chewing up filament, failure to feed

hey all, im new to the forums, have recentyl built myself a prusa mendel v2

have a gregs accessable extruder, .35 hot end
my issue is that im not sure why but the hobbed bolt will start to "chew" up the abs filament
see attached pic

im not sure if im over tightening, under tightening or what, after feeding in fresh abs it extrudes beautifully then just stops and eats it up

ive done some fine tuning and have made sure that the hobbed bolt teeth are lined up with the hole that feeds the extruder

i appreciate any help that i can get thanks, paul

What type is your hotend? Are you running a fan on your thermal barrier? Are you running a PTFE liner in your barrier? It looks like you are getting heat creeping up your hotend and clogging in the thermal barrier, common problem.

J-Head MKIV-B Hot End
no fan
no ptfe, is it supposded to go around the outside of the hot end?

There should be a short piece of PTFE inside the the thermal barrier. It's probably in there or your filament would be more of a mess when removed.

Most likely you are getting heat creep. When the heat rises to far up the hot end, the filament 'plug' rises up and will jam in the barrel. If you can, try mounting a small fan to blow across the barrier piece.

I've been having the same issue with my (0.5mm) MK IV-B hotend. For the record, there is a PTFE liner on that hotend. I have no trouble printing PLA with a fan, but ABS always seems to jam. When I'm printing with PLA I have my fan set at 100% for the entire print, but I've been using 50-60% for ABS since everything I've read says that ABS doesn't like air flow and doesn't have the same problems with jamming that PLA does (yeah right). With my job and family I just don't have much time every day to experiment with different settings so it's going to take me a while to figure out what the problem is. I'm sure there are people out there who have already figured this out.

I print ABS with a J Head regularly with no fan. Are you using a genuine one from hotends.com or one from eBay or elsewhere?

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i got mine from the kits sold at makerfarm.

id also like some suggestions about tightness of the accessable hinge on the extruder, how much is right? how would i find out?

I got my J-head MK IV-B from ebay.

Springs need to be tight yes, but any restriction in the pipe will make the hobbed bolt munch at the filament.

Just finished putting my prusa mendel from Makerfarm together, and had a few issues with munching the 3mm ABS. My fix was to take the Extruder apart and ream out all the holes and ensure no parts are tight or binding. They should all have a clearance fit. I had an issue with the guide roller bearing that compresses the ABS against the hobbed bolt. The bearing did not spin freely in it housing and when compressed againt the hobbed bolt cause too much friction and tore the material.

I also ensure the J end is hot - 230oC for approx 5 minutes before printing, and I always extrude 1mm @ 50mm/min, 3 times before commencing a print to ensure the material flows well. I'm using Slic3r and Proterface. So far I have printed 10 pieces, so I'm still calibrating.

Had a similar issue with a hotend using PLA. Took 10mins to get to 185C. Would run for a while then jam
The hotend had a resistor heater. Even though the temp sensor was showing constant I belive the hotend was fluctuating
Checked the temp is stable with another thermometer.
Replaced hotend with a wirewound heater - 185C in 3mins and no more issues