Gauging Machine

an opticomechanical instrument for measuring the external and internal linear dimensions of parts. In the USSR gauging machines are manufactured with an upper limit of measurement of external and internal linear dimensions of 1, 2, 4, 6, 8, and 12 m (external dimensions from 0 mm; internal, from 13.5 mm). The part being inspected is mounted on a bench (the parts may weigh up to 10 kg; on special benches, up to 60 kg) or on supports between the tips of the tail spindle and the reading device. The tube of an optical caliper or interferometer is used as the reading device.

Measurement is made by the relative (comparative) or absolute method. The relative method consists in a comparison of the size of the part being inspected with the known size of a standard part. Plane-parallel end standards of length are used as standard parts. The deviation of the size of the part being measured from the standard is indicated by the reading device. In absolute measurements the size of the inspected part is determined according to two scales: the first has a division of 100 mm and a length equal to the upper limit of measurement; the second has a division of 0.01 mm and a length of 100 mm. In the absolute method the gauging machine is set for the nominal size of the part by adjusting the tail spindle to the first scale and the measuring spindle to the second. The reading device is used to determine the deviation from the set nominal size. Readings from both scales are usually fed through an optical system to a microscope in the measuring spindle.

Gauging machines are used primarily for inspecting and adjusting inside calipers, which are used to check large dimensions and to measure large end standards. There are gauging machines, such as those made by the K. Zeiss Company in the German Democratic Republic, that make it possible to measure the pitch of guide screws. The permitted error of measurement of end standards by the absolute method, with corrections according to scale, is given by the formula ± (0.4— 4 X 10^–3L) microns, where L is the nominal measured length in millimeters. Sometimes the term “gauging machine” is used incorrectly to designate complex stationary measuring equipment used to check various parameters.