PLA jamming before hot end


I’ve been searching around and thought I found a solution to this problem, but it just happened again and I’m hoping someone out there might have some insight.

I have a TAZ4 with the dual extruder. I am trying to print PLA and PVA for dissolvable supports. I’ve successfully printed a fair amount with ABS, but am now starting with PLA. Twice now I’ve had a problem while printing the PLA. The print starts fine, but eventually I get a hot end jam and the filament strips in the feed bolt. I’m unable to pull the filament back out while the hot end is still heated (185-200C). When I take the head apart, I’m able to extract the filament from the hot end, but it appears the filament has melted/expanded in the channel leading to the hot end and is stuck (see attached photo - this is the channel right before it enters the hot end). When this first happened (ruining that part of the original extruder), I did some searching around and it looked like the problem was likely that things were getting too hot and that a fan might solve the problem, so I printed the Dually Cooly attachment and added a second fan so that both print heads and heat sinks in the dual extruder were being cooled. Unfortunately, the same thing happened with my first print with the fan on this time. I fear that I now have 2 irreparably damaged extruder channels. I’d be most grateful for any suggestions you might have.

Dan Fletcher

I’ve dealt with the same issue with a client’s dually PLA/PVA setup recently. The fans were the right first step. Check that the hotend’s mounting plate is getting adequate cooling air.
Be sure to only heat the head when you’re ready to print.

In this other case, a fresh roll of PLA also reduced sticking. Try a freshly opened roll to ensure you’re not fighting bad/moisture absorbed filament (and potentially save yourself a BUNCH of time - voice of experience…)