An apparatus for removing machine lines from the gasket groove in the flanges of a header box has a support plate mounted for linear movement on rails connected to the header box. The support carries a tool driver which can be pivoted below the support to bring a grinding or polishing tool, rotated by the tool driver, into and out of the groove for grinding and polishing away the machine lines in the groove as the support slides along the rail. This grinds and polishes the grooves while avoiding a wavy effect which was a disadvantage of using a hand-held grinder for the same purpose.