Variable to Constant Gearbox Prototype

Check out the details here: http://www.thingiverse.com/thing:5020

PLA: Highly Recommended

I purchased PLA from Makerbot and MakerGear, and am happy to say that PLA has definitely lived up to the hype.

I've had no noticeable warping, even when printing the largest part sizes possible on the Makerbot, like these planetary gear quarters that are part of a prototype for one of our Senior Design groups. PLA forms a harder part than ABS, which is preferable for sharp edged parts such as these.

PLA is a bit more demanding than ABS, in that as it melts it goes through a "gummy bear" stage, which can jam in the nozzle. When warming up, it requires a bit of finesse that ABS didn't need, in order to get started. I use the same temperature settings as with ABS (225C target), since the material I received has a declared melting temperature a degree higher than what I observed with ABS (ABS 209C, PLA 210C). This allows for the temperature swings I get on the extruder, and caused no observable issues. When the extruder warms up to 225C, I clear the drippings, which can be substantial, then I loosen the tension screw on the MK5, and manually press the filament in to the extruder a couple inches, which clears out some of the melted PLA in the barrel. I then tighten the tension bolt and run the extruder motor from the control panel for 15-30 sec to make sure I'm getting a nice extrusion. I clear the extruded gunk, then start the print.

Between prints, I've noticed that if I let the extruder cool, then heat up again, it has a tendency to create a "gummy bear" plug in the extruder barrel. This can be pulled out and clipped off, as in the pic below, or just wait 5 min after hitting target temp to make sure the "gummy" has melted to goo before printing the next part.

This is what happens when you get impatient and run the hot PLA part under cold water, rather than letting it air cool. I then popped it off with a pair of vice grips, and the long-suffering orange acrylic plate gave up the ghost. I had another orange plate, so I wasn't forced to mill something from aluminum , although that would probably be a good idea, longer term. When I put the new plate on, I tested printing on blue painter's tape, and that's working very nicely.