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Roundness Measurements Using the NIST Fiber Probe



Balasubramanian Muralikrishnan, Jack A. Stone Jr., John R. Stoup


We have described a fiber probe for dimensional measurement of micro-holes in the 2004 and 2006 ASPE annual meetings. In this abstract, we describe the adaptation of this probe for measuring roundness of tiny holes and knife edge apertures. In its current configuration, the part is mounted and centered on a precision spindle. The probe, although sensitive in X, Y and Z, is used as a 1D probe. The fiber probe is brought in contact with the test artifact along X, and deflections along the sensitive direction of the stem are monitored while the spindle is rotated. In order to overcome surface adhesive forces, the fiber is excited at a frequency near one if its natural frequencies, when the spindle is being rotated to present the next sampling location on the part. However, because there is no available node on the stem, we are unable to image the stem when it is vibrating. Therefore, the spindle operates in a start-stop mode, where images are gathered when there is no spindle motion. This is unfortunately a drawback; however, our technique does pose an advantage in that by being able to monitor the stem bending along the tangential direction as well, we can assess if the fiber displays any stiction with the surface. We are currently measuring roundness of knife edge apertures which cannot be measured with conventional probes because ultra-low force probing is required to avoid damaging the knife edge. Preliminary results indicate excellent repeatability of only 60 nm at any radial location for 10 consecutive circle measurements (180 sampling points). We plan on measuring the roundness of small spheres that can then be compared against measurements made using traditional roundness instruments. Also, measurement of roundness of tiny holes - too small to be measured by existing instruments - will be performed in the coming months. We will also detail an uncertainty budget for these measurements.
Proceedings Title
Proceedings of the Annual Meeting of the American Society for Precision Engineering 2007
Conference Dates
October 14-19, 2007
Conference Location
Dallas, TX
Conference Title
Annual Meeting of the American Society for Precision Engineering 2007


fiber probe, form metrology, roundness


Muralikrishnan, B. , Stone, J. and Stoup, J. (2007), Roundness Measurements Using the NIST Fiber Probe, Proceedings of the Annual Meeting of the American Society for Precision Engineering 2007, Dallas, TX, [online], (Accessed June 23, 2024)


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Created January 1, 2007, Updated February 19, 2017