Force versus Part Squareness

[[Mi...]]

Have one part family where -X styli was making squeal ( not quite like fingernails on old blackboard). Then starting noticing same on another part in +/- x and +/- y. The first part is aluminum with +x side being stock. The second family is A2 steel ground to approximately Ra = 16. Am using ruby tips on steel and SiN on aluminum parts.
Dropped the measuring force to 160 (meas. plan only), but no noticeable change in symptom. We were taught in class that part could be in any orientation as long as base alignment was a good one.
How far can the measurement be dropped without seriously affecting data? What else can be changed to alleviate apparent high friction?

[[Ch...]]

I have had a very hard time producing data that shows the squeal has an impact on the measured value. If there is an impact, it seems to me that filtering the data would solve the problem. I'm my opinion, changing your probing force to eliminate the squeal may be more detrimental to the accuracy as opposed to dealing with the squeal and possibly filtering.

[[SH...]]

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Probing force has any significant impact on the measurement??

[[Ch...]]

That's a good question. I know Zeiss CMM's utilize the tensor value of the probe to help improve accuracy. I think probing force would have an impact on measured values since the probing force directly impacts the tensor calculation.

[[Ro...]]

Are you using a vast XT?
With my XT I generally use 100 mN with my 1mm - 4mm Styli. I go down to 50 mN with anything less than 1mm due to the shaft being so thin & fragile.

[[Ke...]]

I have gotten mixed messages/opinions on probing force...

I have been told to calibrate the probe using the same force settings that are used to inspect features that the probe is being used for (by an experienced user).... and told that it doesn't matter one way or the other (by experienced Zeiss trainer)

[[Ch...]]

I remember from training that they said to qualify using the same force that you measure. Everything I measure is fairly sturdy so I almost never tweak my probing force. Therefore, I don't have any statistical data to support the theory that changing your probing force will change the results. My intuition says that it would, However, the value of intuition without data is debatable.

[[Am...]]

The only probes ive used the sensitive setting is when I need to use a really long extension (100mm) and on some plastic parts with features that can deflect with enough force. The only time ive noticed any noticeable accuracy issues is when the probes are qualified with a different measurement force then what the feature is being measured with. Early on I was under the impression qualifying with sensitive would measure with sensitive measurement force on any features using that probe. After changing the features themselves I was getting the results I was expecting.

[[SH...]]

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How you change to 50mN, in my cmm it is minimum 100mN...

[[Da...]]

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You can type in the number you want, it isn't necessarily selected from drop-down list.
Just for the info, I read somewhere that 50 mN is the specified minimum on XT head.

[[Mi...]]

Thanks a bunch to everyone for the replies! For the record, am using an ACCURA II with an XT probe. We had a power outage Thursday due to storms and had Friday off so haven't been able to collect any new data. Also, always probably over-cautious about dropping settings too far. Will see what results if dropped lower....