150 A MANUAL FOR NORTHERN WOODSMEN 



foot log takes but a small percentage out of its total yield 

 at the saw, while a 6-inch log with the same sweep is 

 practically useless for full length, edged lumber. Again, 

 strong taper may largely neutralize the effect of consider- 

 able irregularity in outside form. Lastly, in practical 

 scaling, a certain amount of irregularity in outside form 

 must be considered normal and be taken care of by the 

 conservatism of the log rule. 



Shakiness in logs is far more frequent in some species 

 than in others. Thus hemlock is largely affected by it, 

 while there is very little of it in spruce. In large measure, 

 it should be considered as an element of quality, affecting 

 the grade of the product, not a defect affecting the scale of 

 the logs. When, however, a considerable section of a log 

 is rendered worthless, it should be thrown off in the scale. 

 How much to throw off is a matter of judgment and of mill 

 experience. 



Decay may be complete, utterly destroying the value of 

 a whole log or a section, or it may be partial, allowing the 

 production of a low grade of lumber. Decay varies much 

 according to species and locality, and it occurs in various 

 forms. Of the northern soft-wood trees, fir is most liable 

 to unseen defects, a log perfectly sound to all outside 

 appearance may " open out " very poor at the saw. To 

 a less extent white pine in some localities is affected in the 

 same way. 



Generally, however, the ends of a log or some mark on 

 its surface, such as rotten knots, " punks," and flows of 

 pitch give indication to the practiced eye of defect beneath. 

 How much to allow is then a matter of judgment based 

 on mill experience. 



The following table 1 has been made up, giving the loss 

 due to round center defects extending through or affecting 

 the full length of a log. For four- or five-inch defects, it 

 amounts to the same thing as throwing out a scantling 

 having the same side as the hole has diameter. 



As stated at the start, careful mill training is the only 

 safe basis for the correct culling or discounting of logs. 

 Some sealers have that; some do not, and have to rely either 

 1 Graves' " Forest Mensuration." 



