Gauge inspection workpieces usually have pass-stop method, coloring method, light gap method and indicator table method. 1. Pass and stop method: Use the pass end and stop end of the gauge to control the size of the workpiece so that it does not exceed the tolerance zone. For example, when measuring the aperture, if the through end of the smooth plug gauge passes but the stop end does not, the aperture is qualified. The gauges inspected by the pass-stop method are also called limit gauges (Figure 1). Common limit gauges include threaded plug gauges, threaded ring gauges, and calipers. 2. Coloring method: apply a thin layer of appropriate pigment (such as Prussian blue or red lead powder) on the working surface of the gauge, and then grind the surface of the gauge with the surface to be tested. The size of the colored area and uneven distribution of the measured surface indicate its error. For example, use a cone gauge to inspect the taper hole of the machine tool spindle and use a flat rule to inspect the straightness of the machine tool rail. 3. Light gap method: make the surface to be measured contact with the measuring surface of the gauge, and put a light source behind or use natural light. When the gap is small to a certain extent, the transmitted light becomes colored light due to the phenomenon of optical diffraction, and the transmitted light can be seen when the gap is 0.5 microns. The size of the gap can be judged according to the color of the transmitted light. The size of the gap and the degree of unevenness indicate the size, shape or position error of the measured size, for example, use a ruler to check straightness, and use a square and a flat plate to check verticality (Figure 2). 4. Indicator method: Use the accurate geometric shape of the gauge to compare with the measured geometric shape, and use the dial indicator or micrometer to indicate the error of the measured geometric shape. For example, use a flat plate and a dial indicator to measure the straightness of a ruled workpiece; use a sine gauge, a flat plate and a micrometer to measure the angle.
