6. Surface grinding
Many surface grinders used in rock mechanics are standard metal working machines, with a dust extractor added so that the wheels can be run dry. Real need for a surface grinder arises when prismatic specimens or broad surfaces have to be prepared for close tolerances, as surface grinding on small cylindrical specimens can be done quite adequately on a lathe with a tool post grinder, and on a lapping wheel.
The lather can also be used for grinding the ends of cylindrical specimens. A specimen is held directly in the chuck, rotated at 200-300 rpm, and the grinding wheel, its axis inclined about 15o to the specimen axis is passed across the end of the specimen while rotation at 6,000-8,000 rpm. For finishing, less than 0.0254 mm only should be ground at each pass.