Extruder looping filament around hot end

I was having issues with flexible filaments, and needed to print polycarbonate, so I changed my Threeup V3 hotend from the e3d clone it came with to an e3d v6. I set the ptfe tube so it just barely misses touching the mk7 drive gear. Within 20 minutes of starting a print with seemingly any filament (petg and abs so far), it somehow crimps around the ptfe tube and feeds into the carriage assembly. Any ideas how to prevent this? Let me know what if any of my settings you would need to see. Marlin fw v1.02. I did modify the temp sensor type and maximum temp after changing the hotend in the firmware. I still used the Q3d modified version of marlin, though looking at all the improvements in Marlin 1.1RC8, I may do a diff from stock and see how I can merge them. Using Repetier for the moment with Slic3r.

I would say not enough support to the top of the PTFE tube. It seems to stick out a fair amount from the throat tube. Maybe it is getting warm and becoming more flexible, so that it takes less effort to flex the PTFE tube than it does to drive the filament through the hot end.

Good thought. Ill try to make a support disc with a 3/16in hole to stop maybe 2-3mm from the top of the ptfe tube. I upped the temps a bit, and disabled firmware retraction and I got one print out, but it took two tries, as the first crimped 30min in.

Flexible filaments will find a way to squirm around barriers unless you print very slowly (try 20 mm/s), avoid retraction, use thick layers to minimize backpressure in the hot-end, and reduce pinch wheel pressure on the filament. I've managed to print TPU on two printers with less than ideal extruder designs using these "tricks".

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I actually had a good print of TPE at 15mm/s with the old hot end, with no tube using an abs disc with a 5/64in drilled hole with a chamfer on top. I guess I expected the ptfe tube to be stiff enough guide on its own, but obviously overestimated it. Didnt expect normal stiff filaments to have so much trouble with it though, the abs and petg is kindve surprising.

From here, ill try to guide, I can make that in the machine shop at work today, then slow it way down. Ill attempt to print one of the replacement extruder assembly designs that are posted around for this machine and hopefully that will hold better.Maybe ill modify it to take my old hotend next to it for dual extruders while im at it. Given the shakey design of the frame though, the second should be a bowden im thinking..

Glutton for punishment, I know...

I saw a similar problem with my E3D titan and the 1.75 Ninnjaflex. From what I could tell by closely watching it, your pushing the flexible filament against a flat bearing, and flexible filaments tend to stick to the flat bearing. After realizing this, I went through the time and money and ordered the Flexion extruder for E3D hotends. It has a grooved idler bearing. This means both sides of the flexible filament are now supported without flattening, and no flattening means it doesn't stick to the bearing. Since it doesn't stick to the bearing now, it can't squirm out between the PTFE tube and the drive gear or idler bearing. It also helps if you constrain the PTFE tube so it doesn't deform under pressure. I've had a few flexible filaments fold overthemselves inside the PTFE tube before I put a stiffener collar around the PTFE tube.



This is what the bottom of the flexion extruder for E3D Hotends looks like with the stiffener collar ontop of the E3D hotend. With this setup, I've been able to extruder Ninjaflex at 60mm/s. It doesn't always look that great at 60mm/s, but its able to do it and normal print speeds I've been keeping at 45mm/s for quality purposes.

I use the Titan extruder and have had no problems printing with sainsmart TPU, SINCE getting the new hobbed thread. The original hobbed thread had manufacturing problems .

Ptint speeds are the same as PLA or ABS. The only other thing I did was to push the ptfe guide from the idler right to the bearing.

So I added the guide to sit over the e3d top piece, with a whole drilled out for the ptfe tube. So far,its been alot better but I think the tension is still too tight, since it occasionally starts grinding into the filament leaving a groove where it stops feeding, and a half complete print with a sudden stop. Now 3 out of 4 prints complete successfully, with a 7hr job running fine on the first try back to 60mm/s.