Tips for improving productivity and profitability in the rough mill area.
By Philip Mitchell, Jan Wiedenbeck and Bobby Ammerman
As lumber is processed, value is added at each step of the process. A rough mill processing 12 thousand board feet (12 Mbf) of dried lumber per day, valued at $900/Mbf, can save approximately $58,000 per year simply by improving rough mill yield by just 1 percent.
However, yield alone does not provide a complete picture of profitability in the rough mill. There is opportunity for maximizing the value of the products produced and by minimizing manufacturing costs to impact overall profitability.
Impact on Yield & Value
In choosing the best lumber grade mix to process, it is helpful to run frequent studies in the rough mill using small groups of boards of a given grade. This can be done by using a computer program, such as least-cost lumber grade mix programs or a lumber cut-up simulation program, or a mill study.
In a mill study, the boards are tracked through the rough mill and the yield is calculated based on the tally at the sort station. Several five-board runs can be conducted for each lumber grade in a single day, with minimum disruption. If this is done for every significant cutting order, your rough mill managers will be able to assess the best lumber grade mix for the rough mill to run on the cutting order, given the current prices, equipment, etc. Like the computer programs, it will also tell you what the break-even sales price for the cutting order is when cut from each lumber grade.
It is important to note that the yields from a mill study may be lower and closer to the true amount since simulation programs are based on an ideal, fully optimized operation.
Grade, Productivity & Costs
As contrary as it sounds, higher lumber yields do not necessarily mean greater profits. The cost element must be weighed for every decision. Although the purchase price of higher grade lumber is more than for lower grade lumber, processing costs for lower grade lumber are usually greater than for higher grade lumber because more cutting operations are required to isolate usable board sections from defects.
For FAS lumber, the highest grade of hardwood lumber, most of the cutting is for sizing the parts since only a few defects need to be removed. Also, more cuttings produced from upper grade lumber are primary parts rather than higher cost salvage parts. Other costs associated with processing lower grade lumber that are difficult to quantify include higher part reject rates (due to defecting mistakes and machining defects that arise where cross-grain occurs near knots) and longer inspection times for operators.
The number of cutting operations required to extract needed parts climbs significantly when the lumber grade is decreased from FAS to No. 1 Common to No. 2A Common in both gang-rip-first and crosscut-first rough mills. For a difficult cutting order, the number of chopsaw cuts (in a rip-first rough mill) required per part produced is 27 percent higher for 1 Common lumber than for FAS lumber, and 53 percent higher for 2A Common than for FAS lumber.
The number of crosscuts required (in a crosscut-first rough mill) to fill the same cutting order is 70 percent higher for 1 Common than for FAS lumber, and 200 percent higher for 2A Common lumber than for FAS. For the straightline ripsaw in the crosscut-first rough mill, the number of cutting operations required to extract needed parts also increases significantly as lumber grade is reduced. Fortunately, this increase is not as great as for the crosscut saw. The productivity of the crosscut saw-straight-line ripsaw system is less affected by a reduction in lumber grade when cutting an order that is made up of shorter and narrower parts than when cutting larger parts.
Many operating guidelines for defect/grade markers working with optimizing saws are similar to those for operators of manual crosscutting/chopping saws.
In an article by Phillip Mitchell, he recommends the following:
- A rule of thumb for many mills is that only those defects that occupy at least one-half of the board’s width should be removed on the crosscut saw.
- When cutting C2F parts, place the worst face of the board or strip up for easy viewing. When cutting C1F parts, orient the best face up.
- Usually, spike knots, fuzzy grain and badly distorted or cross-grain should be removed at the crosscut saw in a crosscut-first rough mill. Presurfacing lumber to make defects more visible before the crosscut or ripsaw increases yield and reduces the number of rejected parts.
It is common for rough-mill managers to conduct in-depth feasibility studies and justifications that include yield standards before investing in optimizing technologies, but then quickly shift focus to production rates after installation. A combined emphasis on lumber yield, part quality and mill productivity needs to be in place if a rough mill is going to realize the benefits projected in the feasibility analysis.
This article was excerpted from Rough Mill Improvement Guide for Managers and Supervisors, a publication of the USDA Forest Service. Philip Mitchell is a wood products extension specialist at North Carolina State University, Raleigh, NC. Jan Wiedenbeck is a project leader with the USDA Forest Service, Northeastern Research Station in Princeton, WV. Bobby Ammerman is an extension associate at the University of Kentucky in Quicksand, KY. To view the complete article, visit fs.fed.us/ne.
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