Inconsistent Prints
I just got my Prusa Mini a few weeks ago and for the most part love it! However, I have run into some inconsistency in prints. It will do 5-6 absolutely perfect prints, then one will have strands of filament going all the wrong places, then it will print correctly on the next print.
I've tried the calibration wizard again, adjusting the Z settings, and so forth. I keep getting beautiful prints... for a while. I've tried cleaning the bed more frequently but still have the issue recurring. It works most of the time. Here's a picture comparing what I consider a good successful print with one of the failures.
Ideas? What am I missing or doing incorrectly?
RE: Inconsistent Prints
You are experiencing delimitation due to poor inter-layer adhesion. As the nozzle moves around those inside curves, the filament is under tension. If adhesion fails, strands will pop loose and taut as you're seeing. There are a few things you can do to improve inter-layer adhesion:
- Increase filament printing temperature/decrease cooling. Higher temps will bond better with the underlying layers.
- Slow down. Giving the filament a bit more time to adhere improves adhesion.
- Reduce layer height. If you're using thicker layers, there's proportionally less surface in contact with the layer below.
I encountered these issues with the visor overhangs on the NIH-style shields when doing high-volume printing. I found that reducing layer heights (0.4mm with a 0.6 or larger nozzle) usually cleared up these issues.
As to why it only happens on some prints, hard to say. You might be right at the edge of getting good adhesion. Perhaps the layers closer to the bed stay just a bit warmer. I wouldn't expect Live-Z or bed cleaning to be a factor here as it looks like the parts are staying put, just some strands get pulled loose.
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