Capillary effect on 3D printer nozzle threads.

[gwatson1990 1]

Hey all,  I've been running a custom build with a MK8 nozzle and an E3D titanium heatbreak for a while now, solely printing PETG. As I'm sure most of you know, often times PETG can make a pretty good mess of your hot-end especially during long prints. I recently went to switch my nozzle from a 0.4 to a 0.6 and when I took my hot-end apart there was filament along the threads of the nozzle and some of the heat break. After dozens of hours of printing I had no issues that would indicate a loose nozzle (oozing filament out of the heater block or flow issues) and it didn't seem to me that any filament had leaked from the inside out as I did a successful cold pull prior to disassembly and there was no filament pancaked between the two mating surfaces of the nozzle and heat-break. So my question is can the capillary effect cause filament to creep up the threads if there is space between the nozzle flange and the heater block? Or... am I just in denial that I didn't tighten my nozzle well enough?

[geert_2 557]

Normally, a well-tightened connection of a pipeline is absolutely gas- and watertight, even up to pressures of 200bar, as in my hydraulic machine. This is brass on brass, or brass on inox. However, the tiniest damage can cause it to leak.

 

So I could imagine that one of both parts has an uneven mating surface from earlier contamination, or from careless machining, or from dropping or hitting something. Or one of the treads could be too short. Or, if the thread-cutting is done after machining the part to length, it will cause deformation and an uneven surface close to the cuts. That sort of things could also be a cause...