Mechanical Pencil Tip

I was experimenting yesterday and came up with this:



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.

Well finally! Thanks for actually doing something the rest of us have been talking about doing for the past year or so, Steve.

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.

Here's a closeup of the extrusion, along with a 0.5mm pencil lead.

Interesting. No swell to speak of. You say that it takes a lot more force to extrude. How much is a lot more. Are you using the Mk II, or are you forcing it by hand?

I've got a Mk II with the flexible shaft removed, a pipe clamp on the hot end of the PTFE and deck screws through the cold end. It managed to hold up for a while but eventually came apart at the pipe clamp. Currently rebuilding it.

That clamp thing doesn't work for much of anything aside from PCL.

You can see a different approach that can handle much higher extruder barrel pressures there...

[3dreplicators.com]

and here...

[3dreplicators.com]

Yeah, I'm starting to realize that the PTFE barrel just won't take the stresses involved.

I finally broke down and replaced my old vernier caliper with a digital micrometer. It says the extrusion from the pencil tip is 0.65mm, compared with 0.55mm for the pencil lead.

put sone of the nicrome wire on the dome nut aswell and solder the pencil tip on to the nut with plenty of lead that helps with heat conductivity so the tip is warm aswell

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.

ronanwarrior Wrote:
-------------------------------------------------------
> 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.

Yea, logically it makes sense. The plastic wants to stay in its former shape, so if you spend a longer time introducing a new shape (ie longer extrusion channel) then the result will be the the plastic takes more closely to that new shape.

---

Jay

I had a similar idea. The suitability of parts of these pencils struck me, like many others probably.

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?)



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!

I like the graphite idea. I remember, as a kid, making an arc lamp from a pencil.

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.

The carbon rods in standard batteries always made the best arc lamps.

You saw that correctly. The graphite fits in just a little loosely. They were made of stainless, chromium-nickel steel.