Filament feed issues

I've had two long prints fail on me because the filament gets stuck and the extruder just grinds it down. Aside from losing 650mm of filament, I also can't leave the printer for any extended length of time because i'm worried this will happen.

I've got an acrylic case and printed the spool holder which holds a 2lb Protoparadigm spool nicely. Extruding generally isn't an issue, but I've noticed it starts binding during retracts. If I look at the hole in the case that the filament runs through I can see it's actually been worn down where the filament crosses the front of the case and comes in the hole. It appears that notch has just enough grip that when the extruder retracts, the filament binds there and instead of moving backwards through the hole it bows out between the inside of the case and the extruder and it actually physically pushes the case apart at that corner (you can see it separate and hear the acrylic squeak). Eventually it seems that this stops happening and the extruder can't grip the filament well enough to push it back so it just starts grinding on it. At that point no more filament comes through and I stop getting new layers.

If I move the spool to a different spot so that it doesn't cross along the front then it feeds and retracts just fine (no bad angle through the hole), but it's not an ideal solution since I have no good place to put the spool so that it will feed nicely and instead have to constantly remove loops of filament from the spool so it can feed it in. I've tried putting the length of teflon tube on the filament as it enters the case but it's flexible enough that it follows the curve of the filament and the filament binds anyways.

Any thoughts? I'm envisioning a two sided spool holder that can still attach to the case for transport/storage, but that can pop off and stand freely in front during a print. That's a bit overkill and I think detracts from the design of the printer, though. Would just drilling out the hole in the front of the case do the trick? Seems like it would put the filament at a sharper angle and eventually suffer the same problem.

Edited 1 time(s). Last edit at 08/29/2013 09:39AM by maik.

I would suggest the following:

- Move the spool slightly away as to have the smallest angle in between the filament entry path and the filament path to the extruder.
- If the size of the opening for filament is indeed too small, do make it bigger by gently drilling... gently, otherwise you could end up with a cracked case.
- Make sure edges of the opening for filament are smooth on both sides - outside and inside. You can use a small file to help you out.

I thought about using a 20cm teflon tube at the filament entry into the case myself, but never had any problems with the entry so the idea was forgotten. In order for this trick to work you would need to actually put the teflon sleeve through the opening, and that would require drilling.

Good luck

I just noticed the same thing last night and drilled out the hole in the front panel and glued a short piece of PTFE tubing. It appears to work great.

Thanks for the suggestions! I'll try and round out the inside edges a bit so it doesn't have anything to bind on. If that doesn't work I'll go with PTFE lined hole.

Another thing you might want to do is make sure you are printing at high enough temperature. I was having a similar issues, retracts would kill the filament. Sublime suggested to increase the hotend temperature, and it solved my filament stripping issues.

Check out the Tantillus calculator. (The link is from Sublime's signature.)