Since the very first sawmill was built in the United Stated, there has been over 100 log rules developed, all using a variety of methods. Some were based upon the lumber tallies of individual mills, some were developed by diagramming the cross-section of boards in the ends of logs and others were developed using mathematical formulas.
An Inch Is An Inch, Isn't It?
Not when it comes to logs. In general, log rules must account for the taper that exists in all logs, saw kerf or the loss of wood as sawdust, and removal of bark in slabs. Of the many log rules, the Doyle, Scribner and International log rules are the most widely used rules in the Eastern United States.
Doyle Log Rule
The Doyle Log Rule was developed around 1825. It is based on a mathematical formula and is widly used throughout the southern U.S. This rule allows for a saw kerf of 5/16" and a slabbing allowane of 4", which is about twice the normal amount. The Doyle Log Rule will underestimate small logs and overestimate large logs. The Doyle Log Rule is somewhat inconsistent.
Scribner Log Rule
The Scribner Log Rule was developed around 1846. It is a good example of a diagram rule. It was created by drawing the cross-sections of 1" boards within circles representing the end view of a log. A space of 1/4" was left between the boards to account for say kerf. The Scribner Log Rule does not have an allowance for log taper and it will typically underestimate logs, particularly if the log length is long.
The Scribner Decimal C is a different form of the Scribner Rule; it rounds the volumes to the nearest 10 board feet. So 392 board feet on the scribner would be 390 on the Scribner Decimal C.
The International 1/4-Inch Log Rule
The rule was developed in 1906 and is based on a reasonably accurate mathematical formula. The rule allows for a 1/4" saw kerf and a fixed taper allowance of 1/2" per 4 feet of log length. Deductions are also allowed for shrinkage of boards and a slab thickness that varies with the log diameter. Overall, the International Log Rule is the most consistent and accurate. It is for this reason that Greater Michigan Timber Management uses the International Log Rule.
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