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Measuring the same part on 2 CMMs, Different Results

acgarcia
We have 2 4.5.4 SFs. I ran a part 5 times on CMM A and then ran the exact same part on CMM B. Got different and same results.

CMM A runs 2016 and CMM B runs 2017. Both use the same star probe build. Both checked the same features with the same parameter... number hits, prehit retract, etc..

One CMM seems to read a little larger than the other. CMM B measures one feature 0.002" smaller than CMM A and CMM A measure a feature 0.0006" smaller than CMM B. One feature was exact on both CMMS, exact nominal and deviation, 0.000.

Essentially I copied the program from CMM A to CMM B and just adjusted some movespeeds.

Is this something normal? Operators at night sometimes will fail parts on one cmm and then take them to the other cmm and it pass so they pass the part through. I know they CMM will not match perfectly but they should be closer than 0.002". I'm trying to build confidence in the CMMs for the operators as its only be a few years of having CMMS.

Any advice or ideas on this?
Parents
  • : Whenever I write a new program, I never go into "file/new". Instead I have a blank program with some pre-set parameters. I open it up & save it as my new part number and then begin programming. Once of the settings I have built in is:

    I always have "Display Absolute Speeds" checked (you get this box by hitting F5). The reason for this is because if this is unchecked, pc dmis will read move speeds and touch speeds as a percentage, not as an absolute value. With this checked, you can control exactly how fast you qualify as well as move at, regardless of how fast one of your CMM controllers can be vs the other one. Make sense?
Reply
  • : Whenever I write a new program, I never go into "file/new". Instead I have a blank program with some pre-set parameters. I open it up & save it as my new part number and then begin programming. Once of the settings I have built in is:

    I always have "Display Absolute Speeds" checked (you get this box by hitting F5). The reason for this is because if this is unchecked, pc dmis will read move speeds and touch speeds as a percentage, not as an absolute value. With this checked, you can control exactly how fast you qualify as well as move at, regardless of how fast one of your CMM controllers can be vs the other one. Make sense?
Children
  • in reply to DAN_M
    Same here. Blank template program. Even though that doesn't work for everything.
  • in reply to DAN_M
    Blank template program, good idea. I'll look at the settings in the older CMM to see what it was set to and compare it to the newer CMM.

    When the tech was here setting up the new CMM, he said the machine needs to run at full speed for the best accuracy. is this contradicting that?
  • in reply to DAN_M
    If they aren't measuring at the same touch speed, this could definitely help play into the dimensional variation between the two machines. So good definitely look into that my friend.

    Running at full speed? I've never been concerned with how fast the CMM moves from feature to feature.....how fast it touches is what you need to control. You want your touch speed to be the same on both machines for when you qualify your tips as well as when you're measuring your part. Checking off this box ensures this is taking place. I have this box checked off, set my touch speed to 3mm/sec in every program, and I always qualify tips at 3mm/sec. Everything is the same speed on each of my machines...just some have a faster move speed than others.
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