SURFACE LAPPING MACHINE

PURPOSE: To provide a new sizing device capable of easily measuring the height of an upper surface table for detecting the thickness of a workpiece with a simple mechanism while removing obstacles to the measure acompanying the deflection of the upper surface table in a surface lapping machine. CONSTITUTION: The detecting surfaces of a length measuring sensor 36 and timing sensor 37 are opposed to each other on the surface 24a of a mounting member mounting the upper surface table of a surface lapping machine. The detecting signal from the length measuring sensor 36 is converted to a digital signal through an amplifier 41 by an A/D converter 50. A rotation averaging process means 51 in a computer 50 reads out four detecting values per one rotation of the upper surface table on the basis of the timing signal of the timing sensor 37 to obtain the average value of these ones. This average value, i.e., a predetermined number of the rotation average detecting values are used to obtain shift average by a shift average process means so that a workpiece thickness detecting value is obtained.