UBC Theses and Dissertations
Analysis of the sawmilling practices in the state of Durango, Mexico Zavala Zavala, David
Control of sawmilling operations, including log bucking practices and sawing processes, is one reasonable solution to the Mexican lumber shortage problem. This is particularly so if available techniques to improve sawmill efficiency can be included in normal manufacturing processes. Sawmilling analyses were carried out to assess the relationship of log volume input to lumber volume recovery, evaluated in actual and nominal dimensions. Six sawmills were selected, based on the most frequent type of band headrig in the State of Durango. A statistically representative sample size of sawlogs was used in each sawmill, amounting to a total of 870 logs. The proportion of log volume breakdown into lumber and byproduct volumes was analyzed. It was found that the proportion of chippable residue accounted for 26 per cent of the total log volume throughput. This suggests the possibility of allocating a large amount of this volume to pulp mills, rather than continuing present practice of burning as waste with no economic return. Sawlog types and lumber recovery characteristics under normal manufacturing processes were included in the study. A significant 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 practices, lumber dimensions, and sawing variation, in respect to their effect on both potential lumber recovery percentage and potential revenue to the sawmill industry. It was found that excessive log trim allowance resulted in a 4.34 per cent wastage of the total log volume input at the trim saw. Over allowance in lumber thickness dimension resulted in a 3.55 per cent loss of the total lumber volume recovered, and sawing variation accounted for a 2.76 per cent loss. It was concluded that closer control of sawmilling operations to minimize poor bucking practices and sawing variation has significant potential for lumber recovery increment. It was also concluded from this study, that future sawmill analysis would require inclusion of log length and sawing variation in an assessment of sawmill performance.
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