Removing old filament? Stuck!

Hi guys! So I purchased the Prusa Mendel i3 from Monoprice (or at least it's a Prusa Mendel clone?).

I'm trying to figure out a problem I've had....

Since there is no way to tell the machine to back out the old filament (at least on my printer), you have to manually control the forward/backward of the filament feeding using the knob on the control box. When I back it out as far as it will go (with the printer head heated up) it will only go so far....then stops. No matter how I tug the old filament won't come out. I can feed it back in, and then feed it back out to a point, but the damn thing is completely stuck. I push down the feeding lever. No luck. I leave it alone. No luck. I'm flabbergasted. I don't want to break the thing, yet it seems like it should come out easy.

There is no community for this specific printer yet, but since this seems to be a monoprice rebranded prusa mendel i3, I thought I would come here for advice. If I am in the wrong place, I apologize! I am a newbie to 3d printing, and don't want to break my machine.

I've never had that problem with ABS, but I recently started printing with PLA and ran into the same problem when trying to change the filament. Several solution were posted, including heat up the hot end, grab the filament with a pair of pliers, release the pinch wheel tension and jerk the filament out of the hot end. I tried Ultimaker's method which was to heat it to 80C and then retract and it jammed up tight. I haven't tried the pliers method, but I'm guessing it will work. I think the extruders should be designed with a break in the feed tube leading to the hot end that will allow you to cut the never-melted filament and easily remove it, then start the new filament feed and have it push the short piece of old filament through the hot-end and out the nozzle.

Edited 1 time(s). Last edit at 12/18/2015 04:07PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Wonder if it's formed a plug that won't go past the hole in the extruder arm. You might have to take that fan/heatsink off of it so you can see.

post a picture of your extruder setup. My filament WILL NOT come out until i manually turn on the extruder through Repetier, and push down on the white springed tension thing. When i do that it comes out effortlessly.

To figure out if you have a huge blob stuck, try manually feeding the extruder a solid amount of filament to squirt out on the bed. If it does, there is no blob.

I finally managed to get it out after much tugging. It was stupid. I had the dang thing heated up to a fairly high temp and was still not able to pull it free. What a pain in the butt. When I DID get it out, it was thinner at the end, as if the temp had caused the plastic to contract/expand and make it impossible to pull the old stuff out.

I had a similar thing with my Chinese "E3D" hot end. Pulling out slowly jams up inside the hotend. What works for me is to heat the hotend to normal extrusion temperature (190 for PLA), release the tension, push the filament down until it starts to come out the nozzle, then quickly pull it out of the top of the hotend.

If it is not an original you have a good chance that the melting chamber is a bit oversized.
This goes along with the problem of edges and corners in the "cold" end / heat break.
There are only two ways that worked for me until I fixed my hotend for good:
a) Instead of forcing it out you use the new filament and feed it through, which won't really work in bowden systems.
b) Turning the fan on the hotend off and heating it up until the cold end is actually very hot to touch - this only works with high temp plastics if you have no teflon liner or can stay below 250° C.

Those troubles are one of the reasons I abandoned the bowden system on my printer.
Really only see the benfit for printers that are too small to hold an extruder on the carriage or these delta printers as they are usually quite limited in space anyway.

I use DD's mentioned method with my Prometheus V2. 80c and retract. Pulls out right to the tip.