How does the hexagon hot end work?

General Hardware
1

I’m starting this post to try and gain knowledge on exactly how the Hexagon hot end works.
Here are the PDF for the mechanical drawings for the Feed Tube and 0.5 mm Nozzle
tube ASM long HB.PDF (173 KB)
brass_nozzle_3mm-0.50mm_v0.2.PDF (155 KB)

Feed Tube.jpg
Feed Tube.jpg248×683 22.4 KB

nozzle.jpg
Where I am confused is with the 3.20mm Inner Diameter of both the feed tube and the nozzle being larger than the filament. I understand that it needs to be somewhat larger for an easy slip fit of the filament into the extruder.

What keeps the melted filament from pushing back up the nozzle back into the feed tube? Is this where the Estep configuration comes into play?
I’m picturing this like the nozzle is full of water, and I stick my finger in it. Some of it will squirt out of the hole in the nozzle, but a lot more of it will squirt back past my finger to equalize the force of my finger. You will have the same pressure balance that has to occur multiple times as it extrudes and retracts.
Please excuse my horrible paint drawing.
nozzle1.jpg

2

My understanding of how the hexagon hotend works is as follows

  1. Cold filament enters the top of the hotend in a solid state and acts as a rigid plunger to move plastic down the bore. The bore cooling fan keeps it solid until it reaches just above the heater block where it starts to soften and mushrooms out to start sealing the bore the fillament below that point is molten and extrudes freely.

  2. With multiple filament types and diameters you can realistically expect to see filament up to 3.2mm so the bore has to accommodate that.

  3. Pla filament in particular expands as it gets warm before it melts. This causes a phenomenon called bore lock sometimes. If you were only ever printing abs a smaller bore would be fine.

The nozzle theoretically seals to the heater block. Some filament oozes out even under normal conditions but excessive oozes indicates an air leak.