Q: Our percentage yield of usable parts varies from supplier to supplier. If we are buying the same grade and same species, why should it vary?
A: This is a good question that we never think much about, but we should. There are many reasons why yields will vary; here are six ideas that I have. Maybe you can think of another one or two? Let me know.
First, it could be that one supplier isn't measuring the footage as accurately as another. It would not be unusual to see footage variations of 10 percent from the true value. Often these errors are due to worn equipment or careless operators rather than intentional cheating. So, recheck the footage now and then. Of course, there is the issue of net or gross tally that I have discussed in this column before. I would never buy lumber that has a certain percentage added back to account for shrinkage.
Second, it could be that there is a grade variation from suppliers. For example, perhaps the one supplier also sells FAS-1 Face lumber, which means that the best of the No. 1 Common lumber is pulled out from the No. 1 Common you are buying. Or maybe their grader is not very good and so their No. 1 Common is above (or below) the typical No. 1 Common. Or maybe they have two grades of No.2 Common, with the higher going to another operation. It's illegal but it happens!
Special note: Many mills use NHLA certification to assure you that their graders have been constantly rechecked to make sure they are grading correctly. I would tend to use an NHLA-certified mill if yield is important to me, especially if I measure yield and use that yield number in managing my operation.
Third, maybe one supplier has a lot of lumber with wane defects or pith defects, because of a small log resource, while another has lumber, with knot defects, which come from larger logs. Even though the grade is the same, the lumber with wane or pith will have substantially lower yields.
Fourth, one supplier could have better drying practices, meaning higher-quality lumber. There is no doubt that poor drying, or even average drying, is an overlooked, large contributor to poor yields. I would tend to look for operations that use drying personnel that are certified as Master Kiln Operators.
Fifth, there are some companies that actually have better lumber than the competition's. Perhaps they use predryers instead of air drying. Perhaps they remanufacture or they pull out lumber that "makes the grade," but just looks bad.
Sixth, perhaps the higher yields come from lumber that has been end-coated before any drying began, thereby eliminating most end checking. End coating can easily increase yields by 2 to 4 percentage points in a species like red oak.
You might be reluctant to work with your supplier to improve the quality of the lumber and its measurement. However, many of your competitors are on the path to quality improvement.