Shaping the broad sides of crossheads by planing is sufficiently treated at pages 237 and 238, and it is now requisite to here mention their shaping on slotting-machines.

The treatment of a crosshead previous to slotting resembles that which is adopted previous to planing, the lining, turning of the pivot-ends, turning of the boss-faces, and turning of the arms, narrow sides, being usually completed when the shaping of the broad sides is to be commenced. It is not quite necessary to finish the hole in the centre boss, although it may be roughly bored, nor to turn the boss-faces, until the broad sides are finished. But if the hole is entirely finished before commencing the broad sides, the boss-faces must be also turned while the crosshead yet remains on the same lathe or boring-machine that executed the boring of the hole. This must be done to make the faces exactly right angular to the length of the hole, because when the hole is finished and the arras require reducing, it must be done so that the length of the hole will be parallel with the broad sides when produced, the result being obtained by placing the truly formed boss-face into contact with the table-face, which puts the length of the hole right-angular, as intended; whereas, if the broad sides are first reduced to the ultimate or specified dimensions, the crosshead must be adjusted on the lathe with the broad sides parallel to the axis of the lathe-spindle's motion, that the hole may be made parallel with the broad sides, as intended.

Reducing the broad sides of a crosshead with slotting-tools is very similar to that of a connecting-bar or lever, with the addition of an extra amount of shaping in order to form the curved junctions of the middle boss, and also the curved junctions with the pivot-portions or ends. If the faces of the boss have been turned to the right-angular position with the hole referred to, one of the faces is selected and put into contact with a parallel ring on the table, the ring being thick enough to provide a space for the clearance of the tool, similar to that before mentioned for other slotting. By placing the boss-face upon the ring, the length of the hole is put exactly right-angular to the table, and therefore parallel with the direction of the cutting tool's motion, as required; the same act also places the two arms of the crosshead equidistant from the tabie-face, if they were equidistant from the lathe-chuck while the boss-face was being turned; but because it may happen that they were not so, it is sometimes needful to apply a scriber-block to the centre recesses in the extremities of the pivot-ends while the crosshead remains on the packing-ring. This operation is also necessary in case some irregular or hollow part of the table, in contact with the ring, causes the crosshead's arms to be put out of the parallel condition desired; consequently, if one centre recess is found by the scriber-block to be nearer to the table than the recess at the opposite end, a piece of thin packing is put beneath one edge of the boss-face. Such packing-up is, however, but rarely required, because no great precision is requisite when the intention is merely to shape the broad sides.

After a crosshead is fixed right-angular to the table, it is adjusted to make its middle boss concentric with the table's rotary movement, because this movement is required to about half rotate the crosshead and thus shape one side of the boss. The adjustment for this situation is effected by reference to one of the circular gauge-lines, unless an arbor-chuck is used the stem of which fits the hole in the boss, in which case the crosshead boss is put into the exact position required by merely placing it upon the stem, in the same manner as that described for lever-bosses (page 275).

While a crosshead is on the stem of an arbor-chuck, it can be swung around and either broad side presented to the tool, the shaping of the straight parts of the arms and that of the curved corners being executed with the same sorts of tools as those employed for levers and bars. Each time a flat portion of a broad side is to be reduced, the crosshead requires adjusting by one of the gauge-lines on its lathe-turned narrow side, or edge, as it is usually named. This line is put parallel with the traverse, and the crosshead is then fixed until the shaping of the surface is completed, which shaping is performed by the advancement of the crosshead by means of the traverse screw. The cutting tools employed are the same as those for levers and connecting-bars (Figs. 787, 793, 794, and 792).