424 APPLIED SCIENCE 



the degree of softness or hardness of the wood being cut, 

 and the grain of the wood. 



488. The Cutting Action of a Knife. A knife, like a 

 chisel, operates on the principle of the wedge (Fig. 202). 

 If the edge of even a very sharp knife is examined under the 

 microscope, it will be found to consist of a series of very 

 small teeth or wedges. The knife cuts by the passing of the 



FIG. 202. Knife Edge Cutting a Board. 



sharp edge to and fro over the material. The depth of the 

 cut depends upon the hardness of the material, the length 

 of the beveled edge of the knife, and the sharpness or acute- 

 ness of the blade. By acuteness is meant the smallness of 

 the angle at the cutting edge. A knife will readily cut soft 

 material, like paper, but will cut medium hard material, 

 such as 1 in. stock, only with difficulty. When the blade of 

 the knife is drawn across wood stock, it makes a small cut, 

 say fa in., and then simply glides along. The blade is 



