Out-of-Roundness Gauge

a measuring instrument for determining out-of-roundness—that is, the greatest distance from a surrounding circle of points on the actual cross-sectional profile of a cylindrical surface (see Figure 1). They became wide-spread in the 1960’s.

The principle of measurement of out-of-roundness gauges is based on rotation of a measuring tip relative to the part being

Figure 1. Diagram of measurement of out-of-roundness

inspected, or vice versa. The most frequently used gauges have a rotating tip (Figure 2). The main assembly is a precision arbor or the precision guides of a table. Out-of-roundness gauges are used to check internal and external cylindrical surfaces 3-1,000 mm in diameter and 100-1,600 mm long. The results of measurement are recorded by an automatic device with magnifications of 2 × to 20,000 × on a disk or strip chart; the smallest measuring error is 0.05-0.8 micron.

Figure 2. Diagram of determination of out-of-roundness for a cylindrical part by means of an out-of-roundness gauge: (1) instrument table, (2) part, (3) precision arbor, (4) primary transducer (sensor), (5) screws of centering device

An out-of-roundness gauge with a tip that moves along the axis of the part is used to detect deviations from a cylindrical shape (the greatest distance of points on the actual surface from the surface of the surrounding cylinder). In this case the out-of-roundness and the deviations of the cylindrical profile in a longitudinal section of the part are determined simultaneously. The most advanced out-of-roundness gauges have devices to isolate the harmonic components of the out-of-roundness and devices to eliminate the initial centering error of the part from the results of measurement.