Good detailed description!
From: WThM de Groot Sent: Wednesday, September 26, 2012 06:48
The thin neck part in the brass connection to the peek in the V2 design has
been introduced to act as a heat transfer barrier to the peek and to the alu
plate, which remains much cooler now.
Consequently this part of the brass inside the peek is somewhat colder than
the alu block and the nozzle itself, especially when a lot of cold filament
is transferred into that part as well.
The Teflon part in the V2 is well fixed because of the 10 mm wide rim
between the wood and the peek and that is major reason why previously
occurring unmovable plugs are not being formed anymore.
The Teflon part with an inner diameter equal to the bowden diam. (3,2mm) or
preferably slightly less (3,1mm) should be the place where liquid and solid
filament exists side by side.
(In fact that is the movable plug inevitably being formed (pressure induced
back flow, filling the full 'diameter' of the Teflon insulator).
It is movable because of the low friction of (well drilled) Teflon inside
The length of the this movable plug and the place where in the insulator
this is formed depends on a number of parameters like the local temperatures
and the feed-in and flow out of filament.
It will be close to the brass end and shorter with average fast extrusions.
It will move to the bowden end and gets longer with very slow average
But that movable plug is easily pushed out from the Teflon part into the
brass part where it melts again and also fully.
If the feed-in of filament of the system is very high or requires a lot of
heat for temperature increase and melting (perhaps with ABS more that
withPLA) this movable plug tends to shift into the colder brass part inside
the peek, where it melts too slow and sticks to the brass surface. Hence too
much resistance and consequently grinding of the filament feeder.
It is also important that the Teflon insulator is well supported by the
peek. Peek material has better mechanical strenght characteristics than
Teflon (so a snug fit of the Teflon part in the peek is required).
It should not be possble to blow up the teflon part.
It also is important that the Teflon passage and the brass passage are
nicely concentric and that the plug from the Tefon part fits nicely into the
brass tube (3,2mm) .
I have got such an Teflon insulator in the hot-end in my Ultimaker for over
a year now and had to replace it recently because the teflon passage
increased to > 3,2 mm. (Blown up or some wearing?)
I tapered in the lathe the entrance to the brass pipe slightly from 3,2 mm
to 3,4 mm, in order to have an easier entry of the brass tube.
A further inprovement to my mind, expecially for very fast printing or ABS
would be a less thin neck (e.g. 5mm diam.) but at the same time a shorter
thread of the brass in the peek (currently 11 mm).
Mechanically 5-6 mm length would be sufficient and I applied this in a few
The higher heat transfer in the thicker neck is compensated by the shorter
The temperature of the peek and of the Teflon part should be low while
preventing a too cold brass end in the peek.
May be you have to reread this contribution a few times to fully understand
what I wanted to say and what I think is happening in our hot-ends.