The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

The New Hotness

  • MPCNC: GRBL Configuration

    This collection of GRBL settings gets the MPCNC hardware up and running:

    $$
    $0=10
    $1=255
    $2=0
    $3=2
    $4=0
    $5=0
    $6=0
    $10=1
    $11=0.010
    $12=0.002
    $13=0
    $20=0
    $21=0
    $22=1
    $23=7
    $24=500.000
    $25=1000.000
    $26=250
    $27=2.000
    $30=1000
    $31=0
    $32=0
    $100=100.000
    $101=100.000
    $102=400.000
    $110=6000.000
    $111=6000.000
    $112=3000.000
    $120=1000.000
    $121=1000.000
    $122=1000.000
    $130=650.000
    $131=475.000
    $132=100.000
    ok
    view raw MPCNC-GRBL.cfg hosted with ❤ by GitHub

    Conveniently, the $$ command (in the first line) produces output in exactly the format it will accept as input, so just pour the captured file into GRBL’s snout. I used ascii-xfr with a 250 ms line delay:

    ascii-xfr -s -v -l 250 MPCNC-GRBL.cfg > /dev/ttyACM0

    Now, to be fair, the MPCNC hasn’t yet done any useful work, but it moves.

    Notes:

    Setting $22=1 requires home switches to be installed and working, with $23=7 putting them on the negative end of the axes, which may not work well in practice. In particular, having the Z axis homing downward is just plain dumb.

    The step/mm values in $10[012] require 1/16 microstepping with 2 mm belts on 16 tooth motor pulleys. The MPCNC’s Marlin config uses 1/32 microstepping, which doubles the step frequencies and (IMO) doesn’t provide any tangible benefit.

    The speeds in $11[012]=6000 seem aggressive, although they actually work so far.

    The accelerations in $12[012] may push the motors too hard with anything installed in the toolholder.

    The travel limits in $13[012] depend on the rail lengths you used.