easy flow design hot end concept it works, give a try!

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this links a design image and a concept for easy flow of 3mm feedstock. it reduces pressure required to push material thru hot end. the theory is since more surface area of material is heated quicker, that the viscosity changes and allows easier pushing through of material.

it basically is a 3 stage size reduction in feedstock from 3mm, to 2mm, to 1mm and then the final nozzle size.

give it a try!

works wonders for bowden designs, and should work on any hot end.

Wouldn't that be prone to back-flow issues when pressure gets too high (i.e. extruding at a high rate)?

Where does the heater block or nichrome wire go? Near the bottom at the 1mm part?

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net

heater block goes near the nozzle. the concept is in the making and drilling of the barrel. back flow is restricted by the ptfe tubing

I'm assuming the 1 and 2mm sections need to be at melt temperature (otherwise you're not going to get 3mm filament through there). As there is no thermal break between the sections the 3mm section of the brass bolt is also likely to be at a temperature very close to this. So you end up with the whole 50mm bolt length of molten/semi molten plastic as opposed to most hot end designs where only the heater block height is expressly designed to be molten. This seems like a lot of extra resistance to me and the potential for both major blockages and more difficult filament changes (say from one colour to another). Does this cause a problem in practice? What are the operational advantages that you see with this design?

ok. well try it i get at least 150mm/minute with 0.4mm nozzle. this is with a bowden cable design. probably will push 200mm/s with regular design, but lets get this sorted out. I'm game for comments and reason here.


the benefit is reduced force, not more force. you got to think amount of hot surface exposed to feedstock. feedstock more quickly reaches melting temp, the viscosity changes from a rubbery state to liquid state and moves easier.

you could easily push feedstock thru by hand into a 0.4mm hole.

i could run at 70mm/m with old nozzle style, and with new 150mm/m flow-rate

I don't have a formal way of testing it currently, but your thought are welcome into methods i could try. thanks.

currently i am using an aluminum nozzle drilled to those specs to 3mm, 2mm,1mm and 0.4mm, then a 6mm hole for ptfe tubing, as long as the tubing stays flush against the brass or whatever you are using, then the hot zone is contained. I should also change the drawing to reflect a little metal going past the ptfe as a sleeve. thanks.

i am making some brass barrels and also getting nozzles from maker gear to test 0.25 and 0.35

Edited 2 time(s). Last edit at 10/05/2012 07:23AM by jamesdanielv.

What's it like printing slow? and how much ooze when not printing - at temperature with feedstock fitted. Long melt zones usually give me lots of ooze, but can be good for really fast printing.

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it prints consistent at slow speeds and high speeds.

it does ooze a little, but retraction stops that. how much do peoples nozzles ooze without retraction? i need something baseline to compare against. and this is also being used on a bowden machine currently.

perhaps I'll do a video in the next few days.

anyone want to post a video of there extruder starting and stopping for comparison? it needs to be 3mm feedstock, and I need to know the start speed and length extruded

Edited 2 time(s). Last edit at 10/05/2012 07:51AM by jamesdanielv.

ok, diagram is updated. includes head block. also i don't necessarily think it is needed for 3mm,2mm and 1mm step down size sections to be the lengths I gave them.


when my design is primed and left idle it oozes for about 40mm of filament, when retraction of 3mm is used no oozing for about a minute. that seems about normal. Also this is in a bowden designed system so there is always the spring action of the stretched cable.

Just a small addition to this design. It's quite good but you must remember that the plastic expands upon entry in the first hot area. This needs to be large enough to accomodate that beyond the liner which is slippery enough to contain and funnel it.
1.75mm filament needs a melt chamber of 2mm and 3mm filament requires 3.4mm to avoid breaking against the walls.
Try it and you will see your feedrates go way up with less force.