In general, this is how most hot-ends are assembled…
Starting with Un-assembled condition with clean parts (removed filament, goop…):
Heat the hot-end (I usually use the filament pre-heat feature on my printers. If not on the printer, use a small torch/etc). Don’t need to fully heat it, just enough to expand metal. About 150C.
Screw the nozzle into the heat-block, leaving a gap the thickness of a sheet of paper (~0.1mm/0.004inch - the thickness of a human hair). Very-Light-Finger-tight will provide this ‘hardly noticeable’ gap.
Screw the hot-end’s heat-tube into the heat-block until it meets up with the nozzle. Snug it up but, DON’T tighten it (can break the tube - it’s thin walled).
Now, tighten the nozzle to remove the gap thus, it will press tightly against the heat-tube. Don’t over-tighten - the thread section on nozzle can break off!
Pre-heat as usual and re-snug (by hand) the tube section.
Re-tighten the nozzle.
In above condition, no plastic can ooze out from between Nozzle and Tube, thus, no plastic to leak out of the interface between nozzle and/or top of block.
Know your hot-end’s construction: some have PTFE in the heat-tube, some have PEEK, some have full metal (stainless steel…). Depends on brand and purpose.
I have 6 different hot-ends and some came in kits with interchangeable parts for different filaments…
The Key-to-success: Ensure the tube (PTFE, PEEK, Metal) fully butts up against the nozzle inside the block.
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