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  1. #1
    Join Date
    Mar 2008
    Posts
    60

    Travel Accuracy

    We have a 1996 4020 with factory pallet changer. We have a simple job of drilling holes down a part the length of the X axis travel. The actual measured distance started out .017 less than the distance programed at 37 inches. We took machined parts to our Romer Arm for inspection. We tried several things to verify the problem. We had vises at each end of the table that we could measure with our 40 " Versa-Gage. Edge find the outside and measure it. Machine travels are short to Versa-Gage measurement. Took the part and put it in the other similar Fadal and using a pin jogged from hole to hole. Machine travels match the measured part. So far we have swapped drive cards, new resolver and swapped Y and X axis motors. We have no backlash as the screw was replaced in the last couple of years. Checked machine level. Gibs and straps are properly adjusted. The values in the ball screw calibration are zero. We now see .010 on a test part. And yes, it appears progressive down the travels. We have talked to our Fadal service techs that have been in here for years and they have no ideas.
    Simply stated: It appears the actual machine travel over the length of the X travels are less than the value programmed or stated on the machine display.
    Any other ideas?

  2. #2
    Join Date
    Dec 2013
    Posts
    5717

    Re: Travel Accuracy

    Sounds like you have checked everything. The only possibilities that I can think of is that the encoder calibration is off or the ball screw has a lead error. You might try to reset the encoder calibration to 1 less and see what happens. About 0.0005''/inch is quite a bit of error.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
    Join Date
    Mar 2008
    Posts
    60

    Re: Travel Accuracy

    By encoder, do you mean resolver? Where would that encoder calibration be? Also, this machine does not have scales, as we saw an "SV" command and we wonder if that is what you meant. There is a list of numbers there that can be changed by .0001. We discounted a ball screw being that far off.

  4. #4
    Join Date
    Dec 2013
    Posts
    5717

    Re: Travel Accuracy

    Yes, resolver. Somewhere in the system the resolver input is converter to digital pulses I think. Doesn't really matter, somewhere in the parameters there is an axis calibration for number of pulses (or something like that) per unit (inch). I'm not that familiar with the Fadal systems, but all systems have that adjustment. You might have to check with your Fadal tech for exactly how to do it.

    I would be surprised if the ball screw was that far off, but anything is possible.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
    Join Date
    Mar 2008
    Posts
    60

    Re: Travel Accuracy

    I am looking for the Fadal tech right now.

  6. #6

    Re: Travel Accuracy

    BK1955,

    Regardless of what feedback device you have, encoder or resolver, you can be off over the travel of the axis you are looking at due to the ballscrew compensation table being from other axis or all zero values. You would need a laser calibration done to get the axis dialed in over the full travel of the machine. Generally those who provide this service will charge $500 to $1000 for the service.

    I would also try exchanging controller cards, X to Y and see if the problem follows. If so, replace the controller card, if not, the problem is with the axis and I would start looking for a mechanical problem. Put the controller cards back in their original slots when this test is done.

    Give me details on how your tests turn out and I will help as I can.

    FadalCNC.com Tech Support.

  7. #7
    Join Date
    Jul 2005
    Posts
    100

    Re: Travel Accuracy

    I would look at the survey for that axis, you can comp for errors starting from the X- limit. We had a similar condition no backlash but over .010 accumulated error at full travel.
    The screw is worn but still has preload. I drilled and bored a bar every 1.000, measured on the CMM and then entered those errors in the SV screen.

    It is now within .0005 every inch and at full travel with that old screw.

  8. #8
    Join Date
    Jan 2015
    Posts
    417

    Re: Travel Accuracy

    .017 to .010 error Did you check the alignment of the screw? Easiest way is to move to each end of the screw Hit the emergency stop and feel the screw, move to the other end hit E-stop and feel if it feels the same as the other end . Should turn freely.

  9. #9
    Join Date
    Apr 2005
    Posts
    1194

    Re: Travel Accuracy

    Did you know the coupler can get worn? The old style had a keyway which was great but the actual keyway can wear a groove in the coupler. With a pallet on there for 23 years I would be looking at that.
    We have had good luck with our Fadals milling mostly soft steel and aluminum up to 5 axis. We are always looking for spare parts If you have a broken down Fadal give a shout.

  10. #10
    Join Date
    Jan 2015
    Posts
    417

    Re: Travel Accuracy

    Thats possible Carbide but it would give you alot of backlash and bk1955 says he has none, but yea i dont like those brass coupling spyders they are good at first then get sloppy. Have you done a positioning reputability test? With an indicator to the vice, or mag base anything solid and stationary. Set your indicator to Zero and move off and on, say 10 inches... pause and then repeat. See if it repeats. I would write a program to do this. If you do G0 it might heat up the screw and cause growth. So

    O1234*Test
    L100
    X-10.F100.G1
    X0
    G4P3000
    M17
    M30
    G90G17G80G0
    L101.1
    M2

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