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More "drifting" X Axis

Discussion in 'CNC Mills/Routers' started by ElRowlando, Apr 30, 2015.

  1. ElRowlando

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    Hey! So I thought I had all of this worked out, but apparently not. I've tried to cut the same shape about 10 times now, and every single time the router slips and moves to the left in the same exact spot. I ran the code on a simulator as well as in the air and everything looked fine. There was no slipping or anything. I've also tried multiple different feed rates to no avail.
    I've also checked all belts and pulleys and there is no play that I can see.

    I'm cutting .5" birch plywood @ 45-50 ipm
    16k rpm with a DW611
    1/16th" per pass

    I've tried all sorts of different depths for the pass as well as slowing and speeding up the feed rate and it still does it! The bit i'm using may be a bit dull, which is also annoying because i've cut out maybe 3 things with it. Multiple passes and very long cuts so probably my fault.

    Anyway, here is a video. Someone please help because I'm about to rip my hair out!
     

    Attached Files:

    #1 ElRowlando, Apr 30, 2015
    Last edited: Apr 30, 2015
  2. Tweakie

    Tweakie OpenBuilds Team
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    You need to be somewhat methodical with fault finding in order to locate the cause so...

    Mark your work surface at X0, Y0 and add the line G00 X0 Y0 at the end of your Gcode then complete the job (which probably won't go wrong when you want it to). When it has finished does the cutter return exactly to the X0 Y0 position or is there an error in position ??

    Tweakie.
     
  3. ElRowlando

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    Tweakie,

    I just did what you said and the tool position is about 1/4" to the left and maybe 1/8" +Y from the original starting position. Do you think it could be caused by a dull bit? Because just yesterday I did a cut and had zero issues with it using the same depth, feed, and material.
     
  4. Tweakie

    Tweakie OpenBuilds Team
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    Perhaps the first thing you should do is check everything mechanical thoroughly paying particular attention to the tightness of grub screws on pulleys etc and possible binding or tightness of axes movement, tightness of belts etc.
    If your motors are not getting hot to the touch (they should run hot but not greater than 60 deg.C) then increase the drive current settings to provide more torque.
    Reduce your Velocity and Acceleration settings in motor tuning.

    Obviously, a dull bit will not help but with such a shallow depth of pass it is unlikely to be the root cause of the problem.

    Tweakie.
     
  5. ElRowlando

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    Thanks for the reply. I will go through and check everything out. As we speak its cutting .5" ply at 50ipm 1/16th pass depth without a hiccup. I didn't change anything either. I dunno what the deal is but I will keep digging!
     
  6. GrayUK

    GrayUK Master
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    Hi ElRowlando.

    As Tweakie has said, it really sounds like a mechanical fault.
    What is worse, it sounds like an intermittent fault!!
    It is easier to find a constant fault.
    I appreciate you have most probably tried this, but how about putting your machine through some tests to establish some definite answers.
    Forget about cutting for the moment, and concentrate on movement for now.
    That 1/4" error on the X axis was quite a lot in the world of CNC.
    I guess you usually set your Zero axis to the bottom left, so this time set your Zero's to somewhere about centre of your baseboard, so we stress a different area of your machine, and use as much travel as possible.
    Fit as small a bit as possible, and if you are confident that your baseboard is level, set it about 1mm above the board. Like before, get a very sharp pencil and mark the exact Zero point on your board.
    Program your machine for a run to the extreme left of Zero and back again. Watch the return point. Is it exactly right? Increase the speed of travel to stress the parts. Repeat several times, each time looking for a non return to exact ZERO. If there is an error, mark it on the board.
    Set the machine to repeat the action ten times without stopping. Zero to extreme left and back to Zero. Is the error getting worse, adding to itself each time, incrementally?
    If not, and all is well, repeat operation, but to the extreme right of Zero. Watching for an error on Zero.
    And yes, repeat in the Y axis, up the board and down.
    I am seriously hoping this will show up the error. If it does, then we have something to work with.
    An additional test would be to set up to cut a wide circle with a small bit, in ply or similar, so you are using about 3/4 of your base board size. Only cut about .5 deep, and, providing it is returning to Zero, keep repeating the same cut over the same area, watching for any increase in the width of the line after each completion.
    As I said, I'm sure you've already thought of these things, but as Tweakie says, "You must be methodical to find the fault."
    Perhaps another video showing something like a circle, with a straight line connecting to another circle. With repetition.
    Anyway, hope this may help.

    Gray
     
  7. ElRowlando

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    Thanks for getting back to me. I have a pretty busy weekend ton finish out so i Won't be able to test anything out for a few days but I will as soon as I can!
     
  8. Donald D. Parker

    Donald D. Parker Well-Known
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    @GrayUK you need to clarify that depth of cut for the circle. @ElRowlando while running the tests also use your ears to detect skips by the motors or loading from hard material or tight parts. The sounds tell you how hard it is working.
     
  9. GrayUK

    GrayUK Master
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    Donald
    The depth of cut is immaterial, you could use a pencil/pen, if you can fix one up to hold its position.
    How about 1mm? It will only matter on the first cut, after that you are looking for deviation of cut. :)

    Gray
     
  10. Donald D. Parker

    Donald D. Parker Well-Known
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    @ Gray Sorry I wasn't clear, you gave a quantity but no unit " .5 " ? (miles ;) )..
     
    Joe Santarsiero likes this.
  11. Jonny Norris

    Jonny Norris Veteran
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    I know I may sound like a broken record here to some of you, but I had a similar issue, it was caused by underpowered stepper motors.

    What drivers are you using?

    If not its mostly likely a pinion slipping. They can seem solid when put under pressure by hand but these things are under a fair bit of torque.

    What i did was take these off, remove the grub screws and re drill with a 4.2 mm drill and re tap to m5. I've even put m5 bolts in these and they work fine. You will them be able to get masses more torque into them and rule out slipping.
     
    GrayUK likes this.
  12. Donald D. Parker

    Donald D. Parker Well-Known
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    You can also grind/file one side of the shaft flat.
     
    Joe Santarsiero and Jonny Norris like this.

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