Alternate Extruder Design

[Rick]

Two of my extruders have been destroyed when the teflon threads gave
way. In one instance the temp was around 240C but in the other
instance the temp was only about 210C but the bot had been printing
continuously for approx. four hours.

After the second meltdown

http://www.flickr.com/photos/makergear/3948098514/

I created an alternate design that uses the teflon rod as an insulator
but not as a structural unit (not threaded)

http://www.flickr.com/photos/makergear/3948315803/in/photostream/

As you can see - two nuts are used to lock the lower washer into
position and compression is used to hold the teflon rod in place. The
teflon is not threaded, the brass rod simply slides in (i think i have
it going in about half an inch) and the top ~0.5mm of the teflon is
turned to fit into the washer and press against the acrylic. There is
one layer of ceramic tape between the upper washer (connected directly
to the acrylic) and acyrlic as a precaution. The two long screws
(stainless, have not tried black oxide) seem to do a good job as
heatsinks as the upper portions of the screws are not getting hot
(running for a while at 210C).

This approach uses two washers (one with four holes), two M6 nuts and
a small piece of ceramic tape. The acrylic piece used to attach the
lower washer the upper unit is no longer needed.

[TeamTeamUSA]

Interesting design.

Did you have to change the dinos to accommodate the increased overall
length/height of the nozzle/barrel assembly?
Have you been able to continuously print longer than before?

Go!

=ml=

[Rick Pollack]

I saw this after posting here
http://www.thingiverse.com/thing:1031

Good info. Will update after further testing.

[lichy]

Hey Rick,

after the same crashing as you I'm thinking about a little different
solution.
Instead of the ring above you can use a nut.

http://www.flickr.com/photos/mlichy/sets/72157622446044082/

Question: Why are you using PTFE? Only, because it has low friction or
about thermal aspects?


On 24 Sep., 16:09, Rick Pollack <rick.poll...@gmail.com> wrote:
> I saw this after posting herehttp://www.thingiverse.com/thing:1031

>
> Good info. Will update after further testing.
>

[Zach 'Hoeken' Smith]

I think you can actually even simplify it further....  just an M6 nut on the heater barrel between the PTFE and the washer.

really all you want to to is to remove the need for the ptfe to hold the heater barrel in place.  the large washer already holds the heater barrel assembly in place, and it works pretty reliably at that too.  by putting a nut on the heater barrel above the washer, then it is not just holding the PTFE in place, but the heater barrel as well.  no new forces are added to its load, since before it was holding the heater barrel by virtue of holding the PTFE barrier.

anyway, i'll give this a try and see how it works.  we should probably toss in an extra m6 nut in the plastruder kits too... pretty easy fix. :)

Zach

[Zach 'Hoeken' Smith]

one more thing... what is the nozzle you're using on the end of that extruder?  if its a custom design, its possible that it needs more pressure to extrude with, thus putting more load on the PTFE leading to failure.

regardless, the main problem is that the PTFE threads aren't a good mechanical connection and shoring that up with a nut is a good idea.

On Wed, Sep 23, 2009 at 6:49 PM, Rick <rick.p...@gmail.com> wrote:

[Tox]

This is actually what I did with the most recent rebuilds. Last
rebuild I also added a copper sheet between washer and nut to help act
as a heat sink to shorten the melt zone. So far (8 hours runtime) it
seems to be doing the right thing. (This on the formerly balky
extruder)

Tox

--
Scott Small

[Zach 'Hoeken' Smith]

I'll try to rebuild an MK4 extruder this weekend and document this upgrade.  I need to retake a few pics anyway, so it will be a good excuse.

Zach

[Rick Pollack]

@lichy - using PTFE as I was trying to find a very basic modification that would solve the immediate (meltdown) problem.

@Zach - good eye! that is not exactly an extruder (pictured with the upgrade)...it is hand-held plastic injector (like a glue gun) that I'm experimenting with. The nozzle has a wider opening and it is functional - need to put a faster motor on it.

My 0.5mm nozzle extruder (the one in the meltdown photo) is standard MB issue and for the most part it works fine. However, I needed to print a bunch of stuff and after a several hours of continuous printing it broke. I think it was the combination of heat and vibration resulting from the filler between narrow walls (a lot of vibration). Adding one M6 is probably enough but after switching to the two washer approach, I now prefer it (eliminating the upper acrylic mount).

I've upgrade my experimental 0.4mm nozzle using one M6 and a 2nd washer: http://www.flickr.com/photos/makergear/3951520841/

Have had a lot of trouble getting this to extrude consistently...hope this helps.

[Zach 'Hoeken' Smith]

cool.

we also had lots of trouble getting 0.4mm nozzles working reliably.  i think it is some sort of threshold diameter that puts us up against the limits of our machine.

i've been doing a ton of work on extruder prototypes lately.  hopefully some of them will be coming to fruition soon.  i think i'll post the latest prototype extruder design on thingiverse here soon.

Zach

[Bo Lorentzen]

Zach,

YEAH,  looking forward to extruder rev2 shipping form the store.   

  Bo

[rbisping]

I had suggested the adding a nut between the washer and the ptfe
myself but found out that the heat transfer up the washer and holding
nuts to be a issue. and that i couldnt get a stable and reliable temp.
I may try it again now that i have the new barrels and insulators.

> > lower washer the upper unit is no longer needed.- Hide quoted text -
>
> - Show quoted text -