Major adhesion problems after changing nozzle  

Major adhesion problems after changing nozzle

Hello, I'm new here so a little about me and my printer: I bought a da Vinci mini earlier this year so my son and I could learn a little about 3D printing, and we both quickly fell in love with it. However, it doesn't take long lurking in printer forums to learn that the printer I really wanted was the Prusa i3 MK3. Two weeks ago, I got my kit and opened it all up, but found I had 4 X-axis rods instead of 2 X and 2 Y. Last weekend, I got the rods and mostly got it all put together, but found both the trapezoid nuts on the Z axis were just too tight to turn.

I asked for replacements but I didn't want to wait another week to make any progress, so I found a model and printed one on my mini in PLA. Too tight again, probably because tolerances on the mini are terrible, so I opened it up a bit and reprinted and they're just a tad loose; they'll slowly turn down the Z rod under their own gravity. Seemed good enough though, so I got the rest assembled. Self test and calibration went great, I felt a little clueless about the first layer tuning but -0.720 looked pretty good so I tried some prints. There was some shifting on the Y-axis so I tightened it up a bit, and (choir of angels) everything was amazing. Did lots of prints that were all so beautiful and painless, the planetary gears, Adalinda, Benchy, some stuff off Thingiverse, some of my own designs. No issues on anything.

So, I wanted to try some glow in the dark PLA but I read the stuff will wreck your nozzle, so I got the E3D hardened steel nozzle and decided to try changing it out. (thunder crackles) The process itself took me quite a while but I felt pretty good about the results, then I ran the first layer calibration again, got some OK looking results, and started trying some prints.

They would all start OK-ish, but eventually something in the first layer would peel off practically every time and wreck the print. I tried to live adjust the Z every which way, and some temperature adjustments, but I just couldn't get a consistent print. Slowing down the first layer would sometimes let it succeed, but generally the results had a bit of stringing.

Eventually (after a few hours) I threw up my hands and decided there was something wrong with the nozzle, and tried changing back to the bronze. It was a lot easier the second time, and went through calibration again, but it was even harder this time to get first layer adhesion. When I can get a fill going, I've adjusted it to a height that seems all right, but it's just so rare and tenuous I can't really be sure of anything anymore. After hours of this, I'm starting to forget what a good first layer even looks like.

So... it's possible my Z adjustment is just way off and I don't even know it but I really doubt it. I feel like somewhere between -0.700 and -0.650 looks best and going above or below it is just getting worse. This is not so far off the initial -0.720 that was working so well with this nozzle. How precise do you have to be with this number; i.e. what's the distance between "perfect" and "just won't stick"?

I've cleaned with 91% IPA frequently, I just tried dish soap as suggested in another thread, and I'll pick up some acetone and try it tonight. But I also don't think it's a cleaning issue (I had no problems keeping it clean enough for printing before the nozzle change). My suspicions:

- Could the nozzle be a bit too loose? I really didn't torque it so I'm pretty certain it's not too tight. And it's not leaking around the base.
- Could degraded trapezoid nuts (remember they're homemade PLA nuts) cause an issue like this? Maybe running them all the way up and down the Z for the nozzle changes did something to them? Hopefully I'll get my genuine replacements soon.
- I'm pretty certain I've caused some light scratches in my PEI (it's the smooth one BTW) in my desperate search for the right Z. How bad is a light scratch here and there? Could it just be detaching every time it crosses something like that?

Anything else I might be missing? Thanks!