8 Forest Mensuration 



PARAGRAPH XV. 



UNITS OF LOG MEASUREMENT IN THE UNITED STATES. 



The units of log measurement used in the United States differ greatly. 

 Graves' Handbook gives 43 "rules." The rules can be subdivided into 

 three main grops : 



Board feet group (Par. XVI.) ; 

 Standard log group (Par. XVII.) ; 

 Artificial cubic foot group (Par. XVIII.). 



PARAGRAPH XVI. 



BOARD-RULES. 



A foot board measure is a superficial foot one inch thick, in boards one 

 inch or more in thickness. It is a superficial foot, irrespective of thick- 

 ness, in boards less than one inch in thickness. 



The "board rules" merely guess at the number of feet board measure 

 obtainable from logs of a given diameter. The guess is based upon 

 either graphical considerations, circles of specified diameters being sub- 

 divided into parallelograms i% inch thick (diagram method), or else 

 on mathematical considerations, with a view to the fact that a cubic foot 

 of timber should theoretically yield 12 board feet of lumber, whilst the 

 actual loss for slab, saw kerf, etc., will reduce the output by 30% to 

 50%. In the Biltmore band saw mill, by over one thousand tests, the 

 actual loss for logs 12 inches to 40 inches in diameter has been found to 

 amount to 30%, or close to 1/3. Consequently, it is safe to say that the 

 band saw obtains from a cubic foot of log 8 board feet of lumber. 



The number of board feet which a log actually yields depends on : 



1. The actual cubic volume of a cylinder having the length and small- 

 est diameter inside bark of the log. 



2. The defects of the log (heart rot, wind shake, bad knots, crooks), 

 which are usually eliminated by edger or trimmer. 



3. The gauge of the saw, on which the saw kerf depends. The kerf 

 of band saws amounts to l /% inch, of circular saws to usually J4 inch, of 

 inserted tooth saws (of large diameter) to ^ inch, of resaws to 1/16 

 inch. 



4. The exactness of the work, especially depending on trueness of saw, 

 proper lining of saw and sawyer's skill ; further, on the exactness of the 

 setworks. 



5. The thickness of boards obtained ; the minimum width of boards 

 permitted ; the amount of lumber wasted in the slabs ; shrinkage in drying. 



The following table compares the contents of logs in cubic feet with 

 their contents in feet board measure as found by C. A. Schenck through 

 a thousand tests of actual yield in yellow poplar, as given by Doyle's 

 rule and by Lumberman's Favorite rule. 



The figures given in columns c, f and i show the contents of a 

 log in feet board measure after Schenck's findings, Doyle's and Favorite 



