Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 124

A description of screwdrivers in this chapter may seem out of place, but as they are tools of impulsion, even as is the hammer, they may fitly be dealt with here. Two or three screwdrivers at least will be required, long and short, and with wide and narrow blade. For general work, a tool of medium length should be obtained, although there are on the one hand enthusiastic advocates of a short tool, and on the other hand of a long tool for any and every purpose. Any advantage gained by a short over a long tool, or the reverse, is one of advantage in special circumstances only, and not one of saved energy; theoretically, the length does not enter into consideration at all, except when, in starting to extract a difficult screw, the driver is tilted from the upright, but this is at the risk of a broken tool edge and defaced screw-head. The worker then must decide for himself what sizes will best suit his purposes. The principal patterns are illustrated here. Figs. 347 and 348 are the London patterns, the, former with handle of beech or boxwood, and the latter with an oval ebony handle. Cabinet screwdrivers are shown by Figs. 349 to 351, Fig. 349 having a plain beech handle, Fig. 350 an oval boxwood handle, and Fig. 351 a fluted or “firm-grip” boxwood handle. For special work, it is necessary to have a long spindle-blade screwdriver, as shown by Fig. 352. The power gained by a screwdriver in turning a screw depends entirely on the diameter of its handle, quite irrespective of the length of its blade. Taking two screwdrivers having blades of the same length and breadth, but one A having a handle one-half again as broad as that of the other B, then A will turn the same size of screw as will B with exactly one-third less power expended; it is purely a question of leverage, and quite independent of the length of the blade. Of course, in correctly proportioned screwdrivers the longer blades generally have the wider handles, but it is not always so, and the increased length of the blade is usually disadvantageous except as already noted. An important point in working with large screws is to see that the point of the blade fills the entire width of the slot in the screw-head. A useful screwdriver is the one illustrated by Fig. 353. The handle is that of a gimlet, and can be separated from the blade, a great convenience for carrying, although the whole tool is only 6 in. long. In the handle are two hardened steel pawls acting on a ratchet, so that in driving a screw the right hand never moves off the handle, the left being thus at liberty to guide the screw. Reversing the handle on the tang of the blade puts the ratchet in position for withdrawing a screw. The handle is 4 in. long, which gives it, theoretically, great mechanical power. Practically, the advantage over the ordinary form is more than it is theoretically, as owing to the shape of the handle the power is better applied. Another very convenient form of screwdriver is shown in use by Fig. 354, and consists of a screwdriver bit (Fig. 355) used in an ordinary brace. It is chiefly useful where many large or medium-sized screws are required to be driven. The power gained is considerable, owing to the length of lever afforded by the sweep of the brace, and it has the additional advantage that the entire weight of the workman can be applied to keep the driver in the screw-slot without decreasing his power of turning as in the ordinary pattern; it is also very speedy, as the turning is continuous. The ordinary screwdriver may be found in the way when screwing a lock on or off, inside the front of a drawer, as this is generally done with the drawer in position. The short screwdriver illustrated by Fig. 356 is well adapted for work of this description, and the handle being broad and flat is convenient to hold in the hand. Another short screwdriver is shown by Fig. 357, and this is designed especially for unscrewing plane irons, as shown on p. 45, Fig. 163.

Fig. 349.—Plain Handle Cabinet Screwdriver.

Fig. 350.—Oval Handle Cabinet Screwdriver.

Fig. 351.—Fluted Handle Cabinet Screwdriver.

Fig. 352.—Spindle Blade Screwdriver.

Fig. 353.—Gimlet-handled Screwdriver.

Fig. 354.—Brace Screwdriver in use.

Fig. 355.—Screwdriver Bit.

Fig. 356.—Short Screwdriver.