Z home or z probe?

I have grbl mega up and running on my primo. I have my touch plate connected to the z min, and I can home z and everything works fine. Ultimately, what I want it to do is raise to a predetermined height after homing that is the appropriate focus height for the laser. I “think” z home is really intended for end stops, so the touch plate probably makes more sense for probing, and I could set the thickness of the touch plate to be larger than it really is to get the laser to the correct focus height.

Does this make sense? Any suggestions on which way to go, or alternate suggestions?

On my CNC Shield I’ve got both a Z Max endstop and the probe connection set up. These are separate pins. Since the probe is not tied to a particular axis it can be used in multiple directions by adjusting the gcode probe command used. But I don’t currently have a laser mounted.

For your situation, probing the top of your workpiece as Z min probably makes the most sense as you can use that as the datum for your focus adjustment relative to the surface. I’m not familiar with the grbl mega settings. Can you set a z probe offset?

I always worry about building in hidden “fudge factors” like artificially inflating the Z probe thickness. If I forget about it when I’m away from the machine for a while or replace the original probe I spend an inordinate amount of time re-learning why things aren’t lining up as I expect.

I’m not sure if there is a z probe offset. Right now, I am manually just moving the z axis and resetting it with a G92 Z0 command. For the laser, I am pretty much exclusively using Lightburn, so I can probably just make a macro in there to home and focus the laser all in one command. That might help prevent the issue you brought up of forgetting about the hidden fudge factors when I switch back to a router.

I do like the idea of multi direction probing for the CNC, and finding edges, etc…

How do you have your zmax endstop setup? I would like to do that on mine. Are you running a primo?

IMHO, making a gcode script to set that up is going to be much easier to edit, now and later. You can put this in a script on the ad card or as a macro in octoprint:


G28 Z
G1 Z50.25 F300
G92 Z0

Mine is a Burly model. I found a model on Thingiverse that allows mounting a switch to a cap that goes on one of the Z axis bearing bolt heads. I Hopefully you can make it out in these photos. The cap is white with 2 bolts poking out and you can just make out the leaf of the switch.

I home Z up away from the bed so the structure trips the lever as the tool rises. I know it’s hard to tell since everything is white and in the way, but it’s the top of the tool mouniting plate, not the tool holder, that trips the switch, so it works reliably with different tool mounts, e.g. pen holder or drag knife.

This works for me as I can probe the tool independently.


It’s tight trying to get the phone in there without dismounting the spindle.

Here’s a newer endstop mount designed for Primo using Burly tool mount which I came across today when looking for the one I used. Like I said, mine is a Burly, but as this just fits over the head of the bolt you can probably adapt it to your needs.

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Looks like your design is not available

Just to be clear, neither of those are my designs. The second link (which still seems to work) is the one I am using on my machine. The first is one I came across while searching. I don’t know why that link broke.

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No problems, the link seems to be working now for some reason. Thanks!