Setup a touchplate with Dual Endstop MPCNC

Mostly Printed CNC - MPCNC Advice
1

Dear all,

As I couldn’t find (maybe I am to dumb for searching) a simple description on how to setup a touchplate, I wrote something together to help others!

As you may know, I am running my MPCNC with Dual-Endstops and it works great.

For the time being, I didn’t use any Z-Endstop or touchplate yet and I always set my worksurface manually.

Today, I had a bit of spare time and I attached two wires to the Z- endstop pin and GND.

I went into the firmware configuration.h and set

Z_MIN_ENDSTOP_INVERTING =true,

I flashed and tested by initiating a Home Z from a save height and then connecting the wires. Z-Homing worked as expected.

Now I attached one wire to the endmill and one to a 2.1 mm thick flat piece of metal.

Then I went to the firmware configuration.h again and uncommented

#define Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN

and

#define FIX_MOUNTED_PROBE

After that, I set

#define X_PROBE_OFFSET_FROM_EXTRUDER 0
#define Y_PROBE_OFFSET_FROM_EXTRUDER 0
#define Z_PROBE_OFFSET_FROM_EXTRUDER 2.1

This will automatically compensate for the 2.1mm thickness of my touch plate. If your plate is thicker, change this value accordingly.

Now I flashed the firmware again.

VERY IMPORTANT!!

After MPCNC boots up, go to Configuration -> load factory defaults

This sets the correct probe-offset! If you forget this step (like I did), you won’t have the correct Z-height after homing with your touchplate.

 

I homed Z, took the touch plate away and checked the actual Z-position on the display. It showed 2.1 as expected.

Done!

Using my joystick-controlbox https://www.v1engineering.com/forum/topic/manual-joystick-control-fro-mpcnc/, I now can do the complete setting for a new job without using the screen and rotary knob. Love it!

Another hint:

I used a pair of very long, almost untwisted 28 gauge wires to hook up to Z-min.

I faced the issue that my gantry only came down 1-2cm and the went up again. Homing failed. Turned out that I caught noise in the wires which prevented correct homing. First I twisted the wires which helped a bit. Then I went to the firmware again and enabled

#define ENDSTOP_NOISE_THRESHOLD 3

This totally solved the issue for me.

So I hope this helps people to easily get the touchplate going!

 

Cheers

Armin

 

5 Likes
2

My firmware should work as is, If you use a G92 command with the thickness of your plate it can all be done without touching the firmware. I have a little blurb on the milling basics page I believe. Unless maybe you are doing something different I am not seeing?

3

Ryan,
if I understand correctly, you issue a G28 Z first (or a G28 X Y Z) and then a G92 Z(thickness) which works fine but needs a terminal input.
With my method, the height adjusts automatically with the homing command (like on any 3d-printer with a probe for the Z- height).
As my machine is not connected to a PC directly, I only have the display and my joystick box. The lesser (correct English?!) inputs I have to make, the more convenient it is for me.

And I am coming from printing! G92 is not very present in the back of my head! LOL!
I totally overlooked the start G-code section in your milling basics with the Z- homing. Sorry for that. And I am also not using a start gcode in Estlcam yet, which would have solved my issue for sure. Still new to CNC machining! Maybe, you can address the Z homing a little bit more prominently and in more detail and maybe you even consider my solution as an alternative way.

Cheers
Armin

4

I add G92 in my start G-code. That way if I change touch plates for some reason I do not have to reflash the board, I just change it in CAM (starting gcode section). When I am doing metal there is no need for an offset, so for me the value varies.

5

When using probe mode, you can change offset from the printer menu and save it.

Cheers

Armin

6

I think you can also do M851 Z-2.1 to save the value in the EEPROM without modifying the firmware. M851 from the Marlin Docs.

Edit: You need to enable EEPROM in the firmware to do this. Looks like EEPROM is disabled by default in github.com/allted/Marlin