Abstract: Apparatus for machining a groove in an arcuate workpiece segment comprises a horizontal milling table, a carriage mounted on the table and supporting a workpiece to be machined, a milling guide mounted on the carriage and including a vertical post, an arm extending radially from the post, and a milling assembly attached to the arm and including a cutting tool overlying a workpiece mounted on the carriage. The table is movable in x and y directions in a horizontal plane to displace the workpiece along an arcuate path relative to the cutting tool, and the milling assembly is displaceable along a vertical axis to move the cutting tool toward and away from the workpiece.