I took my replicator's dual extruders completely apart last night. I couldn't really get a picture of how deeply disassembled they were because it was just a mess, but my point was getting a look at those potentially troublesome Delrin plungers. And here they are:
It's difficult to see, but what they've got I wouldn't exactly call a "groove". More like a scratch. I'm surprised if that would be enough to prevent the extruder's teeth from getting a good bite.
A little bit of education. Delrin is the plastic that those little parts are made out of. The point of those little parts is to press on the other side of the incoming filament to make sure the extruder gear can grip the plastic and push it into the filament head where it's heated and squirted out. That plastic is supposed to be tough as steel, or darn near. So why, after only a couple of months, would that be the problem?
I'm not convinced those little scratches are the problem but if they are there are a few solutions. Buying replacement plungers is one. Upgrading the whole assembly with metal bearings that roll so they don't wear down is another. Painting the top of the plungers with clear nail polish to fill in the grooves is another. Actually, I'm just hoping that'll work because that was my hack solution last night before putting it back together. To tell the truth I'm not holding out much hope but if it can just work for long enough for me to get the parts to do that upgrade I'll be happy.
Then, while I was putting everything back together...