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CMM consistently reports .0001" higher than micrometer

xbigfatgoat
Here is the cmm set up:

I'm using a Global S 7.10.7 Green

Probe Setup:
HH-AS8-T2.5
HP-S-X1H_T
HP-S-X1H_26_SH
HP-S-X1h_M3_5WAY
Connection #1 tip3x10mm
Connection #5 convert to m2thrd tip3x50mm

The room is temperature controlled to 68 degrees. Everything being measured has had time to temperature adjust to the room.
I have temperature compensation enabled.

I'm measuring a diameter that is 1.7720" +/- .0002"

I calibrate the angles with 25 hits each angle answering "no" to has the sphere moved. The sphere was set based off a 5x50 master.
I've tried calibrating the sphere with and without temperature compensation enabled.
I've noticed when I don't use temperature compensation my stddev can range from .0002 to .0003, I even noticed .001 one time. With temperature compensation the stddev is always less than a tenth.

I'm scanning outer diameter's. I scan one half T1A0B90 90 to -90 degrees with no filters and the other half -90 to 90 degrees T1A0T-90 with no filters.
I then construct a best fit circle out of the two halves from every single scan point using no filter.
I create a constructed filter out of the constructed circle and use Gaussian filter type with UPR of 177 and remove outliers set to 2. For the UPR I found an equation online that gives you a UPR based on the diameter: (D(mm)*PI)/.8
I construct a final best fit circle with no filters from the constructed filter and report this diameter.

Initially, I was consistently getting one to one results between the cmm measurements and a micrometer.

Recently however, I'm finding that the cmm is consistently reporting .0001" higher than what I measure using two different micrometers.

I know .0001" is extremely small and I'm trusting that the micrometers are giving me the more accurate results.

Am I doing something wrong?
Is it reasonable to assume that I can get the cmm and a micrometer to match to one 10 thousandths of an inch?
There has been a couple crashes (not huge crashes), could this have thrown off the probe by .0001"?

Thanks for any help in advance.
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Parents
  • Every time I crash my Leitz, I conduct a new Lower Matrix calibration.
    Not only does this help correct for changes to the sensor, but it also is a means of determining if the sensor sustained enough damage to need replacement.
    chasing a tenth is a challenge, and if you allude that you've nailed correlation in the past, and changed nothing other than the fact that the machine crashed, it's probably best to start with assessing and calibrating the probe system entirely after the crash.
  • in reply to louisd
    I took off the scanning probe and reseated it. It was then reporting 3 tenths off. So I re-did the lower matrix, recalibrated everything and boom its looking like the measurements are lining up with the micrometer again. I don't want to speak to soon though, we'll see what it decides to do next week. Maybe the last time it crashed it somehow caused the probe to slightly unseat?? Is that even possible idk but thanks for your help.
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  • in reply to louisd
    I took off the scanning probe and reseated it. It was then reporting 3 tenths off. So I re-did the lower matrix, recalibrated everything and boom its looking like the measurements are lining up with the micrometer again. I don't want to speak to soon though, we'll see what it decides to do next week. Maybe the last time it crashed it somehow caused the probe to slightly unseat?? Is that even possible idk but thanks for your help.
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