Hot end blocks

Hi!

I finally finished building my own 3D printer. I have calibrated everything, and it's almost ok.

However, now I would like to print a test cube (40x40x40mm). However, I still have a problem with my extruder (hot end). It always blocks after a while, sometimes after 1 layer, sometimes after more. The temperature is perfectly OK. I am using PLA.

Is there anything I can do to better investigate what might be causing this blockage? It is quite difficult to continue, as the printer does not printer reliable...

Thanks!
Steph

What type of hotend?
Actively cooling heatsink fins?

I forgot to mention this :-)

I use the following hotend (0.4mm hotend):
[www.aliexpress.com]

It worked OK for quite some time, but since a week or two, it completely blocks after a random time...

It has a fan to cool the cold end. It is running continuously.

When I extract the filament, and then reinsert a new one, often I can continue. Sometimes however, I physically have to push it through.

Thanks for all suggestions!
Steph

Try taking apart and cleaning.
Or carefully clean with 3mm long bolt and push in while hot

Try heating 10-20 beyond the PLA limit to FLUSH the system

I use them. Take it apart and replace the inner PTFE liner 4mm OD 2mm ID. Should work, but measure yours just in case. Most likely it melted on the lower section restraining the filament flow.

I damaged mine extruding nylon. Don't go beyond 260.

Edited 1 time(s). Last edit at 10/21/2014 10:54PM by ggherbaz.

Hey! Sorry for the late reply, but I am only able to work on my 3D printer in the weekends and I wanted to give you full feedback...

I took the hotend apart and cleaned it. The hot end consists of the nozzle (brass) and a nozzle throat that does not have PDFE (I lost the original PDFE lined throat :-( ). I will replace the throat with one lined wid PDFE, but that will take time. The current one is a design like this one.

The strange thing is that when I flush the system using the software (just let the extruder run on its own for a few minutes), it works fine. All extruded material comes out quite nice. But when I start printing something, after a few layers, the whole thing blocks The temperature is OK, but - sometimes - I see at the location where it blocked a brownish deposit. The filament is white, so this seems to be some kind of pollution. Anybody experience what might cause this?

I keep on trying, and will replace the nozzle throat. Sadly I do not yet have a spare nozzle... Once I have that, I will fully clean everything and start over.


BTW: I understand that it is possible to dissolve ABS. Any idea if there is a way to dissolve PLA as well, to fully clean nozzle throat, nozzle and heating block?

Thanks!
Steph

Yeap, I did the same and doesn't work, all metal barrel will clog quickly, the orifice is too big and PLA expand too fast, since the barrel itself isn't actively cooled the filament will stick to it. You can try to polished it, but you may risk making the diameter bigger and make issues worst. If you can, just drill the barrel with a 4mm drill bit and put a PTFE liner.
To clean the barrel used a small butane torch and heat the barrel until Filament melts and come off, then just use a 2mm drill bit and manually scrappe and residue.

Hey!

Thanks! That sounds like a logical reason why my extruder blocks. Indeed, when I extract the blocked filament, it seems like the filament has bloated a bit in the nozzle throat. This agrees with your reasoning that the nozzle throat is only partly cooled and a bit bigger in inner diameter.

As for the cleaning, I hoped it would be possible with some kind of solvent, but indeed the torch is a good solution as well.

Thanks again!
Steph

good chance the brown stuff is burnt plastic (thus the discolouration)

by removing the PTFE there is nothing to fill that space....except melted PLA.
so you've got a big "bubble" of PLA and trying to push it out with a thin stick (the PLA filament from your extruder). While the continuous heat on the outside layer of PLA dries and burns the polymer.

But the PTFE is supposed to insulate the Filament from the metal parts a little bit, so that the pressure from the filament will force the tip of the filament against the _little_ bubble & heated tip of your hot end. This gives it a consistent melting rate and pressure for nice even flow.

With too much room, the filament will just hit a pool of mostly molten (and partly burnt) PLA, and soften and melt. I'm thinking the retraction process is whats unsticking the burnt PLA, and then it acts as a contaminant until your nozzle blocks. The filament design isn't orientated to pressurising a bubble of liquid like an inkjet or icing bag (or pellet printer), They're more like a hot glue gun when the solid glue melts at the tip and solidifies quickly.