WOODCUTTERS IMPLEMENTS. 201 



Forest saws which cut both ways require teeth of a different 

 They are always symmetrical, aud usually bounded by 

 straight lines, as in fig. 69, by curved ones, as in fig. 70, or 

 are so-called M teeth, figs. 71 and 72, which cut both ways. 



American saws have teeth as shown in figs. 73 and 74. 



Space must be allowed between the teeth for the escape of the 



sawdust, which requires six times the space of the wood from 

 which it is taken. This is provided by giving the teeth a much 

 greater depth at a h (fig. 75) than their cutting edge a c, and by 



leaving a larger space between the teeth than their own area. 

 In old-fashioned saws this was provided for by breaking-off the 

 tops of some of the teeth at regular intervals, as in fig. 76, but 

 such imperfect teeth are not found in modern saws. The tri- 



FiG. 76. 



angular teeth between the combined M teeth of American saws 

 may be considered as plauing-teeth for removing splinters of 

 wood, as they are not set like the other teeth. 



(c) Shape of Saws. — Various kinds of saws have come into 

 use in difi'erent countries, of which the following are the most 

 serviceable : — 



i. Tir()-]i(()idcd Sdirs. 



The two-handed or forest saws comprise the straight, bow, 

 and curved cross-cut saws. 



