I learned my lesson the hard way.

I tried some bad filament that got stuck in my budaschnozzle hot-end. I used my old trick of heating the hot-end to pull the PLA filament out at the top.
For some crazy reason, I left the heat on for a few seconds and tried inserting the new filament in.
The hot vapors/air from the hot-end heated the PTFE tube in the meantime. When it came in contact, it melted PLA plastic filament inside the 3mm PTFE tube. It clogged up the hot-end in a very bad way. No heating/pushing was enough to dislodge it.

I had to go through a lot of tricks (drilling into the filament) to dismantle the hot-end (PLA got smushed due to heat and pressure and held it together firmly) to get to the PTFE tube, and then to get the stuck filament out of the ptfe tube.

Lesson learned: NEVER leave the hot-end HOT for inserting new filament into it. No matter how much easier it slides in, it will get stuck in a few seconds at the PTFE portion!

Which version of the hot end? What temperature did you have it set to?

I was under the impression that changing the filament could only be done while the hot end was hot. I would do it quickly, push forward on the old filament by hand slightly and then withdraw to get a nice "lump" at the end instead of a long spider-silk thread, then quickly insert the new filament and push by hand until I see some plastic come out the nozzle, which would generally be the old color. Then clamp up the extruder and extrude into free air until the color change is complete with the old color flushed out. I would do this at 185C because the PLA was pretty thin at this point and I wouldn't need to go hotter, and I certainly have everything set up and ready to go instead of letting the hot end linger at temperature.

Tugging on the filament when the hot end is cold just plain isn't going anywhere.

This was with a v1.0. These days I'm trying to use up some plastic I'm not too happy with so I just push the start of the next coil along with the end of the previous coil, sometimes even during a print, so I actually haven't had to remove any filament for changes in a while.

You want to lower the hotend temperature to 170 for ABS and 100 for PLA according to Whosa whatis before pulling the feed.

After two years of printing PLA with home made hotends and J-heads I have never had an issue like this. I have let my hotends sit hot for a long time before changing/loading/unloading filament.

If the PTFE is getting that hot you need some cooling on the thermal barrier or a better hotend.

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Ive read and I use a fan to blow across the nozzle all the time to disrupt the convection currents which make the cold end heat up. This clogging problem can also happen when the fan is not on an it's a long print. The heat creeps to far up the chamber and makes the pla expanded to early which catches.

I am using Buda v1.2 at 187C (3mm Silver PLA from ProtoParadigm) and 190C for first layer.
I think I left it open (hot at 187C) for a minute when I had the problem. I suspect (do not remember) the fan was off that time. I was plagued by bad filament issue with a previous vendor (OnlineFilament.com) who shipped PLA filament to humid FL in a tattered plastic bag. That filament was always getting stuck - no matter what.

I do heat the hot-end to remove PLA filament out. However, to replace it with new filament, the best solution that works for me is to let it cool down to room temperature and insert the new PLA filament in. I just have to rotate it by 90deg if it catches on anything in the hot-end and I do verify the length of the filament in the hot-end by pulling it out 1 time.
Extrusion in air is the next step to confirm it is extruding.
I also poke the bottom of the nozzle sometimes (twice todate) if I do not see filament ooze when it reaches 180C.

peddiparth Wrote:
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I just have to rotate it by 90deg if
> it catches on anything in the hot-end

This is your problem. There should be nothing for it to catch on. If there is that means you have a gap between the ptfe and heater barrel.

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Sublime Wrote:
> This is your problem. There should be nothing for
> it to catch on. If there is that means you have a
> gap between the ptfe and heater barrel.

Actually, this is a Budaschnozzle v1.2 problem as there is a small gap between the hot-end and wades extruder.
I have tried using a small (custom) 1/2" PTFE tube with 3mm hole to plug this gap.

Edited 1 time(s). Last edit at 11/20/2012 08:31PM by peddiparth.

You can also print one out. But a 3 mm hole is too small for a 3 mm feed. You should make the hole at least 3.5 mm. You can also print a Wade's extruder without that hole for that's meant for mounting a J-head or Makergear hotend by modifying the openscad file.

I agree with Sublime. I've inserted feed many times into a hot nozzle and I've never had it get stuck.