in the compact transmission of a hand - held reciprocating power saw , conversion of rotary to reciprocating motion is through a speed reducing bevel gear set closely coupled by an eccentric drive pin in the crown wheel to a reciprocating saw blade carrier bar . a guide or bearing plate extending between the crown wheel and the saw blade carrier bar does double duty , guiding and supporting the saw blade carrier bar on one side and , on its opposite side , providing a thrust surface for the crown wheel . the crown wheel engages the guide plate through a thrust ring about equal in diameter to the diameter of the crown wheel . in this way , the shallow crown wheel may be positioned , supported and stabilized entirely by two simple bearings -- a large diameter plain thrust bearing of essentially no radial capacity and a short radial bearing subject to virtually no bending or thrust loads . in an alternative embodiment the guide plate is eliminated and the reciprocating carrier bar receives the thrust load of the crown wheel .