Abstract: Apparatus is described for grinding glass to form optical elements, especially prisms. The apparatus has an improved mounting for grinding wheels which are used for different grinding purposes, specifically roughing, finishing and polishing. The finishing wheel is usually an expensive, diamond-abrasive wheel which is trued to provide finishing grinding operations with high accuracy. The finishing wheel, which can be used for the critical final grinding of the workpiece, is semi-permanently mounted on the grinding machine spindle in a manner which allows the less critical roughing (semi-finishing) and polishing wheels to be temporarily mounted in front of the finishing wheel in interlocked, stacked relationship therewith without disturbing the truth of rotation of the finishing wheel. When the finishing wheel is used alone, a plug is inserted in a socket, which receives a shank extending from the other wheels, so as to prevent dirt from entering the socket.