Q: I am part of an employee team that has been given the assignment of developing ways to improve the yield at our facility. Can you assist in collecting information?
A: I am delighted to work with you in this effort. First and foremost, I think you should push for an outside person to come in and evaluate your present operation. Often, this outside person (I am one of the best - just ask my mother!) will see things that escape notice by even the most diligent employees and managers. I am also sending you a copy of the appropriate pages from the Wood Doctor's' Rx, which is available from the FDM Book Store. Another good book is A Handbook for Improving Quality and Efficiency in Rough Mills. I have listed below the top 10 controllable items that affect rough mill yields and profits. Each 1 percentage point increase in yield is a savings of over $30 per thousand board feet of parts.
1. Grade of lumber. Increasing the grade of lumber will likely increase yield 5 percentage points or more, but will often increase costs 15 percent or more.
2. Drying quality. I am continually amazed at the amount of drying defects, especially end splits and warp, that are present in lumber but are ignored by management. Poor drying can easily decrease yield by 10 percentage points.
3. Cutting bill sizes. Did you know that the shortest part determines the overall yield? Did you know that cutting 4-inch-wide rather than 2-inch-wide pieces can reduce yield about 15 percentage points? Did you know that 5/4 yields are 5 percentage points lower than 4/4? And 8/4 yields are 8 percentage points lower?
4. Operators' skill and decision making. Some operators can get within 1 percent of what a computer can do; some are 3 or 4 percentage points lower. Continuous training is important.
5. Part quality. Do you have a guide as to what is acceptable and what is not acceptable in the parts? I like to see some displays of these defects on the wall in the break room as a constant reminder. Once you know what defects are OK, then do they ever show up in the parts, or do you still cut clear faces? How about C2F versus C1F?
6. Mill layout. Theoretically, in most cases a rip-first mill will achieve the same yield as a cross-cut first mill. However, to achieve this yield on a X-C requires considerable thinking - essentially a fast computer to evaluate many options. Operators seldom get within 5 percentage points of the ideal yield in an X-C mill. In a rip-first mill, the decisions are much less complex. Operators often can get within 1 percentage point of ideal.
7. Kerf. Approximately 12 percent of the incoming lumber is converted to sawdust. A savings in saw tooth width of 1/64 inch will increase yield by 1 percentage point. A special note: If you are gluing after ripping, it is the sides of the teeth, not the top, that produce the gluing surface. You need to have the sides of your saw teeth in perfect shape!
8. Edging practices. Did you know that for a typical rough mill if the edging on a rip saw (the thin piece of wood thrown away) can be reduced by 1/8 inch, then the yield will increase 3 percent! I am surprised at the amount of wood we lose when edging. Computerized edging systems are well worth the money.
9. Lumber length, thickness and width. Did you know that a 2-inch end split on an 8-foot-long piece of lumber is 2 percent loss, compared to 1 percent on a 16-foot piece? Have you ever considered if there are certain width pieces of lumber that produce poor yields because the width parts you need just do not fit well? One operation I was at recently had some width pieces yielding just over 50 percent, while some widths yielded 84 percent.
10 . Grading practices. It is not unusual to find footage errors in "bought" lumber. The grading rules also vary from species to species, when lumber is graded after kiln drying, and when lumber is graded after planning. Did you know that after planing, the grading face for hardwood lumber switches from the worst face to the best face!
Have something to say? Share your thoughts with us in the comments below.