Very small features and touch speed

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  • Very small features and touch speed

    Has anyone else seen this? Today I had two narrow openings to measure they are 1.78MM (.070") wide. I started with a 1mm ruby and calibrated. I measured the openings as edge points and initially reported them as big by .15 a side. I used calipers and gage pins and found them to be right on size. I recalibrated my probes and tried it again. Still big. I then recalibrated and set my touch speed at 1% and they measured correctly. I'm thinking that with the tiny prehit and retract distances (.25mm) I had to use to get into the opening, that 2% was not enough settle time for an accurate measurement. Has anyone else seen anything like this?

    Bill

  • #2
    I have seen this many times before. never new how to get around it though.many hole that i measure are small like that .069 Hmmm i will have to try some things next week.
    Global Status 777 PC-DMIS 2014
    Windows 7
    ever stop to think and forget to start again?

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    • #3
      Same here. Nice catch. I will remember to try that.

      Paul
      sigpicSummer Time. Gotta Love it!

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      • #4
        Dang, I run my touch at 1% all the time. But then, I have that old, heavy machine that takes awhile to stop, too.
        sigpic
        Originally posted by AndersI
        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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        • #5
          I used to use 2%. Had some similar issues. Changed to 1%. I hate to admit this, but I think on Matt's advice.
          Thank you O' Wise One.
          When in doubt, post code. A second set of eyes might see something you missed.
          sigpic

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          • #6
            I'm going to try that, to see if it helps me.
            sigpic


            Was
            Pc-dmis 3.5 MR1 B & S 2009 MR1

            Now
            2010 MR3

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            • #7
              Hi Bill,

              I am measuring a slot right now that is .034" wide. I am using a .5mm probe and I use 8 wrist angles. I did set my touch speed to 1.0 and also slowed my movespeed to 25. I do this at least once a week and it works fine. You are on the right track. My prehit & retract is set at .006". Hope this helps.
              PCDmis 3.5mr2 CAD++

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              • #8
                Originally posted by Bill McCafferty
                I'm thinking that with the tiny prehit and retract distances (.25mm) I had to use to get into the opening, that 2% was not enough settle time for an accurate measurement.
                Bill
                I've seen that before too. The CMM needs to be travling the same speed when it touches the part as when it was calibrated. If the distance is too short it can't get up to a higher speed like 2%.
                PC-DMIS 2016.0 SP8

                Jeff

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                • #9
                  but if touch at a speed of 1 should you also calibrate at a speed of 1 right??
                  Global Status 777 PC-DMIS 2014
                  Windows 7
                  ever stop to think and forget to start again?

                  Comment


                  • #10
                    Originally posted by Marty Schwab
                    but if touch at a speed of 1 should you also calibrate at a speed of 1 right??
                    Absolutely. Never measure at a different speed than you calibrate with, this is especially true for TP200s.
                    PC-DMIS 2016.0 SP8

                    Jeff

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                    • #11
                      I have 2 machines one global and one mistral.I use to run both machines at 2 percent and ran into problems.Slowed both machines down to 1 percent and everything runs fine.B & S will tell you up to 3 percent.Try it and see what happens to your numbers.Also if you are using fly mode turn it off for features under .200 inch.

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                      • #12
                        Always run and calibrate at the same speed. That is why I always use 1%. You'd need to remember all the "oddball" speeds you use, or have special probe files for different speeds. Not efficient. It doesn't affect your program running times that much unless you use huge prehit/retract distances.
                        When in doubt, post code. A second set of eyes might see something you missed.
                        sigpic

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                        • #13
                          This sound like good advice. Now could some one tell me how to change the it? Thanks
                          B. Jacobs
                          B&S Global 12.15.10
                          2014.1

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                          • #14
                            the it? Change the speeds? Its in the parameters,Motion. And when you calibrate your probe there is a setting there also.
                            sigpicSummer Time. Gotta Love it!

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                            • #15
                              I set everything to a 1% touchspeed and calibrate the same
                              we do a lot of small size dimensions-features and this definitely improved repeatability and accuracy
                              was probably Matts advice many moons ago

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