Extruder Keeps Jamming

Hey guys, I need help/advice.

I recently rebuilt my whole extruder and am having problems with the hot end, hope someone can shed wisdom. I decided to go for a 0.4mm Makerbot tip, steel tube and PTFE liner mounted on Greg's Hinged Accessible Extruder. When I start feeding my PLA in at 200-210 degrees, it starts extruding just a bit, but then the PLA stops advancing and the hobbled bolt starts stripping the filament. Even if I try to grab with pliers and push it in, it will not go. Any ideas on why this is happening? One observation I've received was that because I have the steel tube covered, it is heating the filament up top causing expansion into the PTFE liner. But, I can easily reverse the filament out, so I'm not sure if that is it and wanted to check before I start hacking away at the PTFE Rob and adding a fan.

Here's a detailed look at my setup starting with fully assembled progressing to taken apart:
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If there is steel inside, it needs to be very thin and have a big heat sink. It also needs to be stainless steel, which has much lower thermal conductivity than regular steel.

Yes, it's stainless steel. I just never thought the filament would expand so much to cause it to get stuck. Does it make sense that I can reverse the extruder and get it out easily though if that is the cause?

I'm thinking that if that is the issue, I will need to cut most of the PTFE sleeve away, add more heatsinks + a fan. What do you guys use to stick the heatsinks to your tubing (pic 13)?

If it gets hotter than its glass transition temperature it becomes like rubber so when you push on it it expands but when you pull on it it contracts. That is why you can reverse it out again.

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[www.hydraraptor.blogspot.com]

I'm running the exact same makerbot lower components on 3mm PLA at 170 without few problems. Instead of a plate I have a frame that houses a pair of ceramic resistors. Tip screws into the frame and the steel tube screws down on to the back side of the tip. The PTFE is totally trapped where only a small ridge remains where the tube tends to swell into I found that the PTFE can't back out of the tip or the material will feed around it and no longer feed, so it shouldn't move up. After hours of use it just stopped extruding and I found that really hard material built up in the tip causing it to clog. not really sure where it came from . I don't have any insulation around the metal tube, where I'd rather let it cool in air, but my heating zone doesn't travel up the steel tube as much as yours. Seems like you are close.

@ dean448

Do you have a picture of your "frame that houses a pair of ceramic resistors". Curious to see what that looks like.

Project for tonight, I will be cutting away the PTFE sleeve to expose the stainless steel tube and figuring out how to wire up a fan. I'm using Techzone's Gen3 electronics, so I guess I have to do a bit of research on whether I can just wire it into the board as is so Repsnapper can control it or if I need to edit the firmware. Has anyone hooked up a fan to Techzonecom.com's Gen3 electronics?

I need to do some work to my extruder lower end over the week end, so I'll try to take a photo then. I started out with gen 3 but couldn't get to work very well so I moved on to Ramps. I actually wouldn't bother with controlling the 12V fan and just wire it thru a switch to the PS. I'ts not a big deal to just turn it on and off as needed at this point. I guess you could leave it on all the time and adjust the temperatures for the type of print. The fan isn't going to solve your problem, just another feature of the printer. I printed two bracket that allow a pair of fans to hang level to the hot end but rise and fall with the z axis. Fits nicely between the z axis carriage and the platform.

Heres the lower end of my extruder using makerbot nozzle, stainless tube and red PTFE liner. The frame has a trough hole in it just larger then the 3/8-24 threads of the nozzle, It threads into a 3/8-24 nut that has a washer welded to an undercut on the opposite face. Screw the nozzle into the nut, through the frame, and it locks the ceramic resistors. The stainless tube is threaded on one end and it gets threaded into the same bolt. I could stop there, but to further secure the frame from turning I lock another 3/8-24 nut on the remaining threads of the tube. You could also not weld the washer to the nut. By the way I started with winding wire around a bolt to make your own resistance coil hot end and I would never go back to that after using ceramic resisters.

Nice design! I like how you used nuts as a heating block. So, I assume you keep a fan on the stainless steel tube to keep the heat at the tip?

I have fans on both sides which are directed just about where the frame is. I don't think this is critical. The whole hot end is insulated. I have a non contact thermometer and measured 36 at the top of the tube when the hot ends is running at 170. The reason I could take these photos is because I had something let go in a previous design. Its amazing that you can get a decent quality print even when the extruder is flexing. I guess that would happen as long as it flexes the same amount on every pass. Anywhat this rebuild is very stiff and the printed parts are very nice.