Q: Can you give me any practical ideas on how to begin looking at yield improvements? I have already studied your report on the 10 important factors that influence yield and it was helpful. Any specific ideas on what might assist us?

A: One of the most powerful tools that you have to evaluate and improve your present cut-up operation is to perform an analysis of the pieces of "waste" that are going into the conveyor and into the waste hog. Let me give you an example to help explain what I mean. I was at a mill in the southeastern United States recently, conducting mill improvement training and analysis. First, I painted one end (the tail end) of the rough lumber red and the other end green; this lumber was processed in the rough mill while I was collecting samples. The paint allowed me to tell if the end pieces were from the front end of the lumber or the tail end. Then, for a 10-minute period, done twice in one day, I collected all the pieces of wood (except for sawdust-size pieces) that were in the waste conveyor. (I also looked at rejected pieces that were found later in processing, but that did not get into the conveyor. This examination was a separate study.) Each piece of wood was put into one of the following 21 categories that described why this piece was in the conveyor:

  • Knot and acceptable cross-grain around a knot (about 1 inch allowed)
  • Knot hole and acceptable cross-grain around a knot hole (about 1/2 inch allowed)
  • Insect hole
  • Knot, knot hole or insect hole with excessive clear wood around the knot
  • Interior check or honeycomb (includes deep surface checks)
  • Stain that was drying related
  • Stain or color problem that was resource related (including mineral and brown heartwood in maple)
  • Normal end trim (under 1 inch) on the front end
  • Normal end trim (under 1 inch) on the tail end
  • Excessive end trim at the front end of the lumber, but not a split
  • Excessive end trim on the trailing end of the lumber, but not a split
  • End split
  • Edging strip, with clear wood under 1/4 inch in width
  • Edging strip, with clear wood over 1/4 inch in width
  • Edging strip that indicates side bend in the lumber
  • Edging strip with wane
  • Planer skip (included thin lumber and cupped lumber)
  • Fuzzy grain
  • Chipped or torn grain
  • Oops...has potential for remanufacturing into a smaller acceptable part
  • Miscellaneous and unknown

After putting the conveyor parts into separate piles, I then weighed each pile so I had a numerical method of comparing the 21 categories. In such comparison, you should probably look at the percentage of weight in each category rather than the raw weight data. Further, this weight data can be used for before and after comparisons, comparing weights before and after changes in the mill have been made to see how big the improvements are. (This really does not require my presence to conduct the study. You can certainly do this on your own.)

As an additional note, you can also use the so-called cart survey, which is similar to the 21-category comparison just mentioned, to assess yields. In this survey, you clear the mill of all material and then process a bundle of lumber through the mill. At each step in the cut-up process, you would weigh the incoming lumber (or parts), weigh the processed lumber (or acceptable parts) and the waste. Sawdust weight is obtained by subtraction; incoming weight minus processed weight minus waste weight equals sawdust. Weight comparisons of processed lumber or parts, of waste (in 21 categories if you wish) and of sawdust to the incoming weight (in percent) gives you the percentage yields of processed lumber or parts, of waste (broken down into 21 categories if you wish) and of sawdust. If you take data after each processing step, that is after planing, after ripping and after crosscutting, you can see exactly where you are losing yield. Obviously, you would direct attention to the big loss items. Certainly, this cart survey will provide a wonderful, useful and detailed profile of your cut-up operation.

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