Can't get extruder to work properly

I'm having a devil of time with my extruder. I don't know if I'm not getting it hot enough or if I'm getting too hot. I'm trying to figure out where to set the temp to get a good flow. I'm manually pushing the filiament through. I can get a little drool but only if i really push hard. The barrel is coming loose from the PTFE so I need to fix that. I started it at 220 and went up to 255 by 10's and 5's. At 255, it was coming out a little brown so I lowered the temp but I can't get a good flow. I can only get a really slow drool. It doesn't look like any of the videos I've seen. I've tried several things but can't get it to work. I'm setting the temp with the RepRap host software. I'm probably going to have to take it apart again and drill out the melted plastic.

Any suggestions would be appreciated. I've already built this thing 3 or 4 times.

I took the extruder apart and drilled out the barrell. Like I said, I have red ABS but what I drilled out was kind of a grey substance and it was kind of crunchy like it had been crystalized. Does that help in determining what I'm doing wrong?

Sounds like it was too hot. Did it smoke? ABS normally starts to degrade around 260C and go brown around 280C, but I have never tried red, so that may be different.

The other way you get hard crunchy stuff is if the plastic is left hot for a long time exposed to air.

If there is a gap between the end of the brass and the PTFE then it will be very hard, or impossible, to push plastic through it because soft plastic expands into the GAP and jams.

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[www.hydraraptor.blogspot.com]

I had used some teflon tape on the threads so I would think there would be a nice tight fit with the PTFE. However, when I broke it down there was a plug in the PTFE that I had to drill out. So, do I need to screw the brass into the PTFE tighter?

There was no smoking, it just gradually got browner. As long as I had it around 230 or 235 the color was good I just couldn't get a flow I still had to push pretty hard to get even the drool to come out. Should I try setting the temp aroun 180 or something and going up from there?

Since I had to drill out the PTFE, will that make the hole too big? I'm not sure it's a nice smooth track any more. I had to work the drill bit some to get all the plastic out.

Edited 1 time(s). Last edit at 08/03/2010 09:33AM by bbriggstkd.

I use 220 - 240 for ABS. I find it a bit too stiff to extrude reliably at 180.

If you are not able to fill the barrel with plastic to exclude the air then it will eventually go hard if you leave it cooking for long enough. It doesn't normally go hard at 255C when there is no contact with air. Perhaps your temperature control isn't accurate.

If I drill out an extruder I use an undersized drill to prevent enlarging the barrel. It would be easy to damage the PTFE though as it is very soft. I always start at the brass end and do it with the heater on so the plastic is soft.

You do have to push hard to extrude at a reasonable speed, 5Kg would not be unusual.

If the hole in the PTFE is too big, or the join to the brass is not seamless then it can jam solid or require massive amounts of force. If your nozzle is separate try pushing filament through without the nozzle attached. If it jams it is a sure sign of a gap where the brass meets the PTFE.

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[www.hydraraptor.blogspot.com]

I did what you suggested and left the tip off the brass tube. I was able to get it to melt several inches of plastic. I started at 200 the 205, 210 and finally 220. I also tried white ABS in addition to the red ABS. It might have been my imagination but the white seemed to melt and push through easier. As the temp went up the red seemed to melt a little faster and flow a little smoother but the color also turned a little darker. A little brown. It also smoked a little at higher temps. My temp may just be off.

I'm going to let it cool down then put the tip on and see what I can get.

I put the tip back on and heated it up to 210. As I was pushing the filiament through, and getting some out of the tip, the barrel slipped out of the PTFE again. I didn't think I was pushing that hard either. Is there a good way to secure that or do I need another insulator piece? I can put more teflon tape on it but that may not be strong enough.