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which may be done in a turret lathe with several sets of tools, each of which in turn does part of the work. In some shops much of this work is done on a horizontal turning and boring mill. Fig. 39 shows a crosshead for two slide bars,

Fig. 39.—Crosshead and Slide Blocks.

from which its complicated form will be seen. The piston rod end fits into the taper hole A; the connecting rod small end fits between the jaws B, and is secured by a pin which passes through the holes C. The slide blocks D, shown in chain dotted lines are separate pieces with channels planed in them to fit over the slide bars.

The slide bars are plain rectangular bars of steel which are planed to within a fraction of the finished sizes, the ends faced, and the holes drilled for the bolts which connect them to the cylinders at one end and to the motion plate at the other. The faces on which the slide blocks move were formerly draw-filed to a true surface on a surface plate. This involved much fitters’ work. Now the bars are placed on the reciprocating table of a grinding machine, and the surfaces are ground