Extruder keeps jamming

I bought a used Mendel, so I'm not sure what all the parts are that are in it. I'll attach a picture of the extruder and hotend.

The extruder looks like a Wade's geared extruder. The hotend appears similar to the J-Head MK V-B. Its square brass about 13 MM x 13 MM. I don't know the size of the opening in the nozzle. I see common sizes appear to be .5, .35, and .25 MM.

I have issues with the nozzel jamming up quite a bit. I can sometimes get one print to work well, then the next ones it won't extrude any material. Most of the time I can clear it by removing the nuts, springs, and the block with the bearing, heat the head up to about 160 degrees C and pull the filament back by hand. It usually comes out with the end deformed, sometimes as a big blob. Then I can heat the head up to 185 C and usually push the filament through by hand until some material starts coming out the bottom. Then I reassemble the bearing block, springs, and nuts. It will usually work for a while and then stop advancing filament.

This is my first 3D printer and before taking the hotend out to soak it in acetone or anything else I want to make sure I don't break anything. Any tips would be greatly appreciated.

Hi, another newbie here going through similar problems allthough on a prusa i2 ive built myself.
With a similar j head.
Ive just started to get mine to print but was experiencing the same problem.
It looked like the filament was sticking and not extruding enough during a print.

It turned out to be the cool tube leading down to the hot end getting too warm because Cura was not turning on the fan to keep it cool.
So the first short print was ok but the next print it got too hot and stuck.
When i turned on the fan myself to about 50% power. It was enough to keep the tube cool and stop the filament from sticking.
Also im using 210c for black pla. Maybe you also need to turn up the temp of the head a bit as well as cool the tube.

Also read that a drip of olive oil on the filament, as it goes into the extruder, occasionally also helps it not to stick.

Good luck
Gordon

Edited 1 time(s). Last edit at 08/17/2014 06:45PM by gordonendersby.

If you don't know the nozzle size how are you configuring your slicing settings? A real JHead from RPW will have a number stamped on the nozzle block to indicate the size. It's on the same face as the thermistor hole.

You may have an issue with the PTFE liner in the hotend that is causing the material to jam or bind. RPW (hotends.com) sells replacement pieces though it's available at McMaster-Carr though for one or twi it's best to get it from hotends.com. If it's an original Mendel it might be older and either have worn PTFE or have collected enough debris in the nozzle to clog.

To get to the tube, heat the nozzle, while it's still hot unscrew the nozzle from the PEEK liner (also called a nozzle holder). There will be a hollow set screw on the feed end of the nozzle holder. Unscrew that and you will have access to the PTFE liner. It may be metled or stuck in the holder. Make sure it's not frayed or otherwise hindering the feeding of fliament. If it's OK you can clean the nozzle (brass part only, remove the thermistor and heater cartridge/resistor) by using a small MAP gas or propane torch. I've only done that as a last resort and these days have spare nozzles in case I can't get it fixed.

You shouldn't need any external cooling or have to resort to tricks like lubes as long as the hotend is properly designed and manufactured. If you don't have a genuine JHead that could be an issue particularly if it's older. The best thing I can recommend is to get a new JHead or Aluhead and take it from there. An E3D is good as well but for beginners I find the JHead or Aluhead is more forgiving and eaiser to master.

So I managed to take my extruder completely apart and clear out the jam.

Here is what I did.

- Removed Kaptan tape
- Removed Thermistor
- Removed heater resistor
- Unscrewed brass nozzle from PEEK
- Found a glob of PLA up in red tubing in the cold end of the extruder. It probably got lodged there when I tried to change filament.

I was able to clear the glob of PLA by pushing it out the top. I soaked the brass nozzle in acetone overnight to clean it up.

I think my extruder was originally built for 3 MM filament and was adapted to 1.75 MM filament with a piece of 4 MM OD/2 MM ID PTFE tubing. That tubing disintegrated when I disassembled my extruder. Now when I try to use 1.75 MM filament its a very loose fit where it goes into the hotend. So I get very inconsistent flow out of the nozzle.

It appears really hard to source the proper size PTFE tubing locally. I'm considering three options. I received two 1 KG spools of 1.75 MM filament with the printer and it would be nice to be able to use those.

First, find the proper size PTFE tubing some place and try to cut a piece just the right length to adapt my extruder back to 1.75 MM filament. This is probably the cheapest option. It might take a couple of tries to get the tubing cut and installed just right.

Second, buy a new extruder designed specifically for 1.75 MM filament. The only issue with this one might be difficult to replace the existing extruder. the PEEK appears like it's glued to the bottom of the geared extruder. I've seen they have nice aluminum plates to mount the j-head extruder to the bottom of a Wade's geared extruder. I just don't want to damage the printed part of the extruder to remove the existing PEEK tube. I don't have a working printer to print myself some spare parts. There is no marking on the brass hotend to tell me what size nozzle it is, so it's probably a copy, not the original j-head.

Third, switch to 3 MM filament. My local Micro Center has 1 KG spools for 3 MM filament for $30.99 each in stock in many different colors. Of course I have about $60 worth of 1.75 MM filament, so I could buy a whole new extruder and the aluminum mounting plate for about what a couple of spools of filament cost.

Does anyone have any recommendations, comments, or suggestions?

Here is an update. I went and purchased a roll of 3 MM PLA and tried it out.

The first couple of prints came out great. Then I started to have issues. I realized that my Kapton tape was getting ragged. The previous owner of this printer covered the thick aluminum bed with lots of thin strips of Kapton tape. After printing many parts and cleaning with acetone, the seams were getting rough and causing problems. I didn't have any wide Kapton tape, so I peeled off all the tape and covered the bed with blue painter's tape.

At first I had trouble getting the prints to stick well. I tried hair spray on the blue tape and that helped a lot. I had to cut out a cardboard box with a hole in the bottom to spray the hairspray on the bed and not get it all over everything else. The first layer still doesn't come out as nice as when I had new Kapton tape on the bed. I'm sure if I cut some glass, put blue tape and hair spray on it, and tried it I might get a slightly better result. No matter what you do, blue tape is not as smooth as Kapton tape and will never give you as nice a finish on the bottom of your print.

I tried printing some larger prints and ran into trouble when the X axis was near the end of it's travel. It turns out the 3 MM filament is much stiffer than the 1.75 MM filament. When the X axis was extended that far out, the filament was actually causing the carriage to bind and move. I had to change the way I routed the filament from the spool to the extruder to fix that. I also noticed that some of the bolts on my carriage were loose and I had to tighten them back up.

I have some wide Kapton tape and some PTFE tubing on order so that I can get back to what worked the best for me. That was a heated bed to 60C with Kapton tape and 1.75 MM PLA. As long as I keep the tape very clean and heated up, the PLA sticks very well. So well that after it cools it can take quite a bit of force to pry the piece off.

For now I have a useable setup with the bed heated to 60C, blue tape, hairspray, and 3 MM PLA.