Log Rules
Tree versus Log Volumes
• Trees contain
sections that
resemble different
geometric solids.
• Trying to fit one rule
to approximate the
entire tree is difficult
Tree Felling
Tree Felling
• Undercut
The undercut serves as
the guiding or aiming
slot for the tree. Basically
it is a V-shaped notch
placed on the side of the
tree in the direction of
falling.
• Back cut
For all three undercuts,
the back cut is made on
the opposite side of the
tree, slightly above the
hinge point of the
undercut.
Escape Paths
• Plan two escape paths (B)
opposite the planned
direction of the fall of the tree
(A) and at about a 45 angle
from each other. Remove all
obstacles from the paths.
Place all tools and equipment
a safe distance away from the
tree but not on the escape
paths. Select a place to set
the chain saw in case of
emergency. Never run while
holding a chain saw, operating
or not. Rather, turn off the
chain saw and set it down
before making your escape.
Tree Bucking
• The process of cutting a tree
into usable lengths is called
bucking. Bucking often occurs
as a tree is being limbed.
When cutting full-size
products, such as sawlogs and
veneer logs, you must cut logs
longer than the final product
to leave a trim allowance. For
an 8-foot log, a trim
allowance of 4 to 6 inches is
common. Many bucking cuts
are angled, and the trim
allowance allows the ends of
the boards to be cut square at
the mill to the desired board
lengths.
Top Bind
• Arrows indicate saw travel
direction and cross-hatching
indicates the heartwood that
will break. Depending upon
the soundness of the wood
and the timber lie, it may be
advantageous to use the end
of the bar and bore from
point (C) in making cuts
number (1) and number (3) if
it appears there could be a
danger of the log slabbing.
NOTE: A wedge section could
be removed when sawing cut
(2) if the top bind is excessive,
to allow the tree cut to close
as cuts (4) and (5) are made.
Bottom Bind
• Cuts are similar to
those for top bind,
except top and
bottom cuts are
reversed.
Logs better approximate
geometric shapes
Butt Log
Upper logs
What are Log Rules?
Since the first sawmill was built in the United States, over 100 log
rules have been developed, using a variety of methods. Some
were based upon the lumber tallies of individual mills, others
were developed by diagramming the cross-section of boards in
the ends of logs, while still others were developed using
mathematical formulas. In general, log rules must account for the
taper that exists in all logs, saw kerf (or the loss of wood as
sawdust), and a fixed procedure for removing wood on the
outside of the logs for slabs. The Doyle, Scribner, and
International log rules are probably the most widely used rules in
the eastern United States.
Kerf and Slabs
Doyle Log Rule
The Doyle Log Rule, developed around 1825, is based on a
mathematical formula and is widely used throughout the
southern United States. This rule allows for a saw kerf of 5/16
inch and a slabbing allowance of 4 inches, which is about twice
the normal amount. Because of this, the Doyle Rule is somewhat
inconsistent; it underestimates small logs and overestimates
large logs. As a seller of timber, you must be aware that for
smaller logs the Doyle Rule will underestimate the actual volume
of wood that you have in your trees.
• Doyle is V = [(D - 4)/4]2 * L
Tree vs Log Volume Formulas
• Doyle Log Vol. = [(D - 4)/4]2 * L
Scribner Log Rule
The Scribner Log Rule, developed around 1846, is a good example
of a diagram rule. It was created by drawing the cross-sections of
1-inch boards within circles representing the end view of logs. A
space of 1/4 inch was left between the boards to account for saw
kerf. The Scribner Rule does not have an allowance for log taper
and typically underestimates 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. For
example, 392 board feet on the Scribner is equivalent to 390
board feet on the Scribner Decimal C scale.
Scribner is V = (0.0494 x D x D x L) - (0.124 x D x L) - (0.269 x L)
Tree vs Log Volume Formulas
Scribner Log Vol. = (0.0494 x D x D x L)
- (0.124 x D x L)
- (0.269 x L)
International 1/4-Inch Log Rule
This rule was developed in 1906 and is based on a reasonably
accurate mathematical formula. The rule allows for a 1/4-inch
saw kerf and a fixed taper allowance of 1/2 inch 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 1/4-Inch Log Rule is the most consistent and is
often used as a basis of comparison for log rules.
International is V = 0.905 x ([0.22 x D x D] - [0.71 x D])
for every 4 foot length of log
Tree vs Log Volume Formulas
International ¼ inch Log is Vol. = 0.905 x ([0.22 x D x D]
- [0.71 x D])
for every 4 foot length of log
Scaling Stick
This is a piece of wood (about 1/4 inch thick and 1-1/2
inches wide) that has the footage numbers printed on
the stick. The numbers are located on the stick at the
spot that represents the diameter for that number. (For
example, a 16" diameter log that is 16 feet long scales as
180 BF; the number 180 will be located 16 inches from
the end of the stick.) There will be several sets of
numbers representing different log lengths. The stick is
held up to the end of the log (running across the log
measuring the diameter) with one end of the stick at the
edge of the bark and wood. Where the bark and wood
cross the other end of the stick, the appropriate number
scale is read to determine the footage.
(Measure diameter at widest end using the maximum
and minimum diameters averaged)
Log Scaling Stick
Mill Output
Lumber Scaling Stick
Using a Lumber Scaling Stick
• Measure the length of the board in feet rounding off to the next lower footage
value. The board footage values for the various lengths are linear, so that, for
example, a seven-foot board can be measured with the fourteen-foot scale
using half the reading or a twenty-foot board with double the footage on the
ten-foot scale.
• Next, the rule is placed with the proper length scale face up across the width of
the board and pulled so that the rule head is against the board’s edge. The rule
is bent slightly by pushing down so that the rule is flat against the board. The
number corresponding to the board footage is then read from the rule at the
point where the edge crosses the rule. This board footage reading is taken from
the scale corresponding to the length of the board. There are delineation
marks half-way between the numbers defining the plus or minus cut-off points
for each value. Thus, a particular board footage value is used whenever the
width of the board falls within its range which is half-way to the next value
either up or down.
• The figure read is the board footage for that board assuming the board is one
inch thick (4/4 lumber). Adjustment of the figure is required for other
thicknesses. As examples, the footage read must be doubled when measuring
two-inch thick (8/4) boards or multiplied by 1-1/2 when measuring 1-1/2 inch
boards (6/4). When many boards of the same thickness are measured, usually
this adjustment is made using the total.