Saturday, February 17, 2007


Extruding HDPE in the Mk 2.1

Just a note in passing. I've tweaked the Mk 2.1 for use with HDPE. It is currently extruding HDPE at a rate of just a shade over 4 mm/sec through a 0.5 mm extruder orifice with the extruder heater consuming 2 amps at 12.34v. The thread expands to about 0.75 mm after leaving the orifice.

I'm using the gearmotor in pseudostepping mode with an 80 msec power pulse followed by 160 msec pause.

It's important to remember with the Mk 2.1 that all of the spring loading on the filament must be put on the top two springs. Tightening the bottom two, something I intuitively do which is dead wrong, stops the flow.

I took a video of the extruder operating and put it on YouTube.

It's a little difficult to see the HDPE coming out of the Mk 2.1 in this YouTube video in that the molten plastic is transparent. About the height of the cardboard covered work surface, however, it cools off enough to go opaque which lets you see it being laid down.

One little note, that loop of cooling HDPE that you see is being laid down in mid-air. The filament leaned against the edge of the xy positioning table and then just started coiling up in the air about an inch above the level of the cardboard.

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