MPCNC: Tweaked GRBL Config

These GRBL configuration constants seem to work well with the DW660 router in the MPCNC gantry:

$$
$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=1
$21=1
$22=1
$23=0
$24=500.000
$25=2500.000
$26=250
$27=3.000
$30=30000
$31=0
$32=0
$100=100.000
$101=100.000
$102=400.000
$110=8000.000
$111=8000.000
$112=3000.000
$120=2000.000
$121=2000.000
$122=2000.000
$130=635.000
$131=465.000
$132=103.000
-----
$n
$N0=F150
$N1=G10L2P1X-633Y-463Z-3
-----
$#
[G54:-633.000,-463.000,-3.000]
[G55:0.000,0.000,0.000]
[G56:0.000,0.000,0.000]
[G57:0.000,0.000,0.000]
[G58:0.000,0.000,0.000]
[G59:0.000,0.000,0.000]
[G28:-418.670,-282.016,-3.000]
[G30:-628.000,-3.000,-3.000]
[G92:0.000,0.000,0.000]
[TLO:0.000]
[PRB:0.000,0.000,0.000:0]
view raw MPCNC-GRBL.cfg hosted with ❤ by GitHub

The overall XY travel is slightly smaller than the initial configuration, because the router sticks out further than the penholder I’d been using. Increasing the $27 Homing Pulloff distance to 3 mm leaves a comfortable space beyond the limit switches after homing to the positive end:

MPCNC - X-axis endstop - home
MPCNC – X-axis endstop – home

Adjusting the $13[01] XY travel distances and switch positions on the other end of the rail leaves a similar comfort zone at the negative end:

MPCNC - X-axis endstop - X min
MPCNC – X-axis endstop – X min

Both switches now live on the rear X-axis rail and appear as seen from behind the bench; they just look backwards. The Y-axis switches are on the left rail and look exactly the same.

The XY travel works out to 630 × 460 mm = 24.8 × 18.1 inch, which is Good Enough.

Some fiddling with the Z axis limit switch tape mask produces a nice round 100 mm = 3.9 inch vertical travel. The Z-axis rails just barely clear the table at the lower limit and just barely stay in the bottom bearings at the upper limit, so it’s a near thing. In practical terms, the rails or the tool will smash into the workpiece sitting atop the table before the limit switch trips.

Setting both $20=1 Soft Limits and $21=1 Hard Limits may be excessive, but I vastly prefer having the firmware detect out-of-range moves and the hardware forcibly shut down if the firmware loses track of its position, rather than letting it grind away until I can slap the BRS. The steppers aren’t powerful enough to damage anything, of course, so it’s a matter of principle.

The $N0=F150 sets the initial speed, as the default F0 seems to (sometimes) confuse bCNC’s auto-level grid probing.

The $N1=G10L2P1X-633Y-463Z-3 sets the default G54 coordinate origin to the front-left corner, with Z=0 at the home position up top, so as to prevent surprises. I expect to use G55 for most work holder touchoffs, although we’ll see how that plays out.

The G28 and G30 settings depend on the tool change location and the Z-axis probe location, so they’re still not cast in concrete.