HOW TO DETERMINE THE SCALE OF A LOG

SCALING CYLINDER:

Two measurements determine the scaling cylinder of a log segment – scaling diameter and scaling length. The scaling cylinder is an imaginary cylinder extending the scaling length of a log segment with identical diameters on both ends.

The large end diameter of the cylinder is the same as the scaling diameter on the small end. Gross scale of a log is based on the total board foot contents within this imaginary cylinder.

LOG DIAMETER MEASUREMENTS:

The Coconino Scribner decimal “C” log rule measures diameters on the one-half-inch rather than the full-inch. For example, using a standard tape measure, a scaling diameter of 10” would be any diameter that measures between 9 ½” to just under 10 ½”. The minimum top diameter normally considered in scaling is 6” (5.51 actual inches). When the narrow-way is less than 6” (5.51 actual inches), the log will be scaled back to the next shorter log length that meets the minimum top diameter requirement (this shorter log length is reflected in two-foot multiples with full trim). Log segmenting will then be done using this ‘new’ or ‘cut-back’ length.

When making diameter measurements, always remember the following:

· Diameters are measured on the smallest point on the log.

· Measurements are taken inside the bark.

· Measure through the true center of the log.

· Disregard all abnormal bumps and depressions (such as knot clusters, swells, or broken ends).

Diameter measurements are taken by finding the narrowest way first. If all logs were small and round, one measurement would probably be all that was needed. However, trees grow in a variety of shapes. When logs are delivered that are odd or oblong in shape, a second diameter measurement is needed. The second measurement is taken at a right-angle (90 degrees) to the first (narrowest) measurement. If one diameter measurement falls exactly on the half-inch, raise it to the next higher full-inch. If both measurements fall exactly on the half-inch, raise one and lower the other. The two measurements are then added together and divided by two. If the final calculation ends in one-half, the one-half is dropped. As an example: a log with a diameter measurement of 12” the narrow-way and 15” at a right angle, has a scaling diameter of 13”.

12" + 15" = 27"

27" ¸ 2 = 13 ½"

Drop the final ½"

Scaling diameter = 13 inches

LOG LENGTH MEASUREMENT:

Acceptable log lengths are generally in two-foot multiples, plus 6” for trim allowance per segment. The maximum scaling length for a single segment log is 20’ plus trim. When logs exceed 20’ they are scaled as two or more segments, with the length of each segment being as close to the same as possible. On a butt-cut, measure from the shortest side on the small end to the point where the scaling cylinder emerges on the butt. Second cut logs are measured from short side to short side.

LOG TAPER RULES:

To improve productivity, handling, and storage capabilities, logs are frequently manufactured in lengths longer than 20’ 6”. Since log segments are scaled with a maximum scaling length of 20’, it becomes necessary to obtain a small-end scaling diameter for any other segment(s) within the log.

Determining Midpoint Diameter on Second-cut Logs

Measure the small end diameter and the large end diameter; add both measurements together and divide by two. If the final calculation ends in one-half (1/2), raise it to the next higher whole number.

This log has small end diameter of 13” and a large end diameter of 18”. 13” + 18” = 31” divided by 2 = 15 ½”; raising the final ½ to the next higher whole number = 16” midpoint diameter.

To determine the rate of taper in butt logs, extensive studies were conducted on logs from different areas. Results of these studies were used to develop “standard taper rules” for butt logs. Because of distinct differences in the rate of taper from various areas, different taper rules will apply to various regions.

Midpoint Taper Determination for Multi-segment Butt Logs
1. NORTH IDAHO AREA (north of the Salmon River, and including the northeastern Washington area bounded by the Snake River on the south, to the Columbia River, north to the Okanogan River, north to Canada) --- midpoint taper shall be a standard taper as follows:
Larch & Lodgepole Pine Larch & Lodgepole Pine Cedar All Other Species All Species (except Larch & Lodgepole Pine) All Species	21’- 48’ 49’- 60’ 21’- 40’ 21’- 40’ 41’- 60’ 61’ and longer	Shall be 1-inch per segment. Shall be 2-inch top segment, 1-inch remaining segment. Shall be 2-inches per segment. Allow 1-inch taper on pieces with an odd top diameter; allow 2-inch taper on pieces with an even top diameter (Odd-Even Rule). Take two measurements, small end and 16’ up from the butt. The diameter at the 16’ measurement point shall be determined by actual measure. Apply calculated taper distribution to determine scaling diameter of the second segment. Take two measurements, small end and top of the second segment up from the butt. The top diameter of the second segment shall be determined by actual measure. Apply calculated taper distribution to top segment(s) and standard taper rule for the appropriate species to bottom segment.
2. SOUTHWEST IDAHO AREA --- midpoint taper shall be a standard taper as follows:
Larch All Other Species	21’– 40’ 21’– 40’	Shall be 1-inch taper. Shall be 2-inch taper.
Multiple-segment butt logs not addressed shall be determined with actual taper applied.
3. SOUTHEAST IDAHO AREA --- a. TARGHEE NATIONAL FOREST AREA – midpoint taper shall be a standard taper as follows:
Douglas Fir, Alpine Fir, & Engelmann Spruce Lodgepole Pine Lodgepole Pine	21’– 40’ 21’– 31’ 32’- 40’	Shall be 2-inch taper. shall be 1-inch taper. shall be 2-inch taper.
b. OTHER SOUTHEAST AREAS—midpoint taper(s) shall be determined with actual taper applied.
c. Multiple-segment butt logs not addressed shall be determined with actual taper applied.
4. Except as previously addressed, the butt-log taper tables developed by the USFS at the point of origin of the forest products shall be utilized on all forest products scaled within the state of Idaho. Multiple-segment butt logs not addressed shall be determined with actual taper applied.

DEFECT DEDUCTION METHODS:

There are four types of defect deduction methods used in scaling logs. These methods are used to arrive at the net scale volume of a log by applying a given set of rules and procedures.

(1) Length cut is used to reduce the gross scaling length to a usable net scaling length. This method is used for larger interior rots (such as butt rots or conk rots) and also for undertrim or overtrim log lengths.

This log has a 16” scaling diameter and a 16’ scaling length, giving a gross volume of 16. The log has butt rot which is estimated to extend 4’up the log. A log with a 12’ scaling length and a 16” diameter would have a gross volume of 12, this would be the net volume for this log.

16 (gross volume) - 12 (net volume) = 4 (defect)

(2) Diameter cut is used to reduce the original gross scaling diameter to a smaller net scaling diameter. This method is used for defects such as sap rots and surface checks.

This log has a scaling diameter of 20” and a scaling length of 16’; the gross volume would be 28. The log has a collar of sap rot (one-inch thick) extending all the way around, leaving a firm 18” core. The gross scale of a 16’ log with an 18” diameter would be 21; this would be the net scale for this log.

28 (gross volume) – 21 (net volume) = 7 (defect)

(3) Pie cut is used to reduce the gross scale for a portion that is missing or not merchantable. This method can be used for defects such as lightning scars or cat-faces that do not affect the entire scaling cylinder.

This log has a scaling diameter of 20”, and a scaling length of 16’ with a lightning scar that is estimated to affect ¼ of the scaling cylinder. The gross scale of the log would be 28, divide this by 4 (one quarter of the cylinder) to determine the defect deduction.

28 (gross volume) = 7 (defect)

4

(4) Squared defect cut is used to make deductions in the form of squares or rectangles from the interior of a scaling cylinder. This mathematical method is used for pitch seams, heart checks, and smaller interior rots. The formula for this is:

Width (inches) x Height (inches) x Length (feet) = Defect volume in board feet (round this to the

15 nearest “ten” and drop the final zero)

Numerous rules apply when using squared defect:

· one inch is added to allow for waste on both width and height dimensions

· logs 15’ and shorter - measurements are taken from the large end of the defect

· logs 16’ through 20’ - measurements are taken from the large and small ends of the defect, then averaged to get the mid-point dimensions for the width and height

· if the squared defect equals or exceeds the gross volume of a segment, the scaler must use a different method of deduction.

This log has a pitch seam that measures 1” x 11” on the small end and 2” x 14” on the large end. Since the log is shorter than 16’, the largest end of the defect is used and one inch for waste is added to both the height and width measurements.

15” (height) x 3” (width) = 45 x 14’ (length) = 630 = 42 rounded to the nearest zero = 4 (defect)

15

This log has a heart rot that measures 14” on the small end, and 16” on the large end. Since this log is 16’ or longer in length, the two measurements are averaged to obtain a midpoint diameter of the rot. One inch is then added for waste to the averaged midpoint diameter.

14” + 16” = 30 = 15” (avg. midpoint) + 1” (waste) = 16”

2

16” (height) x 16” (width) x 16’ (length) = 273 rounded to the nearest zero = 27 (defect)

15

Since lumber is usually sold in two-foot multiples, the net scale of a log is also determined in two-foot multiples. Any defects that would result in lumber length recovery shorter than six feet are treated as if they affect the entire length. Each log segment is always scaled on its own individual merits.

This diagram shows a two-segment log with a scaling length of 32’. The top segment has a scaling diameter of 9” and a scaling length of 16’ for a gross volume of “4”. The butt segment has a scaling diameter of 10” and a scaling length of 16’ for a gross volume of “6”. There is no defect in the top segment. The butt segment has crook defect affecting ½ of 7’ – the remaining unaffected portion of the butt segment is 9’. To reflect lumber length recovery in two-foot multiples, the crook defect is treated as if it extended for 8’. The defect deduction is determined by the fraction of the length affected, converted to an equivalent length cut – in this example, ½ of 8’, or a 4-foot length cut. The defect volume deduction for a length cut is always the difference between the gross length volume and the net length volume.

16’ (gross length) – 12’ (net length) = 4’ (defect length)

6 (gross volume) – 3 (net volume) = 3 (defect volume)

Top segment + Butt segment = Total Scale Volume

Gross 4 + 6 = 10

Defect 0 + 3 = 3

Net 4 + 3 = 7