Easel Stepping Too Far in Z-axis (S2 w/Acme & NEMA 23 Z)

[ajacocks]

All,

I asked the same question on the Inventables forum, but I figured that I'd put it to the larger audience here, as well.

I'm having an issue with Easel making Z steps that are too large, on the Z axis only. I have a mostly stock Shapeoko 2, with a Dewalt 660 router, ACME Z screw, and a NEMA 23 Z motor, to handle the extra weight of the router. The X and Y precision seems to be right on, but the Z axis is making steps that are much too large. The only configuration settings that I could find, in Easel, are the selection of the Z axis screw type (I did pick ACME), and the feedrates. Has anyone else encountered this problem?

I have $2 set to the recommended value, in GRBL, for the ACME, being 188.947. I used UGS to do that.

The rest of my config parameters are as shown, below.

Code: Select all

Grbl 0.8c ['$' for help]
>>> $$
$0=40.020 (x, step/mm)
$1=40.020 (y, step/mm)
$2=188.976 (z, step/mm)
$3=30 (step pulse, usec)
$4=250.000 (default feed, mm/min)
$5=250.000 (default seek, mm/min)
$6=252 (step port invert mask, int:11111100)
$7=255 (step idle delay, msec)
$8=25.000 (acceleration, mm/sec^2)
$9=0.050 (junction deviation, mm)
$10=0.100 (arc, mm/segment)
$11=25 (n-arc correction, int)
$12=3 (n-decimals, int)
$13=0 (report inches, bool)
$14=1 (auto start, bool)
$15=0 (invert step enable, bool)
$16=0 (hard limits, bool)
$17=0 (homing cycle, bool)
$18=0 (homing dir invert mask, int:00000000)
$19=25.000 (homing feed, mm/min)
$20=250.000 (homing seek, mm/min)
$21=100 (homing debounce, msec)
$22=1.000 (homing pull-off, mm)

I noticed, when I posted this, that $2 was set back to 188.976, and not the 188.947 that I set. I wonder if Easel changed it.

It was suggested to me that upgrading to GRBL 0.9i would help the situation, but I am reluctant to do that, until I get a real handle on the problem.

Any advice would be greatly appreciated.

Thanks!
- Alex

[WillAdams]

I have $2 set to the recommended value, in GRBL, for the ACME, being 188.947. I used UGS to do that.

Does it move twice as far as it ought?

If that's the case, it might be a mismatch for the microstep values, or maybe you have 400 step 0.9 degree motors.

Try measuring the movement, then doing the math to adjust.

[ajacocks]

Will,

I will cut a test piece and see if that is the case. I did check Inventables' spec sheet for the NEMA 23 motor that I bought, and it does say 200 steps, as that was one of my first ideas.

I do know that setting the cutting depth for a pocket to 0.300" will cut slightly deeper than a 7/16" piece of plywood, plus double-sided tape. It just slightly (1/32") scores the wasteboard. So, I doubt that is 0.600", but I'll cut and measure, on a thick scrap, with a shallow pocket.

Thanks!
- Alex

[ajacocks]

Well, that is interesting. I cut a basic square circle test pattern, and indeed, the S2 is cutting twice as deep as it should! A 2.5" square containing a 2" circle, with the square being a pocket 0.125" deep, and the circle being a pocket 0.250" deep actually comes out to be a 0.250" square containing a 0.500" circle.

So, I checked my settings, and just as the default, I have a jumper on MS1, on the gShield, meaning that my Z axis should be set for 2x microstepping. I have an Inventables 25311-03 NEMA 23 Z motor, which is a 200 step/rev motor. With the ACME screw, I have a patch of 2.117 (got it from Improbable Construct). So, based on the GRBL calculator, and the wiki, I should have a $2 of 188.9466225791214, or 188.947.

So, given that is very close to what I have, I'm confused. Based on observation, I would guess that $2 should be 94.4733112895607, or 94.473. That would indicate that my microstepping is actually set to 1x, which makes no sense, given the the MS1 jumper.

Any further thoughts?

Thanks!
- Alex

[ajacocks]

So, the answer to the problem just occurred to me, and it should have been obvious, from the beginning: I have installed IC's belt-drive Z-axis mod, and this applies a 2-to-1 multiplier to the Z-axis speed. So, indeed, my $2 should be 94.473.

However, that is a problem, when using Easel, as it automatically sets $2 to 188.947, for me, based on the fact that I have an Acme Z-axis screw. Can anyone think of a good work-around for this, other than just dividing all my Z-axis dimensions by 2.

Thanks!
- Alex