ANGLE OF IMPACT 37 



the direction of which exactly coincides with 

 the line A 13 (see Fig. 3). Such a hook will 

 never engage properly. 



The chisel with the bevelled surface of the 

 blade placed uppermost will bite, but the 

 extent to which it will bite depends upon the 

 angle at which the blade is inclined. The more 

 steeply the blade is inclined the deeper will it 

 bite ; but a stage is reached at which the 

 edge, instead of biting, merely scrapes along 

 the surface of the wood. This represents the 

 point of a hook the direction of which is 

 outside the line AB (Figs. 4, 5, and 6). The 

 depth of engagement will depend upon the 

 size of the angle formed by the line AB and 

 the line representing the direction of the point. 

 This angle is sometimes referred to as the 

 angle of impact (a in Figs. 4, 5, and 6). 

 Within certain limits, the larger this angle is 

 the deeper will be the penetration. 



The blade of the chisel may be inclined 

 so as to shave off either fine or coarse 

 parings. So long as it continues to shave 

 off parings, it represents the point of a 

 hook with a very small angle of impact. 

 Such a point engages, but does not pene- 



