The effects of sawing methods on the lumber recovery rate and lumber grading of Eucalyptus globulus at the small-scale sawmill enterprise, Addis Ababa, Ethiopia

The sawmill industry process a significant quantity of the logs into lumber for wood industry in Ethiopia. The cost of raw materials have a significant role in the wood industry. Therefore, it is critical to pay attention to the proper log sawing method, which optimize the sawing process and increase the lumber recovery rate and lumber grading. Eucalyptus, is currently gaining significance in wood industry for lumber production and for construction purposes in Ethiopia. In the present study, Eucalyptus globulus logs were processed into lumber using plain, quarter and radial sawing methods. In the plain sawing, the results showed that a total 6.77 m³ of lumber were produced from log categories 1, 2, 3, and 4. In the quarter sawing, a total 5.07 m³ of lumber were produced from log categories 1, 2, 3, and 4. While in the radial (rift) sawing, a total 4.76 m³ of lumber were produced from log categories 1, 2, 3, and 4. Overall, the lumber recovery rate 49% were recorded. There was a highly significant difference (P ≤ 0.001) in the sawing methods. Visual grading is based on a visual inspection of the each piece of the lumber and the judgment of the grader. In the present study, lumber grade yield was classified into percent’s of 83–100%, 66–82%, 50–65%, and below 50%, and lumber grade names were No. 1C and better, No. 2AC, No. 3AC, and No. 4 (economy), respectively. The major structural factors that determined in the sawn wood grade were the size and frequency of the defects on the lumber because log characteristics would appear in a given piece of the lumber and affects the grading of sawn wood or appearance. The study results shows that the logs with a lower grade or more defects resulted in lower lumber recovery and grade yield. In conclusion, the plain sawing method is the most commonly used for E. globulus lumber production in the sawmill industry. Apparently, plain sawing is a least wasteful, most economically used for sawing the logs, and producing the widest lumber than others. However, the lumber produced using this method are more liable to warp, split, shrinkage and distortion than those of other methods. Quarter sawing has the benefits of reducing warping, shrinking, twisting, and cupping, checking and splitting lumber rather than those which are plain sawn. This is the best technique for E. globulus lumber production, especially more appropriate for sawing a large diameter of the logs. Lastly, radial sawing has the highest wood waste, the time consuming and expensive, and the strongest sawing technique for E. globulus lumber production. This investigation confirms that the quarter sawing method is suitable for producing high quality lumber from E. globulus. The enhanced lumber recovery and grade yield increase the profitability, energy efficiency, optimum use of the resources, manage wood waste (e.g., recycling and prevention), and mitigate climate change impacts effectively for green economic development and industrial transformation.