Welcome to Our Community

Unlock hidden features. Sign Up for Free Today!

GT3 16 tooth pulley?

Discussion in 'CNC Mills/Routers' started by Chillimonster, Mar 10, 2016.

  1. Chillimonster

    Chillimonster Journeyman
    Builder

    Joined:
    May 6, 2015
    Messages:
    43
    Likes Received:
    20
    Is it worthwhile to drop to a 16 tooth pulley for added accuracy (20% more accurate in theory)

    Have done a search and not come up with anyone that has done this mod.

    I will slow the cut speed down a little but may be worth the better accuracy?

    Anyone have any thoughts?

    Thanks
     
  2. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder

    Joined:
    Aug 6, 2013
    Messages:
    521
    Likes Received:
    250
    First we must ask the question:
    is microstepping accurate?

    the answer is no, it is non linear unless the stepper motors have some sort of feedback device (shaft encoder).

    why is this? magnets are non-linear, you know when you bring one near a bit of steel is becomes very hard to control the distance the closer it gets? the attraction gets much stronger as you get nearer. same thing happens inside the stepper motor, and the microstepping is trying to stop it at some point in-between full steps. full steps are reasonably accurate, half steps a bit less, and 16th steps are sometimes quite imaginitive (-: It does depend on the internal construction of the motors, I have some that appear to be very smooth and 'linear', while others visibly 'gallop' unevenly at 16x microstepping (with NO LOAD!)
    smaller microstepping values, 8x and 4x etc, magically make them smoother and more linear. add in some load, friction, cutting force, gravity, acceleration, sticky bearings etc, and it only gets worse.

    so, using a smaller pulley gets you more 'resolution', ie mm/step is smaller, but actual resolution is not as good as we like to think it is in the first place (-:

    I like to think of it like this:
    just how much resolution do I need?
    the answer varies from person to person. If I am trying to cut engraving on jewelry, then I certainly need 'more resolution', maybe 0.01mm.
    If I am making foam airplanes then 0.25mm is laughably small compared to the springyness of the foam.
    So having considered what we NEED, set the microsteps to the smallest value that gets us close.

    So, a 16 tooth on GT3 should give us 0.015mm/step at 16x microstepping.
    roughly half a thou. Do you need that? or would a thou be just fine for what you do?
    8x microstepping is quite a bit more accurate and powerful. 4x even more so.
    4x would give 2.36 thou per step, 0.06mm/step, yes, 6 hundredths of a mm. can you even see 2 thou? (-:

    so, if you need/want more power, go to the smaller pulley and reduce microsteps, otherwise, it may not be worth the effort.
     
    Joe Santarsiero and GrayUK like this.
  3. Chillimonster

    Chillimonster Journeyman
    Builder

    Joined:
    May 6, 2015
    Messages:
    43
    Likes Received:
    20
    Very informative post David - Really appreciate the information, and i'm sure it will be of interest to others.

    Thats what i like about the Openbuild Community - everyone (so far) is really helpful.
     

Share This Page

  • About Us

    The OpenBuilds Team is dedicated helping you to Dream it - Build it - Share it! Collaborate on our forums and be sure to visit the Part Store for all your Building needs!
  • Like us on Facebook

  • Support Open Source FairShare Program!

    OpenBuilds FairShare Give Back Program provide resources to Open Source projects, developers and schools around the world. Invest in your future by helping others develop theirs!

    Donate to FairShare!