by Professor Gene Wengert
What is the rule of thumb for wastage in oak lumber air dried as a percentage of total sawn?
I believe your question is "How much loss is there in air drying?" This question was examined some years ago by the US Forest Service. They looked at a variety of grades and species dried in Pennsylvania. These drying degrade losses presented here for No.1 Common grade do not consider any value losses due to ordinary shrinkage. Drying losses were higher for FAS lumber and lower for No.2 and No.3 Common.
It's important to note that the data was collected by grading the lumber before drying and then again after drying. As almost all grade losses occur during air drying, not subsequent kiln drying, this technique is very good. However, it does tend to underestimate the loss to a furniture or cabinet plant that is cutting the lumber--grades do not reflect the loss in yield very well. So, I would double the losses for them.
For lumber that was No.1 Common when freshly sawn, the loss after air drying amounted to a value loss of:
Basswood - 8%
Birch - 6%
Hard Maple - 14%
Red oak - 13%
White oak - 15%
Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.
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Comment from contributor A:
I also graded lumber at a concentration yard for some years. First, with a grader at the rough mill... If you send a load of #1C to the concentration yard, the inspectors at the yard will tend to find the lower grade while overlooking anything better than a #1C. So if you sell a load of #1C to the yard at a set dollar and footage amount, they will find the lower grade.
Have you ever had a complaint of too many FAS boards in a #1C load? But you have had a complaint of too much lower grade in a #1C load or a footage difference. If you do not grade your lumber within close tolerances governed by the NHLA rules, you will be giving away your upper grade lumber. I feel a knowledgeable inspector governed by NHLA rules is a must at the sawmill if you donít know how much your lumber is worth when it leaves your mill. No one will tell you there are too many FAS boards in a #1C load they bought from you.
Now, the mill without a grader selling to the same concentration yard... The graders will tend grade the load by the appearance of the load. Here is what I mean. If you are sawing larger logs that produce more upper grade lumber, the graders at the yard will look for and find the upper grade. On the other hand, if you have a mill run of smaller logs and the lumber is in the majority of lower grades, the inspector will fail, in most cases, to find the upper grade. If I were to sale a load of lumber, no matter the grade, I would want to know these things and trust them to be true. I would separate the loads or the bunks in a mill run load to be uniform in:
Example: A pack of lumber of #1C Red Oak 8í long with 550bf in it. Will or should be within a + or -≠ 1% footage and grade of any two inspectors grading that pack of lumber.
On the other hand, if you have a pack of lumber that is of all grades, lengths, and specie, the grader at the yard will in many cases be running a production quota. This pack will have a much higher difference between the graders in both footage and grade. So in my opinion, the sawmill needs to do all he can to present the lumber to the costumer in the most uniform packs possible. You will increase the value of your lumber just by making it easy to re-inspect by the grader at the concentration yard. So I agree the rough mill should have a grader governed by the NHLA rules and separate the lumber into uniform packs.