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Wade's extruder stalling

Posted by jsadusk 
Wade's extruder stalling
January 26, 2011 01:49PM
I've been working on my mendel for a long time, and I've gotten it *almost* working. My axis are pretty accurate, my extruder seems to consistently draw in filament, but I have one remaining problem. It seems that my extruder will randomly just stop spitting out plastic. I've checked the filament and it looks like its still being drawn in, but no plastic comes out for around ten seconds. Also immediately after this happens it seems that plastic will continue to come out for a few seconds after the extruder tries to stop the flow. Its almost like there's a momentary jam which bursts out once the pressure builds up.

I've tried playing with temperature and feed rate with no change. This is especially a problem when it happens during infill on the first layer. Since plastic stops coming out, the head starts catching on already laid down threads and pulls them off the bed.

I'm working with ultimachine black PLA, I have a Wade's extruder with a PTFE thermal barrier. I've tried temperatures between 190 and 210 with no change. Does anyone have any ideas of where I can look?
Re: Wade's extruder stalling
January 26, 2011 04:12PM
Check where the top of the barrel meets the PTFE. Unless the PTFE is well constrained it will tend to expand and allow plastic to leak around the threads, as well as push the barrel out slightly. This can cause a plug to form at the top of the barrel and won't allow plastic to flow well.

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Re: Wade's extruder stalling
January 26, 2011 06:52PM
Can you post any photos of the extruder, showing the nozzle, insulator, and extruder body? I'm curious as to what's happening there; the type of hot end mount might be significant.

I had an old 0.6 mm extruder that used to jam occasionally; there seemed to be some crud blocking the nozzle. Poking it with a 0.5 mm pin would clear it temporarily. More likely it's a problem with the barrel to insulator interface, as NewPerfection pointed out.

Re: Wade's extruder stalling
January 27, 2011 12:43PM
I took the extruder apart last night and unscrewed the barrel, and I didn't see any plastic around the threads. The barrel was filled with plastic, but I didn't have the heater on when I backed out the filiment so I guess that's to be expected. Even s, to make sure it was constrained I put a hose clamp on the end of the PTFE when I put it back together. I didn't have time to try running it again, so I'm not sure if it helped.

I'll take some pictures of it tonight, though its all wrapped in kapton so I'm not sure how much you'll get from them. If it helps, the PTFE, barrel and nozzle are all Makerbot MK4 parts. I can try clearing the nozzle though. Did you have the heat on when you cleared it?

Thanks for the help!
Re: Wade's extruder stalling
January 31, 2011 05:49PM
So, thanks for the help you guys, I think I have it working pretty well now. While I had the extruder apart I noticed that the hobbed bolt had one small patch where the teeth weren't cut as deep as the rest. I recut them, and some combination of that and the hose clamp around my PTFE seems to have completely fixed my problems.

Now on to deal with the fact that my Z-axis is slightly off square...
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