Z home location

Machine: FullSpectrum conversion

Board: _mini

Firmware: _Smoothie

Problem/ Question: Hello
We are using Lightburn

We are setting up our machine for the first time and we are having issues the material thickness setup.

We are using a cohesion3d variant of the smoothie board with our z home set to max and we have a working limit switch at our max position.

Currently, after homing we have the table z value set at 0mm which is our focus distance away from the lens. (everything with our homing seems to be working correctly. After homing our z it goes to z0 and when we press “Get Position” on the move tab it says z:0)

Now when we run a job with a material thickness of 3mm, I would expect the table to move down 3mm to compensate for the height of the material, but instead, it moves up 3mm so now I am out of focus and too close to the laser. The material thickness box does not allow for a negative number.

The z offset does allow for negative numbers but it returns to z zero after the cut so if we had a tall project on the table it would collide with the head.

Does anyone have any ideas on what we are doing wrong?

Our goal is to have the bed automatically go to the right height for whatever thickness material we are using based on our library.

I posted this in the light burn forum and they said it would be better suited for the cohesion3d forum.

If I save the gcode and edit the z line to a negetive then open it back in light burn number everything works as I would like it. Below is my edited gcode with a " G0Z-5.9" instead of the “G0Z5.9” lightburn created.

; LightBurn 0.9.02
; Smoothieware device profile, absolute coords
G00 G17 G40 G21 G54
; Cut @ 50 mm/sec, 100% power

Does anyone know if the “Smoothie device profile” output is editable like it is with post processors in the CNC cam world?


They answered it on the lightburn forum.

Z positive needs to be moving the table down then everything works like it should with the material settings.

Yes, that is what I had in mind and wanted to see which direction it needed to be for your exact setup.

Please attach your config file. If you have a Z endstop mounted at the max position physically, then you need to set it that way in your config file and adjust the home direction and distances.

It’s confusing. Attach your config file.

I can’t attach my config file for a few days as I am out of town but I think I got it. I have my z home switch at the max which is up by the head. Its actually 9.5mm above the ideal point for our laser to focus if it was something thin that was on the table. So I set my Gamma max to 9.5mm and after homing the table ends up at zero.

My confusion was my brain wanted the table moving down to be a negative number. For it to work moving the table down needs to be a positive number (I wish there was a way to flip the up and down arrows in Lightburn)
Toggling the reverse the z direction in the lightburn settings did this.

I should have thought of that before as its similar to how you have to think about milling on a Bridgeport mill. To move the bit in a positive direction in relation to your part you have to move the table in the negative direction.

Thanks for the help

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