Sunday, January 4, 2009

Hot Stuff! First Extrusion with New Extruder Design.

It's very late, but I have to put *something* up, because I just extruded my first plastic!

Not only that, I did so using a new design for my extruder's "hot zone." The design uses an Aluminum heater barrel, with inside-out nozzle inserts (made of brass.) The melted-plastic zone is under an inch long. The stem is stainless steel, with a reduced cross section just above the (threaded) junction of Al/Stainless, to confine the heat to the hot zone.

Above: Exploded view of the key parts of my extruder's "hot zone." The melt zone is deliberately kept short, and the heat is confined by the stainless steel stem, and its reduced cross section, just upstream of where it mates with the Aluminum barrel. The coarse threads on the barrel are to accept the nichrome wire.

Above: Here is the hot-zone assembly, after adding the nichrome and coating it with my DIY ceramic glue. It's not as clean looking as I'd like, but it seems OK mechanically and electrically. Aesthetics will have to wait for awhile....

But here's the real news (drum roll please.....):

Above: First extrusion with my new extruder design.
I fed the ABS welding rod by hand, and controlled the temperature (open loop) by varying the PWM duty cycle, while monitoring the thermistor resistance with a DVM (to the left of the extruder.) The temperature is approx. 200 deg. C. Note that the barrel is not yet insulated, except by the thin coating of ceramic glue.

Above: With some ceramic-fiber blanket to insulate the heater barrel, I can get to higher temperatures, and extrude HDPE. Based on the thermistor's resistance (visible via the DMM), the temperature here was ~245 deg. C. The PWM was set to 150; so the duty cycle was 150/255 or ~59%

Above: A (very, perhaps too) candid photo of my "highly organized" electronics workbench in my basement. I could clean it up, but I'd rather work on my repstrap!
The alert viewer may discern the beginnings of Cerberus' horizontal mechanism (left-hand side of the photo), based on a compound (X, Y) table, fitted with two stepper motors. More about that later.

That's all for now. I may add more photos and details later.
Next step should be closed-loop temperature control, based on the thermistor reading.