alternatives to nozzil - hyperdermic needles

Hi

Has anyone considered hyperdermic needles for the nozzle of the extruder?

I assume they are cheap. Can be easily cutdown to size with snippers and if
made from steel would take having hot plastic shoved down them by a stepper motor.

Looking at [wapedia.mobi]

Guage 23 has an outer size of 0.64mm and an inner of 0.337mm
Guage 34 has an inner size of 0.08mm for super high resolution plastic delivery.

Probably get them free at the needle exchange ..... Yep I am a reprap addict and I need my fix.

Just a thought.

But if it worked creating a nozzle with 8 high precision outputs would not be far away. (I am thinking of the 8 pin dot matrix printer style here)

Stephen

... i tried with high viscous fluids (nearly like tooth paste) and even thinner needles (until 0.1mm outer- and 0.06mm inner diameter).

I had to cut the needles complete down and still had some issues with viscosity.

As friction is even more a problem with molten plastics you should try with thicker needles cut short.

For adapting the needles you have to use Luer-Lock-adapters from steel or you'll receive big problems with heating the tip and slipping free when applying pressure.

Much better will be adapters from copper or brass, but i think you have to make them on your own or lathe and drill a treaded brass-rod and fix the needle with a nut ...

Viktor

Edited 1 time(s). Last edit at 10/12/2009 03:24AM by VDX.

reply thanks for the advice.

Stephen

Needles are cheap, if you can legally purchase them. Here in California if you go into a chemists and try to buy one they will just about call the police unless you have a doctor's prescription. Doctors are very hesitant to prescribe them for non-medical uses.

This is bizarre in that the California gov't provides clean needles free to people using illegal drugs.

That said, you can go to the vet counter of any good feed store and get them as long as you sign a waiver that you will not be using them on humans.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

There is a company called "Small Parts, Inc." that sells needles online. I'm not sure if they sell the sharp injection type or not, but I have ordered blunt needles from them that were 28 gauge. I seem to remember that they had the blunt needles with luer lock from sizes 10 to 32 gauge. The price was reasonable, they shipped fast, and because they were blunts there was no paperwork involved.

A word of caution about using needles under high pressure though. I've seen the metal needle part come flying out its plastic luer lock end due to a high pressure situation when the needle got clogged. So if you are going to test with them, please wear safty glasses and heavy clothes. Blunt or not, under high pressure, the needles become flying darts when they break loose.

... when used with FDM you can't work with the plastic versions

For the same reason i mentioned luer lock adapters made from steel or fixing nuts on a brass-tube.

Another interesting source are the nozzles from micro-plasma-welding - they're made from copper, have a common thread and inner diameters down to 0.1mm ... the drawbacks could be the price for single counts or the high thermal mass ...

Viktor

Viktor,

take a look at these... used for solder paste dispensing

SMD solder paste dispenser needles

price is really an issue, they go for something around 25€ each (vieweg). The normal alu hub stainless steel needle versions are way cheaper.

Hi energetic,

... look here, at the last page: [www.globaco.de]

When you grind the tubes short, you can dispense extreme viscous pastes too and the smallest ID is 0.172mm (0.0068 inch) - but then you're highly limited by viscosity too

Viktor

Yep,

vieweg lists them at even higher prices than the aluminum ones i think.
There is a really cheap variant with al hub and stainless tip here:
aluminum hub/ stainless steel tip

even if they add 1 € for purchasing them in quantities of 1-2, they are really cheap.

Remains the problem with viscosity...

Does MOLDLFLOW do academic versions? This would be extremely handy in terms of material properties, they are usually a pain to aquire (cross-WLF) without MF.

There is a nice tool here that converts cross-WLF parameters into power law parameters for a quick estimate.
power law fitter
the rest is written in any good injection molding tool design handbook ( the books from Walter Michaeli are very good).

I did a quick spreadsheet, so no guarantee on typing errors or twisted parameters in formulas for now .

I put in the cross-wlf parameters for ABS (at least i think, its late ), this definetly needs to be replaced with accurate values from MF database.

Cheers,

Torsten

Hi Torsten,

... thank you for the infos!

The problems with viscosity at very fine nozzles are the main reason why i'm working with fluids and pastes at room-temp instead of FDM

For an even smaller/finer application i developed a sort of pico-dispenser capable of dispensing droplets in micron-size (or even in submicron-size ) - look here: [dev.forums.reprap.org] at the atached image "Folie3.jpg".

The array is made from single droplets of an extreme high viscouse glue (something like 40000 MPa or the consitsency of tootpaste) with a diameter of 30 microns and heighth below 10 microns - the first droplet in the lowest row is bigger ... here i stacked 3 times ...

Viktor