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IndustryArena Forum > Machine Controllers Software and Solutions > LinuxCNC (formerly EMC2) > Former Mach 3, now LinuxCNC user hitting a few snags
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  1. #1

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    Nov 2019
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    Former Mach 3, now LinuxCNC user hitting a few snags

    1) Zeroing. In Cambam/gcode and Mach 3 I was configured to zero the Z axis on the top of the workpiece. How do I set LinuxCNC/Axis GUI to understand the Z axis as being to zeroed on the top of the workpiece?

    2) In Axis GUI, I can see the pre defined work area visually as a set of dash red squares (photo attached). How do I configure this size and location? They appears to be soft limits that will prevent gcode from running outside of even though it is not out of the range of the cnc's physical space. Some of my Cambam gcode appears outside of this software limit and as such Axis will not run the program (gives me an error).

    Yes I am a complete LInuxCNC newb. At the moment I want to run back to Mach 3 where I know how to do enough.

    Thank you.

  2. #2
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    As your machine has no way of knowing where the workpiece actually is,you need to help it a bit.I have to admit to being a few small steps ahead of you with LinuxCNC and I like it's utter reliability.I really need to do more about installing the home and limit switches on my machine and learning how to configure them.The only reason it hasn't been too pressing is that the system helps me more than I had expected.When I power up and before doing anything at all I click the home tab for each axis.Once the job is positioned I move the tool to it and use the touch off function to tell the machine what the job coordinates are and the really nice thing is that even if the part datum is way outside the physical size of the machine,it still accepts the program as long as the job size is within the machine envelope.

    Once you have the X and Y datums established you can touch off the top of the material if you know the part Z position of this surface-that is to say if you have a piece of stock X amount thicker than the final piece,which is datumed at zero then you can enter this value when the tool is in the correct place.If you use an electrical touch off sensor you obviously need to calculate for it's height.For tool changes you can repeat the process unless you have a tool library in place with the correct tool lengths in place.Done manually it isn't really a big deal unless you are chasing very small discrepancies and if you are then you need a touch plate anyway.

    Do you have a CAM system with a LinuxCNC post processor?I use Freecad and the Path module which does have the right post processor and while it does have quirks,it usually gets the job done.Can hardly wait for the refined version of 3D surfacing to happen.

  3. #3
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    I almost always program offsets G54 -G59.
    If Home as correctly defined in machine set-up and machine travel limits are correctly defined it 'just works'. Or at least it 'just works' if machine is moved to defined Home position at start-up.
    This is expected even in simulation.
    The GUI has a button labelled 'touch-off' for setting G54 - G59 offsets. I move the to workpeice zero and enter zero in the touch off dialogue box for each axis.. If you're not using G5x offsets things will be slightly different, it's the only work method that makes sense to me.
    Anyone who says "It only goes together one way" has no imagination.

  4. #4
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    In the axis GUI use the touchoff button to set the work offsets (G54 I think). The size of your work area is set by the MIN_LIMIT and MAX_LIMIT in your .ini file.

    I use a plasma machine so what I do might be a bit different.
    Rod Webster
    www.vehiclemods.net.au

  5. #5

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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    Touchoff for offsets is precisely what I was looking for. Thank you.

    Now this has me curious how Touchoff is different from zeroing the axis as they seem similar.

  6. #6
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    It would be similar if the zero is at the same corner as the location of the feature you use to touch off.For components where the zero is elsewhere,such as the centre of a shaft or similar,you can do the arithmetic and designate the feature as any value even if negative.It all depends on the datum point of your component.

  7. #7
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    It took me a long time to use the touchoff feature. Before that I used G92 until a predefined config got me into trouble. Now I finally get it.
    See G Codes
    But with my plasma machine, I run a cross hair laser pointer which I place over the zero point I want and I click on a gmocappy macro button that moves to that position and touches off the X & Y axes (becasue I don't need to worry about the Z axis)
    Rod Webster
    www.vehiclemods.net.au

  8. #8
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    The numbers in the link rodw provided are stored in a text file labelled .var in the machine config directory. That file is a handy reference but it's not good practice to edit it directly (and I don't believe rodw was suggesting doing so)
    Now this has me curious how Touchoff is different from zeroing the axis as they seem similar.
    How I think of it (a text book may disagree):
    A machine has only one "true" zero which is the machines defined HOME position. The more correct term is probably absolute zero.
    Work piece zeros are offset some distance from true zero, so it makes sense to call these positions offsets. In the link rod provided parameter 5221 will be the distance G54 X is offset from absolute zero. The 'touch off' button sets those offsets.

    I hope that makes some sense, my mind is a messy place.

    Edit/ Forgot to mention the .var file references the HOME position defined in the .ini file. For example if X HOME is +30 inches an offset -1 inch from that position will display as 29 in var. Hmm.. this stuff can get confusing after all.
    Anyone who says "It only goes together one way" has no imagination.

  9. #9
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    Imagine a large machining centre that has say 4 different milling vices (or some other fixture) on it and you set up to gang 4 parts at once. Each fixture has its own set of offsets from the origin so each fixtures origin would be defined with G54, G55, G56 and G57 offsets. So you an can simply reuse the one block of code and change to the appropriate offset for each part in the run to select the correct fixture.
    Rod Webster
    www.vehiclemods.net.au

  10. #10
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    Just to add more... Coordinate Systems

    G Code list... G Codes

    M Code list... M Codes

    I use a 2nd Desktop and have the browser set to "Show my windows and tabs from last time" in Preferences
    Happy Holidays

  11. #11

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    Nov 2019
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    Re: Former Mach 3, now LinuxCNC user hitting a few snags

    Thank you for your help. It helped lead me to my solution. My issues was a loose connector for one of the limit/homing switches. This was causing erratic behavior when homing. Because of changes I had made, I assumed it was a software configuration issue and not a hardware problem.

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