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Thread: "X" axis ballscrew locking up at high speed

  1. #41
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    Quote Originally Posted by ger21 View Post
    Correct. More force is required with the higher lead screw, so more work is being done.

    I think if you had a machine with servo motors, and an ammeter, you'd see the motor draw more current with higher lead screws, for a given load, and all else being equal.
    But doesn't the servomotor provide constant torque regardless of current or speed (except maybe peaking intermittently)? So the scew would only know it's getting x Nm of torque, not how much current is being pulled by the servo.

    I agree that it would take more force to turn the higher lead screw. But my whole argument is that with a higher pitch ballscrew Barefootboy4 could utilize his stepper's power better than with the 5mm pitch screws he's now using.

    As an example, haydn (havevn't seen a post from him in a long time) built a very nice machine using 740 in*oz steppers, but with 10mm ballscrews. His rapids over 500 ipm, and still has very good power and resolution. Of course he's also using Geckodrives, but not sure what his power supply is. His build thread is somehwere if if searched you canfind it.

    [nomedia="http://www.youtube.com/watch?v=ecWNTGk8AP4&feature=mfu_in_order&list=UL"]‪DIY CNC Rapid demo‬‏ - YouTube[/nomedia]

    edit: this video explains his power supply as well...

    [nomedia="http://www.youtube.com/watch?v=3_qdZB9iGhU&feature=mfu_in_order&list=UL"]‪CNC Stepper Motor Demonstration‬‏ - YouTube[/nomedia]



  2. #42
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    But doesn't the servomotor provide constant torque regardless of current or speed (except maybe peaking intermittently)? So the screw would only know it's getting x Nm of torque, not how much current is being pulled by the servo.
    No. A Servo motor only provides as much torque as it needs to do what it was commanded to do. It basically just keeps trying to get to where it's encoder says it should be. If you push on an axis and backdrive a ballscrew, as soon as the encoder position changes, the drive will send more current to the servo to correct the position error.
    If a servo had constant torque all the time, it would burn up quickly.

    But my whole argument is that with a higher pitch ballscrew Barefootboy4 could utilize his stepper's power better than with the 5mm pitch screws he's now using.

    I'm 100% in agreement. We just got off on a tangent.


    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  3. #43
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    LOL it was one hekuva tangent!

    Anyways, some good info here, hope it helps Barefootbou4 with his machine...



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"X" axis ballscrew locking up at high speed

"X" axis ballscrew locking up at high speed