Abstract: A machine or apparatus has been devised for accurately reconditioning or truing the sealing rim or flange of a door or window frame of a heavy piece of equipment, such as a furnace or coke oven that is subjected to relatively high and variable temperatures. The apparatus has a base-supporting and furnace-mounting frame, and movable secondary and head frames. The head frame carries a milling means that extends centrally through the other frames, and the secondary and head frames are mounted for back and forth movement in a supported relation on and along the base frame in such a manner that the milling means may be advanced along the sealing flange to be trued or planed. The movement of the head frame on and with respect to the lower or secondary frame and of the latter with respect to the base frame may be controlled by pre-setting the advancing movement effected by motor drive means in such a manner as to provide a progressive advance of the milling means along the full extent of the sealing flange.