Q: We have recently switched from a "chop-first" to a "gang rip-first" mill. I think our yields have dropped; on some days we have terrible numbers. I do not think it is our employees, as they are pretty good. Does this seem right to you?
A: I would expect that your yields should increase when using a rip-first mill. So, something is not right here. After further discussions with you, we found the problem. Your sawmill that supplies green lumber likes to provide a lot of lumber that, after drying, is about 6.2 inches wide. With your gang saw, you are ripping strips that are 2.03 inches (2-1/32 inches) wide. If you figure out the geometry, counting the kerf of the hogging saw and the other saws, you will get only two 2.03-inch strips from 6.1 inches wide lumber.
That is a yield of 66 percent at the rip saw. For a piece of lumber 4.88 inches wide, you will be able to get two strips, but the yield is 83 percent. Likewise, for a piece 7.06 inches wide, you can get three strips and a yield of 86 percent. In short, fixed-width rips, or even variable gang rips sometimes, will have certain width lumber that results in very poor yields.
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