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Non-Captive Linear Stepper for 1500mm+ Screw Axis

Discussion in 'CNC Mills/Routers' started by Adam Filipowicz, Dec 28, 2018.

  1. Adam Filipowicz

    Builder

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    I am interested in the idea of using a Non-Captive Linear Nema 23 stepper with a long 8mm TR8*8-2p Acme screw (Standard OB) for long actuators/machine axis.

    With Non-Captive Steppers the Stepper motor moves along the Screw, the Screw is stationary,
    since the screw does not move or rotate, it is not prone to screw whip and longer screws can be used (1500mm+) to create much larger machines then commonly available with Screw motion

    Would appreciate thoughts and comments about this idea,
     
  2. Gary Caruso

    Gary Caruso OpenBuilds Team
    Staff Member Moderator Builder

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    Should work great, would love to see it! Two issues
    Have you found a supplier with longer leads? all I can find are 2mm lead screws, this would make the movement slow. Openbuilds screws for example are 8mm lead (4 start 2mm pitch)
    second, when the nut wears out you will need to replace the whole motor unless they have serviceable nut, which I have not seen in Nema23 size.
    Cheers
    Gary
     
  3. Kevon Ritter

    Kevon Ritter Master
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    How do you plan to compensate for backlash?
     
  4. Rob Taylor

    Rob Taylor Master
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    Rotating-nut builds are semi-common in long-travel screw-based machines where rack and pinion isn't an option for whatever reason- accuracy, typically, though torque at speed and holding power could also be issues. I used one on my laser z-axis for design optimization, and plan to use one on an upcoming ballscrew build for the longest (1500mm) axis to avoid screw whip, since it should be a fairly high speed machine. It also allows you to tension your screws more than you typically would be able to without binding in a traditional rotating-screw setup.

    LaserGantryGIF.gif

    Since mine's purely for positioning, gravity provides all the anti-backlash I need. Obviously on a mill it wouldn't be that simple.
     
    Kevon Ritter likes this.
  5. Adam Filipowicz

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    I have sourced a custom Non-Captive Nema 23 with Tr8*8-2p I should have it in 3-4 weeks to test
     
    Gary Caruso likes this.
  6. GrayUK

    GrayUK Openbuilds Team Elder
    Staff Member Moderator Builder

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    Adam. Please keep us posted on this.
    Cheers
     
    Adam Filipowicz likes this.

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