Friday, October 1, 2010

Getting into polypropylene

In which your narrator begins to familiarise himself with the vagarities of printing with polypropylene.

I cut a 3/8 inch black HDPE print bed for printing polypropylene (PP). PP doesn't stick all that firmly to it but it should be adequate for my purposes. Before getting into designing and printing ligaments, I decided to just do some sample prints to get used to how it behaves and what the settings are.

I found that my ABS temperature settings were quite adequate for PP. PP does, however, tend to swell after leaving the extruder orifice considerably more than ABS. Whereas ABS swells from the 0.3 mm orifice to 0.458 mm, PP at the same temperatures and extruder stepper rates swells to 0.58 mm. This means that you're running 60% more PP through the extruder than you are ABS for identical extruder settings. That quickly became apparent with several trial prints.

Just for fun I printed the middle finger metacarpal.

The print didn't have the fine definition of ABS, but then I don't have the flow compensated completely for the faster flow rate that PP does.  The metacarpals were quite flexible.

I printed a few flat plates of PP several layers thick with no raft and it appears that PP will work very well for ligaments.