Such tools sometimes save a few steps at a critical period; that is, when the tool is well set and in place, so that the work is done better and more expeditiously. Apart from this consideration, there is the chance of cutting or injuring the hands, by the proximity of sharp edges. Under the control of an expert, however, there is little danger from this cause, as inspection will show. Skilful men that have worked a lifetime at their trade, have few marks or scars on their hands, as a general thing.
When these scrapers are used on cast iron, or, indeed, on brass of a peculiar composition, they sometimes “chatter,” as it is called, and leave the work full of deep, unsightly marks, like those on the edge of coins. The cause of chattering is the rapid vibration of the tool, so that it springs away from, and against the work, with great rapidity, leaving traces of its edge on the work. Chattering may be prevented, by putting a piece of sole leather on the rest, between it and the tool.
The tools with long handles are chiefly intended for heavy work, or that which requires both hands to the cut, but there are smaller tools than these, used by amateurs, wherein the common file handle, or one like it, only a little longer, is employed instead.
CHASING AND SCREW CUTTING.
In an engine, or power lathe, all screws are cut by trains of gears, as mechanics well know, but in the hand lathe, which was the first machine, screws, both male and female, must be made by chasers or hubs, both inside and outside. The chaser itself must be made first, however, and that is done by a simple tool called “a hub.”
Fig. 13.
Fig. 14.
Fig. 15.