable error. If the volume v a r i a t i o n of the log population i s unknown, then a preliminary 18 sample of 60 logs should be taken at random to determine the variance by the formula v 2 . l E x l 2 Where Zx z i s the sum of squared values of a l l i n d i v i d u a l measure -ments, (£x) i s the square of the sum of a l l measurements. Using this procedure Dobie (26) found that i n B.C. the sample size for small i n t e r i o r log m i l l s ranges from 249 to 343 logs and for coastal sawmills ranges from 210 to 779. Dobie and Warren (42) reported that the number of logs i n two-inch diameter classes diminished as diameter increased. For 95 per cent confidence l i m i t s , with half-width of 5 per cent of the mean LRF, about 100 logs of the 4-inch class and 60 of the 10-inch class should be sampled. 2.2 Log-Lumber and Byproduct Proportion Sawmill residues such as slabs, edgings, trims, sawdust and bark, that were once wasted, are now being sold for pulp chips, f i b e r and p a r t i c l e wood products, mulches, s o i l amenders and ground covers. Wood-chips are sold to pulp m i l l s , f i b e r or p a r t i c l e board plants for processing into paper or boards; bark residue i s screened, washed and marketed as s o i l amenders, mulch and ground covers, sawdust i s sold for mulching and l i v e s t o c k bedding or burned at the m i l l as f u e l (19, 20, 21, 85, 86, 87). Because of the increasing value of sawmill residues, increased attention has been given to estimating the amount of each byproduct. Factors a f f e c t i n g the lumber y i e l d of log input also a f f e c t the y i e l d of 19 sawmill residues: log diameter, log q u a l i t y , scaling p r a c t i c e s , sawmill type, saw kerf, dimension of lumber produced and sawmill recovery pr a c t i c e s , among others. 2.2.1 Volume and Weight Method Using a band headsaw to process shortleaf pine logs, ranging i n diameter from 9 to 20.4-inch, P h i l l i p s and Schroeder (87) determined the y i e l d of lumber and byproduct from the sawlogs. Each log was weighed with and without bark, and scaled p r i o r to sawing in a 3/16 inch kerf band headsaw into lumber of unusual dimension, 1 by 5 inches and 1 by 3 inches, for export. The proportion of the d i f f e r e n t log components was: 54 per cent lumber, 26 per cent chippable residue, 10 per cent bark residue and 10 per cent sawdust. Lumber y i e l d increased from 43 per cent i n small trees to 58 per cent i n large diameter trees. The percentages were determined by weighing the chippable residue from each log. Sawdust weight was determined by substracting weight of chippable residue and lumber from debarked log weight. P h i l l i p s (85, 86) studied black-oak logs varying i n diameter from 11.9 to 25.6 inches. He processed them on a band headsaw into grade y i e l d of 4/4 and 5/4 inch lumber with a minimum of wane, and found a r e l a t i o n of 55 per cent lumber, 20 per cent chippable residue, 15 per cent bark residue and 10 per cent sawdust. As scaling diameter increased lumber y i e l d increased from 46.3 to 61 per cent; 25 per cent of small diameter logs went into chippable residue compared to only 16.4 per cent for large diameter logs. The percentage of bark residue and sawdust remained r e l a t i v e l y constant over the range of tree diameters. Clark (19) and Clark et a l . (21), sampled 230 yellow poplar sawlogs ranging from 11.7 to 28.4 inches i n diameter. The logs 20 were weighed with and without bark and scaled by the Smalian formula p r i o r to sawing them into 4/4 inch lumber, with a 3/16 inch kerf band headsaw. A proportion of 54 per cent lumber, 15 per cent bark, 18 per cent chippable residue and 13 per cent sawdust was found. They also found that chippable residue decreased from 29 per cent i n small logs to 16 per cent i n large logs, while bark residue decreased from 17 per cent i n small logs to 12 per cent i n large logs. Lumber y i e l d increased as tree size increased, ranging from 42 per cent i n 12-inch diameter trees to 59 per cent i n 28-inch diameter trees. Using a conventional 5/16 inch kerf c i r c u l a r saw headrig, Clark and Taras (20) processed slash pine sawlogs ranging i n diameter from 9.6 to 21 inches into 4/4 and 8/4 inch lumber and determined a r e l a t i o n of 51 per cent lumber, 22 per cent chippable residue, 10 per cent bark residue and 17 per cent sawdust. They also found the LRF increased with tree size up to 18 inches and then decreased s l i g h t l y . The average LRF ranged from 5.3 i n 12-inch d.b.h. trees to 6.5 board feet per cubic foot i n 18-inch d.b.h. trees, and the average was 6.1. Taras et a l . (104), with merchantable stems of l o b l o l l y pine ranging i n diameter from 9.8 to 19.4-inch d.b.h., and processed on a c i r c u l a r headsaw into dimension and board lumber, reported a proportion of 50.3 per cent lumber, 28.5 per cent chippable residue, 7.6 per cent bark and 13.6 per cent sawdust from the sawlogs; 88 per cent of the lumber cut was 8/4 inch dimension and 12 per cent was 4/4 inch boards. Lumber y i e l d increased as tree size increased, ranging from about 37 per cent i n 10-inch trees to about 55 per cent i n 20-inch trees. Chippable residue on the other hand, decreased, ranging from a high of 39 per cent i n 10-inch trees to 25 per 21 cent i n 20-inch trees. Bark y i e l d decreased as tree size increased ranging from 9 to 7 per cent. Sawdust weight decreased s l i g h t l y with increasing tree size ranging from 14.4 per cent in small trees to 12.9 per cent i n large trees. Fahey and Hunt (50) studied grand f i r thinning logs, ranging i n diameter from 4 to 14 inches processed at a band m i l l and from 4 to 12 inches at a chipper headrig, producing standard and better grade lumber. They found that the proportion of lumber, sawdust , and chippable residue was 53.6 13.3, 35.1 per cent, and 49.5, 5.4, 44.1 per cent, r e s p e c t i v e l y , for the two machine centers. An empty chip bin was used to c o l l e c t the chips and s o l i d residue volume was determined from the oven-dry weights. Schroeder et^ al. (96), according to the statement that weight- s c a l i n g i s the accepted method of buying and s e l l i n g pine logs i n the southern United States, formulated tables based on weights to estimate the proportion of lumber and other primary products of pine saw timber trees. Lumber was produced on a c i r c u l a r headsaw which had a 5/16 inch kerf, into 4/4 and 8/4 inch thickness and the proportion was 54 per cent lumber, 26 per cent chippable residues, 16 per cent sawdust and 9 per cent bark. LRF increased with diameter from 5.80 for 10-inch trees to 6.84 f o r 20-inch trees. In a l l these studies a s i m i l a r procedure to determine the proportion of lumber and byproducts from sawlogs was followed. Regression equations were formulated to predict either the weight or the volume, or both, from merchantable stems and the primary products. 2.2.2 Saw Kerf and Cutting Patterns Method A d i f f e r e n t approach to determine lumber volume and byproduct proportion from sawlogs was used i n the following studies. Sawdust 22 volume was determined by using the average saw kerf and the computed surface area of the rough green lumber from each log. Chippable product volume was determined by subtracting the lumber and sawdust volume from the gross cubic log volume. Using band headsaws to process old-growth coastal Douglas-fir ranging i n diameter from 5 to 67 inches, Lane j2t a l . (73) employed an average saw kerf thickness for each m i l l which was producing optimum values of board, dimension, select and shop lumber. They found that about 63 to 64 per cent of the cubic content of the log was manufactured into rough green lumber of which approximately 25% was lost as planer shavings and shrinkage. Henley and Plank (65) used a band headsaw with an assumed average saw kerf of 7/32 inch and computed cross sectional area of the lumber i n each 6 to 34-inch log of Engelmann spruce. When producing nominal 2 by 4, 2 by 6 and 1 inch boards, they found that an average trim allowance of 6 inches would increase the gross cubic volume by 3.3 per cent and there would be a corresponding increase i n the volume of residues. Pong and Fahey (93), applying a saw kerf of 8/32 inch i n a band headsaw processed red and white f i r ranging i n diameter from 7 to 50 inches. They manufactured select, shop, common and dimension lumber, i n a similar way to the former studies, and tabulated the varying propor-tions of lumber, sawdust and chippable residue from different log diameter classes. Snellgrove et a l . (100) with a band headsaw and an average saw kerf of 0.25 inch, processed low grade coastal Douglas-fir logs into board, dimension, and select items. He found that about 62.5 per cent of the cubic content of the sawn-length logs was manufactured into rough green lumber and about 8 per cent of the volume was sawdust. 23 The remaining 2 9.5 per cent cubic content of the logs was considered m i l l residue. They also found that the residue volume w i l l increase with a 6-inch trim allowance, which increases the gross cubic volume of the average log by 24 per cent. Lane et^ _al. (75), used a single cut bandsaw with an average saw kerf of 0.25 inch, to process Sitka spruce logs ranging i n diameter from 6 to 56-inch into rough green cants for export. They determined the proportion of lumber,. sawdust and chippable residue by log diameter c l a s s . Fahey and Martin (48) studied 292 second growth Douglas-fir logs ranging i n diameter from 7 to 44 inches, using a double cut bandsaw produced lumber of which' 49 per cent was 4 inches or thicker. They reported that the proportion of lumber, sawdust and chippable residue was 60 per cent, 9 and 31 per cent, respectively. The portion of the log converted to sawdust, 9 per cent, was low due to the high per cent of 4-inch dimension lumber produced in this study. Normally approximately 11 to 12 per cent of the log volume becomes sawdust. Processing small diameter logs, Kerbes and Mcintosh (69) using 3/8 inch kerf for the headsaw and edger with logs ranging i n diameter from 4 to 14 inches. They determined the proportion of sawlog volume converted i n lumber, sawdust and s o l i d residue for each diameter log c l a s s . The o v e r a l l recovery was 61, 19 and 20 per cent of lumber, sawdust and chippable residue, r e s p e c t i v e l y . * Since cubic s c a l i n g i s becoming more common i n sawmill studies Hanks (61), i n his analysis to predict the lumber and chippable residues from 10 species of hardwood trees, calculated sawmill residue volume in *The previous information including section 2.2.1 has been summarized i n Table 2. 24 cubic feet for each tree by subtracting the cubic-foot volume of lumber and sawdust from the gross cubic-foot volume of saw log material. The logs ranging i n diameter from 10 to 30-inch, were sawn i n c i r c u l a r and band m i l l s with kerfs of 7/16 inch and 10/16 inch r e s p e c t i v e l y , processing lumber with thickness of 4/4, 5/4, 6/4 and 8/4 inch. He presented p r e d i c t i o n equations and tables to estimate the gross cubic-foot y i e l d s of lumber, sawdust and s o l i d wood residues. Bennett and Lloyd (8), i n contrast to the former study, used the International and Scribner log rules to estimate the portion of a log that goes into slabs and edgings. In t h e i r analysis i t was found that the volume of byproduct varies according to the length of the log. This v a r i a t i o n r e s u l t s because the International Rule makes no allowance for such increase; thus, the proportion of log volume converted to lumber increases with log length by the International Rule, but decreases by the Scribner Rule. Consequently, the percentage of the log volume going into slabs and edgings decreases s l i g h t l y with log length by the International Rule but increases by the Scribner Rule. The proportion of lumber and byproducts from small-diameter logs, defined as being from 4 to 15 inches top diameter, changes according to the type of sawmill and processing c h a r a c t e r i s t i c s . These r e l a t i o n s are c l e a r l y shown i n Table 1, (18, 2 9, 37, 41). Saw kerfs used to calculate the volume of sawdust produced were 11/32 inch for c i r c u l a r headsaws, 3/16 inch for band saws and gang saws, 5/16 inch for edgers, 7/32 inch for trim saws, 1/8 for twin band saws and 1/4 inch for scrag saws. It has been generalized (105) that, for c i r c u l a r sawmills, the appropriate cubic contents that develop from green, debarked logs are: lumber 37 to 47 per cent; kerf 16 to 21 per cent; chips 17 to 35 per 25 cent; and planer shavings 12 to 18 per cent. This includes oversizing, sawing variation and planning allowance. The figures for bandmills with the same variables are: lumber 44 to 53 per cent, kerf 12 to 15 per cent; chips 20 to 29 per cent, and planer shavings 11 to 15 per cent. A general procedure i s described by Dobie (26) to determine sawdust volume according to log breakdown patterns and the various pieces of equipment i n a m i l l . The saw cuts are recorded and the thickness of pieces removed at each machine center either measured or estimated. Over a period of time s u f f i c i e n t data can be gathered to give sawdust y i e l d for each diameter class at each machine center for each processing pattern used. This procedure increases i n complexity as the number of processing stages and cutting patterns grow. A different approach i s described by Steele and Hallock (101), analyzing the methods used to calculate the volume of byproduct i n the sawing process. They concluded that most of the methods have one weakness i n common; r e l a t i v e l y few of the variables that can affect residue volumes are considered. An accurate prediction of sawmill residue production requires including in the analysis a l l the important variables that can affect this production. A geometric model i s suggested to calculate volume of green lumber, dry lumber, green chips, green sawdust and dry planer shavings. 2.3 Quality Control 2.3.1 Log Length Allowance The most common lengths for logs processed into sawn lumber are 8, 10, 12, 14, 16, 18 and 20 feet in nominal dimension, with an additional over-length ranging from 4 to 12 inches (95). Log length v a r i a t i o n has high impact on log volume l o s t and on value return on investment of raw material. When the actual dimension exceeds s i g n i f i c a n t l y the nominal dimension, the lumber wasted at the trim saw i s greatly increased. Dobie (30), i n his analysis of 13 coastal sawmills i n B.C., found that 3.1 per cent of the t o t a l log volume processed was l o s t due to an over allowance of log length considering 6-inch trim allowance for long logs. Aune and Lefebvre (4), i n the i r analysis of 72 small log sawmills i n the i n t e r i o r of B r i t i s h Columbia, reported a log volume l o s t of 1.8 per cent due to over length of the logs. Zavala (115) i n his report of the cha r a c t e r i z a t i o n of the sawmilling industry i n the State of Durango, found that 3.2 per cent of the log volume processed was l o s t due to an over length. However, he considered, as a common log bucking pra c t i c e , an allowance of 4 inches of the nominal log dimension for any given log length category, while Dobie (30) and Aune and Lefebvre (4) considered 6 inches as allowable length for long logs. 2.3.2 Lumber Dimension Allowance The most common dimensions for cutting and s e l l i n g sawn lumber range from 4 to 12 inches i n width and from 4 to 20 feet i n length, i n in c r e -ments of 2 inches and 2 f e e t , r e s p e c t i v e l y . Thickness ranges from 1/2 inch to 2 inches i n nominal dimension. Rough dry lumber allowance for f i n i s h machining ranges from 1/4 to 1/8 inch i n thickness, at le a s t 1/2 inch i n width, and 3 inches i n length (95). 27 Among the few studies i n lumber dimension analysis Rodriquez (95), processing 755 logs i n 7 sawmills, reported that the actual volume l o s t , as a r e s u l t of over-allowance, ranged from 20 to 34 per cent of the nominal volume. Cardenas (17) established the minimal thickness dimension and volume allowance for sawn lumber most commonly processed. For 1/2, 3/4, 4/4, 6/4 and 8/4 inch, the corresponding lumber thickness should be 16, 22, 28, 41 and 54 millimeters, y i e l d i n g a volumetric allowance for f i n i s h i n g of 40, 30, 22, 15 and 8 per cent, re s p e c t i v e l y . The allowance i n dimension i s a common practice for production and commercialization of sawn lumber, due to the volume l o s t by sawing v a r i a t i o n , by planing, and by shrinkage from green to dry dimension. Minimum size requirements for rough green lumber are determined by taking the required f i n a l dry-dressed lumber dimension and adding allowances for planing and shrinkage. The target lumber size i s determined by addi-t i o n a l allowance which represents sawing v a r i a t i o n . Over allowance i n sawn lumber to compensate for thickness sawing v a r i a t i o n , increases lumber volume l o s t which r e s u l t s i n lower lumber recovery. Sawing v a r i a t i o n i s a measure of the mechanical p r e c i s i o n i n manufacturing lumber thickness and widths (102). S k i l l and tra i n i n g of machine operators and maintenance of machining conditions have a d i r e c t influence on sawing v a r i a t i o n and on planing v a r i a t i o n of rough lumber. I t i s , therefore, possible to control and reduce these two types of va r i a t i o n s (2, 11, 13, 14, 106, 107). Sawing v a r i a t i o n can be quite s i g n i f i c a n t as indicated by Kerbes and Mcintosh (69) who reported i n the i r study that, i n the actual conversion of trees to f i n i s h e d lumber, oversize amounted to 10 per cent of the 28 rough-green lumber volume. The wasted volume was determined by applying a volumetric-shrinkage factor of 6.8 per cent to the green lumber volume, obtaining the volume at 12 per cent moisture content. A sawing accuracy of 1/8 inch i n thickness and 1/8 inch i n width were allowed i n sawing and a s i m i l a r allowance was used for planing. The p o t e n t i a l rough-green lumber l o s t due to planer shavings amounted to 25 per cent of rough green lumber volume. In a s i m i l a r study Mueller and Bager (82), with a sample of 194 boards, 4/4 inch i n thickness, taking three thickness measurements along the length of the boards, found that the average thickness that occurred most frequently was the target thickness of 1.063 (34/32) inch, which accounted for 25 per cent of the lumber sampled. Stern et_ al. (102) i n the i r evaluation of sawing v a r i a t i o n and lumber oversizing found tremendous differences between m i l l s ; sawing v a r i a t i o n ranged from 0.025, (8/32) to 0.534, (17/32) inch, with a mean v a r i a t i o n of 0.165, (5/32) inch. In a study to evaluate the performance of sawing v a r i a t i o n of 13 sawmills i n B r i t i s h Columbia, Valg (106) found that only one m i l l was operating under s t a t i s t i c a l control and the rest of them had a v a r i a t i o n of 1.536 to 2.228 inch, with an average range of 0.25 (8/32) inch which could be reduced to 0.094 (3/32) inch i n most of the sawmills studied. He also found no c o r r e l a t i o n between m i l l size and sawing p r e c i s i o n ; nor did any p a r t i c u l a r headrig type seem to dominate over the other. With a sample siz e of 25 pieces of lumber from each of the 22 sawmills analyzed, Bramhall and Mclntyre (11) found a range of sawing v a r i a t i o n from 0.03, (1/32) to 0.320, (10/32) inch. They also determined the r e l a t i o n between sawing v a r i a t i o n and the proportion of undersized 29 pieces among the d i f f e r e n t sawmills studied. The between-board v a r i a t i o n was attributed to errors on the setworks and within-board sawing v a r i a t i o n was due to v i b r a t i o n and wandering of the sawblade. V a r i a t i o n between boards was responsible for most of the v a r i a b i l i t y i n thickness; therefore, the setwork would have been the prime target for improvement in c o n t r o l l i n g sawing v a r i a t i o n . To analyze the possible e f f e c t on sawing v a r i a t i o n , due to techno-l o g i c a l changes adopted by the sawmilling industry 10 years a f t e r h i s f i r s t study, Valg (107) reported a sawing v a r i a t i o n analysis i n 8 sawmills, some of which were covered i n his f i r s t study. He found no s i g n i f i c a n t improvements i n range sawing v a r i a t i o n compared to his f i r s t a n a lysis; that i s , from 0.063, (2/32) to 0.437, (14/32) inch, with an average range of 0.2362, (8/32) inch; t h i s range represented 25 per cent of the t o t a l sawn lumber. In his l a t e s t study he found a range v a r i a t i o n of 0.2206, (7/32) inch, which i s an i n s i g n i f i c a n t change from the range found i n h i s f i r s t a n a l y s i s . Compiling information from d i f f e r e n t studies, Hallock (56) reported an average sawing v a r i a t i o n of 0.146 inch when a l l the sawmills i n the USA were considered together. The range was from 0.234, (7/32) inch i n the best m i l l studied to 0.496, (16/32) inch i n the poorest one. No s i g n i f i c a n t differences i n sawing v a r i a t i o n were found between geographic areas. Defining oversizing i n excess of what i s needed as po s i t i v e when the boards are larger than t h e o r e t i c a l l y necessary and negative when the pieces are smaller, p o s i t i v e oversizing averaged 0.077 inch and varied from 0 to 0.545 inch. Negative oversizing averaged 0.085 inch and ranged from 0 to 0.392 inch. 30 An excess of sawing v a r i a t i o n or any oversizing w i l l r e s u l t i n lower lumber recovery. Reducing unfavourable sawing factors w i l l increase the lumber y i e l d s i g n i f i c a n t l y (105). Accurate bucking of logs w i l l increase LRF by 0.10. By reducing excessive planing allowance to 3/32 inch on 4/4 inch lumber, LRF w i l l increase by 0.30. Avoiding sawing v a r i a t i o n i n excess of 1/8 inch on 4/4 inch lumber w i l l increase LRF by 0.60, while holding oversizing to 5/32 inch on 4/4 lumber w i l l increase LRF by 0.45. LRF can be further increased by 1.0 through minimizing slabbing, edging and trimming. Due to the e f f e c t of sawing v a r i a t i o n on lumber recovery, thickness v a r i a t i o n a n a l y s i s , by means of p e r i o d i c a l observations and measurements, i s becoming more common i n the sawmilling industry. The addit i o n a l cost to c o l l e c t and analyze the data i s well paid for once the assignable causes of the sawing v a r i a t i o n are eliminated. A procedure to analyze the sawing v a r i a t i o n i s described by Warren (108), determining and evaluating thickness v a r i a t i o n between boards and within boards by one-way analysis of variance. He also determined the required sample size for sawing v a r i a t i o n studies, ranging from 50 to 250 boards, and the target thickness for s p e c i f i e d values for the two types of v a r i a t i o n , to get no more than 5 per cent of the production with skip values. Using a d i f f e r e n t approach from Warren, Whitehead (109) described the procedure to develop a lumber size control program to reduce the sawing v a r i a t i o n . The d i f f e r e n t steps needed for the analysis, including c o l l e c t i o n of data, evaluation and i n t e r p r e t a t i o n of information are described. 31 To compute the thickness v a r i a t i o n between boards, and within boards, he used the following formulas: Where Sw, i s the within-board standard deviation, i t i s a measure of the si z e v a r i a t i o n that occurs along the boards; Sb i s the between-board standard deviation, measures the size v a r i a t i o n that occurs between boards; St i s the t o t a l sawing standard deviation. Rw and Rb are ranges of within-board measurements and between board measurements; d2 i s a subgroup size factor that converts range into standard deviation. Target size thickness or optimum thickness dimension can be determined by the following formula: T = (St x K) + SPF [8] Where T i s the green target size; K i s the skip allowance factor that determines the amount of lumber that w i l l be allowed to be under-sized; SPF i s the sum of shrinkage, planing and f i n i s h e d thickness. In a s i m i l a r way to the one described by Whitehead to determine sawing v a r i a t i o n , Brown (13, 14) also described a procedure to analyze the sawing v a r i a t i o n . A l l the formulas are s i m i l a r except the following which i s used to c a l c u l a t e the between-board v a r i a t i o n : 32 Sb = f [9 d2 Where Sb i s the between board standard deviation, Rb i s the range between-board measurements and d2 i s the subgroup factor. 33 3. MATERIALS AND METHODS 3.1 Lumber Recovery 3.1.1 Sawmills Se l e c t i o n In the state of Durango the most frequent band headsaw widths are 6, 8 and 10 inches (Table 3). Of the 84 band headsaw m i l l s i n the state, 60 per cent have an average lumber production per 8 hour s h i f t of 10,000 to 15,000 board feet. From the 40 c i r c u l a r headsaws, 63 per cent have a production capacity of 7000 to 11,000 (16, 115). C i r c u l a r headsaw m i l l s tend to disappear due to the amount of wood converted into sawdust by the tooth kerf. However, at the present time c i r c u l a r sawmills s t i l l represent a very s i g n i f i c a n t contribution to the industry i n the state of ) Durango (Table 3). It was not possible to include any c i r c u l a r sawmill i n t h i s analysis due to f i n a n c i a l l i m i t a t i o n s to c o l l e c t the required data. By production capacity, at least 70 per cent of the sawmills could be c l a s s i f i e d as small sawmills, since they produce les s than 20,000 bd. f t . of lumber in 8 hour s h i f t s (67). Moreover, the percentage of small sawmills would increase perhaps to 95 per cent according to Kirbach's c l a s s i f i c a t i o n (71), since very few produce more than 50,000 bd. f t . per s h i f t . Six sawmills were selected to include two each of the band headsaw width c l a s s i f i c a t i o n s of 6, 8, and 10 inches. A l l sawmills were similar i n t h e i r lay-out and the c h a r a c t e r i s i t c s of the edgers and trimmers were comparable. The edgers had three c i r c u l a r saws and the trimmer a single saw. Production capacity of the s i x m i l l s ranged from 10,000 to 18,000 34 bd. f t . per s h i f t . Thus, the selected m i l l s could be regarded as representative of the industry i n Durango. Production e f f i c i e n c y may be expressed as the r a t i o of thousands of board feet of lumber produced to number of men per s h i f t . An e f f i c i e n t small sawmill would have a r a t i o of 1:1 (52, 67). The six sawmills sampled have a r a t i o of 1:1.86 since they were producing an average of 15,000 bd. f t . per s h i f t with 28 workers. One of the reasons for the low r a t i o i s the lack of automation i n most of the sawmills. 3.1.2 Log Sample Size One of the study objectives was to analyze a representative sample from the log population i n each one of the selected sawmills. The sample si z e was determined by the log volume v a r i a t i o n and the 95 per cent confidence l i m i t s on the mean cubic volume, by use of equation No. 3. 3.1.3 Log Scaling Although board feet measurement i s widely used by the lumber industry, e s p e c i a l l y the Doyle Rule, log scaling rules are not o f f i c i a l l y recognized. In t h i s study the gross cubic log volume was determined by the Smalian formula: v = 0L+Jl).L [ i o ] Where V i s the volume i n cubic meters, B and b are butt and top areas i n square meters and L i s log length i n meters. Two diameters were taken at each end-surface area with a l l measurements made inside the bark, to the nearest centimeter. Log length was also recorded to the nearest centimeter. 35 The sampled logs were grouped by diameter and length categories ranging from 3.05 to 6.09 meters (10 to 20 feet) i n length, with 61 cm (2 feet) difference between consecutive categories. Diameter classes ranged from 20 to 70 cm with 5 cm i n t e r v a l s (Table 4). 3.1.4 Log and Lumber Grading Log grading practices are not common in the sawmill industry i n Mexico. Very few enterprises use log q u a l i t y evaluation to determine the raw material value and the pote n t i a l lumber volume and quality recovery. P r a c t i c a l l y no log trading system exists i n the forest industry. When enterprises do not have their own forest resources, usually the raw material i s purchased as standing trees on a volume basis and quality i s seldom taken into account. When this i s not the case, log trading takes place usually on volume basis only. This practice of trading logs by volume basis i s changing to include log grades, as the sc a r c i t y of high q u a l i t y logs and the price of raw material become more c r i t i c a l . For t h i s study a scale of 5 grades was used to c l a s s i f y the log qua l i t y according to the most common log-grading practices for conifers i n the northern part of the country. Defect-free logs were c l a s s i f i e d as f i r s t grade and the poorest ones as f i f t h grade (Table 5). Standard lumber grades, although recognized i n sawmilling practices, are not very common when commercialization and marketing takes place. The most common system for grading lumber encompasses 5 lumber classes i r r e s p e c t i v e of the end use, ranging from defect free or f i r s t q u a l ity grade to the poorest or f i f t h lumber grade. For t h i s study, logs and lumber were graded by trained personnel f a m i l i a r with the grading practices for conifers i n the northern part of Mexico. 36 3.1.5 Sawmilling Procedure As the sample logs entered the m i l l s they were assigned a sawing order number. These numbers were cross referenced with scale log number to i d e n t i f y scale and grade of log. Because of the d i f f i c u l t y i n t r y i n g to keep track of lumber from a given log, the sample logs were fed into the m i l l mixed with m i l l - r u n -logs, usually on the basis of one sample log to three m i l l - r u n logs. A l l material cut from a given log was properly i d e n t i f i e d with the m i l l - l o g number by a worker positioned at the headsaw as the log was i n i t i a l l y broken down. The study logs were sawn for quality recovery according to normal manufacturing procedure i n each sawmill. Individual log i d e n t i t y was maintained on each piece of lumber through the manufacturing process to the f i n a l point for grading and t a l l y i n g . V i s u a l t a l l y data for each rough green board included width, thickness, grade and log sawing number. 3.1.6 Lumber Y i e l d Evaluation To determine the lumber y i e l d from the processed logs at each sawmill, following the common practice to analyze sawmill productivity and e f f i c i e n c y , the lumber-log r e l a t i o n s h i p was expressed as a percentage of log input recovery as sawn lumber, measuring both volumes i n metric units. Lumber Volume , r , Lumber Recovery Percentage = — : — x 100 [11] J ° Log Volume 37 Two types of lumber recovery ratios were determined. The nominal lumber recovery percentage, which i s the relationship of lumber volume i n nominal dimension divided by the actual log volume, and the actual lumber recovery, which was expressed as the percentage of actual lumber volume by the actual log volume. To determine the actual lumber volume, the average dimensions from each of the boards recovered from 10 logs of the most common diameter classes were used. On each board the actual thickness was calculated by averaging s i x measurements, three at each edge equally spaced along the board. The actual width was obtained by the average of four measure-ments. The two dimensions were taken to the nearest millimeter. For the actual length one measurement was taken to the nearest centimeter. The data collected were used to compute the average actual dimension for each of the nominal dimensions produced by the six sawmills. 3.2 Log-Lumber and Byproduct Proportion At each of the six sawmills lumber, chippable residue and sawdust were determined from 10 logs of the most common diameter classes. Prior to sawing, the logs were peeled by hand. The average diameters were measured to the nearest centimeter at the small end and large end. Length was also measured to the nearest centimeter. A worker was placed at each machine centre to gather every piece of lumber from each of the logs. The rough green lumber was marked with the originating log number to iden t i f y each component of log volume. As soon as the boards l e f t the trim saw they were measured as described i n 38 Section 3.1.6 and weighed. Lumber and chippable residues (slabs, edgings and end trim) from each log were c o l l e c t e d separately and weighed on a platform-type balance to the nearest 0.010 kilogram. A d i r e c t r e l a t i o n -ship was assumed between lumber volume and lumber weight, which was used to determine the volume of chippable products once th e i r weights were known by d i r e c t measurement. The amount of sawdust was determined by subtracting lumber and s o l i d residue volume from the gross cubic log volume. 3.3 Quality Control 3.3.1 Log-length Allowance To evaluate the volume l o s t due to over length allowance, the sampled logs were grouped by actual length i n categories of 2-inch i n t e r v a l s . The volume of the log section exceeding the corresponding nominal length category was determined using the corresponding diameter c l a s s . Log volume l o s t due to overlength allowance was determined for 4-inch length allowance according to the accepted log-bucking practices i n the State of Durango (115). The volume l o s t for 6-inch length allowance was also determined, assuming that the processed logs could be considered as long logs (4, 30). 3.3.2 Lumber Dimension Allowance 3.3.2.1 Board Thickness Selection Due to the wide v a r i a t i o n of lumber dimension commonly produced for the market and, since the thickness dimension has the greatest e f f e c t on 39 lumber volume determination (95), i t was necessary to select the most representative lumber thickness for sawing variation analysis. Data collected on lumber thickness from each of the boards produced by sawing the logs sampled i n each sawmill were used to select the most representative thickness measurement i n nominal production. It was found that 3/4 inch nominal thickness accounted for most of the lumber volume produced under normal manufacturing conditions and obviously i t should also account for the most of the volume lost due to sawing variation (Figure 4). 3.3.2.2 Sample Size and Board Measurements According to the method described by Whitehead (109) and Brown (13, 14), a sample size of 100 boards i n rough green dimension was taken at random by selecting subgroups of 5 boards each, keeping the feed dire c t i o n constant at the headrig. On each of the sampled boards, 6 measurements of the thickness were taken to the nearest millimeter, 3 on each edge equally spaced along the board, avoiding the ends of the board as well as rot, knots or other defects. The following calculations were then performed. For each board, the range of within-board measurements (Rw), (the largest board measurement minus the smallest from the si x measurements), and the average board thickness (X), (the six measurement averaged) were computed. The range between boards (Rb) was calculated for each measurement point (a, b, c, d, e and f) among the five boards i n the subgroup by subtracting the smallest thickness from the largest thickness of the corresponding measurement points. 40 The average range of within-board measurements (Rw) and the average thickness (X) for the subgroup were determined by the average of the corresponding 5 ranges and averages from the boards i n each subgroup. The average range between boards (Rb) was calculated by the average of the six measurement points of the f i v e boards i n each subgroup. Overall average range within boards (Rw) for the 100 boards was calculated from the average range within boards (Rw) of each one of the 20 subgroups. Overall average range between boards (Rb) for the 100 boards was calculated by averaging the 20 ranges between averages (Rb) of each subgroup. Overall average thickness (X) for the 100 boards was determined by averaging the 20 average thicknesses (X) of each subgroup. 3.3.2.3 Board Sawing Variation Within-board sawing variation was determined by Equation No. 5. Between-board sawing va r i a t i o n was calculated by Equation No. 6. From the between-board var i a t i o n and within-board va r i a t i o n the t o t a l sawing var i a t i o n was calculated by use of Equation No. 7. 3.3.2.4 Target Size Determination Target size i s the smallest size the machine center can be set to cut without developing an excessive amount of undersized lumber. The target size of rough green lumber was determined by Equation No. 8, which i s repeated here for convenience: T = (S t.K) + SPF 41 The value f o r K was determined by assuming 5 per cent as the allowable l i m i t ; that i s , only 5 per cent of the production should have a thickness dimension below the target s i z e , then K = 1.650 standard deviations for a normal frequency d i s t r i b u t i o n . For the value of F, the fi n i s h e d thickness, i t was assumed that the nominal dimension should be equal to the actual dimension. Thus, for 3/4 inch boards the dry f i n i s h e d thickness would be 0.75 inch = 19.05 millimeters. S, shrinkage, was determined assuming that a nominal 4/4 inch green board, when planed, measured 25/32 inch and when dry planed measures 3/4 inch, by difference i t would have 25/32-3/4 or 0.78125 - 0.75 = 0.03125 inch shrinkage (44, 83). P, for planing l o s s , was considered to be 0.05 inch as the minimum volume of wood l o s t during planing (11). The target size was f i n a l l y determined by T = (1.65 S t) + 21.114 i n millimeters, with the corresponding values of S t for each one of the sawmills. This target size would be the thickness dimension that the sawmill should be cu t t i n g the lumber to get only 5 per cent of the production of the 3/4 inch nominal thickness with values lower than the 3/4 inch i n actual dimension when dried and planed. Comparing the target size with the o v e r a l l mean thickness value of the 100 sampled boards (X - T) represented excessive thickness. The lumber volume l o s t by excessive thickness allowance for each of the sawmills, was calculated by the following r e l a t i o n : X — T Volume l o s t = — - — x volume produced [12], X Where X i s the o v e r a l l average thickness and T i s the target value. 42 4. RESULTS AND DISCUSSION 4.1 Raw Material C h a r a c t e r i s t i c s 4.1.1 Raw Material From the analysis of data c o l l e c t e d from the logs sampled at the m i l l s yards, i t was determined that the most frequent diameter class ranged from 30 to 35 cm and accounted for 33.8 per cent of the logs input to the six sawmills. Nearly 80 per cent of the logs were within the diameter range from 25 to 40 cm (Table 5, Figure 1). From this observa-ti o n i t could be concluded that sawlogs have a very uniform diameter d i s t r i b u t i o n . This i s due to the fact that larger diameter logs are already depleted and the smaller diameters, which once were not cut by o f f i c i a l regulations, are usually allocated to some other processes. The most frequent log length class was 16 feet and accounted for almost 80 per cent of the processed logs (Table 5, Figure 2). This i s a well-defined length-bucking practice for sawlogs i n the State of Durango. Similar conclusions are reported by Zavala (115) who found that the most frequent diameter range was from 40 to 45 centimeters and the length was 16 f e e t . Although there i s not a well-defined log grading system, i n the attempt to evaluate log q u a l i t y i t was found that the 4 and 5 grades constituted 80 per cent of the logs processed, accounting for 78.5 per cent of log volume (Table 6, Figure 3). With the grading system applied, the No. 1 grade logs could have been allocated to a peeling process for veneer production, but i n general this does not happen because very few 43 enterprises are h o r i z o n t a l l y integrated, and log grading i s not a common pract i c e . 4.1.2 Log Sample Size The number of logs sampled for each sawmill was determined from the volume-variation analysis of log population being the 95 per cent confidence i n t e r v a l about the mean value for each m i l l . Small v a r i a t i o n i n length and diameter of log population as shown i n Table 5 enables the use of a r e l a t i v e l y small sample size to analyze the sawmilling process (Table 7). Since the study objective was not to cover a fixed number of logs for each diameter c l a s s , but rather to have f a i r l y representative values of the most common c h a r a c t e r i s i t c s of raw material processed under normal manufacturing conditions, attention was not paid to the small number of logs that f e l l under the extreme categories. Moreover, i t was found that, with one or three logs with rather unusual diameters, e s p e c i a l l y large ones, the required sample size to obtain the 95 per cent confidence i n t e r v a l would increase to 250 or even 300 logs. When this was the case these logs were not included i n the computation of sample siz e determination i n order to avoid p r o h i b i t i v e expenses. The number of logs studied at each sawmill ranged from 131 to 150, making up a t o t a l of 879 logs selected at random from the six sawmills. The sample size was s i m i l a r to those studies with i d e n t i c a l objectives (5, 65, 83). In other studies, the number of sampled logs was larger, but the objectives d i f f e r e d from the ones of t h i s study. In some the purpose was to have a representative number of logs by diameter classes or a representative sample of a v a i l a b l e tree c h a r a c t e r i s t i c s to 44 cover the range of log s i z e s , even when they were not representative of a t y p i c a l log mix. In other cases the main objective was to generate information to compare log grading rules or log scaling r u les (34, 42, 73, 75, 89, 93). 4.2 C h a r a c t e r i s t i c s of Lumber Recovery 4.2.1 Lumber Thickness From the sampled logs processed in each sawmill, the boards were recorded according to t h e i r nominal thickness; i t was found that 3/4 inch boards accounted for 52 per cent of the lumber volume produced. By number, t h i s thickness dimension accounted for almost 80 per cent of production (Table 8, Figure 4). Only one sawmill was producing a large lumber volume i n 1-1/2 inch thickness boards. This d i s t r i b u t i o n of lumber dimension i s d i f f e r e n t from the common lumber thicknesses produced i n other sawmill studies (20, 66, 85, 86, 87), and r e f l e c t s market demand for f i n a l end uses of lumber. In Mexico the use of lumber for s t r u c t u r a l framing i s minimal, while i n other countries this end use accounts for the highest lumber demand. 4.2.2 Lumber Grades The r e l a t i o n s h i p between log grades and lumber grades recovered has been established i n many ways (6, 23, 62, 70, 75, 89, 93, 113). Although the scope of t h i s study did not include any s t a t i s t i c a l or economic analysis to evaluate grade r e l a t i o n s h i p s , or to evaluate the grading system applied, the data in Table 9 suggest that the percentage of each lumber grade follows a s i m i l a r trend to the percentage d i s t r i b u t i o n of log grades. The No. 3, 4 and 5 lumber grades accounted for 73 per cent \ . 45 / of the lumber volume produced, and the same log grades accounted f o r 95.3 per cent of the log volume processed (Table 6). 4.3 Log Volume and Lumber Volume Relationship 4.3.1 Lumber Recovery Percentage Lumber recovery as a percentage of log volume input was determined for each sawmill following the normal procedure to evaluate sawmill e f f i c i e n c y . The o v e r a l l lumber recovery expressed by nominal lumber volume, as a percentage of actual log volume, was 43 per cent. Lumber recovery percentage was also determined d i v i d i n g the actual lumber volume by the actual log volume and expressed by the proportion as a percentage. The lumber recovery by t h i s procedure increased to 53 per cent, showing a very s i g n i f i c a n t d i f f e r e n c e between the two expressions of lumber recovery (Table 12). These percentages are f a i r l y representative values of the sawmilling practices i n the state of Durango. This conclusion could even be extended to the sawmill industry as a whole for the northern part of Mexico, since s i m i l a r values have been found i n other studies (96, 114, 115). The d i f f e r e n c e between the two values of lumber recovery represents 23.7 per cent of the nominal lumber volume output by the six sawmills. This volumetric difference i s not taken into account when the f i r s t phase of commercialization takes place between the sawmill and the warehouse. A c e r t a i n percentage of this volume represents extra revenue to the warehouse which usually s e l l s the lumber to the r e t a i l e r by i t s actual dimensions. 46 In general the lumber recovery percentage reported in this analysis, compared to the lumber recovery from other studies, i s lower when the nominal value i s used. However, when the actual lumber value i s used r e s u l t s are s i m i l a r , ranging from 50 to 60 per cent for most of the sawmills (20, 21, 29, 37, 65, 85, 104). This i s an i n d i c a t i o n of the various ways to express lumber recovery percentage, while in other countries the nominal lumber dimension i s larger than the actual dimension. In Mexico t h i s practice i s reversed, with larger values for actual lumber dimension than for nominal dimension (95). 4.3.2 Lumber Volume Allowance Usually, actual lumber dimensions are d i f f e r e n t from nominal dimensions and i n most of the cases they also d i f f e r from the standard allowance dimensions (17). According to the standard allowance for 3/4 inch lumber thickness, the actual volume should be 30 per cent l a r g e r than the nominal volume, while for 1-1/2 inch, 1-3/4 inch, and 2 inch lumber thickness the extra volume should be 15 per cent, 11.5 per cent and 8 per cent, re s p e c t i v e l y . No allowance i s added i n the case of thicknesses greater than 2 inches. From the analysis of the boards produced by sawing 10 logs i n each m i l l and measuring t h e i r actual dimensions to compare them with the nominal dimensions, the t o t a l volume allowance was obtained. The difference between the t o t a l allowance and the standard allowance varies from one sawmill to another (Table 10). The o v e r a l l allowance v a r i a t i o n was examined to determine the lumber volume l o s t for each nominal thickness i n each sawmill studied (Table 11). The lumber volume l o s t at the s i x m i l l s , due to over allowance f o r 3/4 inch, 1-1/2 inch, 1-3/4 inch 47 and 2-inch nominal thicknesses was 0.96 per cent, 5.33 per cent, 4.47 per cent and 7.36 per cent r e s p e c t i v e l y . The r e l a t i v e l y small percentage of 3/4 inch lumber volume over allowance i s made more s i g n i f i c a n t due to the large number of 3/4 inch boards produced (Table 11). The percentage of lumber volume l o s t varies among m i l l s . For 3/4 inch boards the greatest loss was recorded at MIL DIEZ with 2.43 per cent. This sawmill also accounted for the highest percentage of lumber produced i n that dimension. An opposite trend, with the lowest and even negative value i n allowance, was the m i l l - LA VICTORIA - with only 21 per cent of the lumber produced i n 3/4 inch thickness, which was the lowest value of the six sawmills. This m i l l also produced the highest percentage of lumber volume of 1-1/2 inch thickness, 52 per cent accounting for the highest volume l o s t by over allowance i n t h i s dimension. The percentage of volume of lumber l o s t by over allowance in 3/4 inch thickness i s n e g l i g i b l e for the o v e r a l l average. On the contrary for other thicknesses the loss could be very s i g n i f i c a n t , ranging from 4 to 7 per cent of the t o t a l lumber volume produced. The o v e r a l l lumber volume l o s t due to over allowance i n volume by the six sawmills was 2.75 per cent of the nominal volume produced (Table 12). This percentage also varies among sawmills, increasing to almost 5 per cent for the m i l l with the highest percentage of thicker lumber - LA VICTORIA. 4.3.3 Log-lumber and Byproducts Proportion The average product volume d i s t r i b u t i o n for the six sawmills was: 57.97 per cent lumber, 26 per cent chippable residue, and 16.03 per cent sawdust (Table 13). These r e s u l t s compare well with those described i n 48 other studies which report distr i b u t i o n s of 50 to 60 per cent lumber, 18 to 31 per cent chippable residue and 9 to 19 per cent sawdust (19, 20, 21, 48, 69, 73, 85, 86, 87, 96, 100, 104). It i s possible, by the procedure used i n this study, that the volume of chippable residue and sawdust are biased, because the effect on weight by moisture content differences between the slabs and boards was not taken into account for chippable volume determination. The difference i n moisture content could introduce error i n weight-volume relationships when the outer and inner parts of logs are compared. However, the relationship between volume and weight for lumber and slabs was found to be sim i l a r . This s i m i l a r i t y was confirmed by determining the volume of slabs from 5 logs by water displacement when the slabs were dipped i n a f u l l water container. No doubt more r e l i a b l e data on the proportion of each log component would have been obtained by weighing the logs. S t i l l a general conclu-sion can be drawn that 25 to 30 per cent of s o l i d residue i s a large proportion of the log volume that, at present, very few m i l l s allocate to secondary processing, such as pulping chips. A large number of m i l l s just burn these byproducts without recovering any benefit. It i s urgent to find an economical solution to the u t i l i z a t i o n of these large volumes of byproducts that are usually burned. Chipped residues could be shipped to pulp m i l l s to cope with the present d e f i c i t of pulp and paper products. 49 4.4 Quality Control 4.4.1 Log Length It was found that only 4.55 per cent of the logs had 2 inch length allowance over the nominal log length category (Table 14). The sawn lumber produced from these logs would probably not y i e l d lumber with the required length allowance. Usually a f t e r end trimming the board length allowance i s 3 inches, although i n some cases i t i s only 2 inches (95). The small percentage of roundwood with shorter length i s within the acceptable l i m i t s , assuming a nominal 4 inch log-length allowance. Moreover, the lumber volume recovered from these short logs would amount to only 2.25 per cent, assuming a 45 per cent lumber recovery, which again i s within acceptable l i m i t s . A general conclusion i s that the percentage of logs with shorter length values was not s i g n i f i c a n t . On the other hand, the percentage of logs with length-class category over 4 inches increased d r a s t i c a l l y , due to the poor bucking p r a c t i c e s . It was found that f o r 4 inch s p e c i f i e d log-length allowance, 90 per cent of the logs processed through the sawmills studied were misbucked. The over-length volume of these logs accounted f o r 4.75 per cent of the t o t a l sawmill volume input (Tables 14 and 15). When a 6 inch allowance was considered, the proportion of logs with over length decreased to 77.7 per cent; but the log over length volume did not change much, accounting for 4.34 per cent of the sawmills' input (Table 15). Comparing the percentage of log volume l o s t due to over lengths i n t h i s study, with values reported by Dobie (30) and by Zavala (115), there i s a difference of almost 1.5 per cent; they found a 3.1 per cent and 50 3.2 percent of log volume l o s t due to over lengths, r e s p e c t i v e l y . When comparing i t with the value reported by Aune and Lefebvre (4) the difference was 2.5 per cent. 4.4.2 Sawing V a r i a t i o n The average thickness for 3/4 inch nominal boards from the six sawmills ranged from 21 to 34 millimeters (Table 16, Figure 5). Similar values for thickness v a r i a t i o n have been reported i n other studies which have concluded that a great p o s s i b i l i t y for reducing sawing v a r i a t i o n e x i s t s i n most sawmills (11, 56, 102, 106, 107). From the data shown in Table 17, i t can be concluded that only one of the six sawmills was operating with a three standard deviation of 4.269 mm (0.168 i n ) , close to the value 3/32 inch (0.09375 in) defined by Valg (106) as being under s t a t i s t i c a l control or acceptable sawing v a r i a t i o n . In general sawing v a r i a t i o n between boards was the major component of the thickness v a r i a t i o n . This type of cutting v a r i a t i o n i s affected by setworks that do not set with consistent accuracy. Thus, the setworks should be the prime target for improvement i n control of sawing (11, 109). 4.4.3 P o t e n t i a l Lumber Recovery Increment by Cutting to Target Thickness The minimum f i n i s h e d thickness dimension for lumber to meet the requirements for nominal dry dressed of 3/4 inch i s 19.2 mm or 0.75 i n . The amount of shrinkage for green softwood lumber dried to produce 3/4 inch dressed lumber should be 0.794 mm or 0.0313 i n (44). The minimum amount removed for dressing i s assumed to be 1.27 mm or 0.05 i n (11). Thus, the minimun acceptable green thickness of sawn pieces would be 19.2 + 0.7937 shrinkage + 1.27 dressing = 21.264 mm or 0.8313 i n . 51 In order to compensate for v a r i a t i o n i n green thickness due to sawing inaccuracy, the average green thickness must exceed the minimum thickness by some s t a t i s t i c a l value related to the degree of inaccuracy. These values for each of the sawmills studied are shown i n Table 17. According to Cardenas (17), f o r 3/4 inch nominal lumber thickness, the actual thickness dimension should be either 22 mm or an allowance in volume of 30 per cent of the nominal lumber volume. Comparing both thick-ness values, 22 mm and 21.2637 mm, there i s a difference of 0.7363 mm, which i s the allowance for thickness v a r i a t i o n . Most of the m i l l s studied had a sawing v a r i a t i o n larger than t h i s value. Only one sawmill - MIL diez - without making any adjustment i n the setworks, could reduce i t s actual average thickness from 25.429 mm to a target thickness of 23.461 mm and produce les s than 5 per cent of the lumber with skip. This value was the closest to 22 mm. There are indications that i t might be possible to improve the sawing accuracy to reduce the actual target thickness values of most of the sawmills studied without an increase i n skip (106). One of the r e s u l t s of this study i s that, even with the present operating conditions, without any setworks adjustment the six sawmills could reduce t h e i r actual average thickness by 1.918 mm, 2.148 mm, 0.06 mm, 0.434 mm, 1.237 mm and 0.953 mm respectively without increasing skip (Table 18). This reduction in thickness would r e s u l t i n an increase of lumber recovery by 7.74 per cent, 8.14 per cent, 0.23 per cent, 1.76 per cent, 4.87 per cent and 3.8 per cent respectively of the t o t a l lumber volume produced i n 3/4 inch thickness by the corresponding sawmills. The o v e r a l l p o t e n t i a l increment on lumber recovery i n 3/4 inch thickness categories for the s i x sawmills would be 4.46 per cent. 52 The o v e r a l l d i f f e r e n c e between the actual mean thickness and the target thickness for the s i x sawmills, X - T, was 1.134 mm. The po t e n t i a l lumber recovery, by applying this factor to the d i f f e r e n t lumber thickness volumes produced, would be 6.4509 cubic meters, which would account f o r 3.5 per cent of the lumber volume processed (Table 19). 4.4.4 P o t e n t i a l Lumber Recovery Increment by Reducing Sawing V a r i a t i o n An a d d i t i o n a l lumber volume could be recovered by improving sawing accuracy to reduce the target thickness without an increase i n skip. Sawing v a r i a t i o n could be reduced to 0.12 inch or 2.38 mm (106). Only one of the sawmills sampled, MIL DIEZ, was working close to that value with 3 standard deviations = 0.1681 i n or 4.269 mm, with a target thickness of 23.461 mm. This means that even this sawmill has room for improvement. The other f i v e m i l l s with larger sawing variations d e f i n i t e l y should be able to reduce losses to at le a s t the same l e v e l as MIL DIEZ. Adjusting the setworks i n the f i v e sawmills and assuming that t h e i r actual target thickness could be reduced to the same value as the target thickness of MIL DIEZ, the pot e n t i a l thickness reduction would be: 3.22 per cent, 8.96 per cent, 2.81 per cent, 2.97 per cent, 2.53 per cent, for each of the respective m i l l s (Table 18). The o v e r a l l p o t e n t i a l lumber increment would be 3.49 per cent of the lumber volume produced i n 3/4 inch thickness, a f t e r discounting the potential volume gained by sawing to the target thickness. The o v e r a l l average thickness reduction, by adjusting the setworks on the f i v e m i l l s and a f t e r discounting the po t e n t i a l reduction by sawing to smaller green target s i z e , would be 0.849 mm (Table 18). Assuming that 53 this reduction i s also possible for the other board thicknesses produced, an additional 2.76 per cent of lumber volume would be recovered (Table 19). 4.5 Economic Analysis During 1980 approximately 1,152,574 cubic meters of logs were converted to lumber i n the State of Durango (115). Cubic meter losses of roundwood assuming nominal 6-inch log length allowance, accounted for 4.34 per cent of the log volume throughout, which would constitute 50,021,712 cubic meters of logs. Conservatively assuming 45 per cent lumber recovery, the potential lumber volume y i e l d from improved bucking standards would be 22,509.77 cubic meters or nearly 9,544,142.7 board feet, with a conversion factor of 424 board feet per cubic meter. The 1,152,574 cubic meters of roundwood volume allocated to saw-m i l l i n g , assuming 45 per cent lumber recovery, would y i e l d 518,658.3 cubic meters of lumber. The potential lumber recovery of sawing to reduced target thickness would be 3.55 per cent of the lumber volume produced, which would constitute 18,412.37 cubic meters or 7,806,844.7 board feet. It i s l i k e l y that the potential lumber volume gained would be recovered without any additional equipment adjustment or equipment investment, simply by closer control of the bucking and sawing tolerances. By adjusting the setworks, an additional lumber volume could be recovered, which would account for 2.7 6 per cent of the remaining lumber volume once the potential lumber y i e l d increment by sawing to target 54 thickness was discounted. This p o t e n t i a l lumber recovery would constitute 13,806.788 cubic meters or nearly 5,854,078 board fee t . The o v e r a l l p o t e n t i a l lumber volume recovery by the control of log bucking practices, sawing to target thickness and reducing sawing v a r i a t i o n would account for an a d d i t i o n a l 54,728,928 cubic meters or 23,205,065 board feet of lumber produced during 1980 i n the State of Durango. The price of lumber as m i l l - r u n grade, during the l a s t months of 1980, was 8,272.15 Mexican pesos per M bd f t (115). The po t e n t i a l lumber recovery would represent an ad d i t i o n a l revenue of 191,955,780 Mexican pesos or 8,345,903 US d o l l a r s to the sawmilling industry or a p o t e n t i a l savings to r e t a i l e r s by cheaper lumber products. 55 5. CONCLUSIONS AND RECOMMENDATIONS 5.1 Conclusions 5.1.1 In the State of Durango log bucking practices y i e l d a log d i s t r i b u t i o n i n which nominal 16 feet logs constitute 78 per cent of the log population. 5.1.2 Log diameter by class d i s t r i b u t i o n was concentrated i n three 5-centimeter range categories from 25 to 40 cm, accounting f o r 80 per cent of the processed logs. 5.1.3 Sample size required to analyze lumber recovery p r a c t i c e s , with 95 per cent confidence i n t e r v a l s on the mean volume, i s considered to be r e l a t i v e l y small with an average of 150 logs per m i l l . 5.1.4 The most common lumber thickness y i e l d under normal manufacturing practices i s 3/4 inch boards which make up 80 per cent of the t o t a l number of pieces produced and 52 per cent of the t o t a l lumber volume recovered. 5.1.5 Calculated recovery percentage, when based on nominal dimension, i s approximately 43 per cent; when based on actual dimension the value i s about 53 per cent. 5.1.6 26 per cent of log volume i s converted into slabs and end trim residues, from which at the present very few m i l l s derive any benefit . 56 5.1.7 Log over length allowance represented 4.34 per cent of t o t a l log volume throughput of the m i l l s . This amount could be reduced by close control of the bucking practices with r e s u l t i n g p o t e n t i a l for higher lumber volume recovery. 5.1.8 A d d i t i o n a l lumber volume can be recovered by diminishing the actual mean lumber thickness to the s t a t i s t i c a l l y determined target thickness, which would re s u l t i n a p o t e n t i a l gain i n volume of 3.55 per cent of the t o t a l lumber produced. By reducing the actual sawing v a r i a t i o n a p o t e n t i a l y i e l d increment of 2.76 per cent of the t o t a l lumber volume produced could be achieved. 5.1.9 Considerable lumber volume could be recovered by bucking the logs to the appropriate length, by reducing the actual average lumber thickness to the determined target thickness, and by keeping sawing v a r i a t i o n to an appropriate l e v e l . The p o t e n t i a l lumber value recovery i n 1980 i n the State of Durango represented 54,728,928 cubic meters or 23,205,065 bd f t which, translated to d o l l a r values, would be a potential revenue of 8.3 m i l l i o n US d o l l a r s to the sawmilling industry. 57 5.2 Recommendations 5.2.1 Since currently 26 per cent of log volume i s converted into slabs and end trims with no f i n a n c i a l return, i t i s suggested that an economic analysis be carried out to determine the f e a s i b i l i t y of a l l o c a t i n g chippable residues to pulp m i l l s . 5.2.2 The strong i n d i c a t i o n of p o t e n t i a l lumber recovery increment, by c o n t r o l l i n g the bucking and sawing operations, should be exploited. P a r t i c u l a r attention should be directed toward these two factors by the sawmilling industry since no a d d i t i o n a l investment i s required. 5.2.3 Further work should be conducted with d i f f e r e n t sawmill capacities and sawmill c h a r a c t e r i s t i c s to determine a more precise o v e r a l l p o t e n t i a l recovery with regard to sawing v a r i a t i o n and bucking p r a c t i c e s . 5.2.4 Log-length v a r i a t i o n and sawing v a r i a t i o n analysis should be included i n sawmilling studies as a common practice to evaluate sawmill e f f i c i e n c y . 5.2.5 Emphasis should be given to the control of log length and sawing v a r i a t i o n i n t r a i n i n g programs related to sawmilling processes, e s p e c i a l l y the ones offered to operating personnel. 58 BIBLIOGRAPHY 1. Adams, J . J . 1976. The sawing of West African hardwood logs. J. Inst. Wood S c i . 7(4):2-4. 2. A l l e n , F.E. 1973. High-strain/thin kerf. 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Fahey, Thomas D. and Douglas L. Hunt. 1972. Lumber Recovery from Douglas-fir thinnings at a band m i l l and two chipping centers. USDA For. Serv. Res. Pap. PNW-131, 9 pp. Pac. Northwest For. and Range Exp. Stn. Portland, Ore. 50. . 1975. Lumber recovery from Grand f i r thinnings at a band m i l l and chipping center. USDA For. Serv. Res. Pap. PNW-186, 15 pp. Pac. Northwest For. and Range Exp. Stn. Portland, Ore. 51. Fahey, Thomas D. and Richard 0. Woodfin. 1976. The cubics are coming: Predicting product recovery from cubic volume. J . For. 74(11):739-743. 52. Flann, l.B. 1974. Sawing patterns, log grades and log lengths for converting hardwood logs. Can. For. Ind. 94(9):33-38. 53. Freese, Frank. 1974. A c o l l e c t i o n of log rul e s . USDA For. Serv. Gen. Tech. Pap. FPL-1, For. Prod. Lab. Madison, Wise. 62 54. Freese, Frank. 1967. Elementary s t a t i s t i c a l methods for foresters. USDA Agri c u l t u r e Handbook. 317, 43 pp. 55. Hallock, Hiram. 197 9. The e f f e c t of log taper on lumber recovery. Modern Sawmill Techniques, Proceedings of the Ninth Sawmill C l i n i c , Portland Ore. 72-78 pp. 56. . 1978. There i s more lumber i n that log! Modern Sawmill Techniques, Proceeding of the eighth Sawmill C l i n i c Library 8:93-108. 57. Hallock, H., and David W. Lewis. 1971. Increasing softwood dimension y i e l d from small logs - Best Opening Face. USDA For. Serv. Res. Pap. FPL 166, 12 pp. For. Prod. Lab. Madison, Wise. 58. . 1973. Best opening face for southern pine. Modern Sawmill Techniques, Proceedings of the Second Sawmill C l i n i c , New Orleans La. Sawmill C l i n i c L i b r a r y 2:204-225. 59. Hallock, H., P h i l i p Steele and Richard S e l i n . 1979. Comparing lumber y i e l d s from board-foot and c u b i c a l l y scaled logs. USDA For. Serv. Res. Pap. FPL 324, 17 pp. For. Prod. Lab. Madison, Wise. 60. Hallock, H., A b i g a i l R. Stern and David W. Lewis. 1976. Is there a "best" sawing method? USDA For. Serv. Res. Pap. FPL 280, 12 pp. For. Prod. Lab. Madison, Wise. 61. Hanks, Leland F. 1977. Predicted cubic-foot y i e l d s of lumber, sawdust, and sawmill residue from the saw-timber portions of hardwood trees. USDA For. Serv. Res. Pap. NE-380, 23 pp. Northeastern For. Exp. Stn. Upper Darby, Pa. 62. Hanks, Leland F. and Robert L. B r i s b i n . 1978. Lumber grade y i e l d s for graded aspen logs and trees. USDA For. Serv. Res. Pap. NE-423, 12 pp. Northeastern For. Exp. Stn., Broomall, Pa. 63. Harpole, George B. and Hiram Hallock. 1977. Investment opportunity: best opening face sawing. USDA For. Serv. Res. Pap. FPL 291, 9 pp. For. Prod. Lab. Madison, Wise. 64. Henley, John W. 1972. Grading sugar pine saw logs i n trees. USDA For. Serv. Res. Pap. PNW-132, 8 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. 65. Henley, John W. and Marlin E. Plank. 1974. Lumber y i e l d from Engelmann spruce i n Arizona. USDA For. Serv. Res. Pap. PNW-170, 11 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. 63 66. Huber Dean, George H. Sisterhenm, Robert L. Mardock, James L. Rus s e l l , Robert W. Mix and Frank John Banducci. 1976. Building a p r a c t i c a l q u a l i t y control program. Modern Sawmill Techniques. Proceedings of the Sixth Sawmill C l i n i c , Portland, Ore. Sawmill C l i n i c L i b r a r y , 6:186-228. 67. James Shepard, M e r r i l l . 1974. The package m i l l for small operations. Modern Sawmill Techniques. Proceedings of the Fourth Sawmill C l i n i c New Orleans, La. Sawmill C l i n i c L i b r a r y 4:143-158. 68. Kennedy, Joyce. 1978. Log u t i l i z a t i o n can be improved. B.C. Lumberman 62(4):52-53. 69. Kerbes, E.L. and J.A. Mcintosh. 1969. Conversion of trees to fi n i s h e d lumber-the volume losses. Forest. Chron. (10):348-352. 70. . 1968. Some re l a t i o n s h i p s between exterior log c h a r a c t e r i s t i c s and lumber recovery values for samples of B.C. I n t e r i o r spruce. West. For. Prod. Lab. Inf. Rep. VP-X-41, 19 pp. Vancouver, B.C. 71. Kirbach, E. 1974. A survey of sawing technology i n Western Canada, West For. Prod. Lab. Inf. Rep. VP-X-124, 21 pp. Vancouver, B.C. 72. Lane, Paul H. 1963. Evaluating log and tree q u a l i t y for wood products. Forest Prod. J . 23(3):89-93. 73. Lane, P.H., John W. Henley, Richard 0. Woodfin J r . , and Marlin E. Plank. 1973. Lumber recovery from old-growth coast Douglas-fir. USDA For. Serv. Res. Pap. PNW-154, 44 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. 74. Lane, P.H. and Richard 0. Woodfin J r . 1977. Guidelines for log grading coast Douglas-fir. USDA For. Serv. Res. Pap. PNW-218, 14 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. 75. Lane, P.H., Richard 0. Woodfin J r . , John W. Henley and Marlin E. Plank. 1972. Lumber y i e l d from Sitka spruce i n southeastern Alaska. USDA For. Serv. Res. Pap. PNW-134, 44 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. 76. Lefebvre, E. 1978. How improper log bucking reduces lumber revenues. Can. For. Ind. 98(9):21-25. 77. Lewis, David W. and Hiram Hallock. 1973. Using computers to increase lumber yield...best opening face program. 4th Wood Machining Seminar, Dec. 4-6, 1973. Richmond, C a l i f . 16 pp. 64 Malcolm, Fred B. and Hiram Hallock. 1972. Ef f e c t s of three sawing methods on warp of hard maple dimension cuttings. Forest Prod. J. 22(4):57-60. Mason, H.C. C a r l . 1976. Analysis of BOF sawing system. Aust. For. Ind. 42(7):53-55. McBride, C F . 1963. Sawing small logs. Forest Chron. 39(2):175-182. McEwan, T.K. 1974. Analysis of the e f f e c t of the lumber recovery factor (LRF) on sawmill costs. Forest Prod. J . 24(3):17-19. Mueller, L i n c o l n A. and Roland L. Bager. 1963. Lumber grade recovery from Engelmann spruce i n Colorado. USDA Res. Pap. RM-1, 23 pp. Rocky Mtn. For. and Range Exp. Stn., Fort C o l l i n s , Col. National Lumber Grades Authority. 1975. Standard grading rules for Canadian lumber. Vancouver, Canada. 233 pp. Petro, F.J., S.M. Pnevmaticos and R.E. Booth. 1974. Bolt grades and lumber y i e l d s from white b i r c h . Can. For. Ind. 94(10):49-52. P h i l l i p s , Douglas R. 1975. Lumber and residue y i e l d s from black oak saw logs i n western North Carolina. Forest Prod. J . 25(l):25-33. . 1974. Predicted green lumber and residue y i e l d s from the merchantable stem of black oak trees. USDA For. Serv. Res. Pap. SE-120, 10 p. Southeastern For. Exp. Stn., Ash e v i l l e , N.C P h i l l i p s , Douglas R. and James G. Schroeder. 1975. Predicted green lumber and residue y i e l d s from the merchantable stem of shortleaf pine. USDA For. Ser. Res. Pap. SE-128, 12 pp. Southeastern For. Exp. Stn., A s h e v i l l e , N.C. Plank, Marlin E. 1979. Lumber recovery from l i v e and dead lodge-pole pine i n southwestern Wyoming. USDA Res. Note PNW-244, 15 i Pac. Northwest For. and Range Exp. Stn., Portland, Ore. Plank, Marlin E. and John W. Henley. 1976. Lumber y i e l d s by the new timber c r u i s i n g log grades for old-growth coast Douglas-fir. USDA For. Ser. Res. Pap. PNW-203, 30 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. Plank, Marlin E. and Thomas A. Snellgrove. 1973. Lumber y i e l d from western white pine i n northern Idaho. USDA For. Serv. Res. Pap. PNW-153, 30 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. 65 91. Pnevmaticos, S.M. 1975. Improving recovery from softwood bucking i n eastern Canada. Can. For. Ind. 95(5):42-47. 92. Pnevmaticos, S.M., l.B. Flann and F.J. Petro. 1971. How log c h a r a c t e r i s t i c s r e l a t e to sawing p r o f i t . Can. For. Ind. 91(l):40-43. 93. Pong, W.Y., and T.D. Fahey. 1973. Lumber recovery from red and white f i r i n ce n t r a l C a l i f o r n i a . USDA For. Serv. Res. Pap. PNW-167, 39 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. 94. Prestemon, Dean R., Fred E. Dickinson and William A. Dost. 1965. Chinkapin log grades and lumber y i e l d . C a l i f . For. and For. Prod. 42:1-5. 95. Rodriquez, Caballero, Rodolfo. 1978. Coeficientes de refuerzo y de ase r r i o en l a p r a c t i c a mexicana de produccion de maderas aserradas de pino. Mexico y sus bosques 17(l):8-23. 96. Schroeder, James G., Michael A. Taras and Alexander Clark I I I . 1975. Stem and primary product weights for longleaf pine saw-timber trees. USDA For. Serv. Res. Pap. SE-139, 15 pp. Southeastern For. Exp. Stn., A s h e v i l l e , N.C. 97. S i n c l a i r , S.A., G. I f j u and H.J. Heikkenen. 1977. Logging and sawmilling. Bug boards. Lumber y i e l d , and grade recovery from timber harvested from southern pine beetle infested f o r e s t s . Southern Lumberman 234(2900):9-11. 98. Snellgrove, Thomas A. 1977. White pine yields-decrease as time since death increases. Forest Ind. 104(4):26-28. 99. Snellgrove, Thomas A. and David R. Darr. 1976. Lumber pot e n t i a l for c u l l logs i n the P a c i f i c Northwest. Forest Prod. J. 26(7):51-54. 100. Snellgrove, Thomas A., John W. Henley and Marlin E. Plank. 1975. Lumber recovery from large, highly defective, low grade coast Douglas-fir. USDA For. Serv. Res. Pap. PNW-197, 23 pp. Pac. Northwest For. and Range Exp. St., Portland, Ore. 101. Steele, P h i l i p H. and Hiram Hallock. 1979. A mathematical model to calc u l a t e volumes of lumber and residue produced i n sawmilling. USDA Res. Pap. FPL-336, 44 pp. For. Prod. Lab., Madison, Wise. 102. Stern, A b i g a i l R., Hiram Hallock and David W. Lewis. 1979. Improving sawing accuracy does help. USDA For. Serv. Res. Pap. FPL-320, 13 pp. For. Prod. Lab., Madison, Wise. 66 103. Subsecretaria Forestal y de l a Fauna. 1980. S i l v i c u l t u r a 78. SARH. Dpto. de Divulgacion Forestal y de l a Fauna, Mexico. 145-147 pp. 104. Taras, Michael, James G. Schroeder, and Douglas R. P h i l l i p s . 1974. Predicted green lumber and residue y i e l d s from the merchantable stem of l o b l o l l y pine. USDA For. Serv. Res. Pap. SE-121, 11 pp. Southeastern For. Exp. Stn., A s h e v i l l e , N.C. 105. USDA. 1973. Increasing your lumber recovery. Sawmill improvement program. Washington, D.C. 25 pp. 106. Valg. L. 1965. Analysis of sawing accuracy by s t a t i s t i c a l q u a l ity c o n t r o l . B.C. Lumberman 56(6):68-72. 107. . 1978. P r e c i s i o n cutting i s not improving. B.C. Lumberman 63(2):41-43. 108. Warren, W.G. 1973. How to calculate target thickness for green lumber. West. For. Prod. Lab. Inf. Rep. VP-X-112, 11 pp. Vancouver, B.C. 109. Whitehead, J.C. 1978. Procedures for developing a lumber-size control system. West. For. Prod. Lab. Inf. Rep. VP-X-184, 15 pp. Vancouver, B.C. 110. Woodfin, Richard 0. J r . 1978. Ponderosa pine lumber recovery ... young growth i n northern C a l i f o r n i a . USDA For. Serv. Res. Pap. PNW-237, 13 pp. Pac. Northwest For. and Range Exp. Stn., Portland, Ore. 111. . 1976. Po t e n t i a l s from salvage timber. USDA Rocky Mountain Forest Industries Conference i n Missoula, Mont. A p r i l 26-28, 1976. 112. Woodfin, Richard 0. J r . and Marlin E. Plank. 1973. Douglas-fir c u l l logs and c u l l peeler blocks. USDA For. Serv. Res. Pap. PNW-164, 13 pp. Pac. Northwest For. and Range Exp. Stn. Portland, Ore. 113. Woodfin, Richard 0. J r . , Marlin E. Plank and Thomas A. Snellgrove. 1976. Western hemlock i n southeast Alaska ... u t i l i z a t i o n , lumber recovery and chip y i e l d . USDA For. Serv. Res. Pap. PNW-208, 33 pp. Pac. Northwest For. and Range Exp. Stn. Portland, Ore. 114. Zavala, D. 1980. Rentabilidad de l a t r o c e r i a de pino en e l proceso de a s e r r i o . In press i n Ciencia F o r e s t a l . 115. Zavala, R. 1981. Caracterizacion de l a Industria de Aserrio en e l Estado de Durango. In press i n Ciencia F o r e s t a l . 67 TABLE 1: Proportion of lumber, chippable residue and sawdust by log diameter range and sawmill type (18, 29, 35, 37, 39, 41) Proportion i n Percentage Headrig type Log top Green S o l i d diameter lumber residue Sawdust (in) Band, Conventional 5 - 15 56 31 13 Band, High St r a i n 4 - 15 68 20 12 C i r c u l a r 6 - 15 54 31 13 Log-Gang 6 - 14 . 55 32 13 Scrag 5 - 14 51 26 23 ) Chip-n-saw 6 - 14 55 40 5 Chipper Headrig ) ) Beaver canter 6 - 14 52 43 4.5 TABLE 2: Summary of references i n log-lumber and byproduct r e l a t i o n s h i p Proportion i n Percentage Reference Species Log diameter (in) Head saw type Saw kerf (in) Lumber dimension (in) Lumber Chippable residue Sawdust Bark 87 Short l e a f pine 4-20.4 Band headrig 3/16 1x5, 1x3 54 2.6 10 10 85, 86 Black oak 11.9-25.6 Band 4/4, 5/4 55 20 10 15 19, 21 Yellow poplar 11.7-28.4 Band 3/16 4/4 54 18 13 15 20 Slash pine 9.6-21 Cir c u l a r 5/16 4/4, 8/4 51 22 17 104 L o b l o l l y pine 9.8-19.4 Ci r c u l a r 8/4, 4/4 50.3 28.5 13.6 7.6 96 Pine Ci r c u l a r 5/16 4/4, 8/4 54 21 16 9 65 Engelmann spruce 6-34 Band 7/32 2x4, 2x6 93 White f i r 7-50 Band 8/32 100 Douglas-fir Band 62.5 24.5 8 75 Sitka spruce 6-56 Band 48 Douglas-fir 4-44 Doublecut band 60 31 9 69 4-14 3/8 61 20 19 50 Grand f i r 4-14 4-14 Band Chipper 53.6 49.9 35.1 44.1 13.3 5.4 TABLE 3: Type and number of sawmills i n the State of Durango BAND HEADSAWS CIRCULAR HEADSAWS Number of M i l l s Band widths (in) Number of M i l l s Headsaw diameter ( i n ) 2 4 2 36 4 5 1 46 19 6 4 48 7 7 1 50 33 8 13 54 17 10 16 56 1 11 3 60 1 12 Source: Caracterizacion de l a Industria Forestal en e l Estado de Durango (115). 70 TABLE 4: Log grades Log spading practices i n the State of Durango vary l o c a l l y , making i t impossible to present a single log grading r u l e . As noted from Table 6, 95% of the logs were found to grade no better than Grade 3 which i s defined approximately as: Diameter: Minimum 12 unches Length: Minimum 12 feet Knots: Live permitted up to 1/6 of diameter Dead permitted up to 1/12 diameter One knot over maximum size permitted. TABLE 5: Sawlog distribution by length and diameter categories Number of logs by length classes Number of logs by diameter clas 1 8 ' 1 2 ' 1 4 ' 1 6 ' U ' 20'. >20<25 >25<30 >30<35 >35<40 >40<45 >45<50 >50<55 >55<60 >60<65 >65<70 MIL DIEZ . 6 21 7 116 8 52 47 26 12 4 0 1 LOS BANCOS 2 6 12 106 5 1 19 33 45 13 17 2 1 LA CIUDAD 4 9 90 30 17 2 26 49 43 26 1 1 1 CHAVARR1A 116 9 23 1 27 44 " 34 15 11 9 5 EL BRILLANTE 12 2 117 7 12 13 57 49 21 9 1 LA VICTORIA 2 144 1 3 5 30 66 39 8 2 No. OVERALL 8 43 32 689 52 55 17 167 296 236 95 44 13 8 % 0.9 4.9 3.7 78.4 5.9 6.2 1.9 19.0 33.8 26.8 10.8 5.0 1.5 0.! 1 2 9 0.1 0.2 TABLE 6: Number of logs and volumes by grading classes Sawmills Number of logs by grade s Log volumes by grades (nr*) 1 2 3 4 5 1 2 3 4 5 MIL DIEZ 1 19 130 0.5314 9.6521 53.2845 LOS BANCOS 17 38 76 9.8234 13.7668 38.7550 LA CIUDAD 5 32 64 32 17 2.7666 19.6662 35.6697 17.1110 9.5863 CHAVARRIA 1 11 44 92 1.4816 9.3160 28.4041 51.6792 EL BRILLANTE 3 16 33 98 1.7530 10.3694 16.5936 54.3393 LA VICTORIA 1 25 37 87 0.5567 12.2137 18.3560 38.4227 No. 5 37 134 203 500 2.7666 23.4575 77.9226 113.8836 246.0371 OVERALL % 0.6 4.2 15.2 13.1 56.9 0.6 5.0 16.8 25.5 53.0 to TABLE 7: Number of logs sampled to give 95 per cent confidence i n t e r v a l about the population mean Parameter S a w m i l l s M i l Diez Los Bancos La Ciudad Chavarria E l B r i l l a n t e La V i c t o r i a Preliminary log sample size Mean log volume (m 3) Standard deviation (m3) Variance (m ) Student t value Xr value Standard error of the mean 2 E value Required sample size Sample size studied 80 .453284 .150552 .019775 2 4 .022664 .000514 153 150 80 .537002 .149350 .022305 2 4 .026850 .000721 123.76 131 80 .506059 .152422 .023232 2 4 .025303 .000640 145.15 150 80 .516400 .154327 .023817 2 4 .025820 .000667 142.89 148 80 .569200 .159536 .025452 2 4 .028460 .000810 125.68 150 80 .547814 .164348 .027010 2 4 .027318 .000750 143.99 150 u> TABLE 8: Volume and percentage of pieces of lumber recovered by thickness classes LUMBER RECOVERY BY THICKNESS CATEGORIES 3/4 In thickness 1-1/2 in thickness 1-3/4 in thickness 2 in thickness 3 in thickness Others // Pieces Volume m // Pieces Volume m // Pieces Volume m // Pieces Volume m // Pieces Volume ra // Pieces Volume tn" MIL DIEZ 92.3% 2198 77.6% 21.4890 1.0% 23 2.6% .7265 6.8% 161 19.8% 5.4204 --LOS BANCOS 78.9% 1528 46.6% 14.9673 13.3% 257 29.8% 9.5718 6.9% 135 16.1% 5.1814 .8% 16 2.5% 2.416 LA CIUDAD 77.6% 1342 58.1% 20.6184 20.3% 352 33.1% 11.7577 .2% 3 .4% .140 1.9% 34 8.4% 2.992 CHAVARRIA 77.7% 1944 48.6% 19.4208 12.3% 307 26.0% 10.3784 8.8% 222 22.5% 8.9841 .7% 17 1.1% .4545 .2% 6 1.1% .4191 .2% 4 .7% .264 EL BRILIANTE 88.1% 1974 63.3% 21.8255 2.6% 59 5.4% 1.8661 6.8% 153 20.2% 7.0313 • 2.5% 55 10.8% 3.758 LA VICTORIA 59.6% 1045 21.7% 6.5064 29.2% 498 51.8% 15.5343 9.2% 157 21.2% 6.3446 1.4% 34 . 5.4% 1.6087 No. OVERALL X 79.0% 10002 52.6% 104.8279 13.1% 1496 24.8% 49.8348 3.8% 521 9.8% 19.7254 2.7% 327 7.1% 13.8304 .3% 40 1.1% 2.0278 .9% 109 4.6% 9.43 4> TABLE 9: Lumber volume recovery by grade categories (based on log volume) LUMBER VOLUME BY GRADES Sawmills MIL DIEZ LOS BANCOS LA CIUDAD CHAVARRIA EL BRILLANTE LA VICTORIA Mean OVERALL Lumber volume recovery (m3) Grade 1 (m ) Volume 27.6359 32.1368 35.5078 39.9219 34.4810 29.9940 2.5260 3.98 3.6900 4.99 4.1721 4.92 6.9069 7.25 5.4069 6.51 1.7451 2.51 Grade 2 Grade 3 Grade 4 Grade 5 Volume (mJ) Volume (m J) ^Volume (m ) % -Volume (m ) 2.4120 3.80 10.1180 15.94 5.6501 7.81 13.0293 18.01 4.2823 5.05 16.1967 19.10 7.4976 7.90 14.8752 16.02 3.3554 4.04 12.7739 15.38 3.2479 4.69 7.9425 11.42 12.5799 19.82 9.6436 13.33 8.4291 9.94 10.7693 11.50 12.9400 15.53 16.9630 24.39 2.6711 3.15 4.0746 5.02 4.4067 5.54 12.4892 15.97 11.8874 15.76 0.4451 0.52 Total 199.6774 24.4475 12.24 26.4453 12.24 74.9356 37.53 71.3249 35.72 3.1162 1.60 T A B L E 10: D i s t r i b u t i o n o f l u m b e r y i e l d b y n o m i n a l a n d a c t u a l d i m e n s i o n o f t h i c k n e s s , w i d t h , l e n g t h a n d v o l u m e S a w m i l l s T h i c k n e s s it o f b o a r d s W i d t h s ( i n ) L e n g t h ( f t ) V o l u m e (m^) P e r c e n t a g e s N o m i -n a l ( i n ) A c t u a l (mm) 4 6 8 10 12 8 10 12 14 16 A c t u a l N o m i n a l S t d . A c t u a l I ^ ^ ^ e T I e n c e K I L D I E 2 3/4 1 1/2 1 3/;. 2 " . 0 2 5 3 . 0 4 3 3 .C4(:5 C r J 4 7 (.11f>2) 42 ( . 1 6 4 5 ) 34 2 6 ( . 2 1 2 4 ) 13 2 1 ( . 2 7 4 5 ) ( . 3 2 9 5 ) ( 2 . 4 6 ) 10 ( 3 . 1 2 9 ) 10 1 ( 3 . 7 4 9 ) 8 1 ( 4 . 3 7 9 ) 8 . 2 ( 4 . 9 0 0 ) 45 3 4 1 .4144 . 1 5 2 6 . 2 5 9 4 .954-, ' . 1 2 0 5 . 2 2 5 7 3 0 % 1 5 * 1 1 . 5 * 32.43 2 1 . 0 2 1 3 . 9 2 2 . 4 3 6 . 0 2 2.42 L C S DA'JCC 3 3/4 1 1/2 1 3/4 2 . 0 2 4 3 . 0 4 3 2 • 051c! . 0 5 7 1 1 7 0 16 6 7 ( . 1 1 4 6 ) 17. 1 ( . 1 6 7 6 ) 46 7 2 5 ( . 2 1 9 3 ) 7 8 4 2 ( . 2 7 7 4 ) ( . 3 2 2 9 ) ( 2 . 4 6 4 ) 13 ( 3 . 0 7 9 ) 3 ( 3 . 6 8 4 ) 16 1 ( 4 . 3 0 1 ) 7 2 1 1 ( 4 . 9 1 0 ) 31 14 5 5 1 . 1 3 4 0 . 6 8 2 6 . 3 0 5 9 . 3 3 6 4 . 7 6 4 6 . 5 4 3 4 . 2 3 7 0 . 2 7 3 6 3 0 % 1556 1 1 . 5% 0 . 0 % 3 0 . 6 1 2 0 . « . 0 2 2 . 5 2 T V . 15 . 0 1 % 5 . 4 0 1 1 . 0 2 1 1 . 1 5 L A C I U D A D 3/4 1 1/2 1 3 / 4 c . 0 2 6 5 . 0 4 3'. . 0 5 1 1 .os'.o 142 10 10 ( . 1 1 1 6 ) 19 ( . 1 6 7 7 ) 33 ( . 2 7 7 5 ) 2 9 3 3 ( . 2 7 1 3 ) 31 2 2 ( . 3 2 1 4 ) 30 5 5 ( 2 . 4 6 6 ) 55 ( 3 . 0 9 2 ) 9 ( 3 . 6 7 4 ) 19 1 1 ( 4 . 2 8 8 ) 5 ( 4 . 8 7 5 ) 54 9 9 * 3 . 0 7 9 5 . 5 e 9 8 . 7 3 2 4 2 . 0 9 9 1 . 4 7 6 3 . 6 4 1 6 3 0 % 15% 6% 3 1 . 8 5 1 9 . 2 2 12.39 1 .65 4 . 2 2 4.39 C H A V A 3 R I A 3 / 4 1 1/2 1 3 / 4 n c . 0 2 5 4 . 0 4 3 4 . 0 4 7 5 . 0 5 2 G 55 10 12 3 ( . 1 1 4 2 ) 22 2 ( . 1 6 4 9 ) 22 4 5 ( . 2 1 3 1 ) 10 6 2 •) £_ ( . 2 6 2 5 ) 2 1 1 ( . 3 1 3 2 ) 3 2 ( 2 . 4 7 6 ) 2 3 ( 3 . 0 9 6 ) 10 1 (3.664) 5 1 2 ( 4 . 3 1 0 ) 9 1 ( 4 . 9 2 8 ) 12 8 9 3 .e738 . 4 0 1 4 . 4 5 7 9 . 1 0 8 2 . 6 0 9 0 .3259 . 3 9 9 0 . 1760 3 0 % 1 5 % 11.534 ex 3 0 . 3 1 1 6 . 7 4 1 2 . 9 0 S . U 9 . 3 1 3.74 1 . 4 0 - 1 . 5 1 E L CH I LLAr .TE 3 / 4 1 1/2 1 3 / 4 2 . 0 2 5 5 . 0 4 5 3 . C 5 0 4 . 0 5 4 ? 108 1 7 4 ( . 1CES ) 30 1 ( . 1 6 1 5 ) 37 1 ( . 2 1 5 1 ) 35 4 3 ( . 2 7 1 6 ) 6 2 1 ( . 3 2 3 7 ) ( 2 . 4 7 4 ) 34 1 ( 3 . D 9 1 ) 0 1 ( 3 . 7 3 5 ) 15 1 ( 4 . 3 7 3 ) 17 1 ( 4 . 9 5 0 ) 34 5 3 1 . 8 2 3 9 . 0 1 2 2 . 3 7 2 3 . 2 4 3 0 1 . 2 5 2 2 . 0 0 9 4 . 3 0 2 8 , 2 0 7 b 3034 1 5 % 1 1 . 5 % b% 31.33 2 2 . 6 4 1 6 . 7 9 14.57 1 .33 7 . 6 4 7 . 2 9 6 . 5 7 L A V ICTOR If. 3/4 1 1/2 1 3 /4 »3 (-• 0 2 4 C . 0 4 3 7 .1)464 . 0 6 0 3 50 3 P. 5 11 ( . 1 1 2 6 ) T i 3 ( . 1 6 4 6 ) t-C 4 1 3 ( . 2 1 5 3 ) 20 n 4 ( . 2 6 5 1 ) 5 5 1 3 ( . 3 1 6 3 ) 3 4 1 1 ( 2 . 5 0 9 ) 31 <i a ( 3 . 1 0 3 ) 6 1 ( 3 . 7 1 6 ) 5 1 1 ( 4 . 3 4 6 ) 3 1 ( 4 . 3 3 C ) 16 22 4 6 .64 ' . : 9 1 . 4 7 0 0 .26i35 . 6 7 4 7 . 6 0 3 3 1.1 '323 . 2 3 7 1 . 5 3 1 5 30 / , 1 5 % 1 1 . 5 * C'/a 2 6 . 9 9 1 9 . v5 1 1 . 7 3 2 1 . 2 1 - 1 . 0 1 4 . 9 5 . 2 3 1 3 . 2 1 ON TABLE 11: Allowance and over-allowance in volume for d i f f e r e n t board thickness 3/4 inch Thickness 1-1/2 inch Thickness Sawmills Volume Standard Actual Over Volume Standard Actual Over (m3) allowance allowance allowance (m 3) allowance allowance allowance MIL DIEZ 30% 32.48% 2.48% 15% 21.02% 6.02% 21.4890 6.4467 6.9796 .5329 .7265 .1089 .1527 .0437 LOS BANCOS 30% 30.81% .81% 15% 20.40% 5.40% 14.9673 4.4901 4.6114 .1212 9.5718 1.435 1.9526 .5168 LA CIUDAD 30% 31.85% 1.85% 15% 19.22% 4.22% 20.6184 6.1855 6.5669 .3814 11.7577 1.7636 2.2598 .4962 CHAVARRIA 30% 30.31% .31% 15% 18.74% 3.74% 19.4208 5.8262 5.8864 .0602 10.3784 1.5567 1.9449 .3881 EL BRILLANTE 30% 31.33% 1.33% 15% 22.64% 7.64% 21.8255 6.5476 6.8379 .2902 1.8661 .2799 .4224 .1425 LA VICTORIA 30% 28.99% -1.01% 15% 19.95% 4.95% 6.5064 1.9519 1.8862 -.0657 15.5343 2.3301 3.099 .7689 % 0.96 5.33 OVERALL Vol 104.8274 1.3202 49.8348 2.3562 NOTE: In t h i s sample, 1-3/4 and 2 inch thicknesses were not produced at every m i l l . Where no values appear for volume i n 1-3/4 and 2 inch thicknesses, comparative percentage figures have been obtained from 10 log sample data of Table 10. TABLE 11: Allowance and over--allowance i n volume for di f f e r e n t board thickness (continued) Sawmills 1-3/4 inch Thickness 2 inch Thickness Volume (m3) Standard allowance Actual allowance Over allowance Volume (m3) Standard allowance Actual allowance Over allowance MIL DIEZ 5.4204 11.5% .6303 13.92% .7629 2.42% .1326 LOS BANCOS 5.1814 11.5% . 5958 22.52% 1.1668 11.02% .5709 8% 19.15% 11.15% LA CIUDAD 8% 12.39% 4.39% CHAVARRIA 8.9841 11.5% 1.0331 12.90% 1.1589 1.40% .1257 .4545 8% .0363 6.49% .0222 1.51% .0068 EL BRILLANTE 11.5% 18.79% 7.29% 7.0313 8% .5625 14.57% 1.0244 6.57% .4619 LA VICTORIA 11.5% 11.73% .23% 6.3446 8% .5075 21.21% 1.3456 13.21% .8381 % OVERALL Vol 19.5859 4.47 .8292 13.8304 7.36 1.3068 NOTE: In t h i s sample, 1-3/4 and 2 inch thicknesses were not produced at every m i l l . Where no values appear for volume i n 1-3/4 and 2 inch thicknesses, comparative percentage figures have been obtained from 10 log sample data of Table 10. TABLE 12: Nominal, actual, and allowance volumes related to lumber recovery based on actual and nominal dimension (1) (2) (3) Nominal volume plus Difference (2) and between (1) Difference between (2) and (3) Lumber recovery percentage Sawmills Nominal volume (m3) Actual volume (m3) allowance volume (m3) Volume Percentage (m3) Volume Percentage Nominal Actual MIL DIEZ 27.6359 35.5918 34.8821 7.9559 28.78 0.7097 2.56 43.56 56.10 LOS BANCOS 32.1368 39.8676 38.6585 7.7308 24.05 1.2091 3.76 43.74 55.10 LA CIUDAD 35.5078 44.3624 43.4730 8.8546 24.94 0.8894 2.5 41.87 52.23 CHAVARRIA 39.9219 48.3946 48.3741 8.4727 21.22 0.0205 0.05 44.18 53.25 EL BRILLANTE 34.4810 43.0624 41.8710 8.5814 24.83 1.1914 3.45 41.54 51.85 LA VICTORIA 29.9940 35.7238 34.2760 5.7294 19.10 1.4474 4.83 43.12 51.36 OVERALL 199.6774 297.0022 241.5397 47.3248 23.7 5.4675 2.75 . 43.00 53.32 TABLE 13: Log-lumber and byproducts proportions Sawmills Volume *WEIGHT ' (kg) VOLUMES (m 3) PERCENTAGE DISTRIBUTIONS BY VOLUME of logs (m3) Large dimension lumber Chippable residues Large dimension lumber Short dimension lumber Chippable residues A l l lumber Chippable residues Sawdust MIL DIEZ 3.1205 1815.0 7327.0 1.8283 0.1446 0.7434 63.22 23.82 12.96 LOS BANCOS 3.8205 2136.2 1099.3 2.1186 0.1211 1.0847 58.62 28.39 12.99 LA CIUDAD 7.2111 4034.9 1565.3 4.1263 0.3674 1.1605 62.31 22.33 15.36 CHAVARRIA 4.0601 1513.0 906.3 1.8835 0.1757 1.1087 50.72 27.30 21.98 EL BRILLANTE 4.5054 2279.9 1287.2 2.4304 0.0653 1.3756 55.39 30.53 14.08 LA VICTORIA 6.3605 3430.8 1508.3 3.4281 0.2321 1.5051 57.54 23.66 18.80 OVERALL 29.0781 15209.8 7099.1 16.8152 1.1062 6.9780 57.97 26.00 16.03 * The weight of short boards, i . e . those less than 8 f t i s not included since only f u l l length lumber used to calculate the weight-volume re l a t i o n s h i p used to determine volume of chippable residues. co o TABLE 14: Over-length allowance volume by log length categor ies . Sawmill Total number of logs and volume (m3) •3 Number of logs and over length volume (m ) by over log length categories 2 - i n 4 - i n 6 - i n 8 - i n 1 0 - i n 1 2 - i n 1 4 - i n 1 6 - i n MIL DIEZ 150 63.4G01 3 • .0102 10 .0930 . 27 .4353 39 .6696 32 .6160 • 14 .3324 11 .31614 14 .4734 LOS eANCCS 131 72.3452 16 .0625 17 .2128 26 .4337 20 .4475 14 .4080 7 .2560 4 . 1341 27 -1.0272 LA CIUDAD 150 84.7996 4 .0189-4 .0374 24 .3705 37 .6025 29 .7673 27 • 1.0034 7 .3010 18 .5734 CHAVARRIA 14& 90.6609 4 .0322 11 .1169 28 .5091 30 .7472 46 1.16B5 15 .5693 5 .2960 5 .2664 EL ERILLAPJTE 150 63.0553 12 .0713 2 .0262 1 .0166 4 .0900 5 .1790 17 -.5496 34 1.2565 75 2.9630 LA VICTORIA 150 69.5491 1 .0020 6 .0355 16 .2940 33 .6650 27 .7572 25 .7463 37 1.2624 No. % OVERALL 879 100 40 4.55 44 5.0 112 12.74 146 16.61 164 18.65 107 12.17 90 10.23 176 20.02 Vol . % 464.0984 100 • .2171 .05 1.9863 .10 1.8513 .39 2.9309 .63 4.0038 .86 3.4949 .75 3.1023 .67 6.6208 1.43 TABLE 15: Log volume l o s t by over length with 4 and 6 inches nominal allowance 4 inches nominal allowance 6 inches nominal allowance Sawmills Number of logs and volume 4 inches over length 4-16 inches over length 6 inches over length 6-16 inches over length Volume Logs 5 Logs Volume Volume Volume m m Logs Logs m m m MIL DIEZ 150 63.4682 13 0.1031 .16 137 2.8481 4.48 40 0.5385 .84 110 2.4128 3.80 LOS BANCOS 131 72.3452 33 0.2953 .40 98 2.7686 3.83 59 0.73 90 1.02 72 2.3249 3.21 LA CIUDAD 150 84.7998 8 0.0563 .06 142 3.7085 4.37 32 0.4272 .50 118 3.3376 3.93 CHAVARRIA 148 90.8809 15 0.1491 .16 133 3.5765 3.93 43 0.6582 .72 105 3.0674 3.37 EL BRILLANTE 150 83.0553 14 0.0975 .12 136 5.0799 6.11 15 0.1143 .14 135 5.0631 6.09 LA VICTORIA 150 69.5491 1 0.0020 .01 149 4.0324 5.79 7 0.0875 .13 143 3.9469 5.67 OVERALL 879 84 0.7034 .15 795 22.014 4.75 196 2.5647 0.55 683 20.1527 4.34 oo TABLE 16: Thickness v a r i a t i o n d i s t r i b u t i o n for nominal 3/4 inch boards Number of Boards Sawmills Average Thickness i n Millimeters 21 22 23 24 25 26 27 28 29 30 31 32 33 34 MIL DIEZ 3 18 31 29 18 1 LOS BANCOS 2 6 22 29 19 11 4 4 2 1 LA CIUDAD 7 3 16 21 14 13 14 4 3 3 1 1 CHAVARRIA 2 7 13 24 24 22 7 1 EL BRILLANTE 1 3 7 16 17 31 21 4 LA VICTORIA 3 8 24 29 23 10 2 1 Boards 3 20 36 140 144 148 88 33 8 7 7 2 1 OVERALL Per cent 3.3 6.0 17.3 24.0 24.7 14.7 5.5 1.3 1.2 1.2 co O J TABLE 17: Mean thickness - sawing v a r i a t i o n and target thickness for nominal 3/4 inch boards M I L L I M E T E R S Parameters — _ _ _ _ _ M i l Diez Los Bancos La Ciudad Chavarria E l B r i l l a n t e La V i c t o r i a Average range within boards Average range between boards Ov e r a l l average thickness Within boards standard deviation Between boards standard deviation T o t a l sawing standard deviation Green target size P o t e n t i a l thickness reduction x-3(St) Spread of sawing v a r i a t i o n 5+3(St) 1.796 1.953 2.64 2.878 4.109 6.199 25.429 26.390 25.830 0.708 0.771 1.042 1.234 1.733 2.624 1.423 1.896 2.823 23.461 24.242 25.770 1.967 2.148 0.060 21.160 20.702 17.361 29.698 32.078 34.299 1.964 2.284 2.193 3.450 3.873 3.763 24.574 25.417 25.023 6.775 0.901 0.865 1.662 1.624 1.570 1.834 1.857 1.792 24.140 24.180 24.070 0.434 1.237 0.953 19.072 19.846 19.647 30.072 30.988 30.399 oo -P-TABLE 18: Potential lumber volume recovery i n 3/4 inch nominal lumber by cutting to target thickness and by reducing sawing v a r i a t i o n Sawmills Lumber volume Actual average Target Potential lumber recovery by target thickness P o t e n t i a l lumber recovery by sawing v a r i a t i o n 3/4 inch (m ) thickness (mm) thickness (mm) Thickness reduction Volume % Volume m3 Thickness reduction Volume % Volume m3 MIL DIEZ 21.4890 24.429 23.461 1.968 7.74 1.6632 0 0 0 LOS BANCOS 14.9674 26.390 24.242 2.148 8.14 1.2183 0.781 3.22 0.4472 IA CIUDAD 16.2890 25.830 25.770 0.060 0.23 0.0375 2.309 8.96 1.4561 CHAVARRIA 19.4208 24.574 24.140 0.434 1.76 0.3418 0.679 2.81 0.5361 EL BRILLANTE 21.8256 25.417 24.184 1.237 4.87 1.0629 0.719 2.97 0.5998 LA VICTORIA 6.5065 25.023 24.070 0.953 3.80 0.2472 0.609 2.53 0.1583 OVERALL 100.4983 25.444 24.310 1.134 4.46 4.4822 0.849 3.49 3.3509 86 TABLE 19: Poten t i a l lumber recovery i n d i f f e r e n t nominal thickness by cutting to target thickness and by reducing sawing v a r i a t i o n Nominal thickness (in) Actual average thickness (mm) Lumber volume produced (m3) Pot e n t i a l lumber recovery by target thickness Pote n t i a l lumber recovery by sawing v a r i a t i o n Volume % (m 3) % Volume (m ) 3/4 25.4 100.4983 4.46 4.4822 3.49 3.3509 1-1/2 43.7 47.5433 2.59 1.2314 1.99 0.9216 1-3/4 48.9 19.6798 2.32 0.4566 1.78 0.3422 2 55.8 13.8305 2.03 0.2807 1.55 0.2100 OVERALL 181.5519 3.55 6.4509 2.76 4.8247 FIGURE 1. D i s t r i b u t i o n of logs by diameter classes 70-. 3 6 4 0 4 f t S O 8 5 DIAMETER CLASSES IN CENTIMETERS l 7 0 M i l Diez + - + Los Bancos — H La Ciudad Chavarria + + + + + + t E l B r i l l a n t e La V i c t o r i a oo FIGURE 2. D i s t r i b u t i o n of logs by length classes MIL DIEZ LA CUIDAD EL BRILLANTE to o o O 140-1 1 2 0 -1 0 0 -8 0 -6 0 -4 0 -2 0 -0 1 4 0 - 1 1 2 0 - j 1 0 0 8 0 6 0 -4 0 -2 0 J L J L 10 IX 1 4 l « I t 2 0 LOS BANC0S J . JBL 10 I X 14 I t I t 2 0 I 4 0 i 1 2 0 1 0 0 - j 8 0 H 6 0 4 0 2 0 H 0 I 4 0 - . 1 2 0 -1 0 0 -to-6 0 -4 0 -2 0 -10 I X 14 I t I t 20 CHAVARRIA JL 10 IX 14 I t I t X0 LOG LENGTH " CLASSES 1 4 0 - 1 1 2 0 -1 0 0 -8 0 6 0 - | 4 0 2 0 - | 0 1 4 0 - 1 1 2 0 -1 0 0 -6 0 -6 0 4 0 -2 0 -JL__ 10 12 14 16 18 2 0 LA VICTORIA 1 0 12 14 16 I S 2 0 oo oo FIGURE 3. D i s t r i b u t i o n of logs by grades and volumes FIGURE 4. Proportion of d i f f e r e n t lumber thicknesses produced under normal manufacturing conditions x 100-I FIGURE 5. Thickness v a r i a t i o n i n 3/4 inch nominal lumber 

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