Filament tip problems.  

Re: Filament tip problems.

I just assembled my MMU2 and initially, I didn't replace the PTFE tube. The new kit came with two PTFE tubes, with both ends tapered, but I had already done that, so I didn't swap them out.

My first couple of prints failed. My tips were too fat. After thinking about the whole thing, I took a good look at the new PTFE tube. I could be 100% wrong....but I THINK it's got a smaller diameter than the original one did (or my existing one did -- I purchased a big length off the internet because I kept needing to replace/nozzle issues/etc during my learning curve).

Anyhow....once I replaced my PTFE tube, the tips come out looking good. No jams. Printed the sheep just fine. Got 2/3 of the way through benchy before it jammed (spool fell over during the night and wouldn't feed filament to the MMU and it threw up an error.

Also...FWIW, I've been using Monoprice filaments. Seems to be working nice so far. Good tips.

Thanks!
Eric

Re: Filament tip problems.

I highly suspect filament settings giving me issues since MMU 2.0 running smoothly on dry/dummy run with filament.

Re: Filament tip problems.

My MK2.5 +MMU2.0 unit runs fine when the PTFE tube is disconnected from extruder. I noticed that some tips previously retracted could not be inserted back into the heat break. The tip expands after exiting heatbreak. During ramming it creates negative pressure so when the filament exited the heatbreak it expands. I tried to tweak filament settings but still having issues although reduced tremendously but suffers print speed.

I ordered heat break for MK3/Multimaterial and currently waiting for shipment. There are 2 types of heatbreaks, for MK3/Multimaterial and for MK2. My MK2.5 and MMU2.0 upgrade did not come with heatbreak replacement. Based on my search, MK3 heatbreak inner diameter is larger than MK2. I will see if it will fix the issue once it arrive.

Re: Filament tip problems.

2 types of heatbreak.

Re: Filament tip problems.

Yes there is a special type heatbreak made by e3d for prusa. You also need the special ptfe cold end tube which has 1,85 mm in diameter.

Re: Filament tip problems.

My heat break will arrive on Monday. We will see how it goes.

Re: Filament tip problems.

i think based on the issues you are having that there is shaped difference internally with the heat breaks.

in a normal printer the shape of the inside of the heat break doesn't matter because direction of flow is basically one way with a manual filament change. however since the MMU is bi directional if there is a large cavity at the bottom of the break then you would get a more
mushroomed out tip on the sides that would act like a clog when the pulley attempts to eject.

this is similar to the ruby nozzles that have a flat bottom so it was impossible to really shape the tips on ramming.

for giggles i would bet no ramming and just yanking the filament out of the extruder would keep the tip from mushrooming out and jamming at the entrance to the tubes. the strings would be bad but it would be interesting to see if it would solve one problem.

Re: Filament tip problems.

If I'm experiencing fat tips every ~15-20 layers on my Mk2.5, are y'all saying the heat break could be the answer?

Re: Filament tip problems.

lots of people are using aftermarket parts for upgrades or replacements since the printer is open source you could recreate a MMU2 with off the shelf parts.

prusa is doing all the setup and testing with their own parts. if a heatbreak is from another company it is possible that there are internal differences that are not apparent unless you very closely inspect and compare.

my first rule with this stuff is stay in certain boundaries to at least increase the possibility of success, then play around and see if something causes a failure.

shape with the heatbreak/ptfe/nozzle internals is important because with some internal machine shapes they are basically directional. you can manually remove filament but an automatic system might encounter resistance and thus the entire system fails.

even prusa parts could be machined with defects. one guy kept having the filament jams and could never figure it out. the PTFE tube was jammed and when he finally got it out. there was a machined defect in the bottom and the PTFE and filament had stretch out the bottom to fill the defect and it acted like a plug. you could push the filament through to the nozzle but unloading was almost impossible because of the issue.

Re: Filament tip problems.

My spare heat breaks came from Prusa shop.

Re: Filament tip problems.

it can still be defective.

Re: Filament tip problems.

it can still be defective.

Even my 2 spare heat breaks?

Re: Filament tip problems.

Even the 2 spare original E3D heatbreak bought from Prusa Shop faulty?

Re: Filament tip problems.

well then most likely not and you need to find the next possible cause.
are you using some different nozzle?

Re: Filament tip problems.

Im using the original E3D nozzles bought from Prusa shop as well. No problem when running single mode and I don't think nozzle is the issue since the tip diameter becomes larger when it comes out of the heat break. And I don't get the logic where nozzle causing the enlargement of filament tip.

Kindly read through my posts from the beginning so that you'll get all the information on the issue.

By the way, since I already tear down my extruder, I replaced my nozzle and PTFE tubes with new ones for preventive maintenance purposes.

Printer: MK2.5
MMU: MMU2.0

Re: Filament tip problems.

I just assembled my MMU2 and initially, I didn't replace the PTFE tube. The new kit came with two PTFE tubes, with both ends tapered, but I had already done that, so I didn't swap them out.

My first couple of prints failed. My tips were too fat. After thinking about the whole thing, I took a good look at the new PTFE tube. I could be 100% wrong....but I THINK it's got a smaller diameter than the original one did (or my existing one did -- I purchased a big length off the internet because I kept needing to replace/nozzle issues/etc during my learning curve).

Anyhow....once I replaced my PTFE tube, the tips come out looking good. No jams. Printed the sheep just fine. Got 2/3 of the way through benchy before it jammed (spool fell over during the night and wouldn't feed filament to the MMU and it threw up an error.

Also...FWIW, I've been using Monoprice filaments. Seems to be working nice so far. Good tips.

Thanks!
Eric

Eric,
I also noticed the inner diameter of PTFE tubes provided by Prusa is smaller than the ones I bought from China. I was not able to compare it with PTFE tubes inside the extruder.

My question is why does the filament becomes enlarged after retracting from the heat break? Enlarged to the point it can't be fitted back into the heat break. I simulated it with heat break alone and inserted a piece of filament. I heated up the tip of the filament with external heat source until it melt then manually perform ramming then cool down by hand. I got the similar enlarged tip as well. I tried other brand of filaments and got the same result as well. I suspect Prusa Research forgot to include the replacement of the original heat break to MK3/Multi-material type for MK2.5 upgrades.

By replacing PTFE tube with a bigger inner diameter, what you did was just increasing the tolerance for the enlarged tip.

I'm expecting shipment for MK3/Multi-material heat break and we'll see how it goes.

Re: Filament tip problems.

why does the filament becomes enlarged after retracting from the heat break?

It shrinks in length and while doing so, expands in width.

Peter

Re: Filament tip problems.

forget it, PJR handled it

Re: Filament tip problems.

forget it, PJR handled it

I tried to play with settings but I didn’t work on mine.