Servo tuning or mechanical? - Page 2
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  1. #21
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    Have you checked backlash in the x and Y axis? I've seen the same sort of thing where the turcite was loose on a gib. In that case, the x moves looked ok and the Y moves looked ok but with the gib essentially loose, we got a bad finish on interpolated moves- how do the quadrant crossover points look when you interpolate a circle?? Might show up as a single bump or step when the axis changes driections.

  2. #22
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    What's the machine's backlash comp values? If they're large, record them, set them to zero, run a test part. Then take a tenths indicator, and redo backlash comp to zero on both axis by the indicator reading. See if the values match, or are different than what was in the machine. Run the test part again, are there differences?

    If significant backlash comps are in place, it might be you have excess wear in a thrust bearing pack, the ballscrew nut, or too much play in the gibs.

    That does look like a nice machine, I think it would be worth continuing to track down what might be wrong. Did the person who did the ballbar test have anything to say on his interpretation of machine performance and wear?

  3. #23
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    The y axis has a straight about 1.5 long it looks good. The x has one about .25, looks ok but might be too small an area to get a good feel.
    Ran out of time to look for the backlash comps might have to wait until Monday. The service tech that did the ball bar thinks it is something on the mechanical side but not sure where/what it would be.

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    Got to do a quick check today. pulled back the x axis way cover. Way lube looks flowing. Put an indicator on the end of the ball screw got maybe .0001-.0002 of backlash.
    Management is playing with the idea of getting rid of the machine entirely. It definitely was a good machine. Hate for it to leave the shop for something dumb. But cant find what that is. I don't believe the cost annalists of getting rid of it works out in our favor. But without knowing the problem makes it hard to analyze.

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    I get about 20 minutes in the morning each day to test out things on this machine. Made some observations today. while in warmup it was making a low freq rumbling.
    i modified the warmup program to try and pin point what is doing it. so far it will make this noise while the x and y are in motion. If only the x or only the y then i can not really tell. Get both moving and it rumbles. Any body have similar situation?

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    Have you made the same part on multiple spots of axis travel to rule out any worn out or damaged sections?

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    We have not tried that yet. i have the feeling that's not it.
    After talking to management they said don't bother we are selling it, unless i figure something out real fast.
    Told our tech about my observations today he will be over, offer his advice and we will see what happens.
    I am still all ears.

  8. #28
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    Quote Originally Posted by shanej45 View Post
    We have not tried that yet. i have the feeling that's not it.
    After talking to management they said don't bother we are selling it, unless i figure something out real fast.
    Told our tech about my observations today he will be over, offer his advice and we will see what happens.
    I am still all ears.
    If you can spend any more time on it just cut out a circle.

    If you see it cut fine at 0, 90, 180, and 270 degrees and cuts poorly in between then you know you have axis interpolation issues which I would attribute to servo tuning, or have something loose on one axis that is permitted the motor to turn a bit without any mechanical dampening. Look for any mechanism that could produce backlash in the drivetrain leading to the ballscrews.

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