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I have always had good luck with the fixed QU-BD extruder and ABS. I initially had decent luck with PLA, but now I am having a lot of trouble it and usually don't get through larger prints.

I heard the rough barrel causes some of the problems, but I polished a brand new barrel and still have troubles. If I run really hot (like 235) I can usually get through a print, but don't get a very good print around horizontal holes and bridges.

Sometimes the filament is stuck and sometimes it pulls out rather easy, but has a notch cut in it. I tried playing with speeds, acceleration and retracts. The upper barrel is cool to the touch and the motor is cool too. I may try to increase the pressure on the idler next.

ABS works fine.

Ah, see my thread on jams. I haven't had any luck with PLA at all. 0 success. I'm very disappointed to hear polishing the barrel didn't work. I just got some diamond paste and that was the next thing I was going to try. After that my next stop, if I continue wasting time, was going to be drill the barrel out a bit and get line it with a ptfe sleeve.

I haven't tried ABS, but I'll give that a go tomorrow.

I used polishing compound and string to polish it. It is had to tell how well it worked. The original unpolished QU-BD tube was actually working better.

I almost bought a 2mm reamer from McMaster (~$12).

ABS never fails.

PLA is all that I've printed with so far. I use a very strong spring though. Retract is .5, speed is 100 and temp is 192.
When I tried ABS, I couldn't get it to stick to the bed. I only played with it for a few minutes and gave up and went back to PLA.

Rodney

With ABS I use hair spray to make it stick and a chisel to get it off.

The only issue with ABS is the shrinkage. It never completely unsticks, but long parts can peel up in the corners. The brim feature can help cure that.

I got my first qu-bd to work reliably (with PLA, I haven't tried ABS yet) by drilling the filament barrel out to 2.4mm and replacing the nozzle with their newer .4mm version.

My suspicion is that drilling out the barrel is what did it, but I don't have any data to back this up.

When mine jams, it seems to be because the filament is swelling up in the portion of the barrel between the heater core and the chassis block (i.e. the part that isn't directly heated or heatsinked). Drilling it out gives you wiggle room on the swelling, and might also slow the heat conduction down.

I have a second qu-bd that I've been trying to get working (was jamming like the first in stock configuration) but I've failed twice now trying to drill the barrel out with my rudimentary tools and technique (guess I was lucky with the first one).

I'm sort of interested in trying to shorten the unheatsinked portion of the barrel.

Interesting. I was worried that melted material was flowing back up past the filament. A bigger diameter would make that worse. That puts doubt in my theory.

I'm going to be making some of my own barrels and I'm going buy or have made a 2mm tapered pin reamer That way if it jams, it will still extrude with the slight taper. My theory is the heat moves up the barrel when its not extruding and melts the filament and then the fan cools the barrel and the plastic setup. I hope with a taper when is happens, it"ll still extrude.
Rodney

I was following a hunch that the problem was material backing up in the tube and hardening, I lowered the retract and it is now working on 3 consecutive prints.

At ORD Camp I let anyone play with the delta and it appear someone changed my Hadron slic3r setting. The retract was set to 2mm. It was previously 1mm. That might explain why it got worse this week.

I set it to 0.5mm retract and so far...so good (fingers crossed)

Based on other forum posts I'd set my retract to .1mm and 30mm/s. I'll try moving up to .5 before trying abs. What speed do you have?