How to "refill" filament when it runs out?

Maybe this varies by extruder design... Mine's a direct drive (Folgertech Prusa I3).

I think I did it wrong. I was going to start my second print and knew there wasn't going to be enough -- I had almost used up the 250mm ABS sample from the kit, doing my first print and all the blobs that preceded it. I cut the filament flush with the top of the extruder, heated the extruder, and manually extruded some length. My thinking was that this would take the old filament at least most of the way into the nozzle, and then I could feed the new filament in, manually extrude, and it would all get melted and pushed through, and I'd be good to go.

I'm not good to go.

Once the old cut filament got past the extruder gear, it stopped moving (which I would have realized if I'd thought it through first!) and blocked the new filament from feeding. The picture shows the cut end sticking out of the nozzle feeder tube.

I took the fan and gear housing off and pulled the end of the old filament out of the tube with pliers. That left about 5mm in the tube above the hotend. I was hoping that when I heated it up again the new filament would push it through, but it's still stuck.

Is there a way to clear this now, or am I well and truly screwed?

And what's the RIGHT way to do this? Thanks.

I found instructions for just this problem (cold clog) at solidoodle and got up and running again.

"Clogs can be extremely frustrating!" At last, someone understands my pain!

I´m surprised, how huge the gap between the gear and the tube is.
My tube sits right under the gear. This way the extruder can push the filament through, even when it gets pretty soft.

That won´t help against clogging, though.

I´m not an experienced printer, but when I change filament, I loose the tensioner screw and pull out the still hot filament. ( Do it fast in one motion )
In 9 of 10 times, I have to remove the fan and heatsink to feed in the new filament. It works better for me, when I see what I´m doing.

-Olaf

Edited 1 time(s). Last edit at 05/25/2015 03:23AM by o_lampe.

It sounds like you have a geared extruder. Mine's direct drive, and there's no tensioner. I guess this design leaves that gap too. I've seen some that have a plastic tube in the gap to help guide the filament, but this one doesn't.

I heated the hotend and pulled it out as you said, but then I still had to push the last bit down far enough so it would melt and the new filament would feed.

Now -- what about when I want to switch from ABS to PLA? What kind of deep voodoo does that require?

When removing abs (to switch colours) I heat my hotend to about 190, which makes the filament soft, but not molten, then pull it out with tensioner removed. This seems to be the best way I have found so far for getting the most material out without damaging anything.

The success of this method may depend on the hot end internal profile.

You could also heat the hotend up to ABS temperature and manually push PLA through it, until no ABS keeps oozing out. Then pull back a little ( 4-5mm ) and let it cool down.

With good cooling at the coldend, this shouldn´t be a problem
-Olaf