Geoscience Reference
In-Depth Information
DID YOU KNOW?
Tree cross-sections rarely form true circles, but they are normally presumed to be circular for
purposes of computing cross-sectional areas.
DID YOU KNOW?
When measuring the cross-sectional area of a log, diameter instead of the radius of the log is
measured; thus, this area in square inches may be determined by
Area in square inches = πD 2 /4
(or underrun) is estimated in the process of appraising National Forest timber for sale and presum-
ably by purchasers in determining what prices they will bid. Overrun or underrun is not considered
in log scaling, even though it is very important to any mill.
As a general rule, timber is appraised, sold, and measured by customary commercial unit for the
products involved. Standard practice is to scale saw timber by a board-foot log rule scale, mining
timbers by the piece or linear foot, telephone poles by the linear foot or the piece of stated length,
piling by the linear foot, pulpwood by the solid cubic foot or cord, and fuelwood, shingle bolts, and
similar material by the cord. Other units may be used when better adapted to local trade customs
or local situations.
13.4.2 a uthorized l og r ules
The Scribner Decimal C rule, the International 1/4-Inch rule, and the Smalian Cubic Volume rule
are used by the U.S. Forest Service for uniform scaling of sawtimber. With the exception of the
Smalian cubic volume rule, all specific rules are board-foot rules. Each board-foot rule is repre-
sented by a table showing an arbitrary estimate of the amount of lumber a log of given length and
diameter can produce. Inasmuch as the tables for each rule have a different base, the scale of identi-
cal logs will differ according to the rule used.
13.4.2.1 Scribner Decimal C Rule
The Scribner Decimal C rule, developed by J.M. Scribner around 1846, is a standard rule for U.S.
Forest service saw log scaling. This rule was derived from diagrams of 1-in. boards drawn to scale
within cylinders of various sizes (see Figure 13.3). The rule rounds contents to the nearer 10 board
feet; for example, logs that, according to the Scribner rule, have volumes between 136 and 145 board
feet are rounded to 140 board feet and shown as 14.
13.4.2.2 International 1/4-Inch Rule
Developed in 1906, the International 1/4-Inch rule is based on a reasonably accurate mathematical
formula that probably gives a closer lumber-volume estimate than other log rules in common use.
This rule measures logs to the nearest 5 board feet. As the name implies, it allows for a saw kerf
DID YOU KNOW?
The Scribner rule gives a relatively high overrun (up to 30%) for logs under 14 inches. Above
14 inches, the overrun gradually decreases and flattens out around 28 inches to about 3 to 5%.
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