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PLA filament breaks during cold pull

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Posted · PLA filament breaks during cold pull

Hi Everyone,


I am trying to clean the print cores in my Ultimaker 3 using the standard procedure of hot and cold pulls, however, I am consistently breaking the PLA filament during the cold pull such that a large piece of it is still stuck in the print core. 


Any tips or suggestions for cleaning or how to overcome this?





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Posted · PLA filament breaks during cold pull

The last meter of PLA on a spool is often brittle - particularly if it was left in the bowden overnight.  Just break the brittle part off and throw it away.


To get the filament out of the core it's easiest to just push it through while at 200C with another piece of filament (easier to go forwards than back).


Alternatively you can heat a small exacto blade with a flame and then quickly slice off the filament just above the "trumpet" part of the core and now you can slide the core out.


But then you still probably want to push the rest through anyway.

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Posted · PLA filament breaks during cold pull

I do a way more gentle pull than the traditional brutal cold pullings. Maybe this could help?


- Manuall put print head in a front corner

- Heat up nozzle (with bowden tube removed)

- Push through some filament

- Dial temp down to zero

- Stop pushing filament, do a slight "manual retraction" of a few mm

- Let cool down until nozzle is at room temp (25°C or less), so that the inner core of the filament also cools down well

- If you have oil-free compressed air from a compressor, you can blow onto the nozzle to cool faster (but never use "air" from spray cans: this is often very explosive gas, and you don't want that on a hot nozzle)

- When cold, gently try to rotate and wiggle the filament

- Heat the nozzle to 70°C (for PLA, other materials need other temps)

- While it is heating up, gently keep wiggling and rotating the filament until it comes out


- Repeat as required.


This method requires almost no force, but in my experience cleans as well as the original brutal cold pullings.


The deeper cooling cycle to room temp is to totally solidify the inner core of filament. So, when heating up again, only the outside is molten, but the inner core stays strong and solid. The gentle pulling prevents damage to the nozzle, displacement of the coupler, and bending of the rods. It should also prevent breaking the filament.


More info and pictures here (scroll down a bit):



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