ZMAX home, probe work coordinates

Mostly Printed CNC - MPCNC Advice
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I’ve been searching for a bit now to try to collect info to make appropriate code adjustments.
Is there a guide to hold my hand that I haven’t found yet?

My objective is to enable ZMAX during homing, and then utilize probing for work coordinates.
It is my assumption that ZMIN would be used for probing still.
(I am using the SKR PRO V1.2 board).

Thanks in advance!
Ryan

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I am just trying to get my z axis probe dialed in.
It’s basically a switch, but to properly utilize it you need to change the program to automatically assume your using it all the time. Or put a little snip of certain code at the top, in to use the z min probe and the thickness of the probes base. The V1 is .5mm ss
A z max probe is something I haven’t heard of , as in you should already know what your max height is going to be dusting the job.
Do you mean like a z axis maximum height end stop ?
I am still very new to this so take any advice with a grain of salt.

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Yes I am talking about utilizing the zmax limit switch(n.c) for homing. And using the zmin limit switch (n.o.) for probing.

Ive got the zmax added now in the code, and the board recognizes state change when M119 commanded. So I am making progress.

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I don’t have a specific answer for you, but I might have a recipe to get there. My understanding is that the dual endstop Lowrider, homes up using ZMax and probes down using ZMin. So:

  • Download and unzip the firmware for both the MPCNC and the Lowrider for the SKR Pro board (Dual versions). You are posting this under MPCNC, so I assume that is what you have already downloaded.
  • Download a diff tool of some sort. I use Meld.
  • Compare the configuration.h files of the two versions and make the homing/probing defines match the ones for the Lowrider, expect for homing direction.

I don’t own a Lowrider or a SKR Pro board, but I just did this comparison, and it looked like there were 6 lines of code to be changed. They weren’t all together, so you need to examine all the differences between the two files for ones related to homing/probing.

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I think the key pieces are in here:

This mixes dual Z and the z probe you’re trying to do. The home dir +1 is important, and any of the lines that have to do with probing.

On the LR, G28 Z homes (both sides) up. G38.2 Z0 probes Z down until Zmin is triggered. G38.2 doesn’t reset the Z coordinate, so after that command, you need to use G92 Z0.5 to set the Z value.

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@jamiek and I just had a chat related to G38.2 if this is of any help:

FWIW these are my probing commands.
Z-57 is the surface of my spoilboard in machine coordinates given I always turn the machine on with the gantry in the same location, and I run G38.2 in machine space, not workpiece space. Z is always set to 0 by G38.2 in workpiece space so my Z0 in machine space is unchanged. My touch plate is 7.9mm thick:

G53 G38.2 Z-57 ; Probe Z in machine space
G92 Z7.9 ; Set current offset to 7.9mm for Z to account for touch plate thickness
G0 Z20 F480 ; back up to an ultra safe distance

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