Airwolf JRX hot end continuously jamming

Hello,

I've had my 'wolf for a few years now, she's been hit and miss. The original hot end, JR, actually worked fine. I "upgraded" to the JRX to handle polycarb and other high temp materials.

The JRX, though, even with simple PLA (fresh out of the vacuum sealed bag) , will get through about 3 layers of the print than jam up.

I've seen this now with PLA and ABS. Simple stuff. Each time I disengage the feed, pop off the Bowden from the hot end, and manually push some filament through. Most times it takes waaaay to much force to get it moving. I pull out the filament from the hot end, nip off the 1+ inches of filament that was in the hot end (which has now a larger diameter) and feed in raw filament. Usually works.

BUT this is not acceptable. Print failure rate is about 90% currently.

Ideas?

Situation:
- new 0.5mm nozzle
- clean filament
- feed stepper is fine
- Bowden is locked in place throughout print
- hot end temp is consistent

I have had this problem with a chinese E3D clone also with a Bowden extruder. Due to the bowden tube I needed around 6 mm retraction to counter the oozing. However, which such high retractions, hot rubbery filament is pulled up too high and then cools and sets higher up in the heat throat causing a jam (it sticks to the metal wall). My solution was to convert the all metal heat-throat for a ptfe lined one, which solved my problem completely.

My personal conclusion is that for an all-metal hotend you either need to be lucky with respect to the heat-throat (seems to be a hit and miss issue), or you need a direct drive (no bowden) extruder so that you can keep the retractions to less than 2mm.

Excellent tips, thank you! Here's a stupid question: has anybody ever slipped in a PTFE liner into an all metal hot end with success? PTFE melt temp is about 500 deg F (260 C): http://www.mcmaster.com/#tubing-%28m...fe%29/=11donh7