So I had a bash at getting PLA going last night one thing I discovered is the filament storage box (which has a sort of reel + lazy susan connected to a low friction pipe running the filament to the extruder) is not well designed for changing out the reels. I had to unscrew everything and then found most of it wouldn’t go back together with the new reel in.
Besides that I shoved in the new filament and started it off at an appropriate temperature and off it went. I go some sort of weird hybrid of abs and pla for a while which eventually cleared to a nice clean see through PLA.
So far so good I thought and started on my first test cube. The results I got were a molten mess the cube stayed hot and so distorted. I changed the settings and tried again … but got no filament out of the extruder. I fiddled with the settings for a bit but eventually resorted to yanking the filament out. I found the filament had bulged out and jammed the extruder. I assumed I was running too hot chopped out the broken session and ran it again.
I had about three goes like this till it started repeatedly jamming. What was happening was the heat from the extruder was travelling up the filament and causing it to soften but not liquify in the extruder barrel. This meant that the squishy filament expanded outwards as the motor driving the thing put pressure on it from above locking it in place. Cutting this bit out and starting with a fresh filament and extruding immediately worked but if it sat idle for any length of time so the heat could spread up the filament making it jam and then either ruining a build or failing to produce one. I tried various approaches to fix this higher and lower temperatures increasing the tension in the pusher to try and ram the filament through. But had no luck.
Eventually I managed to jam the extruder such that I couldn’t get the filament out again. I called it a night at this and figured I’ll dismantle the extruder tomorrow and see if I can extract the filament. I might try aiming a fan at the top of the extruder to see if that cools it sufficiently that the filament remains hard enough to still get further into the barrel where the tempertature is high enough to melt there is also a small heat sink on the barrel I might try moving that further down or maybe getting another one. It would be nice to get some consistent prints out of PLA without having to cut a section off each time and risk a jam that requires disassembly. I like the look and feel of PLA it’s hard and glassy and a nice crystal like transparent effect. Plus I have a huge reel of the stuff.
If the worst comes to the worst I’ll switch to the Black ABS I have on standby but I’d prefer to get some use out of the PLA if possible. A lot of people in the mendel world have had better luck with PLA and I did also do fairly well with it on the BFB printer (most of the parts I printed for the mendel are in PLA) so it could be down to the extruder design. With that in mind if I get round to assembling my own mendel I might be able to come up with a hot end that works with the PLA I have and leave the ABS for my little makerbot instead.
