Self Centering Probing??

[[Jo...]]

Can a VAST XXT be used for self centering probing? 

[[Ri...]]

Yes, but it's mainly only really works that well in the Z direction. If you have an RDS you have more leverage because you can rotate the head, so that you are probing in the correct direction. 

[[Da...]]

I tried self-centering on a PEM stud today that Calypso didn't like the placement of, but it didn't help any... 

[[na...]]

It really helps, if you lock (clamp) 1 axis with self-centering on XXT.

 

Regards,

Dane

Edited November 27, 2024
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[[Mi...]]

It depends.

We regularly use Self center probing for POINTS, most often with left or right probes to locate spline spaces and such. That works perfectly fine, expect you have to lock an axis or it tends to slide off your part.

Anything more complicated than that only works in the -Z direction and even then... not really.

[[Jo...]]

Hi All,

Sorry for resurrecting an old topic. 

I am using a Contura G2 Vast XT head and would like to utilize self-center probing with a probe pointing in the x+ direction. 

I am using this on a 1.0mm hole with a true-position tolerance of 0.8mm to describe my application further. Is the machine capable of measuring this accurately using the self-center function? 

 

[[Ma...]]

It will depend on probe radius and accuracy of initial touch.

[[Mi...]]

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Will need some more info but probably, that's a small hole with a large position allowance. Are you intending to self center with a larger ruby to help find the hole before measuring it properly with a smaller probe? I've done that, it works great with XT or XXT. IF the hole has a countersink, otherwise you risk the CMM missing altogether. If it's a production environment run by non-cmm programmers you don't want to risk that.

However I've also done this in the case where there's no countersink. Scan a point set over the holes expected location, make sure it's large enough to capture the worst possible hole. Then set a "Minimum point" on your point set, and use that minimum point as your reference for finding the holes. If it's one hole using Meas. Ref. is probably fine, if it's a pattern using a secondary alignment that moves based on the minimum point is probably easier.

or maybe I'm guessing wrong and my explanation is useless to your question!

[[Je...]]

Only in direction of sensor vector.  Even then, you should VALIDATE the data.  Just because it takes a point, doesn't mean its the point you wanted.

Quick check - Take the point and look at your nominal vs actual.  

[[Jo...]]

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Hi Mike,

Thanks for the feedback. This is for a production setting that will be checked by operators with limited experience. I do not have a .5mm tip in our rack at this time and wanted to avoid it unless absolutely necessary. These small tips tend to not last long as you could imagine. If this is necessary I would probably break this feature in its own program to prevent the entire program from being unusable on off shifts if the situation does arise. 

I do like the idea of scanning for min point for a rough location. I think I might give this a shot.

Thanks again!

[[Jo...]]

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Agreed. I can compare the self-center point vs a .5mm circle to validate this method in another program. 

[[Mi...]]

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If you attempt my suggestion, make sure the evaluation settings for the point is set to mid point. I forgot to include that. I use that method in a production environment where we have 1.5mm holes that I need to check with a 1mm ruby because I also don't want to go any smaller than that, so not much room for the hole to be in the wrong spot. 

I will say, as long as the hole you're measuring is well formed, I bet you will find my suggestion followed by the self centered point will be reliable enough for that huge 0.8mm tolerance. Be careful though, there's a lot of things that could affect it.

 

[[Da...]]

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I know I'm a newbie ion the Zeiss world, but in my experience with numerous other CMM's, you CAN NOT measure a 1.0mm hole with a 1.0mm probe tip; you will create a collision, probably breaking that 1.0mm ruby. Buy some 0.5 tips (get them in a set of 3; they break VERY easily..), or if you want to live dangerously get some 0.3mm tips and pray for the best. When installing tips as small as these, they WILL break if dropped from even a couple of centimetres, so do all probe building over a soft, clean cloth surface.

Edited January 24, 2025

[[To...]]

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Calypso will not let the probe go into the hole if the probe diameter is >= nominal hole diameter.

Edited January 24, 2025

[[Jo...]]

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Hi Dave, I agree that you cannot measure a 1mm diameter using a 1mm probe.

In my comment, I am trying to utilize an oversized probe Ø to measure the position of the hole using the self-centering feature. 

 

[[Cl...]]

Would inserting a best-fit pin into the hole and measuring that work?

[[Da...]]

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That's good to know; PC-DMIS would let you try to cram a 2mm tip in one...

[[Da...]]

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If you have a FULL set of Deltronics for that nominal diameter, then maybe. The problem is ANY amount of a 'slip fit' will allow motion of the pin. Also, pins in a QC lab don't tend to remain completely straight, especially in the sub-.060" (1.5mm) sizes. Additionally, you need to consider how much 'compliance' a small-diameter pin will have when touched by the CMM. Regardless, you will need a pin within .0001" (.004mm) of the actual diameter, and be an interference fit as well.

Edited January 24, 2025