Vibrometer-based Measurement of Turned Diameters

Published

November 3, 2025

Author(s)

Aaron Cornelius, Osian Leahy, Burak Sencer, Gregory Vogl

Abstract

Producing high-accuracy machined diameters requires the ability to check the part accuracy inside the machine tool so that process corrections can be made. Many different methods have been proposed for in situ diameter measurement, including optical inspection with cameras, friction rollers to measure the outside circumference of the part, and laser velocimetry. However, these methods are difficult to apply to large tight-tolerance parts because of uncertainty limitations or restricted measurement volumes. A common approach in industry is to use a displacement sensor mounted on the toolpost to probe the part diameter. Since this probe is moved using the machine axes, it is subject to the same geometric and thermal errors as the cutting tool. There is therefore a need for a compact, high accuracy sensor which can measure turned diameters in situ without relying on the accuracy of the machine tool axes. Laser doppler vibrometry is commonly applied to measure the vibrations of rotating components. The measured velocities also record some portion of the tangential velocity of the rotating part based on the relative positions of the vibrometer and rotation centerline. When measuring vibrations, this component is treated as a bias on the measurement and significant effort has been put into eliminating it. However, in principle this velocity bias can be used to help calculate the part radius. This work evaluates the feasibility of a vibrometer-based system for high-precision in situ measurement of large meter-scale machined diameters. The approach measures the velocity of the part while it rotates at a fixed rate using a laser Doppler vibrometer, resulting in a measurement that is proportional to the perpendicular distance between the vibrometer beam and rotation centerline. Critically, this measurement is independent of the accuracy of the machine tool axis. A simple displacement sensor (either contact or noncontact) then measures the distance between the part surface and vibrometer. The part diameter is calculated based on these measurements and the calibrated laser angle. This study has three main sections. First, the theoretical model for laser Doppler measurements of the part diameter is presented. Second, several potential error sources are discussed to analyze their impact on the desired measurements, along with potential ways to mitigate their effects. Finally, the method is tested on a machine tool using a calibrated stepped-diameter part with diameters from 10 mm to 100 mm to evaluate the measurement accuracy. Ultimately, the vibrometer-based method shows errors of up to 1.4 % of the nominal measurement, which is not sufficient for measuring high-accuracy parts. This large error is assigned primarily to part surface finish and curvature and spindle vibration. Further research on vibrometer behavior and direct current measurement is required, specifically for cases where the laser is not aimed normal to the surface of the part.

Proceedings Title

Proceedings of the 40th ASPE Annual Meeting

Conference Dates

November 3-7, 2025

Conference Location

San Diego, CA, US

Conference Title

40th ASPE Annual Meeting

Pub Type

Conferences

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Keywords

Vibrometer, Diameter measurement, Lathe, Process monitoring

Citation

Cornelius, A. , Leahy, O. , Sencer, B. and Vogl, G. (2025), Vibrometer-based Measurement of Turned Diameters, Proceedings of the 40th ASPE Annual Meeting, San Diego, CA, US, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=960769 (Accessed June 25, 2026)

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