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Thread: CNC sometimes has a mind of itsí own.

  1. #21
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    If different points of the machine are grounded to different rods, then you have a problem. If all the points on the machine and the electrical box are grounded to the same rod, even if there is another rod located elsewhere for the building's electrical system, then you have a good zero point.
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  2. #22
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    Jan 2004
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    Marietta GA
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    Quote Originally Posted by coryatjohn View Post
    If different points of the machine are grounded to different rods, then you have a problem. If all the points on the machine and the electrical box are grounded to the same rod, even if there is another rod located elsewhere for the building's electrical system, then you have a good zero point.
    I just completed building a house last year.
    I failed the final inspection first time around because of improper grounding.
    I needed to bond both the gas and waterlines back to the main, "married to the main" the inspector called it, as well as add a second ground rod at least 60" away from the first, connected to the first.
    So Basically my switch panel, water and gas lines are all grounded to the meter box which is then grounded to the two ground rods.

  3. #23
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    Jun 2018
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    Quote Originally Posted by coryatjohn View Post
    If different points of the machine are grounded to different rods, then you have a problem. If all the points on the machine and the electrical box are grounded to the same rod, even if there is another rod located elsewhere for the building's electrical system, then you have a good zero point.
    If the PC is grounded to 1 rod, and the CNC machine is grounded to a different rod, current can run through the commutation cable between the PC and CNC, and neither machine may be designed to handle current on the ground wire of the comms cable.

    Just being plugged into different outlets can sometimes also cause an issue like that. That's one of the reasons a lot of audio equipment uses fiber optics for connections between distant components. But I think it should be easy enough to test with a volt meter... unless it changes with the weather...

  4. #24
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    Oct 2012
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    Leesburg, VA
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    Check your bearings on each axis. I had an issue with my 2012 Desktop (circles in particular) and found that one of the y-axis bearings was going bad. This drove me crazy for a couple of weeks since it appeared to be random, but in retrospect, was during movements that pushed against that bearing.

    The fact that you're doing a conventional cut on the final pass (thereby increasing the load on the bit) makes me think you might be running into a moment when the bad bearing pushes back just enough against the x-axis to cause it to stall -- think
    "Oh goodness", I forgot to attach the clip to the router bit when zeroing my z-axis, and as soon as the bit hits the plate, it tries to drive through the plate, thereby mucking up the axis zero values
    only the x-axis is able to recover after the stall without you really noticing it (the x-axis motor may have complained a bit momentarily, but the spindle/router racket would likely have covered up any noise).

  5. #25
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    Has the same problem at the same point when doing circles. Brady told me to slow it down a little and I haven't had the problem again

  6. #26
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    Apr 2011
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    Quote Originally Posted by bob_reda View Post
    Has the same problem at the same point when doing circles. Brady told me to slow it down a little and I haven't had the problem again
    I'm the guy that posted the original post. In my case when it happened it was ALWAYS the last inch or so of the final pass. It was ALWAYS on the last CG command. I too climb cut, then finish conventional. Didn't matter if I made the last cut in one pass or several - it was ALWAYS the last iteration around the perimeter. I too was cutting a ton of circles though did have it happen once or twice on rectangles. After those 'circle' jobs of 200 or so circles, cut 30/40 sheets of other stuff with no issue. Last job was a narrow rectangle with a round nose. Problem popped up again. I did several things and got around the problem: 1) Started using spiral ramp, 2) Used a new 1/4" bit, 3) made multiple passes on last conventional cut, 4) watched it like a hawk with finger near the space bar to stop the machine if necessary. May have been lucky but in the first runs of circles got the jobs done. This last time cut 60 narrow 5.5" x 26" rectangles with round nose with no issue. Many suggested a static problem. It is not. A static problem would be random. This was predictable down to the exact spot, exact command where it would happen if it did. Someone suggested a bit can sometimes grab the wood and get pulled in. That MAY be what was happening. I'm claiming it. Or maybe I'm just lucky At any rate, this is an update on my situation that I should have posted a while back.

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