When a lever-boss or crosshead-boss has had its key-way formed, and an end of a rod or pin has been turned to fit the circular hole, the end can be marked while in the hole, which will ensure the required coincidence of the two key-ways ; therefore the usual mode is to adhere to this plan, whenever circumstances permit.

The end of a piston-rod, pump-rod, slide-rod, or similar object, is usually turned to fit its hole while the boss is cold; but crank-pins, pivot-studs, and gudgeons, are usually made to tit the holes while their respective bosses are red-hot, or nearly so ; consequently, the end of a pin which is taper, such as that of a crank-pin, will not enter its hole while cold so far as it will enter while hot, at which time the taper end will be in the exact place intended for it when in future use. Therefore, to properly show the key-slot of a taper end belonging to this class, it must be scribed both while in its hole and also afterwards, when it is out. Presuming that the taper end has been well fitted to the hole, and that it has been hammered into the hole just enough to tighten it, the marking of the key-slot is performed while the pin now remains in, by scribing with a scriber which is put successively into the two extremes of the boss key-way. This will accurately show the place for the key-way's thickness on the pin, but not its width, because the taper end is not now in its ultimate situation. The pin, or whatever other piece may be in progress, is therefore taken out, and the intended width marked; for which purpose it is necessary to scribe the key-slot as much beyond the present lines as the taper end was short of its ultimate situation while it was in the hole. It is also requisite to allow the draught at the proper extremity to make the key bear properly; if not, it may tend to push the object out of the hole, instead of tending to keep it in.

By Fig. 915 a crosshead-boss and rod's end is shown, which end is properly fitted to allow it to enter the full distance intended while cold, no heating of the boss being intended in this case; consequently, it is only requisite to allow the proper amount of draught after the end has been scribed when in the hole, and is taken out to complete the scribing to show the exact place. The crank-pin denoted in Fig. 916 is also seen in the proper place for scribing, although its taper end is not now in its ultimate place in the boss, through the intention of expanding it with heat, at which time the small end of the cone, shown by a dotted line, will be made to coincide with the boss-face. The marking of the key-slot is therefore now partly done, and the pin removed to complete it, when the width of the key-way is shown further along the cone, as represented in Fig. 917.

In many cases the ends of crank-pins and rods can be finally marked to show their key-ways while on the drilling-machines which are to execute the drilling. As soon as the rod or pin has been partly scribed while in its hole, it can be taken to the drilling-machine, and placed upon vee-blocks on the table, as indicated by Figs. 918, 920, and 921. If the object is heavy, a rotator should now be attached, similar to the one shown in Fig. 921, which is in two halves, and may be bolted to the rod at any convenient place. The rotator is much like a gripper for lathe work, and one of these can be used, if necessary. By means of the straight stem or handle which extends from the rotator, the rod or crank-pin can be gradually rotated on the blocks until it is in the exact position desired; therefore if the rod's end has been scribed on two sides when in the hole, a scriber-block's point can now be adjusted to the middles of the intended entrances for the key-way, the rod being gradually rotated until both entrances are seen to be parallel with the table. While the object thus remains, the scriber-block is now shifted to the extremity of the rod or pin, and a line scribed across it, which is now of course parallel with the table, and represents the centre of the key-way or key-slot. This line constitutes a gauge-line, to be used while adjusting for drilling, at which time it is only necessary to rotate the rod or pin on the vee-notch blocks until the line is at right-angles to the table, as denoted in Fig. 920. An el-square is employed to effect this adjustment, as seen in Fig. 919 ; and as soon as this is done, and the length of the object put parallel with the table, the holdfast-plates are fastened across the object, and it becomes ready for being put exactly beneath the drill-point for drilling.

The cutting out of the metal from the key-slot can be entirely performed with a slot-driller, or by means of drilling a number of holes and a slotting afterwards. At the time this slotting is to be executed, the crank-pin or rod is fixed with its length parallel with the slotting-table, as while drilling; and the centre line across the extremity is also vertical, as in drilling.

A slotting-tool suitable for forming a key-slot is shown by Fig. 782, and the one denoted by Fig. 791 is also suitable, if sufficient room exists for the end of the tool to enter at one end of

2 r2 the key-way. An accurate method of making a deep key-slot in a short time consists in first drilling a hole at each extremity of the intended slot, by advancing the drill half way from both sides, and next fixing the object on a slotting-table to remove the remaining metal with a slotting-tool. By this mode no risk is incurred of the drill-point getting out of the proper place while drilling, which risk is involved whenever drilling is effected without a drilling-rod to guide the cutter, whether a slot-driller or one of any other class is used.

It is now needful to close this chapter on shaping, but it should be mentioned that a number of other shaping processes are included in the chapter on turning, because a great number of objects exist which require turning in addition to other paring processes. It is therefore convenient to introduce a number of shaping and slotting processes in the next chapter.