84 



TOOLS FOR rBI-LlNG AND CONVERSION. 



an angle {Fig. 28), or a curve {Fig. 29), or a straight line 

 {Fig. 30). 



Fig. 28. 



Fig. 29. 



Fig. 30. 



A very powerful combination of the two preceding forms, which 

 is of American design, is the M tooth {Fig. 31). 



Fig. 31. 



/\Jvv\^^^^|wl,,^^ 



N 





M'teeth. 



Sawdust occupies from four to six times the space it did in the 

 wood, the proportion being greatest in the case of soft and porous 

 woods. The height of the teeth should, therefore, always be con- 

 siderably greater than the depth cut through at each movement or 

 revolution of the saw, so as to increase the depth of the gullet. 

 Hence the softer and looser grained the wood is, the longer will be 

 the teeth. Greater capacity can be secured for the gullet also by 

 a wider spacing of the teeth, and actually the wideness of the spac- 

 ing is determined by the softness and porosity of the wood ; but 

 it has been found from experience that the force required to move 

 the saw increases with the fewness of the teeth, so that a limit is 



