Replies

1. 
   mapleman | Jan 07, 2009 08:06am | #1

   Search Ebay for "log rule" or "doyle log rule"

   Relatively inexpensive.

   Or you can go here for a new one:

   http://www.forestry-suppliers.com/product_pages/View_Catalog_Page.asp?mi=1449

    

   Lee

2. 
   KiddervilleAcres | Jan 07, 2009 04:09pm | #2

   I just Googled board feet in a log from your post and got

   http://mathforum.org/library/drmath/view/62471.html

   I'm told by a forrester that the rules used vary by geographical location, at least in the U.S.  which just adds to the confusion/complexity.

   Regards, 

   Bob @ Kidderville Acres

   A Woodworkers mind should be the sharpest tool in the shop!

3. 
   JiminFla | Jan 07, 2009 06:27pm | #3

   Orville,

   First you calculate the area of a circle the size of the circumference of the log.  The formula for this is Area = radius squared x pi.  Remember to use the radius, not the diameter.  Divide the radius by 12 to get feet instead of inches (see example below).

   The formula to determine the number of cubic feet of lumber in the log is Cubic Feet = Area (in feet) x Length (in feet).

   There are 12 board feet of lumber in a cubic foot, so multiply the answer by 12 and you get the number of board feet.

   Example: 

   Log is 6' long and 14" in diameter

   Radius in inches = 7"

   Divide radius by 12 to convert to feet: .58'

   Area = .58' x .58' x 3.14 = 1.05 sq ft.

   Cubic feet = 1.05' x 6' or 6.3 cubic feet

   Board feet = 6.3 x 12 = 75.6 board feet

   Jim

1. 
   mapleman | Jan 08, 2009 05:13am | #4

   Jim,

   Great job. I'll have to bookmark that forumla for a later date!

   Lee

2. 
   SteveSchoene | Jan 08, 2009 07:17am | #5

   Just remember that knowing the cubic volume of the log, doesn't tell you all that much about the amount of lumber that could be sawed from that log, though it might be useful in calculating the weight of the log.  There is a lot of waste in the sawing process.  That's what the different measuring systems, such as the Doyle attempt to take account of. 

1. 
   joinerswork | Jan 08, 2009 05:54pm | #6

   Yah Steve, there are two or three different systems used for calculating the BF yield of a given log. As I recall, one works better for smaller logs, and another is more accurate for larger diameters. Throw in the amount of waste from a big circular mill's blade- 1/4" or more, and how little waste a portable bandmill makes, and there is a lot of room for variation. 

   Ray 

1. 
   KiddervilleAcres | Jan 09, 2009 06:14am | #9

   Ray,

   My sawyer uses a bandsaw mill and he claims a 20% gain on the log scale.  He consistently gets at least that much from every log he has sawn for me.  I guess log scales and lumber scales are a whole different fettle of kish.

   Regards,

   Bob @ Kidderville Acres

   A Woodworkers mind should be the sharpest tool in the shop!

   Edited 1/8/2009 10:15 pm ET by KiddervilleAcres

1. 
   joinerswork | Jan 09, 2009 07:18am | #10

   Bob,

   Any scale has a certain range of tolerances.  Lester Flatt, the bluegrass legend told a story about the wife of one of his band members having a  home birth.  Seems the midwife forgot her scales to weigh the new baby after it was born, so they looked around the house and found a set of scales in the husband's fishing gear, used to weigh the fish he caught.  That little baby weighed twenty-seven pounds!

   Ray 

4. 
   SgianDubh | Jan 08, 2009 07:21pm | #7

   Hoppus Feet (Old British form of measure)

   A calibrated girth tape takes log measurements. The user wraps the tape around the log and reads off the Quarter Girth (QG) in inches from the scale. The Hoppus Feet yield of hardwood sawlogs and veneer logs is calculated by taking 1/4 of the logs girth in inches at its midpoint in the length, squaring the result and dividing this by 144. Finally the number of log length feet multiplies the result of the previous sum. The formula is written: Hoppus Volume (h ft) = ((Mid Quarter Girth in inches)²/144) X Length in Feet.

   To put some numbers to this formula, let’s say the girth of a 16 foot long log measured at the midpoint of the length is 69 inches. Wrapping the calibrated girth tape around the log provides a reading of 17.25 inches. This, incidentally, is equivalent to a circle of 22 inches diameter, although here of course we’re not dealing with a perfect circle, we’re dealing with a rough log.

   Example Sum 1: (17.25² / 144) X 16 ft = 33.06 h ft. For those more familiar with board feet (bd ft) ie, primarily North Americans, multiply the result by 12, thus 33.06 X 12 = 397 bd ft.

   Example Sum 2: A log 16 feet long with a 38 inch mid-length girth, ie, a quarter girth of 9.5 inches as read by the calibrated tape. Calculate: (9.5² / 144) X 16 ft = 10 h ft or 120 bd ft. This log would have a theoretical mid length diameter of approximately 12” if it were a true circle.

   Doyle Scale (One scale used in north America)

   The estimated volume yield is calculated using the log length rounded down to the nearest foot length and the diameter at the log’s small end, ie, the end at the top of the living tree trunk. The diameter of the log is measured under the bark twice at the narrow end, once one way and then again at right angles to the first measurement. The result of the two measures is averaged and used for subsequent calculations. The Doyle Scale underestimates the yield from small logs, and the smaller the diameter the greater is the underestimation.

   Additional grading happens at the same time, eg, defects such as crook, knots and rot are noted. Scaling is the term used in the US for estimating the bd ft yield of a log. The information about the log is marked on its end with crayon for later processes.

   The formula for the Doyle Scale is: bd ft = (D-4)² X (L/16) where D = log diameter at the small end inside the bark, and L = log length.

   Example Sum 3: Using this formula where the diameter (D) = 20 inches, and the log length (L) is 16 feet the sum is,

   (20-4)² X (16/16) = 256 bd ft, or in cubic feet, 256 /12 = 21.33 ft³.

   There are dozens of formulae that have been devised for calculating yield from a log. I have only mentioned two well known ones that use the Imperial system of measure. In North America another quite common scaling system is the Scribner Scale. Slainte.

   Richard Jones Furniture

5. 
   Metod | Jan 08, 2009 07:38pm | #8

   Good boards, crappy ones? Flatsawn, riftsawn, quartersawn, thickness of the boards or just the volume of wood?
   Best wishes,
   Metod