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Log Rules

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Tree versus Log Volumes Trees contain sections that resemble different geometric solids. Trying to fit one rule to approximate the entire tree is difficult

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Tree Felling

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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.

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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.

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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.

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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.

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Bottom Bind Cuts are similar to those for top bind, except top and bottom cuts are reversed.

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Logs better approximate geometric shapes Butt LogUpper logs

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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.

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Kerf and Slabs

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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

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Tree vs Log Volume Formulas Doyle Log Vol. = [(D - 4)/4] 2 * L

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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 = ( x D x D x L) - (0.124 x D x L) - (0.269 x L)

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Tree vs Log Volume Formulas Scribner Log Vol. = ( x D x D x L) - (0.124 x D x L) - (0.269 x L)

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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 = x ([0.22 x D x D] - [0.71 x D]) for every 4 foot length of log

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Tree vs Log Volume Formulas International ¼ inch Log is Vol. = x ([0.22 x D x D] - [0.71 x D]) for every 4 foot length of log

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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)

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Log Scaling Stick

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Mill Output

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Lumber Scaling Stick

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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.

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