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Correlation Contura to Contura

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By [Cl...] ,
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[Cl...]

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One of our Conturas is having its annual calibration done by Zeiss. While this is being done, we moved several programs that run exclusively on that machine, over to another Contura. Both CMMs have the RDS/XXT/TL1. We are seeing a .0005" difference between the two CMM's running the same program with the same "Master Part". As well as the same styli. Thoughts?
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https://qualityforum.zeiss.com/topic/10540-correlation-contura-to-contura/
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[Ke...]

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So many questions, like:
For what types of evaluations? Something simple, like point to point distance ...or something more complex, like profile or position?
Obviously, I would give more complicated evaluations more "tolerance"

How many times has the Master Part been inspected by CMM1? What is the range of the Master part reaults by CMM 1? Is the Master Part only checked after a calibration, or before & after calibration, or on some other frequency?

Are the Calypso evaluation settings the same?
Do the styli use the same calibration methods?
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[Ow...]

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1st thing I'd look at is temperature differences, the bigger the part, the bigger the difference.
2nd, what is the probe radius after qualification and does it match what it is on the other CMM. If it does and the reference spheres are of the same type and size, try using the other reference sphere on the other CMM to qualify the probe. Calibration technicians will sometimes change the reference sphere diameter to match the outcome of the sphere they use (sometimes different).
Are the diameters ID or OD?
Are the diameters being scanned a full 360° (or greater) or are they just partial sections?
Are the diameters measured in the X,Y or Z axis? Does the diameter measure different measured in a different axis?
0.0005 (.013mm) is a lot in my opinion. I've run articulating CMM's 20 years ago that would be more accurate than that.
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[Mi...]

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He have 3 CMM's that all the same specs. The machinist usually/Always run their own parts and complain the 1 CMM has zero kick outs and the other has multiple. Usually the roundness on diameters are was kicks out on the other CMM.

We use a Glastonbury Gage to to see the machine differences. They are usually always have .0003 - .0005 difference.

Glad we are not the only ones that see this.
I guess this is the downside to having the RDS/XXT TL3.
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[Ow...]

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I'll retract my statement regarding the 20 year ago repeatability on articulating Renishaw head CMM's.
Of course different sizes of parts/probes and the number of rotations made a difference but, generally, on the standard size most commonly used the they would repeat to around 0.0002 tenths of an inch on diameter sizes. Location is a different story but, also not mentioned is that they both had touch-trigger only point capability, no scanning.

Now if I got 0.013mm [0.0005 inch] difference between two Vast Gold cmm's, I'd be calling the CMM doctor. 😭
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[Ri...]

Posted
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The number one reason I have found for correlation between CMM's, is Styli.
Users simply do not clean the styli.

Wiping off the styli with isopropyl alcohol lint free wipes will help.
Visually inspecting by 1X is, well, not going to help. Use at least a 10X eye loupe or microscope.
Build up from scanning leaves bands of material on the styli that is typically not seen by the unaided eye.

You can clean scanning build up off of styli (Ø2mm or larger) with an electric eraser. I use Mylar erasers with a low speed electric eraser, a little bit of time and the build up is removed. I have yet to damage a stylus with this method.
I've extended the life of styli for 2 or more years.
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