THB SAW. 87 



smoother and more uniform it is, the thinner and narrower a saw 

 yo'i can use. A smooth blade is also less liable to rust. To 

 diminish the friction, most saws are made gradually narrower to- 

 wards one extremity. Some cross-cut saws are made broadest in 

 the middle {Fig. 33), not only with a view to minimise friction, 

 but also in order, without using too much metal, to place most of 

 the weight where it is required. 



When stiffening frames {Fig. 36 and 38) are used, both the 

 thickness and width of the saw are reduced to a minimum. 



The cutting edge is very often made on a convex curve {Fig, 

 33), or with a " crown" or " breast" {Pig. 34), to adapt it to the 



Fig. 33. 





Curved Cross-ciit Saw. 

 Fig. 34. 



'•A'ivi/V.aV/vV^*^^^''''''''"'^ 



Delhi Saw. 



natural rocking motion of the hand and arm. 



A saw should be springy and elastic and at the same time highly 

 tempered. A soft saw dulls sooner, drives harder, and does not 

 last so long as a hard saw. Nevertheless saws of Indian manu- 

 facture are often made of merely tough iron. 



In a straight saw the rake influences the pressure of the saw on 

 the -wood during the progress of cutting. The rake should there- 

 fore be regulated according to the hardness of the wood to be 

 sawn and the height and pitch of the teeth. 



