Crosshead

In mechanical engineering, a crosshead[1] is a mechanical joint used as part of the slider-crank linkages of long stroke reciprocating engines (either internal combustion or steam) and reciprocating compressors[2] to eliminate sideways force on the piston.

On smaller engines, the connecting rod links the piston and the crankshaft directly, but this transmits sideways forces to the piston, since the crankpin (and thus the direction the force is applied) moves from side to side with the rotary motion of the crank.

The crosshead also houses the gudgeon pin (US: wristpin) on which the small end of the connecting rod pivots.

Early double-acting steam engines, such as those designed by James Watt, relied on a parallel motion linkage in part due to the difficulty of manufacturing guide rails.

The cross head was made possible by the introduction of the planer which was suited for producing guides.