Z axis travel is not correct - need help!

Mostly Printed CNC - MPCNC Troubleshooting
1

Z axis movement is not correct

First of all, thanks to Ryan for the incredible work!

I’ve been busy building my MPCNC for a few weeks now and until now everything is working really great(And yes, I’m building the thing in my office room - my wife hates me - but in the spring we’re moving to a house where I can call a workshop my own… ).

However… I just noticed today during the first real test cut in wood that the Z axis travel is not correct. Previously, when drawing with the pen, I have not noticed it of course, because there the Z axis is not needed much.

I use CNCJS for control, Estlcam generates the Gcode. Here is a section of my Estlcam settings, if that matters at all. Sorry, cant upload more than 1 Photo as a new User:

steps per unit: x = 6400, y = 6400, z= 3200
Way per Unit: x = 32mm, y= 32mm, z= 2 mm

Now I noticed while milling (in Estlcam 3mm milling depth in 3 steps à 1 mm set) that the milling depth is not correct (has milled about 1 mm deep).

Now I have checked the following:
If I move the axes 10 mm in CNCJS, the axes move as follows:

X axis = Exactly 10 mm - Perfect!
Y axis = Exactly 10 mm - Perfect!
Z axis = Approx. 3 mm!

So this is off by about a factor of 3.xxx.

M503 returns me the following values:
“echo: Steps per Unit: M92 X200.00 Y200.00 Z800.00”

the coupler is fixed and secured with locktite.

My hardware (unfortunately not purchased from Ryan…shipping USA-Switzerland, lockwdown etc.):

  • Ramps 1.4 with Arduino Mega
  • Firmware: MPCNC_Ramps_T8_16T_LCD_32step_DualEndstop
  • 4x Endstops
  • TR8 x 2mm Leadscrew
  • Steppers: Nema 17 42HS60-1704A (1.8, 1.7A, 0.7 Nm)
  • DRV 8825 Drivers (All jumpers set → 32 steps)
  • Currently a Dremel for testing purposes - AMB 1050 is on the way

I have read across the forum and am now more confused than ever.
I really hope someone can help me with this!

Sorr for my English - not a native speaker :slight_smile:
Thanks a lot in advance!

2

Hmm I am also running Ramps 1.4 with a T8x2 lead screw and my Z step is set to 800 with the 8825 Drivers, but mine is accurate. Sorry!

When you manually control it, does it have the same issue? And is it off by 3X for all Z movements or 2mm for all Z movements?

3

Thank you mike!

When i actually cut something its off by a factor of about 3. When i move it manually up in cncjs by 10 mm it moves about 3 mm, when i move it 10 mm down, it moves about 3 mm. Also about a factor of 3.

X and Y are perfect.

This is the leadscrew, should be ok:

3dware.ch/Trapezgewindespindel-rechts-8mm,-TR8-x-2-/-300mm-De.htm

4

It sounds like you have a 1 start leadscrew. Then it would be moving 2.5mm instead of 10. Steps/mm should be 4x or 3200. The trouble is, you need to slow down that kind of leadscrew because the motors lose torque at high rpms. So start with something like 4mm/s on that axis.

M92 Z3200
M203 Z4.0
M500
5

Thank you so much! I will try this when im home from work!

6

Thank you jeff! Problem solved, travel is exactly 10 mm now!

2 Likes