Return of under-extrusion

[dramsey]

I had an under-extrusion problem recently that I finally, with the help of folks here, identified and rectified via a new nozzle.

Everything printed perfectly for a couple of weeks, but I just had an identical problem 29 hours into a 34 hour print, sigh. So I swapped in a new nozzle and...it made not a whit of difference.

As I see it, underextrusion can physically be caused by:

1. Slipping extruder gear
2. Plugged nozzle
3. Plugged hot end

After another day thrashing with this, I'm looking at #3. The gear teeth indentations in the PLA are exactly as deep as they should be, and simply testing by trying to hold filament as the extruder pulls on it shows that the extruder has a firm grasp.

Of course the hot end is pretty much always going to have plastic in it. Soaking in acetone for 6 hours didn't seem to do anything, so I plugged it back in, heated it up, and pushed as much plastic as I could out with a small hex wrench. Further testing revealed that nothing has changed.

So here's where I am now:

• PLA feeds, but comes out in a very thin stream, often curling up around the nozzle rather than hanging straight down.
• Cleaner filament will not feed at all: it jams solidly once it gets to the hot end.

So my guess is there's something wrong with the hot end, and solvents and physical cleaning don't seem to work, so I should just order a new hot end.

Right? How often do you see jammed hot ends? Could they be carefully drilled out?

[Jules]

Cleaner filament always jams like the dickens - that doesn't actually tell you anything.

Acetone dissolves ABS, not PLA - so if you had a PLA clog in the nozzle - it's still in there. (To dissolve a PLA clog you need paint stripper with methylene chloride in it. Highly toxic. Be careful, and read up in the forum on how other people did it - takes an overnight soak sometimes.) I'd buy a new nozzle for 10$ before messing with the stripper.

Do you run a dust filter on your filament?

You can also stick a short segment of E-string (guitar wire) up into the bottom of a heated nozzle in order to dislodge the clog if you are careful not to burn yourself. I've done that a couple of times. (Never had to replace one of the V4 hotends.)

[dramsey]

Cleaner filament always jams like the dickens - that doesn't actually tell you anything.

Really? Then how do you get it out of the hot end?

[Jules]

Reverse it out. (retraction)

(You generally have to change the tension when you use cleaner filament - it's a bear to get fed in properly)

[dramsey]

Well, then, I will try replacing the nozzle again-- I have a bag of 7 of them...

[Jules]

So do i. (Chuckle!)

[dramsey]

Well, I give up: three different nozzles-- 2 brand new-- haven't made any difference, and the filament, when extracted after extrusion, has the ground-up look you get when you're forcing it and the drive gear strips the plastic.

So I ordered a spare parts kit. I'm pretty sure replacing everything will work, and honestly I'm tired of putting time into it.

[Jules]

If the filament is getting ground up, then you likely just have too high a tension on the filament drive screw. Did you try to loosen the tension a little?

[jimc]

yes if its stripping the the problem is after the drive gear so its tight somewhere. 90% of the time the tension is too high as jules pointed out. it squishes the filament out of round then wont pass through the lower hole in the filament drive. not sure what hot end your running. if its the v3b then that thing is really prone to buildup internally and you should prob upgrade the printer to a v4 or an e3d. they both have teflon liners and a short hot zone. i run e3d myself. i can say i havent had a nozzle jam in prob 100kg of filament and i use no dust filter either.