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Issue link: https://pm.epubxp.com/i/875621
Touch Points on Touch Probe Measurement Contributed by Mike Creney S mall, turned parts can be difficult to inspect. Because of their size and features, choosing the best inspection method can be challenging. Some inspection methods yield better results than others, but it's critical for shops to take into consideration several factors to achieve optimal results. To determine an appropriate inspection technique, potential users should consider a round sample part smaller than 2 inches with some standard tolerances and features. is article will cover the following tolerance types: diameter, radius, roundness, concentricity and threads. Diameter Diameter is a feature commonly measured with touch probes. Typically, diameter is measured by placing the part in a vertical orientation and measuring points along the outside of the workpiece. Accuracy is dependent on both the number of measurement points and their location. Seven or more points should be used to eliminate touch- probe lobing. e points should be measured along the perimeter of the workpiece to encompass the greatest area of the circle. is allows for complete coverage of the workpiece and ensures the circle algorithm is provided with a proper data set. Caution should be taken on short arc segments, since these are actually radii and not diameters. Radius Radius measurement is one of the most difficult measure- ments on cylindrical workpieces because many of these are small. e general rule for measurement of a radius is that if the radius of the stylus is larger than the radius to be measured, then it cannot be acquired. Many customers find that an optical method is better suited for this measure- ment. Alternate measurement techniques include contour measurement systems and profiler devices. Additionally, radius measurement is subject to the number of points and form error associated with the point collection. A touch probe system generally uses a least- :: ABOVE: Thread measurement is difficult for the probe evaluation method. Typically, the stylus radius exceeds the size of the thread area. Alternate methods, such as video systems, are better suited for this type of feature evaluation. SPECIAL COVERAGE 26 PRODUCTION MACHINING :: OCTOBER 2017