Manual VS DCC results different

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  • Manual VS DCC results different

    Our manual hits aren't giving the correct result, but in auto mode it works perfectly. I was measuring a diameter, and manually the machine gives a result about 0.03" different to when I measure the same feature in dcc mode. Anyone know what could be causing this??

    Thanks!

  • #2
    Speed, vector, location, operator, force

    All these have an effect on how manual hits are registered. DCC mode is a constant in all those categories.

    Comment


    • A-machine-insp
      A-machine-insp commented
      Editing a comment
      pcdmisstudent Let me stop you right there... His head is big enough. He doesn't need any help.

    • bfire85
      bfire85 commented
      Editing a comment
      A-machine-insp It's HUGE!!!! lol

    • KIRBSTER269
      KIRBSTER269 commented
      Editing a comment
      could have just said human error That's what your parents said.

  • #3
    In addition, if you construct a BFRE circle from manual hits, you should find acircle closer to the DCC one...
    Look at the image at #5.
    https://www.pcdmisforum.com/forum/pc...f-vs-bfre-line

    Comment


    • #4
      Originally posted by JEFMAN View Post
      In addition, if you construct a BFRE circle from manual hits, you should find acircle closer to the DCC one...
      Look at the image at #5.
      https://www.pcdmisforum.com/forum/pc...f-vs-bfre-line
      ^ this ^ is very important to remember.

      As a side note, I've noticed that if you are using Autopoints, the default is BF, since PC-DMIS assumes you picked the points from CAD and have perfect vectors. If you construct a feature from measured points, the default is BFRE since it assumes you measured them manually and need re-compensation.
      PC-DMIS 2016.0 SP8

      Jeff

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      • #5
        I don't take any measurements in manual mode. I will occasionally do a manual alignment and will then switch into DCC to actually measure the part. I use a read point at the beginning of most of my programs. If the part is super intense in size and features, i will do a manual alignment first.

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        • #6
          Sometimes I'll do a manual measurement and then I'll replace the manual with DCC and let the CMM run my manual hits in DCC.
          2024 can't get here soon enough!!!

          Comment


          • #7
            Most common source of this issue is that you do not have the machine in measure or slow mode. If you're using a machine with the newer jogbox the turtle button must be lit up. Manual measurements not in "slow" mode will not be as accurate.
            Systems Integrator
            Hexagon Manufacturing Intelligence

            Comment


            • Douglas
              Douglas commented
              Editing a comment
              .030 still seems like a lot but I did not know this about the new controller, on our older Brown & Sharpe with a sheffield controller you can pretty much hammer the hits in manual measured features and be within a couple or few thousandths of an inch. Could one old school madman on a new jogbox really be worth .030" on the diameter of a measured circle? The diameter came out larger on an inside diameter so the error was in the wrong direction for vector/recomp to be the cause, for that I would expect those couple or few thousandths anyway not .030


              Also curious if you know the exact effect of the turtle, does it cut speed to a certain mm/sec or to a certain percentage of full speed? Might be useful to know as an understanding of touch speed during a manual hit

            • Peter Fuller
              Peter Fuller commented
              Editing a comment
              It's because the controller isn't expecting hits in fast jog mode. Manual hits are only accurate in slow jog mode.

          • #8
            Originally posted by Peter Fuller View Post
            Most common source of this issue is that you do not have the machine in measure or slow mode. If you're using a machine with the newer jogbox the turtle button must be lit up. Manual measurements not in "slow" mode will not be as accurate.
            ^^^^^ This is important in manual measurements. ^^^^^

            Comment


            • ThePudds
              ThePudds commented
              Editing a comment
              Douglas I don't know the actual speed. But 20 - 30% does sound about right. I'm not sure where you could find this. I'll keep looking for a more exact answer.

            • JEFMAN
              JEFMAN commented
              Editing a comment
              On common controller, under terminal, I would say its "show slow_jog", not sure of it, I'm not at the cmm.
              I believe it's a speed, not a percentage.

            • Douglas
              Douglas commented
              Editing a comment
              JEFMAN I bet you are right, probably a setting for it on the touch screen... all I ever go into that stuff for is to make the beep louder and quieter then play dumb when people ask if something is different

          • #9
            many many moons ago we did a capability study / Gage R&R/ with 6 operators measuring the qual sphear 10 times each comparing the repeatability of each individual operators results, along with
            the overall range of the group . the results were crazy huge numbers, mostly due to inexperience of some along with cosine error of the approach and technique.

            If you have time i highly recommend demonstrating this to the newer operators.

            Comment


            • Douglas
              Douglas commented
              Editing a comment
              taking a high number of hits evenly spaced on the sphere would give bad numbers, taking 5 hits, 4 on the equator and 1 on top would give much better results in this case, just due to how much easier it is to control the approach

          • #10
            From the knowledge base.

            Manual diameters are not measuring correctly - When measuring a ring gage it is deviating by 0.010 - 0.15", yet measuring this ring gage in DCC is within expected tolerance.




            26-May-2018•Knowledge

            Details
            Note the following general statements:
            1. Manual measurements are always less accurate than DCC measurements.
            2. Some machines must be in a certain mode to take accurate manual hits. In particular with a Leitz protocol machine it is necessary to have the Jogbox Slow button on when taking manual hits. This changes the state of the controller so that it is "expecting" hits.
            3. Manual measurement requires some practice and more points than DCC measurements. Practicing on the qualification sphere will let you know how you are doing and give you 3D practice. Measure the sphere, set your origin on it and measure it 5 times in a row. Evaluate your results. When you get an acceptable range, then qualify the tips. Then, measure your parts. In DCC you always qualify the tips at the same parameters used in the measurements. Manually, practice will help you maintain your touch speed technique, helping your accuracy.

            (Topic ID 16101-347)


            Systems Integrator
            Hexagon Manufacturing Intelligence

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