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Board-Foot Scales Compared

Different log scaling systems predict different lumber output because they include different assumptions about waste. October 12, 2007

Question
Can someone explain to me how the Doyle log scale figures small logs as having less footage than they actually have, and bigger logs being closer to reality, when they all use the same formula? BF = Diameter - 4 divided by 4, squared x length

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
The formula is an estimate. It is an empirical relationship basically, so has little to do with the amount of lumber in a log from a theoretical viewpoint. For example, if you have a 4" diameter log, the answer is zero.



From contributor W:
It is my understanding it's based a lot on the labor it takes to get 1 bdft out of a 4" log as per a 12" log, so the small logs are scaled less.


From contributor T:
If I understand this thread correctly, this method doesn't give the bf of a log, or not very accurate bf. Is there a formula that will give you the bf in a log closer, or do I need to buy a scaling stick? Is one kind of stick better than others? If so, which do I need to buy and where would I get one? The old timers around here have told me that they used a scale stick that would give them the bf in a log, but I they couldn't tell me the name of the manufacturer.


From contributor H:
If I remember, the way Doyle works is that you draw a square on the small end of the log and calculate the board footage taking kerf into account. So, if you have a small log, the amount of waste (wood outside the square) in proportion to the amount of lumber inside the square is relatively high. However, if the log is very large, the square that contains the boards comprises a vast majority of the volume and the percent of the material outside the square (waste) is small. That is why Doyle under-predicts the amount of lumber in small logs, because Doyle assumes that anything outside the square is waste when it really isn't, because you can recover some lumber from what the Doyle rule assumes as all slab. With small logs, the percent volume in slab is high relative to total volume and in large logs, the percent volume in slab is low relative to the total volume.


From contributor R:
Different places use different scales. Around here the log buyers use the Doyle scale, and the foresters use the International 1/4-inch rule most of the time. Sometimes the foresters use the Doyle scale for scaling stumpage also.


From Professor Gene Wengert, forum technical advisor:
The International 1/4-inch rule is the closest to reality, especially if you have 1/4" kerf. There is also an Int. 1/8-inch which will do better for bandsaws.


From contributor W:
Scale sticks will only give the same value as the printed scales. Scale is scale no matter which one you use. I use east side Scribner and I will not put anything on the saw under 10" top; everything under is a fence post.


From contributor P:
For an 8" x 8 foot log:
Doyle: 8 bf
Int. 1/4" rule: 15 bf

For a 20" x 16 foot log:
Doyle: 256 bf
Int. 1/4" rule: 290 bf

Looks like you want to buy logs with Doyle and sell with international 1/4"!



From contributor G:
You can use either; you just have to understand how they work.


From contributor J:
I've been running a lumber business for about nine years. We saw mostly cherry, and make very small pallet lumber, 31/2" X 4". If I buy logs on international scale, I never make the scaled footage. On Doyle, I make the scaled footage on grade plus the pallet lumber. In the end, it doesn't really matter what scale you use. What matters most is the dollar value of the logs and lumber.
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