Measurement of small holes

Abstract

1. Instrument SM-168A can be reliably used under workshop conditions for measuring the ovality and tapering of the internal cylindrical surface of racers with hole diameters of 0.6–3 mm at the rate of 200–250 racers per hour with a maximum error of 3σ=+-0.0006 mm (instrumental error). Instrument model SM-152 is suitable for testing racers with a hole diameter of 3–10 mm at a rate of 500 racers per hour with a maximum error of 3σ=+-0.0003 mm (instrumental error). 2. These instruments can be used for certifying with high precision “reference holes” with diameters of 0.6–10 mm. 3. They can also be used for measuring hole diameters (without “reference racers” certified at a TsIL) by setting the index to a block gauge with a smaller total error and without lowering the efficiency of testing. 4. It is simpler to adjust the instruments in measuring the true hole diameters by setting the index with respect to a “reference racer” and, therefore, under workshop production conditions it is advisable to measure by means of these “reference racer”. They can be certified either in Central Measurement Laboratories, or on specially adjusted instruments by the technique described above, or else on a universal measuring equipment.