Mach3 Unexpected Z axis plunge below code coordinate


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    Default Mach3 Unexpected Z axis plunge below code coordinate

    Hi guys.
    Nice to meet you.
    Have been reading the forum for a while and decided to register.
    I had a strange issue today with my machine.
    I was running a gcode file the whole day. Repeated it more than 10 times without any issue. The last time though my machine crashed without any reason.
    I have an aluminum fixture pallet fixed on my table and on the pallet I hold my parts. The pallet is positioned at Z-11, so all my operations have z-10.5 as the lowest point. During an operation the machine suddently plunged into the pallet, broke the tool and thank god I was right infront of it to stop it. I noticed that Mach3 was indicating Z-41.5???. I immidiately looked at the gcode and noticed that 2 lines before it stopped there was the correct command Z-10.5 and no other Z command up to the point it stopped.
    I have hybrid, closed loop servo steppers so I dont think there was an issue with losing steps.
    Also the same program run over 10 times right before this happened without any issue and without me changing anything on it or in mach3. Each time the program ended I just swaped the parts and hit cycle start again.
    I cannot explain what has happened. Should I consider it was a bug with mach3?
    What could have gone wrong?
    Any help welcome

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    Default Re: Mach3 Unexpected Z axis plunge below code coordinate

    That's a very hard question to answer without having seen it in person, and being familiar with all aspects of your machine and what you were doing.

    The simple answer is that it could be a bug, but it could also be many other things.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Quote Originally Posted by ger21 View Post
    That's a very hard question to answer without having seen it in person, and being familiar with all aspects of your machine and what you were doing.

    The simple answer is that it could be a bug, but it could also be many other things.
    I tend dto believe it was a bug too beacause it run normally the whole day. Can't think of anything else that could have happened. And nothing like this jas ever happened before.



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    Default Re: Mach3 Unexpected Z axis plunge below code coordinate

    One thing I forgot to mention is that i happened right after a feed hold command.
    What I mean. The part I was doing had some operations to be done, contours and pockets.
    My spindle is controlled by mach only for On/Off state and I set the RPM by changing frequency from the inverter panel.
    Between two specific operations (rough and finish of a contour) when the tool retracts and before it starts to go down again for the second operation, I hit feed hold, stop the spindle from mach3 button, set the frequency I want, start the spindle again from mach3 and then hit cycle start again to continue. I did this the whole day without any issue.
    The crash happened right after I hit cycle start again after the feed hold command. It started going down again, and didn't follow the code but went straight into the fixture.
    Could something have gone wrong with the feed hold command and bug the software?



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    Default Re: Mach3 Unexpected Z axis plunge below code coordinate

    I had this exact thing happen to me today. But I have video and was able to "sort of" figure out what happened. Doesn't sound like your case though.

    I this situation, I am running a BIG bit (14mm x 125mm), and it has to go almost to the top of the Z stroke in order to clear the rough stock (Guitar neck with heel).

    What I'm seeing happening is that while executing "G0 Z97.750", the Z motor sounds like it is missing steps due to reaching the limit of it's travel. Then, because Z
    stopped moving when the software thought it was, the next Z movement is off by quite a bit. The thing is, even if I had hit the end of the stroke (which I didn't, limit switch wasn't triggered), it wouldn't be off the by amount that I then see on the MACH3 readout (Z of 97 when I'm actually closer to 50).

    This happened to me 3 more times, but I was able to stop, re-zero, and start in those cases.

    I can post vid if you want.



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    Default Re: Mach3 Unexpected Z axis plunge below code coordinate

    Quote Originally Posted by Kosh View Post
    I had this exact thing happen to me today. But I have video and was able to "sort of" figure out what happened. Doesn't sound like your case though.

    I this situation, I am running a BIG bit (14mm x 125mm), and it has to go almost to the top of the Z stroke in order to clear the rough stock (Guitar neck with heel).

    What I'm seeing happening is that while executing "G0 Z97.750", the Z motor sounds like it is missing steps due to reaching the limit of it's travel. Then, because Z
    stopped moving when the software thought it was, the next Z movement is off by quite a bit. The thing is, even if I had hit the end of the stroke (which I didn't, limit switch wasn't triggered), it wouldn't be off the by amount that I then see on the MACH3 readout (Z of 97 when I'm actually closer to 50).

    This happened to me 3 more times, but I was able to stop, re-zero, and start in those cases.

    I can post vid if you want.
    Thanks for the answer.
    This hasn't happened again to me. I think what happened to you is a different thing cause I use closed loop stepper motors and they don't miss any steps. Also if i try to execute a program that drives the axis off its limit it generates a warning before starting. And I had a lot of travel on the retract moves to the limit of Z so I wan't anywhere close to it.



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    Default Re: Mach3 Unexpected Z axis plunge below code coordinate

    Quote Originally Posted by jimskeet View Post
    One thing I forgot to mention is that i happened right after a feed hold command.
    What I mean. The part I was doing had some operations to be done, contours and pockets.
    My spindle is controlled by mach only for On/Off state and I set the RPM by changing frequency from the inverter panel.
    Between two specific operations (rough and finish of a contour) when the tool retracts and before it starts to go down again for the second operation, I hit feed hold, stop the spindle from mach3 button, set the frequency I want, start the spindle again from mach3 and then hit cycle start again to continue. I did this the whole day without any issue.
    The crash happened right after I hit cycle start again after the feed hold command. It started going down again, and didn't follow the code but went straight into the fixture.
    Could something have gone wrong with the feed hold command and bug the software?
    You got lucky with the other Feed Hold stops, this is the most common problem, when in the middle of a program and doing this, stopping and starting is not a good idea with Mach3, when in a program like this

    Mactec54


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    Default Re: Mach3 Unexpected Z axis plunge below code coordinate

    Thanks for the reply. You mean it is not good to stop and start the spindle when on feed hold? Or it is not good to feed hold and continue the program?



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    Default Re: Mach3 Unexpected Z axis plunge below code coordinate

    Quote Originally Posted by jimskeet View Post
    Thanks for the reply. You mean it is not good to stop and start the spindle when on feed hold? Or it is not good to feed hold and continue the program?
    Both, it's a known problem that will never be fixed, start thinking Mach4 or some other control like UCCNC is getting quite good

    Mactec54


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    Default Re: Mach3 Unexpected Z axis plunge below code coordinate

    Quote Originally Posted by Kosh View Post
    I had this exact thing happen to me today. But I have video and was able to "sort of" figure out what happened. Doesn't sound like your case though.

    I this situation, I am running a BIG bit (14mm x 125mm), and it has to go almost to the top of the Z stroke in order to clear the rough stock (Guitar neck with heel).

    What I'm seeing happening is that while executing "G0 Z97.750", the Z motor sounds like it is missing steps due to reaching the limit of it's travel. Then, because Z
    stopped moving when the software thought it was, the next Z movement is off by quite a bit. The thing is, even if I had hit the end of the stroke (which I didn't, limit switch wasn't triggered), it wouldn't be off the by amount that I then see on the MACH3 readout (Z of 97 when I'm actually closer to 50).

    This happened to me 3 more times, but I was able to stop, re-zero, and start in those cases.

    I can post vid if you want.
    Post the code where this happens, it may be just something simple in the code

    Mactec54


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Mach3 Unexpected Z axis plunge below code coordinate

Mach3 Unexpected Z axis plunge below code coordinate