Abstract: A device for undercutting a rotating workpiece is provided wherein the tool carried by the toolholder is actuated into and out of engagement with the workpiece at predetermined feed locations. A base forms the mounting for the undercutter attachment with the toolholder being pivotally mounted on said base. The tool is moved axially in one direction along the workpiece to provide cutting. When the end of the travel has been reached, the tool moves in the opposite or return direction and the tool is automatically disengaged prior to reaching the start of the undercut portion. The actuator for the tool includes a pivoted arm and stationary trip cam on the machine tool. A positive latch holds the tool in the cutting position and a release trigger engages the trip cam to release the latch during the return feed at the proper position. The latch comprises a biased pin and the pivotal toolholder is biased by a spring activated cylinder.