Patent GB-1407461-A (GB)
Title: Method and apparatus for abrading the surface of a workpiece
IPC: B24B21/12
Filed: 1972-09-13
Abstract: 1407461 Grinding TIMESAVERS Inc 13 Sept 1972 [17 Sept 1971 7 April 1972] 42601/72 Addition to 1334256 Heading B3D A method of machining the surface of a workpiece to a predetermined level by grinding with an endless abrasive belt 7<SP>1</SP>, Fig. 1, having a portion thereof supported by a member 9<SP>1</SP> engaging the back side of the belt comprises effecting grinding engagement between the workpiece and the belt, maintaining a feed force between the workpiece and the belt to produce relative feeding motion of the workpiece and said portion of the belt, the feed form being limited to below a predetermined magnitude whereby an increase beyond a predetermined magnitude of the resistance presented by the workpiece is compensated and -the feed force maintained substantially constant, and controlling the rate of the relative feeding motion so that the rate is substantially unaffected by discontinuity of contact between the workpiece surface being ground and the belt.  A machine for carrying out the method, the abrasive belt 7<SP>1</SP> is supported by a contact roller 9<SP>1</SP> and a roller 8<SP>1</SP>, the contact roller being adjacent a work-supporting structure 100 having a rotatable work holding turret 36<SP>1</SP> constructed and driven as described in the parent Specification 1,334,256. The turret is mounted on an arm 51<SP>1</SP> hinged for movement about a shaft 56<SP>1</SP> and connected by hydraulic cylinders 105 to a back-up arm 104 fixed to the shaft 56<SP>1</SP>. The shaft is rotatable by an hydraulic motor to move the arms between a horizontal position, in which a workpiece can be loaded or unloaded from the turret, and a vertical position in which the workpiece is engaged by the abrasive belt 7<SP>1</SP>, latches 107 actuated by control cylinders 108 engaging the back-up arm 104 to releasably return it in the vertical position. The shaft 56<SP>1</SP> mounted in the side walls 103 of a carriage 101 adjustable along horizontal guides 102 by rotation of a nut 111 engaging a screw 110 fixed to the carriage, the carriage being locked in its adjusted position by pneumatic clamps 114. When the carriage has been adjusted and locked in position and the arm 104 secured in its vertical position by the latches 107, the hydraulic cylinders 105 are activated to move the arm 51<SP>1</SP> and press the workpiece against the abrasive belt. The cylinders 105 move the workpiece a finite distance after initial contact, the distance being determined by the position of the carriage. The cylinders are included in an hydraulic circuit having an adjustable pressure relief valve to determine the maximum work feed pressure, and two pressure compensated volume control valves, one of which controls a fast rate of feed during movement of the workpiece to initial contact with the abrasive belt, and the other of which controls the feed rate during grinding. The adjustable pressure relief valve holds the feed force constant even if the work surface has a hard spot. When the limit of the feed motion is reached, the rotation of the limit can be measured to produce a smoother finish on the workpiece. In another embodiment, a rough grit belt 120, Fig. 5, and fine grit belt 121 are entrained around the contact roller 123, and a worksupporting mechanism 124, substantially identical to that shown in Fig. 1, is movable along the shaft 56<SP>1</SP> to present a workpiece W on turret 51<SP>1</SP> selectively to the belts. In a further embodiment, three turrets substantially identical to that shown in Fig. 1, are mounted on a rotatable table indexable to present the tables to a load/unload position, a rough grinding station and a fine grinding station, the rough and fine grinding being effected by rough and fine grit belts on a common contact roller, the belts being vertically orientated as distinct from the horizontal orientation shown in Fig. 1. In another arrangement having rough and fine grit belts vertically orientated and each having a respective contact roller, the work supporting structure is movable along a track vertically adjustable by jack screws to determine the elevation of the work support, feed of the workpiece being effected by movement of the arm 51<SP>1</SP> as described with reference to Fig. 1. In an alternative arrangement, the rate of movement of the arm 51<SP>1</SP> relative to the back-up arm 104 is controlled by a screw engaging a nut which is permitted to move away from the arm 104 in the event of interference with the advance of the arm 51<SP>1</SP>, the cylinders 105 applying the force to feed the arm towards the belt. The machine of the parent Specification 1,334,256 may be operated such that feed rate control is effected by controlling the motors 46 driving the nuts 40 for elevating the platform 38, the pressure in the elastic air chambers 50 being maintained high. During grinding, the table 38 may be oscillated.