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I need some help...

Discussion in 'CNC Mills/Routers' started by BismarckDon, Sep 11, 2015.

  1. BismarckDon

    BismarckDon Well-Known

    Aug 31, 2014
    Likes Received:
    I finally got a little time to work on my CNC machine.

    I'm trying to get the Grbl configuration settings entered, and I'm struggling.

    I found a site on the internet ( http://noblesque.org.uk/ShapeOko/grblcalc/ ) and was trying to work through the calculations. At this point, I have removed all step jumpers on my CNC Xpro controller board. Here is some specific information about my machine: It's modeled after the Open Builds OX design with an overhead gantry. I'll be running a Dewalt DWP 611 1/4" router.
    X and Y axis belt / pulleys: GT3 20 tooth 18.3 mm diameter
    Z axis: 8 mm Acme rod: 1.25 mm / revolution
    Nema 23 stepper motors on X, Y and Z axis (2 on Y axis)

    I do not have limit switches or homing switches installed yet. (Approx. working bit area is X=560mm, Y=380mm, Z=70mm)

    Here are my current Grbl config settings:

    Obviously, I don't know exactly what to do. I can get the x axis to move, but not sure about the scale or accuracy yet. It seems to move slow and almost choppy. I suspect my settings are incorrect. No luck with Y axis.

    Can anyone give me a little assistance?


  2. Joe Santarsiero

    Joe Santarsiero OB addict
    Staff Member Moderator Builder

    Oct 30, 2014
    Likes Received:
    Hey bismark,
    Travel per revolution is going to be the pitch diameter (not the pulley diameter) ├Ś pi.
    Ex. a 19.000mm pitch Dia. >> 19.000mm x pi = 59.690mm per rev.
    So. a stepper with 200 steps per rev.
    59.690mm/200=.298mm per step.

    Running the same stepper in half step will yield a resolution of .298mm/2= .149mm per half step.

    and so on for 1/4 and 1/8 step settings.

    The z is easy. 1.25mm/200 or 400 or 800 and so on.

    While I don't have time atm,
    I'm sure someone will stop by to help you with all of the grbl settings. If not I will later. There are some grbl posts with setting here on the forum and the grbl wiki is handy as well.


    Edit. There may be a number floating around that tells what to add to the pulley tooth pitch diameter to figure out the belt pitch diameter as a shortcut, but I don't have that. plus there are different manufacturers for these belts.
    Gates is the main source of this design I'd read through their material first.

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