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Resetting the Z height before return to 0

Discussion in 'CAM' started by KEITHABEAR, Jun 15, 2020.

  1. KEITHABEAR

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    Does anybody know how to set return to zero without it going to Z zero before X and Y go to zero?

    What happens is, wherever the machine is, it first moves the Z axis to zero and then moves X and Y.
    If I have Z set to the top of the material, it drags the bit.
    In GRBL, it's possible to set which axis moves first, so during a HOME for instance, you can set X and Y to move before Z.
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    OpenBuilds CONTROL moves to Z+5 before moving XY to X0Y0. Only then does it move from Z5 to Z0.

    So are you using a different host? Custom Macro? How are you moving to zero?
     
  3. KEITHABEAR

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    OpenBuilds control
     
  4. KEITHABEAR

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    Is there a way to set Z+5 to a different number
     
  5. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Create your own macros for custom moves. But 5 is above the workpiece if you zero on top
     
  6. David the swarfer

    David the swarfer OpenBuilds Team
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    Keith you are doing something wrong in the way you are setting up the machine.
    'dragging the bit' means you have not set the machine coordinate system correctly (and usually happens when you use the Fusion360 default GRBL post without a fake home and without changing any options).

    All the Gcode generators make assumptions based on industry standards and we cannot ignore those if we want our machines to work correctly.

    Since you do not have home switches you need to do one simple thing.....
    before you turn on the controller make sure Z is as high as it will go.
    or jog Z to the top and then power cycle or reset button (not soft reset from software) the controller.
    (for best effect you also want to move X and Y to the + ends of travel for a good repeatable fake home)

    What does this do?
    When the controller starts it sets the Machine Coordinate System to 0,0,0 aka 'machine home'.
    It also defaults G28 to 0,0,0 unless you have set it elsewhere.
    G28 is always relative to Machine home so having a proper home is vital if G28 (or G53) is going to be used.

    Now you jog the tool to where the part origin is and use the 'setZero' buttons to tell it that the Work Coordinate System is 0,0,0 at that point. These are the numbers that OpenbuildsCONTROL displays.

    The Gcode generator assumed that this is how the machine is set up and now the bit will not drag on the work at the start of a job.

    More info here f360/ob control on post settings and a 'go home' macro that you can use before shutdown so that when you power back up the machine is already at home.
     
  7. KEITHABEAR

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    I am using V-Carve Pro
    and I have home switches
     
  8. Alex Chambers

    Alex Chambers Master
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    Something is wrong about the way your machine is set up though.
     
  9. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Do another test:

    Jog to top surface, front left corner of a piece of stock, and Set Zero XYZ, then right away hit Gotozero, you'll see it do this dance:

    If you dragged maybe you didn't click Setzero after all
     
  10. KEITHABEAR

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    In UGCS when done with a tool path I jog router to change cutter when done I press return to 0 and X-Y moves to X0-Y0 then Z moves to Z0.
    In OpenBuilds Control the Z0 moves first then X-Y witch causes the router to hit clamps
     
  11. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Our thinking is.... What if the bit is NOT above the surface when you click GotoZero? (stuck inside a cut, ran some gcode without a return to 0,0,0 at the end, etc)

    Clicking GotoZero: what happens in UGS then? : It breaks the Bit doing XY first.... BAD

    Ours first clears Z by moving up to Z5, then does XY, much safer....

    Bit is not always above Z to begin with (; remember...


    If your dragging its something YOU are doing wrong, not CONTROL... Control moves at Z5 not Z0.... Don't believe me, check the source code! : OpenBuilds/OpenBuilds-CONTROL

    Do the little test I showed above, to convince yourself

    It works for everyone else (see Github Release Stats for an example, 1.0.237 (current version) has had about 2700 installs on Windows, 180 on Mac and 200 on linux. If it was failing we'd have been inun dated with posts from the other 3180 users by now. And thats just the latest version. Gotozero has been the same since the early 1.0.100s. It kinda shows its something you (1 out of 3000 on current version) did wrong there, so do the little test above :)

    Either you forgot to setzero, or did something else :) causing the drag...

    You can selectively go to zero from the arrow dropdowns next to each DRO: (do whcihever axis you want first..., then the second, then the last)

    goto y0.png

    If you want an even more different behaviour, the Macro buttons is yours to customize to your hearts content.

    Clamps are not really a recommended workholding solution around here, crashes being one of the reasons. Consider the tape method: docs:tips:ca-glue [OpenBuilds Documentation]

    Of course hitting the clamps is a different issue from what you originally mentioned (bit dragging on stock)... so that was the focus of this thread...
     
    #11 Peter Van Der Walt, Jun 16, 2020
    Last edited: Jun 16, 2020
  12. KEITHABEAR

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    I understand now but what is Z5 not high enough to clear clamps when moving to return to zero
     
  13. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Then either:


    or

    or
    3 different options
     
  14. KEITHABEAR

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    Thanks for all the advice greatly appreciated
     
    Peter Van Der Walt likes this.
  15. David the swarfer

    David the swarfer OpenBuilds Team
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    Hi Keith
    I think I get it now...... hitting clamps rather than dragging on the surface itself.

    What you need is a custom macro to move Z safely first, then XY, then Z again

    G90 G21 G17
    G53 G0 Z-5 ; this raises Z to 5mm below the home switch
    G0 X0 Y0 ; go to work zero
    G0 Z5 ; this should be 5mm above the work Z zero, unless your bit length is off
     

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