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Page:Popular Science Monthly Volume 90.djvu/265

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Popular Science Monthly

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����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.

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