emery wheel W (Fig. 38), revolves at a surface speed of about 6,000 ft. per min. The rod R also revolves, the directions of revolution being as shown by the arrows. Finally either the rod or the wheel must have a longitudinal motion so that the wheel can grind the whole length of the rod. The direction of this motion is reversed at the end of each traverse. A is a clamp for holding the rod in its proper position
_Steam_Locomotive_Construction_and_Maintenance_Fig38.png)
Fig. 38. Grinding a Piston Rod.
against the wheel. The bed of the machine, not shown, is somewhat similar to that of a lathe.
Crossheads and Slide Bars. Crossheads, which form the attachment of the piston rod to the connecting rod, are of many different forms, and various methods of machining them are used according to their shape. They are planed between the jaws which embrace the connecting rod, four or five being fixed in an inverted position on a planing machine for this purpose. The turning and boring involve several operations,
