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Help with machine flex..

Discussion in 'CNC Mills/Routers' started by sandman92k, Jan 30, 2019.

  1. sandman92k

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    i have a xyz belt driven system except the z is on a screw drive.. i have gotten it pretty close, i was cutting circles to test the machine and was having issues... today i was checking the machine and found the x axis to have to much flex... you can see the flex in the z axis assembly i have .60mm of movement... only in the center of the x axis.... any ideas on how to stiffen this up to fix this
     

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  2. Kevon Ritter

    Kevon Ritter Journeyman
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    Your gantry is too tall. It's creating a fair amount of leverage.
     
  3. Rob Taylor

    Rob Taylor Journeyman
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    If it's gantry flex, your cutting forces are too high for the height of your gantry (ie. the leverage of your z-axis), and it isn't internally braced sufficiently to deal with it.

    1) Epoxy or cyanoacrylate together your x-axis beams, if this holds through the vibration it would noticably increase torsional rigidity.

    2) Make some 40mm wide aluminum plates, probably 3-6mm, with like 20 or so pairs of holes drilled along the length of them, and screw them to the top and bottom of the gantry. This will have a similar effect as gluing the center.

    3) Turn the speeds and feeds up- faster RPM for a smaller chipload per tooth, dial everything up to the point of pretty much scorching the wood, then pull it back 10%. The less your machine is cutting off per revolution of the cutter, the less force it needs to push through the material, and the less resistance it's going to see.

    Looking at the pictures, though, I'm not entirely sure that's purely flex; it's in multiple directions, perhaps depending on where the initial plunge was, it looks like the belt's jumping/rebounding as the router sees different cutting forces. What happens if you do a helical toolpath? Cut the circle with a shallow ramp, maybe really shallow like 0.5mm per pass, with a final 0.5mm finishing pocket. What does it do then?

    If it was purely flex in the gantry, you'd see weird variations, elongations, distortions in the Y direction, and here you have a clear jump that's parallel with the x-axis.
     
  4. sandman92k

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    thank you for the input, i will be securing the x axis beam to help that. any suggestions on the belt issue how to resolve that, i ve readjusted the v wheels to make sure they are correct how do you fix the belt issue?
     
  5. GrayUK

    GrayUK Openbuilds Team Elder
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    Are you using the dual belt system? If not, you should. :rolleyes:
    If you search Youtube for: "CNC Duel Belts", you'll see how it's done. :)
     
  6. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    “Duel” ???? :):ROFL::ROFL:
     
    Kevon Ritter, GrayUK and sharmstr like this.
  7. joe williams

    joe williams Well-Known
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  8. Rob Taylor

    Rob Taylor Journeyman
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    "...Let's kill the people who point out the socioeconomic biases, inequities and harms endemic in society wrought through lack of forethought or carelessness- or outright malice- toward other people as an authoritarian defence of our privileges under the status quo."

    Certainly an interesting solution. Not very useful for fixing gantry flex or belt stretch, though, I suspect.
     
  9. GrayUK

    GrayUK Openbuilds Team Elder
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    Can't see what you guys are on about!!!! :p
     
  10. sandman92k

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    [QUOTE="GrayUK, post: 76237, member: 236If you search Youtube for: "CNC Duel Belts", you'll see how it's done. :)[/QUOTE]thank yoAre you using the dual belt system? If not, you should. :rolleyes:


    thank you
     
  11. sandman92k

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    I did the dual belt on x axis and waiting for rest of parts to complete on the Y axis, even made my own belt clips

    thank you to everyone for the input
     

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    #11 sandman92k, Feb 2, 2019
    Last edited: Feb 2, 2019
    GrayUK likes this.
  12. Kevon Ritter

    Kevon Ritter Journeyman
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    This escalated quickly. Go on. *grabs popcorn*
     

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