110 



CONVERSION OF TIMHER WITH THE SAW. 



of every scantling to be cut should be accurately traced on both 

 ends of the log. The first set of lines at both ends should be drawn 

 vertically with the aid of a plummet ; the rest will, in nearly every 

 case, run at right angles to these, and can then be ruled with the 

 help of a carpenter's square. Before beginning any cut, the plane 

 along which it is to run should be accurately indicated by joining 

 the extremities of the corresponding lines traced at the two ends. 

 In order to save time, as many such lines as possible should be 

 marked off all at once. The slabs flitched off by the first cuts may 

 often be thick enough to yield small scantlings. 



The wood at the centre of a log is, as a rule, specially liable to 

 decompose quickly and to warp and split. Hence this part should 

 be removed if the sawn goods are to be used for any important 

 purpose. 



Speaking in a general manner, the saw-cuts may follow a radius 

 or a tangent. In the first case, the entire width of the medullary 

 rays, the silver grain, is made visible (whence the designation for this 

 mode of sawing of " sawing with the silver grain "), and the layers 

 of concentric growth run through the piece at right angles to the 

 surface of section (Fig. b5-A). The medullary plates, being lustrous 



Fig. 55. 



E 



MMM 



Sawing (A) with, and (B) across, the Silver Grain. 



and harder than the wood fibres, contribute very greatly both to 

 the beauty and lasting quality of the surface, while the uaiforni 

 disposition of the concentric layers prevents, or at least minimises, 

 any tendency to warp. On the other hand, a tangential section 

 {Fig. 55-B) exposes principally the softer fibrous tissue, and the 

 irregular distribution of the concentric layers exaggerates the ten- 

 dency to warp in the direction of the concavity of these layers, and 

 the medullary plates are invisible, except when they are extraordi- 

 narily thick, as in oaks. Actually the sections are seldom perfectly 

 radial or tangential, but approach more or less one or the other of 

 these two directions. For pieces in which beauty is a requisite or 

 for surfaces which, like floors, are subject to much wear and tear 

 sawing with the silver grain is essential. 



