Taper square keys are seldom forged near enough to the intended finished dimensions to dispense with planing, especially if they are intended for piston-rods, crossheads, middle-shafts, or paddle-shafts; so that lining is required for keys in general. If a taper key is forged solid with a handle at each end to hold the key while on a planing-table, the planing will be easy, because the four sides of the key can be entirely planed without applying any plate or poppet to any part. The planing of such is commenced by first planing those two surfaces of

2f2 the key which are to be parallel to each other. These are smoothly planed until the object is reduced to that particular finished thickness required, after which it is unfastened from the table, and one of the planed sides is lined to show the taper shape of the key, and also its width at the intended large and small ends. This lining is begun by first marking a primary along the middle, and next scribing two circles, one at each end of the key, so that the primary line shall equally divide both circles. The diameter of the circle at the large end equals the finished distance across at that end, and the diameter of the circle at the small end equals the finished distance across at the same end; and when both are marked, a couple of straight lines are marked to connect the circumferences of the circles. By these two lines the shape and dimensions of the taper side is shown, and the key is now ready for planing to the lines, which is done either by packing up the small end while on the planing-table, or by tightly gripping the two already planed sides of the key between a face of an el-chuck and two poppet-screws, such as are seen in Fig. 652.

When a number of large taper keys are required, and all are to be alike, or very nearly alike, they can be made in a ready manner without any forging. By this mode, a long bar of steel about five or six times the length of one key, and rather more than twice the width, is first planed on both its broad sides to the finished thickness of any one key. The piece is next taken to a sawing-machine and cut to lengths, each being long enough for one key; and at this time each is also wide enough for two keys; consequently, each length is scribed on one of its planed sides to indicate two keys, which makes the piece resemble Fig. 655. Being thus marked, the piece is made into two by a planing-machine, parting-tool, or with a saw, if convenient. Whatever means are used to divide them, each one afterwards requires a final planing of the slant sides to the finished dimensions.

When gibs are made of a straight bar without forging, the processes are similar to those for keys, the dotted lines which denote the shape of the gib being shown in Fig. 656.

The screw-key shown by Fig. 657 should be planed, previous to lathe-turning and screwing the small end. By this mode the key can be properly lined and centred to place the screw-part into its proper position. If the key is a middle one, for tightening two gibs, one at each side, the major axis of the screw-part should be in line with the major axis of the taper part, or key proper. But if the key is for only one gib, the screw-portion should be parallel to one of the slant sides or surfaces. By these considerations it will be perceived that knowledge is required while lining, in order to properly place the screw-end, and thus avoid bending or breaking it during tightening the nut.