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  1. #1
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    Mar 2012
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    Question Z axis inconsistency

    I have an Avid CNC machine that I'm having issues with and I can't figure it out on my own.

    We cut 10 different patterns on the machine, over and over. Every once in a while, the machine will cut about a half inch deeper than it is supposed to, destroying the table. I'm not the one operating the machine so it's even harder for me to troubleshoot. From the little I know about stepper motors, I don't know what would cause it to gain steps. Every time I operate the machine, it works correctly.

    Any ideas?

  2. #2
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    Re: Z axis inconsistency

    Quote Originally Posted by jet8300 View Post
    I have an Avid CNC machine that I'm having issues with and I can't figure it out on my own.

    We cut 10 different patterns on the machine, over and over. Every once in a while, the machine will cut about a half inch deeper than it is supposed to, destroying the table. I'm not the one operating the machine so it's even harder for me to troubleshoot. From the little I know about stepper motors, I don't know what would cause it to gain steps. Every time I operate the machine, it works correctly.

    Any ideas?
    Every once in a while during a cut in a series of jobs or every once and a while during the same job?
    If it's between jobs, I could see someone forgetting to set the zero. If working off the same zero as the last job, then accidentally pressing zero at some point during setup could set it below the correct zero.
    I've also resumed after pausing and forgot to set the travel move to the next position to start again and had the cutter drag through the material on the positioning move.

    If the motors were off between a job, I've seen the z axis move down from the weight of it. Only a few times though.
    Otherwise, and it would suck to even check this, take the zaxis apart and see if the ballscrew is shifting somehow.

    Sent from my SM-G996U using Tapatalk

  3. #3
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    Re: Z axis inconsistency

    Every once in a while on a new job, for the whole job the Z axis is lower than it should be.

    This machine is set up to not require the user to zero the tool every time.

    The motors are not being shut off between jobs. I just rebuilt the Z-axis including replacement of the anti-backlash nut. There's no play in the assembly and even with the motors off it does not descend any.

  4. #4
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    Re: Z axis inconsistency

    Mach 3 or 4? I do not have mach 4 so I can't comment on that really.

    In mach 3, sometimes I use some scripts I wrote to do some things. In one script it prompts for input. If I use the entire key instead of pressing the ok button, it will bury itself into the table and move in an arc. I've just to figure this out other than it's mach3 running on windows 10 and I have no way of testing other than repeatability of the problem.
    I would say that it's possible that noise could cause something like that. However, I would expect that to happen more throughout the job. Also, if you got the spindle setup from avid, it's shielded.

    If it's not being zeroed each time and somehow losing position at the end of the last job and you're not homing before the next, maybe something with that. Otherwise, whoever is controlling it may be zeroing even though you don't want that? Maybe something weird with the Ethernet smooth stepper. How long has it been on when this happens? Not that it should matter. Murphy's law though.
    Hopefully more people can chime in on this.


    Sent from my SM-G996U using Tapatalk

  5. #5
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    Re: Z axis inconsistency

    Mach 3. The spindle is indeed from Avid.

    I'm not sure they ever turn the machine off. We run two 10 hour shifts and I don't think they currently power off the machine at the end of second shift.

    I tried making a macro to run the same code as the "reference all" button, but when I put the macro in my gcode the machine does the reference all but stops after that - still trying to figure out that issue.

  6. #6
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    Re: Z axis inconsistency

    Off the top of my head with your macro, it might need to set the offset back to whatever you are using. When ref all happens it is in machine coordinates. You may need to set the work offset back to the recorded one. So, g54 if default.
    I will have to look at some of my macros used. I know I made one for my 4th axis that will reference that axis again between some operations to make sure it goes where it needs to on the next operation. It was overkill after I saw how rigid it was though.

    I know that the screenshot I use has to switch to machine coordinates and back during the auto tool change touch off. It's based off of bigtex screen set and probably has the answer inside of those macros. I know that fusion 360 always sets the work coordinate at the beginning of the file.
    Another way to do it off always cutting the same things in the same order would be to combine it all into one file and add the referencing in between and then have it wait for the command to start cutting again.

    On that note, when it stops after referencing, does it then continue where it should of you hit start?

    Sent from my SM-G996U using Tapatalk

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