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Grbl panel homing, zero xyz problem

Discussion in 'Control Software' started by Cabinetguy, Sep 23, 2015.

  1. Cabinetguy

    Builder

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    Thanks in advance to anyone who can help me here!

    I'm relatively new to the CNC world and finished assembling my c-beam machine last week. I got it working fine by following the 2 hour tutorial and was able to successfully cutout a couple of items I designed in Sketchup.

    The problems started when I installed my limit switches and tried to do a home cycle. The initial tutorial said that the software considers the front, left corner as the zero xyz point. When I enabled homing, it runs all motors in their positive direction which lands the router in the back right corner with the router up as high as it can go. When I tried to run those same files again, the alarm went off immediately as the machine hit its X limit immediately. Apparently the machine didn't get the memo that our new homing direction was the opposite corner. Any ideas on how to fix this?

    grbl panel settings.JPG

    grbl panel interface.JPG
     
    #1 Cabinetguy, Sep 23, 2015
    Last edited: Sep 23, 2015
  2. Joe Santarsiero

    Joe Santarsiero OB addict
    Staff Member Moderator Builder

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    Check out the offsets section on this pagehttps://github.com/gerritv/Grbl-Panel/wiki/Settings
    and see if that helps.

    Joe
     
  3. Critical

    Critical Well-Known
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    Old post, I realise, but this 2 hour tutorial you mentioned, any chance of a link please? :)
     
  4. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder

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    Well, that tutorial is obviously a bit wrong or out of date.

    GRBL follows the industry standard for homing where the home position is at the positive ends of travel.
    This means that a simple 'go home' command will clear the cutter head out of the way for removing the parts and so on, and loading new parts.
    Critically, it also means that the Z home is safely away from the work, up high.

    The home position is the 0,0,0 point of the Machine Coordinate System or MCS.

    Before you had home switches, the WCS 0,0,0 point was wherever you turned the machine on, and then you set 0,0,0 for your part (bottom left corner on the top of the material by default in SketchUcam) and your parts cut fine.
    This will work fine for SketchUcam code because it makes no assumptions about the setup of the machine.
    However, other CAM systems DO assume that the machine is properly setup which can cause some startling and/or unsafe moves! For example, Fusion360 generates a 'G53 G0 Z0' move before any other moves. This moves Z to MCS Z=0 which it assumes is UP safely out of the cutting zone, so it can move to the start X,Y position safely.
    But if you turned on GRBL with Z low down, this MCS Z=0 position is NOT safe.

    Better to follow the standards (-:

    The are at least 6 sets of Work Coordinate System offsets, WCS. (GRBL supports 6, other controllers more)
    This is what gets set when you press the '0' buttons to the right of each axis display in GRBL-Panel.
    This defines where the 0,0,0 point of your part is on the material that you have mounted, and since there are 6 of them (activated by G54 to G59 codes) you can cut the same part in 6 places without changing any code.

     

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