Hi Mark

When selecting a CMM, don't forget the basics: 1. Measuring range and 2. Required accuracy. You might get some more generell info from the document attached.

When it comes to "fixed Probe head" or "indexing probe head", keep in mind that every time you rotate a probe head you have to recalibrate the probe or you loose a couple of microns (depends on the probe length) of accuracy.
That's why high precision CMM's like Brown & Sharpe Germany, Zeiss or SIP usually have fixed probe heads.
You certainly have to spend a little more on probes, but ask for a proposal from an application engineer, not from a salesmen.

Several CMM makers claim that their CMM can do scanning. But what you need to know is how fast and how accurate their scanning is!

Performance of scanning CMM's is described in the ISO 10 360-4 standard. It requires that 4 different lines have to be scanned at a sphere. The resulting form error of all 4 lines combined is the "scanning form error" (a real tough test!). Althought the ISO 10 360-4 at the moment is a draft only, you should ask every supplier for their "scanning form error" according ISO 10 360-4 at a given speed.
For your reference, a Brown & Sharpe PMM 12106 MG has a total scanning form error of 1.4 micron at 10mm/sec.

Best regards
Juergen Roos
Brown & Sharpe, Wetzlar, Germany

How to select a CMM(2).doc
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