Popular Science Monthly 



M9 



51 §t>,^^^ 



> 



When a rip-saw has been used where a cross-cut saw 

 should have been employed the shavings, or rather 

 tearings, will look like this under the microscope 



Above: The sawdust 

 shavings as they appear 

 under the microscope 

 when a cross-cut saw 

 has been correctly used 



The action is quite different with 

 the cross-cut saw. If a chisel is 

 pushed across the grain of a board it 

 sticks and tears up the wood fibers. 

 If a knife is used no great resistance 

 is encountered. After drawing the 

 knife across the grain along two lines 

 the short cylinders of wood-fiber 

 between the two can be easily broken 

 loose, leaving a channel such as that 

 cut by a saw. Now, if you substi- 

 tute the tip of the cross-cut saw- 

 tooth for the point of a knife and the 

 leading edge of the tooth for the edge 

 of the knife, you will see at once the 

 action of the cross-cut saw. Alter- 

 nate teeth cut the ends of the wood- 

 fiber, and the following teeth eject 

 the fibers as sawdust. The ripping 

 process parts the wood-fiber and re- 

 moves shavings, all of which is done 

 so long as the outside leading edge of 

 the tooth is sharp. 



The skillful workman learns to re- 

 gard his saws as well as his other tools 

 as having spheres of usefulness pecu- 

 liarly their own. To use a rip-saw 

 where a cross-cut saw is needed may 

 result disastrously in a fine piece of 

 work. A comparison of the pictures 

 of shavings and "tearings" will show 

 the wastefulness of substitution. 



