Fig. 185. Ratchet-Brace.
Fig. 186. Inserting a Bit in Stock.
Fig. 187. Hand-Drill.
The screwdriver, Fig. 188, is a sort of holding tool for turning, and so driving screws. Various devices have been tried to prevent the twisting in the handle. This is now practically assured in various makes. The other important matter in a screwdriver is that the point be of the right temper, so as neither to bend nor to break. If the corners break they can be reground, but care should be taken not to make the angle too obtuse or the driver will slip out of the slot in the screw-head. The bevel should have a long taper. A shop should be equipped with different sizes of screwdrivers to fit the different sizes of screws. Screwdrivers vary in size, the shank ranging in length from 2½" to 18". A long screwdriver is more powerful than a short one, for the screwdriver is rarely exactly in line with the axis of the screw, but the handle revolves in a circle. This means an increased leverage, so that the longer the screwdriver, the greater the leverage.
| 188 | 189 | 190 |
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Fig. 188. Screwdriver. Fig. 189. Screwdriver-Bit. Fig. 190. Spiral Screwdriver. |