Page:Popular Science Monthly Volume 10.djvu/186

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174
THE POPULAR SCIENCE MONTHLY.

trivance, and the bar of iron is cut with the same ease as though it were of lead. This results to some extent from both jaws approaching each other. The arrangement of levers, cams, and stays, is worthy of examination after the lecture.

PSM V10 D186 Common hand shear.jpg
Fig. 1.

The use of the chisel, however skillfully handled, is not satisfactory over a surface wider than itself, although widened and made two-handed, as Fig. 5, and although the gouge has succeeded, or rather been planned to precede it, there is still a tendency almost unconquerable for the tool to follow the leadings of the fibres rather than cut through them at a very slight obliquity.

PSM V10 D186 Vise held shear.jpg
Fig.2

The only guidance either the axe, the adze, the pick, the gouge, or the chisel receives, is from the skill of the workman. Hence these tools produce such different work in different hands. However much it may be desirable to encourage skill in the workman, it is quite as desirable to furnish him with implements which shall make the least

PSM V10 D186 Spring action shear.jpg
Fig. 3.

demand upon the exercise of this skill—which shall, in fact, so assist the skill in one or more directions as to permit all its care in some other direction. The assistance which the chisel needs is such as shall not only prevent it running deeper into the timber than is de-