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Feb 2015

Switching from ABS back to PLA is very problematic and often causes nozzle clogs. The best deterrent is to do a “cold pull” every time you change filament. This means you pull out all the plastic when the plastic is just above the glass temp such that it ALL comes out - in the shape of the nozzle tip including the .4mm shaft.

Step 1 is to melt the plastic and shove the filament in hard such that a little extrudes (usually UMs retract at the end of a print - if you are there at the end you can cut power and shove the filament back in (both for UM and UM2). 180C is plenty hot enough for PLA - any temp that lets you see some plastic come out of the nozzle is fine.

Step 2 is to cool it to the perfect cold pull temperature. For PLA this is 90 to 95C. For ABS this is I believe 130C (haven’t done it in a while). On the UM2 make sure power is off at the feeder! Pull hard - 10 to 20 pounds force. If it comes out easy you weren’t cold enough. If it won’t come out raise the temp by 10C and try a few seconds later. Also on the UM2 once you pull it out of the nozzle let it sit in the bowden for at least 10 seconds to harden before pulling it through the feeder.

I now do a cold pull on every filament change. When I change colors I don’t have to wait for the mixing to end and the new color to appear.

Thank you so much. I had been disassembling the nozzle every weekend, leaving it in acetone and then cleaning it out.

No. I print with Nylon occasionally which absorbs water very badly and it boils as it prints. You can hear it snap/crackle/pop/hiss as it comes out and you can see the plastic is foamier and whiter (less transparent) when it is humid. I’m pretty sure water content won’t cause clogs.

Simply leaving PLA or especially ABS in the nozzle for 5 minutes at 240C will caramelize it into a brown gunk. Doing a “cold pull” after every 10 hours of printing or on every filament change helps and printing PLA at say 220C rather than 240C helps quite a bit. And ABS I always print at 245C. In general printing too hot or too slow (stopped) can cause clogs. Printing too cold or too fast can cause problems feeding and underextrusion (feeder isn’t powerful enough).