A calibration service for step gauges.

Introduction

Mechanical reference artefacts, such as a step gauge, provide a cheap and effective way of assessing the performance of a Co-ordinate Measuring Machine (CMM) for a length measuring task. Step gauges are particularly well suited for performing formal performance verification procedures described in national or international standard specifications, such as EN BS ISO 10360 Part 2.

The introduction of the new ISO 14253-1 decision rule has implications for users choosing suitable reference artefacts for CMM verification because it gives explicit guidance on the 'pass/fail' criteria. These new criteria take into account the uncertainty of the verification process which in turn depends on both the uncertainty in the calibration of the reference artefact and on the control of the machine's working environment. As a high uncertainty associated with the reference artefact increases the overall uncertainty that has to be assigned to the CMM, it is desirable to have the best possible calibration of the artefact.

NPL has developed a step gauge calibration system which uses laser interferometry to achieve the best accuracy for calibration of step gauges in the UK. Step gauges up to 1500 mm long can be calibrated.

We have extensive experience of calibrating  standard designs by manufacturers such as Mitutoyo, KOBA, TESA, Starrett. Custom designs can also be accommodated, please contact us to discuss your requirements.

Measurement Uncertainties

Measurement uncertainty for a particular step gauge depends on the length of the gauge and its overall quality of manufacture. Typically, a 1 m step gauge can be calibrated with an uncertainty of 0.40 µm.

The best measurement capability expressed as an expanded uncertainty (k=2) is given by:

• (0.1 + 0.3L) micrometres, where (L in the length in metres).

Contact

Customer Service tel: +44 20 8943 8631
E-mail: dimensional_enquiries@npl.co.uk