I was experimenting yesterday and came up with this: [attachment 595 scripto.jpg] It's a mechanical pencil tip in an acorn nut. I drilled a hole a bit narrower than the widest part of the pencil tip. The pencil tip is from a 0.5mm Scripto P200. Tightening the nut on the barrel wedges the pencil tip into the hole. As you can see from the photo, it actually managed to extrude some plastic. Advantages: cheap, easy to make, very little rebound. Disadvantages: cools quickly, requires a lot of force to extrude. Interesting but probably not practical for HDPE. https://reprap.org/forum/read.php?70,10486,10486#msg-10486 Sun, 08 Mar 2026 20:04:25 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?70,10486,11084#msg-11084 https://reprap.org/forum/read.php?70,10486,11084#msg-11084 ErikDeBruijn Plastic Extruder Working Group Mon, 14 Apr 2008 14:37:17 -0400 https://reprap.org/forum/read.php?70,10486,11083#msg-11083 https://reprap.org/forum/read.php?70,10486,11083#msg-11083 Forrest Higgs Plastic Extruder Working Group Mon, 14 Apr 2008 14:35:24 -0400 https://reprap.org/forum/read.php?70,10486,11076#msg-11076 https://reprap.org/forum/read.php?70,10486,11076#msg-11076
Syringe needles might be interesting. The one you've got there looks like it's about the same diameter as the pencil leads.

I remember seeing a syringe made entirely from stainless steel recently. I think it was a marinade injector for meat.]]> degroof Plastic Extruder Working Group Mon, 14 Apr 2008 12:37:56 -0400 https://reprap.org/forum/read.php?70,10486,11074#msg-11074 https://reprap.org/forum/read.php?70,10486,11074#msg-11074
I don't know if anyone thought of this, but I could extrude plastic from such a pen just by applying a voltage to the graphite. I was mostly investigating how I could reduce the dependence on nichrome wire. These graphite (pencil) rods are very straight and become red-hot when you apply power to them. Since this is another heater material, I'd like to know if this allows for measuring the heat by measuring the coefficient of resistance of the material to determine its temperature. This way the heater and the temperature measurement are the same. (I'm sure someone already tried this with nichrome?)
[attachment 628 IMAG0061.jpg]
[attachment 629 IMAG0060.jpg]

A similar diameter hollow tube is a syringe needle. You can isolate that and put pencil rods around that and apply power to that. This makes very close contact over a length. Such a (long) needle may have too much resistance to extrude plastics through, but that may not be so for metals or fluids with less viscosity.

Sorry for going a bit off-topic!]]> ErikDeBruijn Plastic Extruder Working Group Mon, 14 Apr 2008 11:32:10 -0400 https://reprap.org/forum/read.php?70,10486,11047#msg-11047 https://reprap.org/forum/read.php?70,10486,11047#msg-11047 redskinsjbs Plastic Extruder Working Group Sun, 13 Apr 2008 19:19:48 -0400 https://reprap.org/forum/read.php?70,10486,11043#msg-11043 https://reprap.org/forum/read.php?70,10486,11043#msg-11043 -------------------------------------------------------
> In order to reduce some of the stresses you could
> grind down the very tip to at least half. The
> friction on that long of a small nozzle is
> extreme. I suggest grinding because you would be
> less likely to pinch the barrel if you cut it.
> Another thing you can do is use a 0.3 mm pencil
> tip...if you ever get a the new barrel worked out.


It will be interesting to see what effect this modification had on the amount of die swell. IIRC Nophead's trials had significantly more swell for similar nozzle diameters, and the main difference I see here is the length of the extrusion channel.]]> Kyle Corbitt Plastic Extruder Working Group Sun, 13 Apr 2008 17:59:04 -0400 https://reprap.org/forum/read.php?70,10486,11040#msg-11040 https://reprap.org/forum/read.php?70,10486,11040#msg-11040 ronanwarrior Plastic Extruder Working Group Sun, 13 Apr 2008 17:45:27 -0400 https://reprap.org/forum/read.php?70,10486,10996#msg-10996 https://reprap.org/forum/read.php?70,10486,10996#msg-10996 r2kordmaa Plastic Extruder Working Group Sat, 12 Apr 2008 16:57:59 -0400 https://reprap.org/forum/read.php?70,10486,10569#msg-10569 https://reprap.org/forum/read.php?70,10486,10569#msg-10569 degroof Plastic Extruder Working Group Wed, 26 Mar 2008 20:22:19 -0400 https://reprap.org/forum/read.php?70,10486,10523#msg-10523 https://reprap.org/forum/read.php?70,10486,10523#msg-10523 degroof Plastic Extruder Working Group Tue, 25 Mar 2008 15:11:53 -0400 https://reprap.org/forum/read.php?70,10486,10493#msg-10493 https://reprap.org/forum/read.php?70,10486,10493#msg-10493
You can see a different approach that can handle much higher extruder barrel pressures there...

[3dreplicators.com]

and here...

[3dreplicators.com]]]> Forrest Higgs Plastic Extruder Working Group Sun, 23 Mar 2008 16:25:24 -0400 https://reprap.org/forum/read.php?70,10486,10492#msg-10492 https://reprap.org/forum/read.php?70,10486,10492#msg-10492 degroof Plastic Extruder Working Group Sun, 23 Mar 2008 15:42:42 -0400 https://reprap.org/forum/read.php?70,10486,10491#msg-10491 https://reprap.org/forum/read.php?70,10486,10491#msg-10491 Forrest Higgs Plastic Extruder Working Group Sun, 23 Mar 2008 15:30:26 -0400 https://reprap.org/forum/read.php?70,10486,10490#msg-10490 https://reprap.org/forum/read.php?70,10486,10490#msg-10490
[attachment 596 pencilTipExtrusion.jpg]]]> degroof Plastic Extruder Working Group Sun, 23 Mar 2008 14:48:12 -0400 https://reprap.org/forum/read.php?70,10486,10489#msg-10489 https://reprap.org/forum/read.php?70,10486,10489#msg-10489
I'll bet if you wrapped a few loops of your extruder heater around the tip you'd be able to extrude just about anything. :)]]> Forrest Higgs Plastic Extruder Working Group Sun, 23 Mar 2008 14:00:15 -0400 https://reprap.org/forum/read.php?70,10486,10486#msg-10486 https://reprap.org/forum/read.php?70,10486,10486#msg-10486
[attachment 595 scripto.jpg]

It's a mechanical pencil tip in an acorn nut. I drilled a hole a bit narrower than the widest part of the pencil tip. The pencil tip is from a 0.5mm Scripto P200. Tightening the nut on the barrel wedges the pencil tip into the hole. As you can see from the photo, it actually managed to extrude some plastic.

Advantages: cheap, easy to make, very little rebound.

Disadvantages: cools quickly, requires a lot of force to extrude.

Interesting but probably not practical for HDPE.]]> degroof Plastic Extruder Working Group Sun, 23 Mar 2008 12:49:20 -0400