28 LOG RULES BASED ON CUBIC CONTENTS 



Table I indicates that the per cent of error resulting from assuming that the total 

 contents of a log is equal to that of the cylinder measured at the small end decreases 

 with increased diameter, increases with the total nunihcr of inches of taper in the 

 log but for logs with a given diameter and the same nunihcr of inches of total taper, 

 the per cent of error is the same regardless of the rate of taper or length of log, and is 

 determined by the difference in volume of the cylinders based respectively on diameter 

 at small end and middle of log. 



32. Log Rules in Use, Based on Cubic Volume. There are two 

 classes of log rules in use, based on cubic volume. The first class gives 

 the actual or total cubic contents of the log. The second class gives 

 the volume of sawed lumber expressed in board feet, but these rules 

 are based upon the use of a fixed ratio of conversion from cubic volume 

 and not upon the volume of sawed lumber which can actually be obtained 

 from logs of different sizes (§ 39). 



Cubic measure was early adopted in log measurements, but owing 

 to the fact that logs are roughly cylindrical in shape, the custom grew 

 up of using the contents of a cylinder of standard dimensions instead 

 of the simpler standard" of the cubic foot. There is no advantage in 

 this substitution of new arbitrary cubic standards for the cubic foot.^ 



The principle used in the application of such a standard is that the 

 volumes of cylinders of different sizes will vary as the square of the 

 diameter multiplied by the length. The contents of all logs can then 

 be expressed in a log rule in terms of the number of standards they 

 contain. 



The Adirondack Standard, or Market. In the Adirondack region 

 of New York several such standards have been used but the only one 

 of importance is the 19-inch or Glens Falls Standard, termed also the 

 Market.^ This is a cylinder 19 inches in diameter and 13 feet long, 



1 The cubic meter is the standard of volume used in the Philippine Islands. 

 Logs less than 8 meters (26 j feet) long are measured as a cy Under whose diameter 

 is the small end. The average diameter in centimeters is taken, the end area is 

 obtained from tables and multiplied by the length of the log in meters to give the 

 volume in cubic meters. For logs over 8 meters in length, the diameter at the middle 

 is taken, or if this is impractical, the average of the diameters of the two ends is used. 



2 It is assumed that one market equals 200 board feet which is 65.1 per cent of 

 its cubic contents regarding the log as a cylinder measured at the small end of log 

 and neglecting taper. This gives 7.8 board feet per cubic foot. 



Tests of actual output in board feet per market, sawed from 600 logs of each sepa- 

 rate diameter, gave the results as shown in table on opposite page. 



The saws used were a band and a band resaw, both cutting ^-inch kerf. The 

 lumber was 60 per cent 1-inch, the rest l|-inch and 2-inch thicknesses. These 

 ratios are therefore higher than for inch lumber sawed with |-inch kerf. The ratio 

 is still further increased by the fact that the cubic contents measured does not include 

 the entire log but only the cylinder measured at small end while the sawed output 

 is from the entire log. H. L. Churchill, Finch, Pruyn Co., Glens Falls, N. Y. 



Twenty-two-inch Standard, A different unit is in use to a slight extent 



