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  1. #1
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    Join Date
    Jul 2004
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    102

    Mill Turn warped table

    I have a Mill Turn I bought in 2016. It's never been "true" and always skipped steps so it's just been collecting dust. I finally decided to see what I could do with it. I've bought hybrid servos and Acorn controls to upgrade it but decided to figure ought what's going on with the table first.
    "
    If I put a dial indicator in the spindle and move the table around I get variations in height up to .032". Attached is a picture of the measurements around the table. I removed the table, cleaned the ways and adjusted the gibbs. The table "sags in the middle from left to right. When moving the table toward me in the Y direction, the back left corner actually raises up off the way. I initially thought I just needed to have the table ground flat. But, after taking these readings, it appears the whole table is warped. When I bought the machine, I communicated with JT. I knew it wasn't dead on but hadn't done the measurements to know just how bad it was. JT seemed to imply he thought it would be OK.

    I removed the table to indicate the ways, but since they don't move in and out, I could only get a reading across the middle with what I had to work with. It was about .003 different but I don't know if they are actually parallel.

    Has anyone dealt with this problem or have any ideas? What should I expect from a machine of this price point?

    Thanks for any help.

  2. #2
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    Jul 2004
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    102
    Quote Originally Posted by mccafferty View Post
    I have a Mill Turn I bought in 2016. It's never been "true" and always skipped steps so it's just been collecting dust. I finally decided to see what I could do with it. I've bought hybrid servos and Acorn controls to upgrade it but decided to figure ought what's going on with the table first.
    "
    If I put a dial indicator in the spindle and move the table around I get variations in height up to .032". Attached is a picture of the measurements around the table. I removed the table, cleaned the ways and adjusted the gibbs. The table "sags in the middle from left to right. When moving the table toward me in the Y direction, the back left corner actually raises up off the way. I initially thought I just needed to have the table ground flat. But, after taking these readings, it appears the whole table is warped. When I bought the machine, I communicated with JT. I knew it wasn't dead on but hadn't done the measurements to know just how bad it was. JT seemed to imply he thought it would be OK.

    I removed the table to indicate the ways, but since they don't move in and out, I could only get a reading across the middle with what I had to work with. It was about .003 different but I don't know if they are actually parallel.

    Has anyone dealt with this problem or have any ideas? What should I expect from a machine of this price point?

    Thanks for any help.
    Found most of the issue.
    The ball screw mounting on the back of the table was off so as the table moved forward, the screw was exerting an upward force on the table. I slotted the bracket and got it out of a bind. Now the table stays down flat on the ways. The table does have .015 variation across it but grinding should take care of it.

  3. #3
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    Join Date
    May 2016
    Posts
    15

    Re: Mill Turn warped table

    Glad you found your major problem. I had the same issue but it was showing itself as missing steps. I found it by accident when I was taking it apart. Ran the slide forward to take the screws loose on the stepper mount plate and they were so tight I had a hard time getting them loose. Ran the slide back and they came out easily. If yours set for a long time with the slide in a location to exert that much pressure it may have contributed to the warp. How about removing it and baking it in your oven for a while then letting it air cool? It may relax and release the built up stress and self level itself.

    Your discussion makes me think of the other things I've resolved since I got my machine in 2017. I'll briefly list them and their cures:
    1) Z axis max speed was very slow - idler pulleys on drive belt needed additional clearance to rotate freely and one of the air springs had failed.
    2) Excess end play in X axis - clamp nut on leadscrew (by tailstock) came loose several times (always worst possible times). Increased gap size to allow increased clamping force.
    3) Mill spindle running in reverse direction than commanded - switch 2 wires feeding motor.
    4) 3 connectors for limit switches on back of controller not being recognized by Mach - ground was connected to machine ground, not to 48VDC zero voltage. Gecko never sees the signals. Correct wiring so connectors see Gecko ground.
    5) Overall differences in accuracy - Tighten all encoder mounts, verify and correct DRO calibration as needed (do this first when setting up your machine, please!)
    6) Loud clunking noise in X axis handwheel area - excessive backlash in handwheel gear train. Shim as needed to remove.

    I'm sure there are others I have forgotten. But in the long run, would I do it again, YES! I have worked in places with very expensive equipment and had similar experiences.
    I bought what I could afford and fit in my location. I didn't expect it to be perfect, but it gets closer each time I use it......

  4. #4
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    Feb 2009
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    179

    Re: Mill Turn warped table

    Reverse operation of the spindle is a simple matter of changing a setting in mach 3- go to Config, spindle pulleys and just change the setting in reversed box . Yes, the DRO mounts need to be checked periodically, as they measure your motions, but a loose DRO is not an indication of inaccuracy in the machine. There is an upgrade for the Z axis to increase the speeds, very easy to install and you can get multiple increases in the speeds depending on the year and serial # of your machine.The X axis handwheel operates through helical gears and the mesh needs some periodic adjustment as well.

  5. #5
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    Join Date
    May 2016
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    15

    Re: Mill Turn warped table

    Thanks for the reply.
    I know that I can reverse the spindle rotation in Mach 3. I did that for a period of time until I forgot to include that command once. It was not pretty. If I turn on the machine and set it to either mill or lathe mode the spindles should each turn in a normal cutting direction, in my opinion. It was a simple thing to correct so that I wouldn’t repeat my prior mistake.
    As for the accuracy, there wasn’t a mechanical issue, but an electronic one. No matter how many times I tried to recalibrate Mach 3 for accuracy I repeatedly had issues with the Y axis (mill mode). I decided to use long travel dial indicators to verify the DRO readings. I found differences between what the DRO read and the dial indicator. It was a fairly small amount but compounded itself over a longer distance. I read thru the DRO manual and found out how to set a correction figure. This cured my issue. Since the entire setup relies on the accuracy of the DRO I believe this should be verified during setup. It would of saved me days of my time and reduced initial frustration.
    The X axis handwheel backlash was pretty excessive so flywheel effect of the handle kept accentuating the issue with lots of noise and continuously loosening the handle set screws. Tightening all that up makes the machine nice and quiet in CNC mode.
    I believe discussions like this can help owners better understand their machines and improve their experience. Thanks for participating!

  6. #6
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    Join Date
    Feb 2009
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    179

    Re: Mill Turn warped table

    Interesting about the DRO calibration- we never had any issue with the accuracy on ours- when we did the initial setup, we checked the DRO against a dial indicator first.
    Regarding the spindle rotation, once you set the direction in the REVERSED box, then your M3 and m4 commands will always turn it the right direction.

  7. #7
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    May 2016
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    15

    Re: Mill Turn warped table

    Wish I had confirmed the DRO first. As for the spindle rotation, driver to switch mill rotation permanently was me switching between manual and CNC on a regular basis.

  8. #8
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    Feb 2009
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    179

    Re: Mill Turn warped table

    When in manual, you have a reverse button on your VFD keypad, but yes, if you want the manual function to go the correct direction without having to remember the reverse button, then you can swap any 2 of the 3 phase wires, then when in mach 3 adjust the Reversed box and your spindles will always be correct in either manual or CNC.

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