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Thread: Can't Machine a Simple Circle with a Probotix Fireball

  1. #25
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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Yeah, Gerry, that's a photo I posted to show someone the connector layout on the rear of the enclosure. Not my box, and definitely messed up (by shipping and handling, no less). I'm not 100% sure, but I think I've got a vibration problem in the spindle. Everything else has been checked out. My TIR reads less than 0.0005", but when I cut a slot for test purposes, using, say a 1/8" cutter, the width of the slot is around 0.150". Not good. But it IS something to start working on. Everything else was checking out fine.



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    Don’t know if this will help, but when I still had my v90 I had a similar problem. Turned out to be the lead screw of the y axis. Tightened it up and it worked like a charm again.

    Can’t hurt to try.

    Quote Originally Posted by JPX2000 View Post
    For the last two weeks I have been working against degrading operational characteristics of my good old dependable Probotix V90 Fireball. It started with non-circular rings cut out of 1/8" aircraft plywood. It has now gotten so bad that I can't cut concentric circles, let alone hold tolerances to within acceptable levels.

    I'm using Vectric Cut 2D CAM and Planet CNC USB controller. The router is a Ridgid R2401. I checked for backlash, loose rods and guides, and TIR on the router. Everything seems to be fine. I have changed cutting speeds, feed rates, cutters, and even stock hold-down methods.

    I'm using Haas, Hurco, and Bridgeport milling machines at work, so it's not exactly foreign territory. But this problem has me bamboozled.

    Any ideas (besides getting another machine)?




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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Beats me. A randomly loose connector is about all I can think of.
    All I can suggest it that you need a CNC expert - HW I think, to sit there for a day playing with it. Sorry.

    Cheers
    Roger



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Yeah, I went through the whole machine checking for loose rods, drive screws, etc. and really didn't find anything. Replaced the anti-backlash nuts on the X and Y axes. No change.

    Thanks for the suggestion. The V90 served me well, and was the perfect size for what I needed.



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Quote Originally Posted by RCaffin View Post
    Beats me. A randomly loose connector is about all I can think of.
    All I can suggest it that you need a CNC expert - HW I think, to sit there for a day playing with it. Sorry.

    Cheers
    Roger
    Thanks, Roger. I wish I had a whole day to sit down and work this out. All of the connections look and feel good to me. There could be something I missed, though.



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    These things CAN be solved, although it may take some time and what seems to be some pointless exercises.
    Make up a fine XY fiducial (a fine cross), bolt it down. Put fine pointer (pin?) in chuck. Align XY zeroes to cross, then cycle one axis back and forth for an hour, Does the machine retain zero?
    Cycle both X & Y back and forth - return to zero?
    Align X &Y, then move in an XY circle from 0,0 to 5,5 (inches) and check zero.
    Cycle Z up and down for an hour: does either X or Y creep?
    And so on.
    Yes, I do have basic routines for doing these tests too.

    Cheers
    Roger



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Quote Originally Posted by RCaffin View Post
    These things CAN be solved, although it may take some time and what seems to be some pointless exercises.
    Make up a fine XY fiducial (a fine cross), bolt it down. Put fine pointer (pin?) in chuck. Align XY zeroes to cross, then cycle one axis back and forth for an hour, Does the machine retain zero?
    Cycle both X & Y back and forth - return to zero?
    Align X &Y, then move in an XY circle from 0,0 to 5,5 (inches) and check zero.
    Cycle Z up and down for an hour: does either X or Y creep?
    And so on.
    Yes, I do have basic routines for doing these tests too.

    Cheers
    Roger
    This sounds like a pretty good way to check the accuracy to me. However, I'm not real clear on what you mean by 'cycling' the machine. Do you mean jog it, or put a program into MDI and run it from there? Also, making a fiducial and bolting it down - this suggestion eludes me. Make it from what? Align it on an edge or in the center of the cross? Could you explain this a bit more? Sounds interesting.



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Take a bit of stif card and draw a cross on it with a fine point biro. Tape that down to one side of the mill table.
    Put a thin pointy thing in the spindle. If all else fails, try a 1 mm drill bit or a fat darning needle. Make sure it is centred when you spin the spindle.
    Align the pointer to the cross and zero the X & Y DROs.
    Then run a tiny program like this (inches assumed):

    m98 p10 L20
    m30
    %------
    o10
    g0 x5
    g0 x0
    m99

    This will cycle from 0,0 to 5,0 and back 20 times. See if it ends up at the cross.

    Cheers
    Roger



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Quote Originally Posted by RCaffin View Post
    Take a bit of stif card and draw a cross on it with a fine point biro. Tape that down to one side of the mill table.
    Put a thin pointy thing in the spindle. If all else fails, try a 1 mm drill bit or a fat darning needle. Make sure it is centred when you spin the spindle.
    Align the pointer to the cross and zero the X & Y DROs.
    Then run a tiny program like this (inches assumed):

    m98 p10 L20
    m30
    %------
    o10
    g0 x5
    g0 x0
    m99

    This will cycle from 0,0 to 5,0 and back 20 times. See if it ends up at the cross.

    Cheers
    Roger
    Thanks for the tip, Roger. I'm trying to get the unit to accept a sub-program, so I have to go back and look at the capabilities of the software.



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Oops. That code will run on any NIST-compatible machine, but I do not know about other machines.
    So the principle is there, but the implementation may be different.

    Cheers



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Quote Originally Posted by RCaffin View Post
    Oops. That code will run on any NIST-compatible machine, but I do not know about other machines.
    So the principle is there, but the implementation may be different.

    Cheers
    OK, back at it. I ran various programs in different areas of the table. The gantry was actually stalling and then jerking during the simulated cut of a circle. The Y axis definitely has bigger problems than the X. I attached a photo to show a ring that's 1" ID X 2" OD. You can see that the ID is pretty close to the programmed dimension. The 2" OD, however, didn't even start at the programmed position, but at least it was consistent in sucking at being non-concentric through the 10-cycle run.

    Backlash was checked, over tightening was checked, loose motor connectors, etc. I can't find binding anywhere. Oh, and since there was no actual cutting going on (had a dried up plotter pen in the spindle which, ha ha, I didn't realize was out of ink), I certainly can't blame this bad run on a sloppy collet or a flexing spindle mount. The quest continues.

    Can't Machine a Simple Circle with a Probotix Fireball-img_0129-jpg



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    Default Re: Can't Machine a Simple Circle with a Probotix Fireball

    Looks like one of the drive shafts is moving/sliding. If the Y is top/bottom then look at Y. Your backlash test may not be exerting enough pressure to show it. Try using RCaffins RTZ (ReturnToZero) loop to test it in a repeating fashion and at a moderate velocity. Put a pause between direction changes to allow time to see the DTI. The idea is to move quickly and stop suddenly then change direction.



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