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TinyG controlling OX won't cut a round circle

Discussion in 'Controller Boards' started by brokenblade, Nov 24, 2014.

  1. brokenblade

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    Hi All,

    Over the last two weeks I've built an OX and chose the tinyG for control. All seems ok except that I can't cut a round circle. I thought in the beginning that it was just missed steps from cutting too fast or deep but reducing the cut didn't help. I read more and thought then it was a problem with sketchucam and tabs that are longer than the circle segments. With that in mind I tried a manual circle, G3 I.5 J.5, but the results are the same.

    While cutting a circle, when the x axis changes direction it seems to stall momentarily causing the circle to resemble a two lobed cam. This occurs even on a dry run with no cutter. It occurs regardless of cut direction or speed. I thought maybe there was a tight spot but it occurs at any position along the x axis.

    I can cut accurate squares and diagonals. I can also cut 24 segment 'skethucam circles' without trouble.

    Could it be a problem with the controller? I'm not sure what to check next, any ideas or experience would be greatly appreciated.

    Thanks
    Steve
     
  2. slittle

    slittle Journeyman
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    Steve, By chance are you using the free Sketch up? I understand from a how to video the free version can't do perfect circles but the pro version does. The free version does more of a hex type circle.
    I am new at this trying to learn cad/cam as I wait on money to build my cnc so don't take my info as rock solid from
    experience, as it was just info from a tutorial I watched on Sketch Up
     
  3. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder

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    Sketchup does 2 kinds of 'circle'....
    if you just draw a circle, it will default to 24 segments and will look segmented on the screen. (you can change the default!)
    if you do an outside cut around that circle Sketchucam will generate 24 arc segments and cut a perfect circle.
    you could draw a 7 segment circle and Sketchucam will still output code to cut a perfect circle, in 7 sections.

    if you EDIT that circle it may end up being just a collection of straight lines, ie no longer tagged internally by Sketchup as 'arc' and therefore generating gcode from it will result in straight lines being cut.

    I am not aware that the Pro version does it any differently.
     
  4. David the swarfer

    David the swarfer OpenBuilds Team
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    sounds to me like a TinyG problem, you should check on the TinyG forums.
    do you have any backlash compensation enabled, that would cause this if you don't have backlash.
    tighten the belts and recalibrate, though if diagonal squares come out right it is not a belt problem.
     
  5. brokenblade

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    Thanks for the replies guys.

    I ran some zig zag cuts watching carefully when the x axis changed directions. I could finally see that there was a step or two where the motor turned but there was no carriage motion. I had only used my hands when I tightened the belts, it seemed tight enough at the time (like I have experience with this, right ...). This time I clamped a pair of vise grips to the belt and was able to get it tighter and it seems to have fixed the problem. Thanks for the help.

    Steve
     
  6. Zootalaws

    Zootalaws Veteran
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    I can definitely recommend going to the dual-belt setup. My belts are only in finger-tight and they work great (same setup - Ox, TinyG)
     
  7. brokenblade

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    Thanks Zootalaws.

    That sounds promising if it doesn't require much modification. I searched for dual belt and only found references to the original post. Can you point me to the details?

    Steve
     
  8. pmany

    pmany Journeyman
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    Nick W likes this.

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