667,576. Grinding. THOMPSON GRINDER CO. Nov. 22, 1949 [Aug. 27, 1949], No. 29911/49. Class 60. A grinding machine comprises a pair of substantially co-planar and relatively movable wheels 32, Fig. 2, operable to grind the opposite faces of a workpiece 50, and a dressing unit 48 adapted to be moved in one direction into a position in the plane of the wheels and then in a second direction into dressing relation with both wheels for simultaneously dressing them. Each wheel 32, together with its driving motor 30, is mounted on a slide 28 movable on guides 26 on a bed 20, and each slide comprises a hollow upper member 149, Fig. 5, supported by balls on the guides 26, and a sub-slide 150 movable in dovetail guides 148 on the upper member. The slide 150 has a depending portion 152 in the form of a closed cylinder housing a piston 158 formed in two parts 169, 162 threaded at their ends on a lead screw 164 which is journalled in the bed 20. The slides are moved by admitting pressure fluid to either end of the cylinder, movement in the direction away from the workpiece being limited by an adjustable screw 192. Relative movement of the two slides is provided by a ram 202 connected to the slide 150 and movable in a cylinder 200 in the main slide 140 under the action of pressure fluid admitted to the cylinder; the limits of movement are determined by an abutment 208 and adjustable screw 212. The dressing unit 48 and a workpiece support 46 are mounted on a carriage 38 which is disposed centrally of the machine and movable at right angles into the guides 26 so that either the unit 48 or workpiece may co-operate with the wheels. The carriage 38 is slidable on two guide rods 34, Figs. 2 and 3, which are fitted with dustexcluding bellows 44. Reciprocation of the carriage between its two positions is effected by pressure fluid supplied to either end of a cylinder 54 which is mounted in the carriage and movable over a fixed ram 56. The workpiece support 46 comprises a workholder 72, Fig. 4, on a table 70 on the upper end of a cylinder 74 which is movable vertically over a ram 84 on the carriage. Grinding is effected by admitting pressure fluid to the cylinder 74 so as to reciprocate the workpiece which may be given a single pass or a plurality of passes; in the latter case, the wheels are fed inwardly on each pass by metering a quantity of fluid into the left-hand end of the cylinder 152 until finally the outer end of the cylinder abuts the piston 158. Adjustable stops on the cylinder co-operate with limit switches for determining its limits of movement. At the start of grinding, each main slide 140 is in forward position with the screw 212 abutting a stop 210, and the slide 150 is in its outer position with the screw 192 abutting a stop 198. The shaped dressing roll 52 is rotatably mounted on a table 130, Fig. 4, carried by a cylinder 114 which is movable by pressure fluid over a ram 118 on the carriage 38; bellows 134 protect the projecting portion of the cylinder 114. To dress the wheels, the motors 30 are deenergised, the slides 140, 150 moved to their outermost positions, the carriage moved to position the roll co-planar with the wheels, and the roll then moved from a position above the wheels into pressure engagement with them. A lowspeed motor 218, Fig. 2, then drives the lefthand wheel through an over-running clutch 220, or a low-speed drive is applied to the roll or both the roll and wheels, and dressing continues until the axes of the wheels and roll are in the same plane. To compensate for the material removed by the roll, the wheels are fed inwardly an appropriate distance by rotating the lead screws 166 either by hand or automatically. At intervals, the roll 32 is restored to shape by first trueing the right-hand wheel by a diamond unit 216, Fig. 2, mounted on the corresponding slide, and using this wheel to grind the roll; in the latter operation, the roll is brought into engagement with the left-hand wheel and driven at low speed, and the trued wheel is then engaged with the roll while driven by its motor. The complete cycle of the machine may be automatic under the control of solenoid-operated valves. Tapered workpieces having a series of ridges on their faces as shown in Fig. 11 may be formed by suitably shaping the wheels 30. In a modification, the carriage 38 may move at' an angle other than at right-angles to the common plane of the wheels.