PLA + Ignorance = Broken Extruder

I got a roll of PLA to try making some clear objects on the CupCake. I had read on the MakerBot wiki about the techniques for and challenges of printing PLA but still had trouble feeding PLA into the Plastruder MK3 and chasing out the ABS that I’d been using.

MakerBot CupCake Plastruder MK4 with stripped PTFE barrier

When feeding in the PLA, ABS came out for a while and then things stopped. Something happened inside the PTFE (Teflon) thermal barrier and the brass heater barrel was pushed out the bottom.

Later kits have a nut between the PTFE barrier and the metal washer so the long black bolts pulling on the washer in turn pull on the nut which has a stronger grip on the threads than the PTFE, dramatically reducing the risk of the brass barrel slipping out of the PTFE barrier and dramatically increasing the risk of cracking the acrylic retainer at the top. It’s recommended to replace it with a metal retainer.

PLA clogged on MakerBot CupCake Plastruder MK3 nozzle assembly

Today I had time to disassemble the Plastruder and unthread the heater barrel from the PTFE barrier. Looks like the PLA melted, the PTFE got warm and softened, the PLA oozed around the heater barrel, and then the PLA solidified and the barrel was pushed out the end of the softened PTFE.

I chipped the hardened PLA off the end, then searched for a solvent that would dissolve the PLA out of the barrel. I was surprised to find no information online (I do not assert that there isn’t any but merely that I didn’t find it) and tried acetone. During the time I waited, it didn’t dissolve the PLA completely, but it did soften it enough to scrape it out of the threads with a wire brush and goop it out of the barrel with a drill bit.

Scorched nichrome heater wire on MakerBot CupCake Plastruder MK3 nozzle

Since something in the thermal insulation had been previously damaged by deliberate immersion in water, I ended up deciding to peel apart the whole heater assembly. I suspect the water-soaked kapton tape adhesive closest to the nichrome heater is what scorched and I still have faith in the magical powers of kapton. I just know its weakness now.

On the bright side, I get to rebuild my heater from scratch and make it beautiful again.

On the dim side, I need to replace the PTFE barrier, which is swollen beyond even making contact with the brass threads, and the ceramic insulation that wrapped the heater, which was no longer pristine. I see that the MakerBot store has them in stock and affordable, and I reckon I’ll order them this week unless I hear a brilliant alternative first. The nichrome wire’s fiberglass insulation looks and feels intact — I think it’s saturated with scorch from the kapton rather than being damaged itself — but I’ll probably order more of it too.

Anyone successfully using PLA, I’d love to hear what temperature works well for you and what technique you use for changing from ABS to PLA.

One Response to “PLA + Ignorance = Broken Extruder”

  1. James Adams says:

    With the PTFE insulator barrel it looks like you got pretty good mileage out of it all things considered; I mean I permanently expanded mine within the first week of use!

    There’s a couple options available for hybrid barrels from makerbot or makergear. The makergear Hybrid would be a drop replacement and is PEEK external and PTFE internal. You could also have a switchable barrel for ABS and another barrel setup for PLA, and makergear sells all the stuff to do that.

    I was always under the impression that PLA was extruded at a lower temperature than ABS but that doesn’t appear to always be the case. I looked at the mothership project for Makerbot which is Reprap and this is what they have on PLA the temperature varies based on the type of PLA you have. Keep in mine to play with your temperatures for the heated build platform because as I recall from someplace (don’t ask me where) that the temps are different to get PLA to stick.

    Probably on of the most successful printers with PLA arguably within the community is Hydraraptor that’s just one article on his observations there are many many more.

    Good luck, with all that being said I’m still using ABS and have yet to attempt the switch, when you do get it working I’d like to see a write up on your findings.

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