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Diamond-coated probes

A good alternative to probing spheres made of pure diamond

PTB-News 2.2015
Especially interesting for

manufacturers and users of coordinate measuring machines, and of form and contour measuring instruments

At PTB, the properties of diamond-coated probing spheres have been investigated for use with coordinate measuring machines (CMMs). The results show that using such probing spheres in CMMs, form measuring machines and also in contour measur-ing machines allows a considerable increase in the service life of the probing spheres as well as a reduction in the uncertainty of the measurements.

Probe style with sphere diameters from 8 mm to 1 mm for coordinate measuring machines

In coordinate metrology, geometrical measurements are mostly carried out by means of tactile probing, e.g., with ruby spheres. Mechanical wear or material deposition onto the probing sphere (e.g. when measuring aluminium surfaces) reduce the accuracy of the measurements as well as the service life of the probe stylus. As an alternative to expensive and relatively irregular (non-circular) probing spheres made of pure diamond, the properties of diamond-coated probing spheres with diameters from 0.3 mm up to 8 mm were investigated at PTB.

The investigations were carried out within the scope of a cooperation project between PTB and Zeiss IMT. The probe styli are manufactured by the Dutch company DiamondProductSolutions. They consist of a spherical segment of approx. 240° and a stylus shaft. Both el-ements are one unit of hard metal. Since there is no glued joint, cleaning with harsh solvents is, in principle, possible. The probing spheres are coated with polycrystalline, synthetic diamond and are then polished.

Compared to other spheres made of aluminium oxide, zirconium oxide, ruby, hard metal and silicon nitride, which were also investigated, the diamond-coated spheres investigated exhibited the smoothest surfaces, with roughness in the order of 2  nm. The form errors lay in the range from 200 nm down to 20  nm and are, hence, comparable to, or even smaller than, those of commercial ruby probing spheres. Wear was tested on a special steel ring with embedded abrasive particles at measuring forces of 20 mN. At a probed distance of approx. 11  m in length in total, the diamond-coated surface did not exhibit any wear. The abrasion on a ruby probing sphere, however, amounted to approx. 1  µm. When scanning smooth aluminium surfaces with a roughness smaller than 5 nm, no material deposition was detected on the diamond-coated probing spheres. On rougher aluminium surfaces, material deposition from 5 µm to 15 µm was detected, depending on the measur-ing force. In contrast, with ruby probing spheres, material deposition ranged from a few micrometers to 40 µm.


Michael Neugebauer
Department 5.3 Coordinate Metrology
Phone: +49 (0)531 592-5212
E-mail: michael.neugebauer(at)ptb.de

Scientific publication:

M. Neugebauer, S. Bütefisch,
T. Dziomba, S. Koslowski, H. Reimann: High-resolution investigation and application of diamond coated probing spheres for CMM- and form measure-ment technique. Proceedings of the 13th international conference of euspen, 1, 75–78 (2013)