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Z switch homing accuracy & repeatability investigation and findings


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Printing on my recently completed 2.4 has shown excellent overall print quality, but I have been experiencing ongoing issues with inconsistent first layer squish. This prompted me to investigate the thermal expansion characteristics of my printer as well as the accuracy and repeatability of my non-spec custom Z switch. After a number of experiments I had three major findings:
  1. The influence of chamber temperatures on the Z homing accuracy of my specific printer is negligible (from the time the bed reaches target temperature)
  2. My custom Z microswitch is very accurate and extremely repeatable
  3. The root cause of my first layer squish inconsistency is related to trace amounts of filament "oozing" from the nozzle
This issue is likely affecting many Voron owners on printers that are using physical nozzle contact for Z homing. This potentially can also affect the Voron-Tap, but likely to a lesser degree. Please have a look at more details on GitHub:

Z Homing Accuracy & Repeatability

I realize that I may be reinventing the wheel to a certain degree, because this is my first experience with a printer that uses the nozzle tip to contact a physical Z stop for homing. Having said that, I have not come across any similar studies in my searches and this may be helpful to some owners struggling with first layer consistency.
Great write-up! I believe there is no real hit print and walk away. I always look to adjust baby steps on the first layer as much as I don't want to.
Also, the print start should be able to mitigate the filament ooze issue and I do it a little differently than you.
I always reach it with snips and clip the end of the nozzle (hardened steel) before starting.
Then I run through homing, QGL, adaptive bed mesh, ext, and last thing is the hotend heats up to temp, then goes to purge bucket and expels I think 10mm or maybe 20mm of filament, wipes on the brush, then begins printing.

This seems to work well for me but it's perfect.
Thanks for the write-up and the time it took to gather all of that data! I too had inconsistent first layers that seemed to vary between prints, not within the same print. So I assumed it was the homing of Z that was the issue. Thinking also that nozzle ooze was likely a culprit and that I did not have a purge bucket, I eliminated the traditional Z endstop based off the nozzle and used the Klicky probe to be build surface routines for me Z homing. That seems to have cleared up my inconsistencies since I implemented this about 2 weeks ago. In fact, I don't even care about a little nozzle ooze, it is taken care of in the prime line, so I might not even put on a purge bucket.
Interesting writeup.
I have been using Klicky probe with the auto-z library for a while. That got me to hit print and walk away for 99% of the time for a while. I'm just now switching to Tap and hope for the same. I also have a purge bucket and nozzle brush. I've always had a purge & scrub as part of the print start to make sure the nozzle is clear; I've just tweaked my macro to add another scrub just before tapping as insurance. The last thing I do to avoid ooze blob issues is a retract in print end; that also is to help with Revo cold nozzle swaps between prints.
Thanks for the great write-up. I've been trying to get consistent first layer squish with TAP. (That's why I got TAP in the first place.) I've not been concentrating on ooze, but your work is about to change that, I think.
Thanks for the great write-up. I've been trying to get consistent first layer squish with TAP. (That's why I got TAP in the first place.) I've not been concentrating on ooze, but your work is about to change that, I think.

It would be interesting to hear if your challenges were also caused by ooze.

I can also add that with my modified Z homing approach described on GitHub, the first layers on my 2.4 have become consistently repeatable. I have done about 20 prints and thus far all of them have been "press print and walk away" with no need for any adjustments...
I’m having more consistent first layers. Increased hot end temperature to 180. Before, I was probing at anywhere between 40 and 150. 180 is hot enough to soften goo on nozzle tip, I think. Possibly some of my problems were goo and some were thermal expansion of nozzle. Anyway, little if any manual z adjustment is required now.