The invention relates to an apparatus for the grinding or polishing of workpieces, particularly metallographic samples, in which the workpiece is pressed against a grinding or polishing disc under the influence of an operative force which is transmitted to the workpiece, and is thereby subjected to an operative pressure, i.e., grinding or polishing pressure equal to the operative force divided by the surface area of the workpiece being ground or polished.
When such an apparatus is used for grinding (including honing) or polishing, an abrasion takes place, i.e., material is removed from the surface of the sample in contact with the grinding or polishing disc.
It is usually the intention, particularly within the metallographic field, to obtain removal of a surface layer of a predetermined thickness, or in other words to obtain a predetermined abrasion depth, or at any rate an abrasion depth within a predetermined order of size.
To achieve this, it has hitherto been customary to use the process time as a parameter, meaning that the grinding or polishing is terminated after the lapse of a certain processing time which has been established empirically. This method, however, involves considerable uncertainty, seeing that, e.g., a variation of the abrasive properties of a grinding stone will result in an abrasion depth per time unit different from that on which the establishment of the processing time was based.
It will therefore be advantageous to be able to perform a direct measurement of the abrasion depth. Such a measurement could be obtained by means of an optic measuring system similar to the systems which are used on modern machine tools for measuring distances within the .mu.m range. While such systems are very accurate, they are much too expensive for use in connection with ordinary metallographic grinding and polishing, and they would not provide any indication of the grinding or polishing pressure. This pressure, which is also an important parameter of the process, would therefore have to be measured separately.