THE WASTE FROM CROOK OR SWEEP 



51 



When this is done for logs of all sizes it is found that except for the 

 smaller logs the width of these collars is practically the same regardless 

 of diameter. This law does not hold for small logs, because the width 

 of the minimum boards remains the same for all logs and as the diameter 

 of the log approaches this minimum width of board, the proportional 

 waste in slabs and edgings rapidly increases until utilization becomes 

 zero and waste 100 per cent for a diameter of log just too small to saw 

 out the smallest board or piece that is merchantable. 



The waste in slabbing and edging varies, for any log, with the aver- 

 age thickness of the lumber sawed. Logs sawed entirely into 2j-inch 

 plank would show considerably 

 greater waste in edging than where 

 1-inch boards are sawed (§ 21). 

 The results shown by diagram are 

 confirmed by tests in the mill. 



From these investigations it is 

 evident that the waste from slabs 

 and edgings is proportional, approx- 

 imately, to the surface of the log 

 inside the bark. The surface of a 

 log is equal to the circumference or 

 girth, multiplied by the length. As 

 circumference equals xD for all 

 logs, the waste from slabs and edging 

 is then proportional to the diameter 

 of the log multiplied by its length. 



But the volume of the log in- 

 creases as the cross sectional area, 

 which is proportional to the square of 

 the diameter (§ 27). The amount of 

 waste in slabs and edgings from a log 

 20 inches in diameter is just twice 



that for a 10-inch log, since the diameter and the surface are doubled. 

 But the 20-inch log contains four times the volume of the smaller piece, 

 and this reduces the per cent of waste from slabs and edgings based on 

 the volume of the larger log to one-half that for the 10-inch log. 



52. The Waste from Crook or Sweep. Log rules apply only to 

 straight logs. But the standard as to what constitutes straight logs 

 requires definition. For all commercial log rules, this standard permits 

 of " normal " crook (§ 93). This is best defined as crook averaging 

 not over 1| inches in 12 feet, and including no log which crooks more 

 than 4 inches in 12 feet. Crook or sweep in long logs is reduced by 

 cutting them into two or more short sections before sawing. Where 



Fig 



— Relative waste in slabs and 

 edgings from sawing 2j-inch plank 

 and 1-inch boards. If 1-inch boards 

 are sawed, the waste is reduced by 

 the amount of the shaded portion. 

 The greater proportion of waste in 

 sawing thick boards comes from the 

 side cuts, hence the practice is to 

 cut 1-inch lumber from the sides. 



