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CMM Won't Position

BL Metrology
When I set the head to any angle other than A0B0, the CMM will not return to what I set as the X,Y,Z origin during alignment.

For Example:
At an angle of A7.5B-90, if I touch a point on the granite surface, set an alignment as X,Y,Z origin, and then program it to go back to 0,0,0, it will actually go to 0.0145, 0.0094, -0.4356. All of the programming is done in DCC Mode. This problem also occurs when I go through a full alignment on any part.

We do not have this problem when at A0B0, if I do the same thing at A0B0 it will return to 0,0,0 within tenths of a micron. The deviation with the angle is seen with all angles we have tried so far and the deviation does seem to increase with the A angle. All angles used are successfully calibrated prior to use.

The machine was calibrated on 3/17/09 and the technician spent an extra two days trying to troubleshoot the unit (Hexagon). We have also had our local reps in and they have not been able to troubleshoot the problem. The machine seems to be mechanically fine and it seems to be an issue with PC-DMIS.

Has anyone else experienced this and know of a workaround? We are waiting for Hexagon/Wilcox to resolve this, but I am assuming it could take some time.
  • When I set the head to any angle other than A0B0, the CMM will not return to what I set as the X,Y,Z origin during alignment.

    For Example:
    At an angle of A7.5B-90, if I touch a point on the granite surface, set an alignment as X,Y,Z origin, and then program it to go back to 0,0,0, it will actually go to 0.0145, 0.0094, -0.4356. All of the programming is done in DCC Mode. This problem also occurs when I go through a full alignment on any part.

    We do not have this problem when at A0B0, if I do the same thing at A0B0 it will return to 0,0,0 within tenths of a micron. The deviation with the angle is seen with all angles we have tried so far and the deviation does seem to increase with the A angle. All angles used are successfully calibrated prior to use.

    The machine was calibrated on 3/17/09 and the technician spent an extra two days trying to troubleshoot the unit (Hexagon). We have also had our local reps in and they have not been able to troubleshoot the problem. The machine seems to be mechanically fine and it seems to be an issue with PC-DMIS.

    Has anyone else experienced this and know of a workaround? We are waiting for Hexagon/Wilcox to resolve this, but I am assuming it could take some time.
    Well, not to be mean or anything, BUT, you did check this stuff, right?

    1) Is there a command line in the program to check the angle? Manually changing the angle with the key-pad does NOT put the command into the program

    2) If the command is in the program, is your CURSOR below that command? If not, it will still be using the previous probe angle called out in the program.

    Yeah, these are simple things, and probably NOT the issue, BUT..........
  • When I set the head to any angle other than A0B0, the CMM will not return to what I set as the X,Y,Z origin during alignment.

    For Example:
    At an angle of A7.5B-90, if I touch a point on the granite surface, set an alignment as X,Y,Z origin, and then program it to go back to 0,0,0, it will actually go to 0.0145, 0.0094, -0.4356. All of the programming is done in DCC Mode. This problem also occurs when I go through a full alignment on any part.

    We do not have this problem when at A0B0, if I do the same thing at A0B0 it will return to 0,0,0 within tenths of a micron. The deviation with the angle is seen with all angles we have tried so far and the deviation does seem to increase with the A angle. All angles used are successfully calibrated prior to use.

    The machine was calibrated on 3/17/09 and the technician spent an extra two days trying to troubleshoot the unit (Hexagon). We have also had our local reps in and they have not been able to troubleshoot the problem. The machine seems to be mechanically fine and it seems to be an issue with PC-DMIS.

    Has anyone else experienced this and know of a workaround? We are waiting for Hexagon/Wilcox to resolve this, but I am assuming it could take some time.


    How could it ever possibly return to 0,0,0? That is the surface of the table. PC-DMIS goes from the center of the probe. The probe would have to be imbedded into the granite.
  • When I set the head to any angle other than A0B0, the CMM will not return to what I set as the X,Y,Z origin during alignment.

    For Example:
    At an angle of A7.5B-90, if I touch a point on the granite surface, set an alignment as X,Y,Z origin, and then program it to go back to 0,0,0, it will actually go to 0.0145, 0.0094, -0.4356. All of the programming is done in DCC Mode. This problem also occurs when I go through a full alignment on any part.

    We do not have this problem when at A0B0, if I do the same thing at A0B0 it will return to 0,0,0 within tenths of a micron. The deviation with the angle is seen with all angles we have tried so far and the deviation does seem to increase with the A angle. All angles used are successfully calibrated prior to use.

    The machine was calibrated on 3/17/09 and the technician spent an extra two days trying to troubleshoot the unit (Hexagon). We have also had our local reps in and they have not been able to troubleshoot the problem. The machine seems to be mechanically fine and it seems to be an issue with PC-DMIS.

    Has anyone else experienced this and know of a workaround? We are waiting for Hexagon/Wilcox to resolve this, but I am assuming it could take some time.

    How are you doing this? Movepoint? Measuring a point at 0,0,0?

    I'd measure a point; set the point (align) to 0,0,0; back off some distance with a movepoint; measure a dcc point at 0,0,0 and then dimension the x,y,z location of that measured point.

    Where are your 0.0145, 0.0094, -0.4356 values coming from? A dimension? The probe readout?

    If it is the probe readout, I often have noticed that it doesn't update until I execute the program and get past the alignment. Sometimes if my cursor is just after the alignment it will be 'stuck' in the previous alignment until I move the cursor several lines of code past the alignment... Even when it seems 'stuck' it is just the probe readout. Movepoints, measured features, etc. are done in the correct alignment (it is only the probe readout experiencing the problem).
  • Do you have the right probe angle in your probe set-up.
  • Thanks to everyone for the prompt replies, I will try to answer each one here starting with the newest first. Please keep the thoughts flowing, even if it is basic, your help is appreciated. I will also try to copy up the code this afternoon.


    JVau425033 Do you have the right probe angle in your probe set-up.
    Yes, probe angle is correct in set-up.


    cmmguy Inch or Metric? machine Model?
    Metric, Browne & Sharp Global 5.7.5,
    running PC-DMIS 4.2 MR1


    Goodluck How are you doing this? Movepoint? Measuring a point at 0,0,0?
    Your recommended method is how we have been programming the unit.


    Otto Square How could it ever possibly return to 0,0,0? That is the surface of the table. PC-DMIS goes from the center of the probe. The probe would have to be imbedded into the granite.

    Using the method described by Goodluck, measure a point on a surface. Do an alignment making that point my X,Y,Z origin, doing a move point, measure a point with theoreticals of (0,0,0) and a vector of (0,0,1), the measure the position of that point.


    Ironhoe is A7.5B-90 a calibrated probe ang?

    Yes, it is calibrated with the results file indicating a std. dev as a couple tenths of a micron.


    Matthew D. Hoedeman

    Not mean at all, good to start with the basics. Yes, there is a command line for the angle. Yes, cursor is below the command (that has burned me in the past and is always the first thing to check).
  • One more chunk of hardware to suspect:

    Tesa or Renishaw head?

    We had a TesaStar-M fail: would not repeat position when rotating B axis. The error was so small we thought it was our parts until we did some digging. Just one bad tiny gear tooth.
  • Metric? Are you sure your standard deviation is not in inches? Usually they are in the .0000-.0003" range. If that were mm's, then you would have one heck of a machine.
    .001 millimeter(one micron) is .00004 inch.

    Anyhow, are you moving in the Z direction, where your error is?
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