Probe Qualification issues with accuracy

[[Wi...]]

I'm a new Zeiss user coming from Mitutoyo. Our Zeiss Micura has great precision, but I'm struggling with the accuracy. Using a dynamic tensor qualification on two separate probes, I'm not achieving the same results when measuring a standard. The standard is 2.50080", with two different probes I'm measuring 2.50040" and 2.50096" and it repeats +/- .00002". 

Previously with my Mitutoyo, I would modify the probe radius to match the known standard, and this would work very well. Upon trying this with this CMM, it was successful and seems to be the way to go moving forward.

Some questions remain:

• While it works, I'm not sure that this is the "best practice". Is there a better "Zeiss approved" way of achieving accuracy? Just qualifying does not achieve this.
• If this is the best way, why would I go through the qualification process if it will just change the probe radius and cause me to modify it after again?

[[Ni...]]

Why would you modify the probe radius. Part of the qualification is to identify the true size of the probe radius. The probe manufactures have tolerances too, just because they sell it as a 2.50080" probe doesn't mean it isn't actually a 2.50082" probe.

Edited May 23

[[He...]]

A Micura should perform much better than this. Even with quite long probes. Either the probes are broken or the machine are broken.  Carbon fiber extenstions and stem tend to break in a way that causes them to look fine, qualify within expectation and measure poorly. IU would check that first. Probably get a short tungsten stemed stylus and test the result with that one. The move on from there.

[[Ke...]]

Are these brand new probes? I would start by looking at the results of the probe qualification results.

 

[[Wi...]]

I've been looking into the probe qualification results and some probes' sigma are as low as 0.00016. The probe that had an issue was 0.0046. Does this indicate the probe is no good? I've been trying to read up on the measuring force and the probing dynamic in %, should this be modified to receive good values? If so, does modifying this here also change the probing force when running programs?

[[Je...]]

The sigma for a stylus (especially new) should be very low.  Your result of around 0.00016 would be what I would expect.  0.0046 is extremely high.  That stylus configuration is absolutely defective or assembled improperly.  Check the stylus, connection to the plate and the plate itself.

To answer your question, I would strongly advise against modifying the stylus diameter based on a "standard" other than the REF Sphere as it is likely the most precise standard in your facility.  Measuring to an untracked standard also typically invalidates QMS requirements as well.

[[Ke...]]

I'm guessing that the probe with the larger siga is the the same one that is providing you with the larger measurement result on the standard... As Jeffrey alluded to: a slightly loose stylus could be the problem. If that doesn't correct the issue: try replacing that probe with a new one