Ratchet braces are employed to drill holes that are of too large a bore to be drilled by tread drills, and that cannot be conveniently taken to a drilling machine.
Fig. 1792.
In [Fig. 1792] is represented a self-feeding ratchet brace. a is the body of the brace, having a taper square hole in its end to receive the square shank of the drill. l is a lever pivoted upon a, and having a pawl or catch b, which acts upon ratchet teeth provided upon a. When the lever l is moved backward the pawl b being pivoted rides over the ratchet teeth, but when l is pulled forward b engages the ratchet teeth and rotates a and therefore the drill. At f is a screw threaded into a, its pointed end abutting against some firm piece, so that unscrewing f forces the drill forward and into its cut. These features are essential to all forms of ratchet braces, but the peculiar feature of this brace consists in its exceedingly simple self-feeding devices, the feed screw f requiring in ordinary braces to be operated by hand when the drill requires to be fed.
The construction and operation of the self-feeding device is as follows: The feed screw f is provided with a feather way or spline and with a feed collar c, operated by the pawl e. The feed-collar c has at d a groove, into which a flange on pawl e fits, and on its side face there is a groove receiving an annular ring on the face of lever l, these two keeping it in place. The pawl e is a double one, and may be tripped to operate c in opposite directions to feed or release the drill, as the case may be, or it may be placed in hind position to throw the feed off—all these operations being easily performed while the lever l is in motion. Collar c is in effect a double ratchet, since its circumference is provided with two sets of notches, one at g and the other at h. Each set is equally spaced around the circumference, but one set or circle is coarser spaced than the other, while both are finer spaced than is the ratchet operated by pawl b. Suppose, now, that the lever l is at the end of a back stroke, and pawl e will fall into one of the notches on side g of the feed-ratchet, and when lever l is moved on its forward stroke it will operate the feed ratchet and move it forward, a standing still until such time as pawl b meets a tooth of the ratchet on a. The feed screw f is provided with a left-hand thread, and the feed ratchet has a feather projecting into the spline in the feed screw; hence moving the feed ratchet at the beginning of the forward motion of l and before a is operated, puts a feed on, and the amount of this feed depends upon how much finer the notches into which pawl e falls are than those into which b falls. The feed takes place, be it noted, at the beginning of the lever stroke, and ceases so soon as pawl b operates a and the drill begins to cut.
As shown in the [figure], the feed collar is set for large drills (which will stand a coarser feed than small ones), because the notches are finer spaced at g than at h. For small drills and finer feeds the collar is slipped off the screw and reversed so that side h will fall under e, it being obvious that the finer the notches are spaced the more feed is put on per stroke. The spacings are made to suit very moderate feeds, both for large and small drills, because the operator can increase the feed at any stroke quite independently of the spacings on the feed ratchet. All he has to do is to give the lever handle a short stroke and more feed is put on; if still more feed is wanted, another short stroke may be made, and so on, the least possible amount of feed being put on when the longest strokes are made. In any event, however, there will be a certain amount of average feed per stroke if equal length of strokes is taken, the spacing being made to suit such ordinary variations of stroke as are met within every-day practice. When it is desired to stop feeding altogether, or to release the drill entirely from the cut, all that is necessary is to trip the feed-pawl e (without stopping the lever motion), and it will operate the feed screw in the opposite direction sufficiently to release the drill in a single backward stroke of the lever. The range of feed that is obtainable with a single feed ratchet is sufficient for all practical purposes, although it is obvious that if any special purpose should require it, a special feed ratchet may be made to suit either an unusually fine or coarse rate of feed. The feed screw is not provided with either a squared head or with the usual pin holes, because the feed ratchet is so readily operated that these, with their accompanying wrench or pin, are unnecessary.
Fig. 1793.