The pinion wire of clock and watch makers is well known. I am not wholly acquainted with the manner in which it is drawn: but I have made my pinion wire, of brass, in lengths of about a foot, by the Machine described below.
A common Draw-bench (not here represented) is worked in the usual manner: but the instrument which forms the pinion (see [Plate 17], [fig. 1]) is of a peculiar construction. It consists of a plate A B, containing—1st. a guide tube a, ([fig. 2]) to centre and conduct the blank wire;—2d. a ring b c, with nine grooves cut on one of its surfaces, directed to the centre, and in which are well fitted the cutters 1 2 3 4 5 6 7 8 9; and 3d. a ring d e, formed into nine spirals exactly like each other, answering to the cutters, and destined to urge them equally toward the common centre whenever this circle d e, is turned by the endless screw C D, in the direction of the arrow. In [fig. 2], f g is merely a top piece to cover at the same time the cutters and the ring d e; which latter is thus duly centered. The points of the cutters 1, 2, 3, &c. are formed like the spaces of pinion teeth; and in the other direction, are sloped 15 degrees to the common axis, as taken at their pitch line.
The [third figure] represents the drawing clams, or pinchers, with a piece of blank wire d in them, tapered off to give easy entrance to the cutters. These clams have a cylindrical part of about a foot long, in which is cut a winding groove a b, whose use is to turn the wire in the act of drawing; for which purpose also the swivel e f is provided. The method I employ to trace this groove to the obliquity required, is to measure the circumference of the cylinder, and call that 268; and then, to make its length, in the cylindrical part, equal to 1000 of the same divisions. But this is right, only when the pinion to be drawn is of equal diameter with the clam-cylinder a b: so that if it is wished to draw pinions of a smaller diameter, I further say: diameter of clam-cylinder is to diameter of pinion, at the pitch line; As 1000 (present length of clam-cylinder) is to required length of ditto. Thus, for example, if the diameter of the pinion were only 1⁄4 that of the clam-cylinder, the length of the latter would be only 250 of the 1000 divisions, before found: and so in proportion for smaller diameters.
The [figure] shews this groove receiving a guide screw or stud a, which, placed in the fixed headstock a c, turns the clams d, with the wire, just enough to give the teeth an inclination of 15 degrees, thus adapting them to the wheels of which the proportions have been already given; where note, that the real dimensions of this pinion Machine are twice as large as those of the [figures 1 and 2]: but the size of every thing is of course variable, according to the pinions required to be produced.