Blobs, otherwise good print
After recalibrating my z offset and switching filaments (from one Matterhackers Pro PLA to another), my MK3S seems to be printing fine except when I check back on it I find large blobs here and there. See attached photo. The blobs seem to be "free standing" in that they have no obvious connection to the work in some cases, and all were easy to detach. While printing, I spent some time observing the nozzle and it never had a build-up of filament while I was watching, but obviously sometime over the 7 hrs of print it did. Can anyone explain what's going on and how to prevent it? I've never had an issue like this before, but this is my first time printing 0.4mm filament with the new 2.3.0 slicer and updated firmware.
RE: Blobs, otherwise good print
This turned out to be a result of molten plastic oozing up the threads between the heat break and the heater block, then out the gap between the heater block and the heat sink, and dribbling down periodically.
My question now is: what keeps molten plastic from oozing out between the nozzle and the heat break, up the threads of the heat break, and out the gap between the heat sink and the heater block? Does it mean the nozzle was not tight against the heat break? What seals the joint between the heat break and the nozzle? What seals the gap in the threads of the heat-break and heater block joint? If I screw the head sink tight onto the heater block, in theory to prevent this oozing, then the nozzle can't be screwed in far enough (i.e. there is more than a 0.5 mm - 1.0 mm gap between the nozzle and the heat sink.
It would be great if the principles involved here were explained in the nozzle replacement / heater block replacement / instruction manual.
RE: Blobs, otherwise good print
This article has an image in the "final inspection" section of the document: https://help.prusa3d.com/en/article/changing-or-replacing-the-nozzle_2069
You're throwing a lot of questions at once but I'll try to summarize the entire hotend assembly to you in a few simple steps.
So first off we got the Heat Sink (Metal piece with fins). The main purpose of this is to ensure that the filament will only melt in the Heat Block (the rectangular piece of metal). The Heat Break connects the Heat Sink to the Heat Block. The Nozzle Connects to the Heat block and should sit square and firm against the heat break. This is what creates a seal to prevent molten plastic from oozing out of the threads. The threads, as you have seen, do not have any other mechanism to prevent leakage. The only sealing mechanism is the nozzle being tight up against the heatbreak.
And this is why it is important to tighten your nozzle while it is hot. Since metal expands when it heats up, if you only tightened your nozzle cold, then the two surfaces of the nozzle and heatbreak will no longer be butted right up next to each other once the hotend gets to 250*c.
RE: Blobs, otherwise good print
@dragon1291
Thanks! Much appreciated.