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inside caliper[′in‚sīd ′kal·ə·pər]
a measurement device for determining linear inside dimensions (of apertures, grooves, and so on) that may be mounted on the part being measured or inserted into it. Measurement is usually made by two spherical tips placed at an angle of 180°. Most inside calipers have provisions for setting (centering) the measurement line in the direction of the dimension that is being checked, as well as an auxiliary mechanism that transmits the displacement of the measuring tips to a readout device.
There is no strict classification of inside calipers. The types of calipers are most frequently designated according to some distinguishing property, such as design (forceps and ball calipers), type of readout device (for example, an indicator), or type of contact with the surface being measured (for example, rim calipers). The first inside calipers appeared in the 16th and 17th centuries. They were in the form of a compass with the ends of the legs bent outward.
The simplest calipers are limit gauges. They consist of a rod or tube with spherical measuring tips and are suitable for checking relatively large apertures (diameters of 100–2,500 mm). Micrometer calipers are used for more accurate measurements. They have interchangeable extenders for a measurement range of 50–2,500 mm (five standard sizes). Inside calipers of the same type, but for measuring diameters of 1,250–10,000 mm (three standard sizes) also have dial indicators.
Inside calipers for relatively small apertures usually have a connecting mechanism (from the tips to the readout device), which may be of the bevel, lever, or wedge type. Inside calipers for use in small-diameter apertures are built with connecting mechanisms of the bevel type; examples are rim calipers (dimensions starting with 0.2 mm are read on a scale with a vernier or on a dial indicator), forceps calipers (for dimensions starting with 0.95 mm), and ball calipers (3–18 mm) of three standard sizes.
Inside calipers of the indicator type are usually built with lever or wedge connecting mechanisms. Such inside calipers with a lever connecting mechanism have a measurement range of 31,000 mm (ten standard sizes); those with a wedge mechanism have better accuracy and a range of 18–50 mm.
Most inside calipers have two points of contact with the surface being measured (the two-contact measurement scheme). An exception is the indicating plug gauge (C. Zeiss, German Democratic Republic), which has a three-contact measurement scheme using two fixed tips and one movable tip; the measurement range is 19–120 mm. Preliminary setting of such inside calipers is performed using check rings.
REFERENCESMarkov, N. N., G. B. Kainer, and P. A. Satserdotov. Pogreshnost’i vybor sredstv pri lineinykh izmereniiakh. Moscow, 1967.
Gorodetskii, Iu. G. Konstruktsii, raschet i ekspluatatsiia izmeritel’nykh instrumentov i priborov. Moscow, 1971.
N. N. MARKOV