In order to experiment with the filing motion, take two blocks of wood, and try surfacing them off with a file. When you place the two filed surfaces together after the first trial both will be convex, because the hands, in filing, unless you exert the utmost vigilance, will assume a crank-like movement. The filing test is so to file the two blocks that they will fit tightly together without rolling on each other. Before shaping and planing machines were invented, machinists were compelled to plane down and accurately finish off surfaces with a file.
In using the files on saws, however small the file may be, one hand should hold the handle and the other hand the tip of the file.
A file brush should always be kept on hand, as it pays to preserve files by cleaning them.
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