US Patent 7168169 Anti-rotation drive mechanism for a reciprocating saw

An anti-rotation reciprocating drive apparatus for a reciprocating saw utilizes a wobble plate assembly that includes a drive shaft and an elongated arm with an interface structure for engaging a spindle. The interface structure has two ball-type interfaces that are concentrically aligned with one another, with the outer one being smaller than the inner one and both engaging a receiver portion of the spindle. The larger ball-type interface causes reciprocating movement of the spindle and the smaller outer interface prevents rotation of the spindle. The contact between the interfaces and the spindle receiver is a single point contact which reduces operating friction, wear of the parts and heat being generated.