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Trouble setting x/y zero accurately.

Discussion in 'CNC Mills/Routers' started by Pelted, Aug 26, 2019.

  1. Pelted

    Pelted New
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    My LEAD CNC with BlackBox has been working pretty well. I have the z-probe and for the most part no real issues. As I've gotten more experience my expectations have also increased and now I'm running into an issue with accurately locating the zero point for the end mill before beginning a carve.

    I've made jigs that have zero points but even with my most accurate "eyeballing it" I'm often off my .5 mill or a little more. Not a big deal with a lot of things, but when I need tops and bottoms of parts to line up, its not good.

    What methods of edge finding work with this setup? The Shapeoko touch plate is interesting but $$ and not sure it would work anyway. An edge finding tool maybe, but I'm not sure where to start with Grbl and getting that to work.
     
  2. Gary Caruso

    Gary Caruso OpenBuilds Team
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    The best way is.. don't reset the position between sides.. here is a video from Ooznest showing the typical Dowel Pin method of 2 sided jobs.
    cheers
    Gary
     
    Peter Van Der Walt likes this.
  3. Pelted

    Pelted New
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    I've done that for two sided work and it has been okay. I'm making a lot of boxes that have two halves, top and bottom. I actually modeled and cut a jig out of mdf that holds the two blanks and has a zero point hole to drop the tool into. It's still not quite there. Same with some sign cutting stuff. The z-probe it great, need a way to probe for x and y relative to the material.
     
  4. sharmstr

    sharmstr Master
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    You can use a x,y,z touch plate, however, I find using dowel pins for two sided work is better. There are lots of videos on youtube about this. If you're going to be making more than one of the same two sided part, I would suggest making a locating hole in your spoilboard in addition to the dowel pins. I used this technique over several days and multiple machine restarts and re-homing. Basically at the start of every day, I home the machine, then jog over to where the locating hole is. I move the cutter down into the hole (which is the same diameter as my cutter) and then zero x and y. Works great.

    When you do get an x,y,z touch plate (buying or making your own), you can set up macro's in OB control for different size cutters. Here's some info on that. OpenBuilds CONTROL Software
     
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  5. sharmstr

    sharmstr Master
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    I was typing my response when you posted about using a locating hole. If you find that the locating hole isnt working that well for you, perhaps you have some backlash you need to deal with.
     
  6. Gary Caruso

    Gary Caruso OpenBuilds Team
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    On wood you can use aluminum foil tape used for duct work
    video showing use with Estlcam but any program that lets you probe x and y will work.
    Cheers
    Gary
     
  7. Pelted

    Pelted New
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    From my understanding of backlash, I should notice an issue when cutting out something like a full circle. I do this regularly out of 2'x2' sheets of 1/4 mdf and they always cut out super clean.
     
  8. David the swarfer

    David the swarfer OpenBuilds Team
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    I usually use 'the paper method' to set Z and just eyeball X and Y but I think this video shows a really good method of setting tools while reducing the chance of driving the tool into the work.

    jump to 1:05 where Peter rolls a half inch piece of ground steel under the tool to determine Z height.


    So the process is to use a thing of known diameter, measure it with a micrometer and write it down.
    Say we measure our bit of steel at 3.11mm (I have some broken 1/8" tool shanks to try for this)

    now we jog the tool to less than that distance from the work, hold the bit of steel there and try to roll it under the bit while jogging AWAY from the work (use a jog increment equal to your step size). The moment the tube rolls under the tool we know we are 3.11mm from the surface.
    Set Z0 there. (I am going to use Z but this will work for X and Y too)
    now move X and Y so the tool is clear of the work
    give the command G21 G0 Z-3.11
    Set Z0 <- this is the real top surface of the work

    repeat for X and Y but this time you need to move by (3.11 + radius of the tool) to set zero on the edge of the work.
    cross check the position
    G21
    G0 Z3.11
    G0 x0 y0
    and now the tool should be at x0 y0 and the test tube should just roll under it without play.

    Yes of course this all works in inch mode, just change G21 to G20

    hmmm, I wonder if this could be made into a macro... with a touch probe sensing when it disconnects?
     
    Rick 2.0 likes this.

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