Under-extrusion - Is your Bowden tube 'really' clean?

[francfalco 37]

Hi all,

I, like most people on here have had and the occasional 'unexplained' under-extrusion issue - one minute printing fine and then the next, thin layers, gaps and weak extrusion.

Interestingly for me, i was printing Ninjaflex over the weekend and i had an issue with under-extrusion. Nozzle was clean and extruder tension was fine. But then i noticed in the Bowden tube a 'hair' of previous filament stuck in the tube - almost invisible, but had been left behind from the previous 'change filament'. I had to disconnect the tube at both end and run a piece of filament through and then i noticed the 'hair' bundling up into a mini birds nest as i pushed it through and out of the tube.

A quick lube with some Olive oil and the Ninjaflex slid through the tube with ease.

I know this won't be a 'fix all' solution, but something to check if you don't already?

NOTE: don't be tempted to blow through the tube to clear it, it'll only leave behind moisture which will make filament stick like crazy - ask me how i know...

Cheers

[Dim3nsioneer 521]

This fine strains occur when you take out the filament HOT. That's why I always take it out with a cold pull.

To clean the Bowden tube I can recommend to use a piece of pipe cleaning wire which can be pushed through the tube by a piece of filament.

[francfalco 37]

Interesting.

So what is the procedure to change filament with a 'cold pull'?

I just follow the 'change material' sequence on the front panel and as you say, the filament is rewound hot from the nozzle often leaving behind fine strands.

[Dim3nsioneer 521]

This is what I do (with PLA):

- heat the nozzle up to 200°C

- open Robert's feeder

- push a bit of filament manually through the nozzle

- let the nozzle cool down to x (x=90°C on my UMO, 80°C on my UM2 with the original heater block, 70°C on my UM2 with the Olsson Block)

- pull the filament out (requires some force)

- use the 'insert filament' option in the advanced menu to insert new filament