LR4 Problem with Z-Axis Probing

Hey Y’all,
I’m new to the LR community and glad to be here. I’m working on finishing out my LR4 build and I’m at the last little bit. But I’m having an issue with my Z-Axis probing that I’m hoping you can help me with.

Let me back up a bit. Here’s where I’m at. Everything is fully assembled. I’ve squared out my LR. Adjusted my Z axis pulloff based upon my probing. And I’ve even been able to use my LR to cut out my strut plates (but with a couple of problems, one of which sounds very much like the post called “Z-drop during cuts”). I’ve installed the new strut plates, re-squared the LR, and now I’m working on adjust the flatness of the Z-axis.

Here’s the issue:
When I run a probe to set the Z axis zero, not only do I get different values each time I probe they are each generally 0.3mm higher than the last probe at the same place and without moving the gantry in any way. For example, my last three probe values were -80.35, -80.06, -79.75.

If I re-home the Z axis and then probe again, I again get a value at or near -80.35, and progressive probes each set higher values like before.

This seems like a programmatic issue (vs a physical issue) since I can get the very similar Z axis values each time I repeat this process. (I’m using the process @DougJoseph describes for setting the Z axis pulloff values.)

I feel like I’m just missing something easy, but not sure what it is. Also, when I cut my strut plates I had a very similar issue to the one I mentioned above and so I’m wondering if my issue is related to that one. Is there something that is causing the Z axis to creep?

Thanks for you help on this!
Mike

Oh yes, and because I was experiencing the issue in the 3.9.1 firmware with the probing not returning back up after the probe, I updated my LR to 3.9.4.

Sounds like skipping steps.

First thing - check your grub screws.

Second thing - lube your lead screws

Does it do this at both XMin and XMax, or only at one end?

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