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C-Beam, Home, limit switches and movement convention

Discussion in 'CNC Mills/Routers' started by Kevin Brewer, Dec 3, 2018.

  1. Kevin Brewer

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    I have gotten a bit confused here, a simple statement in the build documentation would really help everyone start on the same page. I am using the new OpenBuilds machine Driver software.

    From reading posts I take it that the general understanding of the Home position is:
    X to the right
    Y to the Back
    Z at top

    Also that this is were you would place the limit switches - Min for the Home location and the max at the other extreme.

    Lastly when I Jog / move the machine "positive" it would move away from the Home position
     
  2. PatMcClintic

    PatMcClintic Well-Known
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    I haven't read in many places, but I thought machine home was generally back, right and top (like you said), but work piece home was wherever you set it, and positive would be to the right, back and top compared to work piece home. Clarification would be great for me as well I guess.
     
  3. CNCMD

    CNCMD Veteran
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    Home is where ever you want it to be.

    Now with that said, Z Home should be Up to the Top of Z Travel. This avoids your bit running into the worktable upon a home command.

    Now for X & Y, this can be however you want it to be. My machine homes to the back, left corner.
     
  4. CNCMD

    CNCMD Veteran
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    I'm assuming you are using grbl, it looks like you need to adjust GRBL setting for travel direction and homing direction. You should determine the direction you wish to home, and post your grbl settings.
     
    #4 CNCMD, Dec 3, 2018
    Last edited: Dec 4, 2018 at 10:03 AM
  5. David the swarfer

    David the swarfer OpenBuilds Team
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    NO!

    the industry standard home position is at the positive ends of the travel, so any jogging from there will go negative.
    but, you don't need to work in negative numbers, just jog to wherever your workpeice 0,0,0 is and click the 'set zero here' buttons in whatever GUI you are using and your Gcode will be happy as a clam.

    note that negative and positive motions are in 'tool movement'. so if the machine has a moving table you are looking for tool movement relative to the table (ie the table goes the other way). if it has a moving gantry then tool movement is obvious..
     
  6. Kevin Brewer

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    Thanks everyone for the input! I know it is a bit if trivial thing, but for you'r first CNC machine, starting from a common reference just makes life a bit easier - there are plenty of other thing to "second guess" about.... I really wish they just stated this simple convention in the setup instructions!
     
  7. ChadRat6458

    ChadRat6458 Journeyman
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    I use LinuxCNC. My home is the bottom left corner. I use touch off to zero out everything on the work piece.
     
  8. JustinTime

    JustinTime Master
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    Most of the times I use the same setup as ChadRat6458 uses. It's the most used convention since both x and y are, mostly, positive values. Sometimes it's more convenient, though, to have the 0,0,0 point in the material, in the center of the piece to be cut for example.

    I don't use the limit switches for homing. The way I use my machine, as ChadRat6458 had said, 0 on the axie is dependent on the location of the material and that changes every time I put a new piece since I don't use permanent blocks that define an x and y 0. Also, more than once I used material that I had previously cut and I'm not sure exactly where I will cut a new piece. Having blocks to define x and y zero or using the homing option will not work in those cases.
     
  9. David the swarfer

    David the swarfer OpenBuilds Team
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    but that is exactly what G54-G59 WORK co-ordinates are for!
    you position the tool where 0,0,0 is 'on the part/material' and then click the zero buttons for each axis, thus setting the work offset to 0 at that point (that must match what the Gcode expects of course)

    though I liked Candle as a GUI I stopped using it because the zero buttons set a G92 offset and not a real G54 offset.
    I now use bCNC instead because it knows which offset system is in use and sets 0,0,0 in that system when you press the zero buttons, this allows me to run multiple parts by just setting multiple work offsets.

    This will come in handy when I fit the laser next to the router, then the router can use G54 and the laser can use G55 for perfectly aligned laser marking on routed parts from one Gcode file.

    during all of this I never need to know what the machine co-ordinates are, negative or positive just does not matter.
    I do need to ensure that I power up with the gantry at my chosen home position though (standard + ends of travel for me), because GRBL remembers the offsets and you can crash easily if you start up in random places and then do a 'G0 x0 y0 z0'.

     
  10. Kevin Brewer

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    Thanks again to all for the input, my First project was a reprap 3d printer, some slight differences between that and the CNC setup, but it's all coming together now. I just wish I could take it home and work on this guy - it's a work purchase and side project, so never enough time to devote to it!

    Anyone using the OpenBuilds machine driver? I tired GRBL program at one point but it didn't work with the Smoothie Board, then when I got some time to work on it I came across the Openbuilds Machine Driver, it worked so I ran with that. Any call on what is the better program to work with?
     

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