PVA balling up above Extruder Drive Gear  

Re: PVA balling up above Extruder Drive Gear

After what was probably a longer than expected run of beginner's luck, I'm having problems with Water Soluble Supports. Evidence leads me to think the Extruder drive reverses, but the MMU2 remains motionless. This leaves me with a ball of PVA filament above the gears and the usual "MMU needs attention" message.
This seems to happen about once in ten attempts to unload, so I get a few good layers, then the ball. It could be as often as every unload, but as rare as 10. I keep the PVA in mylar bags when not in use, so it probably has 4 days of air exposure in a very humid environment.
What's going on? Coincidentally this started happening after I upgraded my firmware to 3.5.3.
I've tightened the bolt on the right side of the MMU in an attempt to give the MMU a bit more grip to help retract the PVA in case it's a problem with filament deformation. This made no change at all.

Is this happening on the unload part of the load/unload cycle?

On unload, after the ramming the extruder will rapidly yank the filament out of the hot end. This is done only by the Bondtech, and the MMU is disengaged. The MMU only engages after the cooling moves are complete.

For flexible filaments (which includes PVA), if there's too much friction in the filament path it's possible for the filament to buckle above the Bondtech rather than get pushed back through the MMU. The solution is to try to reduce friction in the filament path, and possibly slow down the "unloading speed at the start" in the Advanced filament settings.

Re: PVA balling up above Extruder Drive Gear

Thanks! That explanation makes a lot of sense. I was using PLA temperature profiles because the PVA temperature profile was not sticking to either the build plate or existing layers.
So if what you are saying is true, I might need to figure out a way to cool the filament above the Bondtech gears. Or stop using PVA,

Re: PVA balling up above Extruder Drive Gear

Thanks! That explanation makes a lot of sense. I was using PLA temperature profiles because the PVA temperature profile was not sticking to either the build plate or existing layers.
So if what you are saying is true, I might need to figure out a way to cool the filament above the Bondtech gears. Or stop using PVA,

I've not heard a lot of success stories with PVA yet, but the usual problem is (lack of) adhesion, not problems loading or unloading.

Re: PVA balling up above Extruder Drive Gear

Isn't PVA incredibly hygroscopic? You'll need to dry it based on your comment it's been in high humidity. Doesn't take long and it gets rubbery, which would cause what you are seeing.

Re: PVA balling up above Extruder Drive Gear

I have almost no adhesion if I print at 200. 205 does great. It's amazing what such a small delta in temperature can do for adhesion. However, one thing I'm not happy about is that regardless of the temperature I get INCREDIBLE stick to the print bed. So much so that I'm thinking of getting some metal sheets and dedicating them to PVA attempts.

And because of that I do have a complaint. I had already figured that I would prefer to have skirt of the 'main' material and have PVA contact that material instead of the printbed, as I've found no way to get all the PVA off my printbed. I would like very much if there was a way to put PETG, PLA, whatever, down on the area the purge block will be, and let the PVA make contact with that instead of the printbed.

Re: PVA balling up above Extruder Drive Gear

I've found no way to get all the PVA off my printbed.

Have you tried soap and warm water?

Re: PVA balling up above Extruder Drive Gear

I've found no way to get all the PVA off my printbed.

Have you tried soap and warm water?

Not as though it's water soluble or anything... 😆 😉

Re: PVA balling up above Extruder Drive Gear

Trying so hard not to be snarky..... Let's see. Water soluble filament, I claim to have tried many methods to remove it from the build plate. This forum of experts suggests I try ... water? GENIUS!! I wish I had thought of that!

I'll give it a shot and see what happens. Hold on.

Nope, the plate still has a very thin film of PVA. Hot water, detergent, soap, scrubbing with a nylon scrub pad, letting it soak overnight. No joy.

Re: PVA balling up above Extruder Drive Gear

the plate still has a very thin film of PVA

For that sort of residue, I use an extremely sharp 1.25" wood chisel.

Peter

Re: PVA balling up above Extruder Drive Gear

Trying so hard not to be snarky..... Let's see. Water soluble filament, I claim to have tried many methods to remove it from the build plate. This forum of experts suggests I try ... water? GENIUS!! I wish I had thought of that!

Aha, I see your mistake! You assumed you were talking to experts!

I'll give it a shot and see what happens. Hold on.

Nope, the plate still has a very thin film of PVA. Hot water, detergent, soap, scrubbing with a nylon scrub pad, letting it soak overnight. No joy.

Since nothing worked that should have worked, let's go back and check assumptions. Are you sure it's a film of PVA that's stuck to your bed and not something else?

Re: PVA balling up above Extruder Drive Gear

Is this the kind of result you're seeing (See image)? I'm having the same result with BVOH, which is quite a bit stiffer than PVA but still kinda flexible.

My system is pretty well set up friction-wise, so I guess I'll try slowing the "Unloading speed at start". Does anyone have any other ideas? Thanks in advance.