Ruby Diameter vs. Sigma Value

[[Ju...]]

I know best practices says to use the largest diameter ruby possible to measure parts. However, would a bigger ruby or a smaller ruby with a lower sigma value give more accurate data if choosing between the two?

[[Cl...]]

A ruby Ø that's too large could give you inaccurate form results, as it would tend to ride over wavy surfaces.

[[Ke...]]

I only say toward "larger" diameter probes for certain tasks.
Smaller for form measurements, as Clarke mentioned.
My most common used diameters are 1mm & 3mm.
Lower sigma values are definitely preferred.. It would depend on how big of a difference are we talking about, and the tolerances are for the measurement task.

[[Ju...]]

In other words, if a part is checked the same way with two different stylus systems and reports two different measurements, would it be better to trust the data from the bigger ruby (3mm vs 1.35mm) or whichever has the smaller sigma value?

[[Je...]]

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Both stylus systems are intentioned to give a plausible, accurate result. If either has an inordinately large sigma value, visually inspect the probe under magnification and make sure it is fastened securely. Are you measuring size such as a diameter or form such as flatness?

In situations where the measurement task is to evaluate compatibility of a mating part, such as an inner diameter, I often use a larger probe and evaluate using outer tangential element. If I need to evaluate form deviation such as flatness, then I often use a smaller probe.

You are probably wanting a simple answer such as "larger probes are more accurate" or "smaller probes are more accurate," but neither answer is true. The correct answer is "use the right tool for the job," or in other words, "use the right sized probe for the measurement task."

This being said, the 1.35mm probe has a thinner shaft, and I have dealt with deflection issues in the past when pairing a 1.35mm probe in combination with longer shafts. If you have a VAST sensor, decrease the measurement force and dynamic probing. Regardless of which sensor you have, decreasing the scanning speed may help.
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[[Ke...]]

Do you have access to a certified ring/plug master that you can measure, to verify your stylus?
If so, you can also use the Gage Correction feature in the Evaluation settings, if needed.

[[Ju...]]

I'm not measuring anything with super critical tolerances, just curious if there is a general rule of thumb concerning this.

[[Ka...]]

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hi,
im having problem with my probes (VAST XXT) and i think the force im using is too much, have tried to lower dynamic % but it didnt do anything 100%, 50% and 10% give me same results

how can i change the measuring force?

i know this is an old thread but hope u still on 😃

[[Ri...]]

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The XXT cannot generally control the measuring force electronically. You can switch to Sensitive, or Robust to slightly decrease/increase the force, but the change is minimal. If you truly need to make the force lower, you have to do it mechanically, by making the stylus system longer.

The % values that you are speaking of are the Probing Dynamics they do not control measuring force. They control the percentage of speed that the machine approaches the surface once inside the retract distance.

[[Ka...]]

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ok maybe i understood measurment force wrong,

i have a problem with VAST XXT, after updating from calypso 21 to 22
which was a bad mistake for the amount of problems it has compared to 21

my biggest issue now is when i try to calibrate my probes (7probes) i got 4x the Sigma value i was getting before,
the only S value that didnt change is the masterprobe
and i thought that Calypso 22 changed some settings or so

any idea why i get high S values?

i have tried almost everything but nth helped
the probes are clean and not damaged at all

[[Ri...]]

Are you performing a Geometry Requalification or a Passive Qualification?

[[Ka...]]

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i tried both, same results

[[Ri...]]

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The only suggestions I have left, is (1) to ensure that the XXT is secured tightly. (2) to try a brand new stylus system with a brand new stylus.

I find it strange that the MasterProbe appears to be fine.

[[Da...]]

This may sound silly, but are you using the same number of decimal places???? MM / Inches?

[[Ka...]]

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idk what u mean, can u explain -_-

[[Mi...]]

Could you post some screenshots of your results?

[[Da...]]

The display of your sigma value can be in inches, or MM. If you were using inches before and now it's in MM you will see much bigger numbers.

[[Ka...]]

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so this one had high sigma value even before
its an L probe with long shaft

normally i would get 0.0185

but now i get around 0.08 i measured this one specifically 4 or 5 times, same results

other 6 probes i was getting 0.002 now it’s around 0.005 - 0.008

[img] https://postimg.cc/xJx3PFQv[/img][/img]

[[Ri...]]

Um... That is extremely high Sigma values. Even your before values.

[[Ri...]]

I'd love to see a picture of your L probe.

I fear you might have put overweight/too long/unbalanced stylus systems and caused damage to the head.

What values are you getting for the MasterProbe qualification?

[[Ka...]]

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ok i was struggling to attach anything here

hopefully this works

Document.pdf

[[Ri...]]

AHHHHHHHHHHHHHH!! I see now. This is CAA Qualification. Yeah - sigma value standards kind of go out the window with a CAA Qualification.

The quality of the qualification purely depends on length, but even then there isn't a published formula to calculate what it should be.

I will say that 80 microns is a lot, but I've heard upwards of 100 is the limit.

I think your L probe is too long as well (axially).

To test and see if it a CAA issue, you can create a new Stylus System with that same buildup that isn't CAA enabled and see what the sigma values show with a standard qualification.

[[Ka...]]

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im not sure if i can create a stylus without CAA but imma try it tomorrow
and for the probe length, i cant do anything about it since the client built it and we need it to use their programms

thanks for the help 😃

[[To...]]

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I posted this once and someone with a larger brain than me said something like "it wasn't the speed but rather the time to reach the designated deflection". Potato vs Potato This works better with audio.