Standard deviation / Sigma value

[[Ni...]]

Good Morning,

I would like to know what value do you guys go by when you're qualifying your stylus.
We had training recently from Zeiss and the guy recommended to use .0010mm as the max. He said Zeiss guarantees the results with probes that were qualified and met the .0010mm. Brand new probes that had higher values had to be requalified using lower probing dynamic.

Because of that, I've set a program that qualifies everything and reports it so anything that is above .0013mm will show as red on the report. I usually requalify those again and they go around .0004mm.

We have one CMM with RDS head where it always gives values of .0016mm -.0020mm.
I am wondering if that's fine or if we should start finding ways to bring those values down.
And what values do you guys go by?

The image I attached is from my offline seat which is why the numbers may be funky but I wanted to show what value i was talking about.


Thank You,

[[Ni...]]

Oh the main reason why i bring it up is because the other programmer never looked at those values before. As long as it completed the qualification, he would just keep running the machine while I would keep requalifying until i met the standard deviation/sigma values.

So now that we are both working on the RDS CMM that he runs, we are at a point of which method do we go by.

[[To...]]

Typically, I have values much less than .001mm, except when qualify a stylus system using CAA. Then, I might see around .0016, but that is based on 12 positions.

Cleanliness of probes and ref sphere are important. Rigidity of connection and wear can play a role. New probes almost always give me good results using standard settings. I only back off probing dynamic on 0.5 diameter or smaller probes.

When qualifying in CNC program, I do find the S to be higher on ocassion.

[[Mi...]]

We go by the sigma,

on XXT machines we aim for the 0.001mm max you stated.

on XT Gold Machines we aim for 0.0003mm max, although as these machines are aging some of the ones we have just can't meet that anymore and we aim for 0.0005.

There are exceptions to every rule, discs we aim for 0.001mm max.

Off brand probes are often not as good.

exceedingly long probes tend to be higher, especially in + or - X we find.

Any custom probes odd sizes like a 0.75mm dia ruby we have tend to have higher S values.

[[Ni...]]

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The RDS CMM is using RDSCAA so it does use the 12 angles.
We do clean everything.
Also when we create new stylus system using the same probes but as traditional instead of RDSCAA, the values go down to .0004mm.

Does that mean the values of .0016 would be good to use for RDSCAA?

[[Ni...]]

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We have some duramax, XTR and Acura machines and they all are using the traditional star probe system. The give numbers around .0004-.0009mm
Our RDS machine uses RDSCAA which always give around .0016mm or higher. If we use those same probes to create a new stylus system but as a traditional, the values also give around .0004mm.

So it sounds like RDSCAA have an impossible time meeting .0010 max?

[[To...]]

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That's what I've consistently seen and have been told by Zeiss.

[[Is...]]

for our most common tolerances 0.030 mm we have these limits:

Sigma: ideal <= 0.0003 mm; recomended <= 0.0005 mm
Rigidity: ideal >= 50 N/mm; recomended >= 30 N/mm

[[Ri...]]

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CAA probes are not as accurate as an RC List probe.
I was informed of this by a Zeiss tech a couple years ago.