Suddenly getting constant jams with V3b extruder

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scatterlaser
Posts: 2
Joined: Thu Mar 17, 2016 11:29 am

Suddenly getting constant jams with V3b extruder

Post by scatterlaser » Thu Mar 17, 2016 11:36 am

I've got a Prusa Mendel with a V3b extruder. The extruder replaced the old ceramic core one that came with the Prusa kit, and it's been working well since I installed it near the end of 2013. Lately, though, it's started jamming more and more often, to the point where I can't really print anything.

The jams normally manifest as the filament buckling between the extruder gear and the top of the insulator. I did have one jam where gear stripped the filament instead of it buckling, though. The jams happen very quickly - I've been printing some 90x60mm boxes, and it mostly jams before or during one of the first two flat layers.

Things I've tried:

- Running some clear filament through the extruder, letting it cool to ~120C and then slowly pulling it out. I did get some black specks in the end of the filament, but I was printing with black PLA before this so it might just be the remnants of that.

- Running clear PLA through the extruder, poking lengths of guitar wire through the nozzle until they came out the top of the insulator, then pulling them out from the top. One time this pulled a bit of black stuff out, but again I think it might just be leftover black PLA.

- I noticed the nozzle seemed to be dragging through the first few layers of some prints, so I adjusted the Z endstop up a bit. The first time I tried that, I actually got a really good print (even though it looked like the plastic was barely sticking to the base). Every print after that has jammed very quickly, though.

- Adjusting the temperature from 205 to 210C. My prints seemed to be coming out fine at 205 for a long time, though there was quite a bit of stringing. Changing the temperature didn't help.

- I did manage to print a small single-wall test object and confirmed that the extrusion width is calibrated correctly. Not sure why this printed while the rest didn't - either I got lucky or it's because it printed slowly because of my cooling settings.

I can't figure out is why this has started now. My setup hasn't changed for a while, and definitely nothing around when the jams started. I did switch to a new spool of filament (1.75mm black Makergear PLA) a few months back, but that worked perfectly well for a bunch of prints before the jams started. I increased my print speed from 60 to 70mm/s a while ago, but again, I got a lot of successful prints with that. Changing the print speed back didn't make a difference.

I'm not sure where to go from here. Do extruders just wear out and need replacing after a while? Does anybody have any suggestions for other things I can try?

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insta
Posts: 2018
Joined: Tue Sep 16, 2014 3:59 am

Re: Suddenly getting constant jams with V3b extruder

Post by insta » Thu Mar 17, 2016 1:29 pm

You have a clog, or more likely a piece of mechanical debris rattling around near the inside of the nozzle.

Remove the entire hotend, and do cold pulls with Taulman 618 nylon until they come out totally clean. 240C in, feed filament by hand until it's curling out the end, cool to 90C and keep pressure the whole time it's cooling, then pull back out by hand. Do this over and over until the end of the filament is just a little cone with a tiny whisker, and zero bits of color or other plastic. Wire brush the nozzle clean on the outside just because.
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Jules
Posts: 3150
Joined: Wed Jan 21, 2015 1:36 am

Re: Suddenly getting constant jams with V3b extruder

Post by Jules » Thu Mar 17, 2016 1:48 pm

Or buy another V3b. (Seriously, three years isn't bad for a replaceable part - might be time to replace it.) :lol:

Failing the cold pulls that insta suggests, you can always torch it clean - that works well and cleans every bit of gunk out of the barrel. (But i'd just buy a new one after 3 years.)

viewtopic.php?f=3&t=2074

scatterlaser
Posts: 2
Joined: Thu Mar 17, 2016 11:29 am

Re: Suddenly getting constant jams with V3b extruder

Post by scatterlaser » Mon Mar 21, 2016 10:58 am

Thanks for the suggestions, I appreciate the help.
insta wrote:You have a clog, or more likely a piece of mechanical debris rattling around near the inside of the nozzle.

Remove the entire hotend, and do cold pulls with Taulman 618 nylon until they come out totally clean. 240C in, feed filament by hand until it's curling out the end, cool to 90C and keep pressure the whole time it's cooling, then pull back out by hand. Do this over and over until the end of the filament is just a little cone with a tiny whisker, and zero bits of color or other plastic. Wire brush the nozzle clean on the outside just because.
I've tried this 10-15 times with clear PLA and I'm getting some black stuff coming out on the filament, but I'm not sure if it's leftover black PLA or charred plastic. Is nylon better than PLA for cold pulls? I'll try again keeping pressure on it while it's cooling, I wasn't doing that before.
Jules wrote:Failing the cold pulls that insta suggests, you can always torch it clean - that works well and cleans every bit of gunk out of the barrel. (But i'd just buy a new one after 3 years.)

viewtopic.php?f=3&t=2074
I did see that thread earlier. I tried taking the hotend apart to get a look inside, but I wasn't able to get the insulator off the barrel. Do you need to do anything other than follow the assembly instructions in reverse to get it apart (i.e. would I have to heat it up)?

I'd like to get this working again if I can, but yeah, if it's going to be far too hard I can buy a new hotend.

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