Tuesday, August 01, 2006
I whipped out a 3d model of my imagined 'wire on/off' switch on the mechanical pencil tip extruder. All theoretical at this stage, but I think it shows the idea a bit more clearly than just text alone.
First time posting images, so not sure if this will come out or not.
The purple stuff was my attempt to wrap the model with an insulation, since the heat will be spread thru a larger portion of the extruder. The idea is that air pressure drives the liquid plastic thru the tip, as has been suggested in other comments.
gotta love the sound of a dozen monkeys poking at high-tech concepts. Creativity is king in this game.
What software was that done with?
The blender STL export didn't seem to work. At some point, I'll try to figure out how to correct it, but I'm not too worried about it at the moment. Worst case, I export to a format that art of illusion can read.
Of course, I'm not in a hurry, I'd have to build a RepRap first! At the moment I seem to be focusing on learning more electronics and programming, would like to know what I'm doing, rather than just building blindly!
Does that help? If not, just keep asking questions and I'll keep trying to make sense.
Does the MkII extruder need to generate the same pressures to get similar flow rates?
One reason I think air pressure might be useful is that the amount of air flow needed is very low. It should be possible to pump up a small air reservoir to 100 psi, and not bother with it until it was reduced to 80-90 psi before refilling. Assuming no leaks,
a 10 liter tank should be able to extrude a kilogram or more of plastic.
That is the question. You're talking about a 0.5 mm extrusion die rather than a 2 mm one, so you can be sure it's going to require more pressure. Just how much more pressure is an engineering study, nothing to be frightened about, but one that will require some feeling around. Best to do some experimentation and see what kind of graph you get for pressure, orifice diameter and temperature, hey?
***A bicycle pump and/or a service station with free air should get you by (Even better, if you have two reserviors.)***
As I said a few days ago, air compressors with small reservoirs running on mains power suitable for running things like nail guns can be had for $20-30. Just froogle "air compressor" and sort prices for lowest to highest. Here's a likely candidate...
By the time you organise a bicycle pump, a reservoir and the connectors to make it all work you'll have spent that much and not have a very good system, too.
On a somewhat similar topic, I did have a flat on my car, and had to use a bicycle pump to get it inflated enough to drive it to the service station -- 100 pumps on the bicycle pump and it seemed good enough to avoid any long term damage while driving it the 1/2 mile to the station. It was a nice workout. I could see this kind of machine being popular with the fitness minded person : "Build Some Muscle And Make A Plastic Comb" machine.
Okay... maybe just buying a USD30 nail gun compressor would be a better solution, long term. :)
How do most commercial fabricators do it? That might be a hint as to which direction to go. Of course, that's why this group is here, so we can each dabble around and try to find the best solution.
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