HAND WOOD-WORKING TOOLS 425 



prevented from entering beyond this point because of the 

 thickness of its bevel or back. If considerable pressure is 

 applied so as to force the cutting edge into the wood, the 

 friction between the wood and knife becomes so great that 

 the blade is jammed or wedged in the board. 



489. Cutting Action of Saw and Knife Compared. In 



cutting hard material, such as wood, sufficient material must 

 be displaced to allow the upper part of the cutting tool to 

 enter the wood. This allows the cutting edge of the blade 

 to be constantly in contact with the wood and prevents 

 side friction and binding. The side friction and binding 

 of the cutting edge may be reduced considerably by the 

 application of lard or a lubricant to the side of the tool. 

 The difficulty of cutting will then be greatly lessened. A 

 knife edge scores the wood; a chisel cuts by separating 

 and- removing the material; and a saw employs in a general 

 way the actions of both the knife and chisel; that is, the 

 saw in action removes successive portions of material by 

 the processes of cutting and tearing. The material is not 

 removed in the shape of long shavings, but in small particles, 

 commonly called sawdust. 



490. Grinding of Wood-working Tools. The cutting 

 edge of wood-working tools tends, of course, to become dull 

 after being in use for a time. This edge can usually be 

 sharpened by a whetstone, but after a number of whettings 

 it will be found necessary to use a grindstone. The whet- 

 stone removes the metal very slowly, while the grindstone 

 removes it rapidly. A blunt tool makes cutting hard and 

 does imperfect work, for when excessive force is necessary 

 the sense of direction is lost, ancj the tool slips or digs in, 



