Grinding and polishing machines

This invention concerns grinding and polishing machines and methods of grinding and polishing discs such as wafers of silicon for use in the construction of semi-conductor devices, and discs of glass or other brittle materials on which magnetic material is to be deposited for forming magnetic memory disks for computer disk drives and the like. A method of grinding the edge of a disc uses a grinding machine having mounted thereon a grooved grinding wheel, in which the groove is formed in situ using a forming wheel also mounted on the grinding machine. After a workpiece has been ground or after a succession of workpieces have been ground, re-engaging the grinding wheel and the forming wheel with the grinding wheel remaining in situ, to re-form the groove in the grinding wheel to correct for wear. A grinding machine comprises a grinding wheel, drive means therefor, a workhead and workpiece spindle and drive means therefor, a forming wheel and drive means therefor, means for moving the grinding wheel so as to plunge grind the edge of the grinding wheel to form a groove therein of precise cross-section and means for effecting relative movement between the grinding wheel and the forming wheel to enable the grinding wheel to engage with the edge of a circular workpiece component mounted on the workpiece spindle to edge grind the component and wherein the forming wheel is also mounted on the workpiece spindle for rotation therewith, and the grinding wheel is a resin bonded wheel.