[vger]

I had the thought of using a hypodermic needle as an extrusion tip. The needle itself would be the heating element. Place a small piece of copper tubing (perhaps turned on a lathe) over the needle and crimp the end near the tip of the needle. The attachment end of the needle would be one contact for power, and the copper tube would be the other. It would take a low voltage high current supply to power it.

[Leintz]

intersting...would you please upload some sketches of it....

the second thought... is it possible to extrude plastic like the TIG welding does...shooting overheated plastic drops in high velocity...just thought

[vger]

Well, did only have the drawings in my head... but... a few minutes with my CAD program and....

I used a 20 gauge needle for illustration. A 20 gauge has an ID of 0.02375" (0.683 mm) and an OD of 0.03575" (0.9081 mm) so the wall thickness is 0.006" (0.1524 mm).

The top ends of the copper tubing are clamped with 0.25" thick copper blocks for electrical and mechanical attachment and are identical.

On the shooting of heated droplets.... I suppose it would be possible to do that similar to an inkjet. Might even be possible to electrostatic steer the droplets similar to the fashion that an electron beam is steered in a CRT. That could make for some really high speed high resolution print capability with a combination of mechanical movement and electrostatic steering.

[EL34]

You may want to check out the reprap extruder board
Differences between types of extruders

I read a post over there about extruder tip design
It's quite critical to have the delivery tube and tip a certain shape and length

If you have too much back pressure, the tip will continue to ooze when the print head is making a move from one place to another
Even if you extract your filament to try and relieve that back pressure, it won't help

I am experiencing just such a thing with my extruder design
I need to rework my hot end from what I have learned on the reprap board
I am up to 4mm extraction and still I have a bit of oozing and strings

I am getting good print results other than that, but it's not good enough

sublime on the reprap forum has spent a ton of time dialing in the ideal design
here is his blog
J-Head Nozzles

[EL34]

Take a look at this thread also for design tips

Update on the E3D All Metal Hotend (Now finally shipping!) [Lots of pictures]