Abstract: A rail base grinding apparatus comprises a self-powered vehicle adapted for movement along a trackway to the location of a welded joint formed between two rails in the trackway. A pantograph linkage extends from one side of the vehicle and supports a lead screw which in turn supports a grinding mechanism. The pantograph linkage serves to manipulate the grinding mechanism between an elevated transportation position and an operating position and to maintain alignment between the grinding mechanism and the plane of the rails of the trackway. The lead screw is employed to control the vertical positioning of the grinding mechanism both prior to and during operation of the grinding mechanism to remove the base portion of the welding flash of the welded joint.