Tungsten needles

[Beatsy]

I've started this topic in answer to Rik's question over in Tech and Studio Photography ( https://www.photomacrography.net/forum/ ... hp?t=41452 )

...I am clueless about tungsten needles. Do you know a reference that can teach me about them?

Glad it's not just me. They've been around for absolutely yonks. Preferred dissection needle material by the looks. Anything from dissecting (down to cell level), counting and sorting (e.g. spores!!), probing ICs, the list is endless. And I only spotted 'em a month or so ago...

I started with fed-up-ness. Glass needle making drives me nuts and I looked for an alternative (again). This time, I stumbled on the IC probes - and it all went from there. Quick summary on how to get/make 'em to start with...

You can buy 'em
https://surgicaltools.co.uk/fst-product ... ders/pins/
https://www.lambdaphoto.co.uk/everbeing ... -tips.html
I bought the second type - pack of ten each of 1 micron and 0.3 micron tips. Totally rigid - tip eventually bends if pressed continually into glass (diatom arranging), but the end can be lapped steeper for an indestructible, but still dead-sharp point.

Or make 'em with tungsten wire. 0.25mm sweet spot for manipulating and small dissecting IMO. I certainly won't be buying any more. Pennies vs pounds per needle cost by making - and I can customise each one as needed.

1. Grind and lap a point on it with a Dremel or two. Eats lapping paper and grinding wheels/disks like crazy. Expensive and slow for thick wire. Fiddly (and therefore slow) for thin wire too. Good for finishing a point to strengthen it or or for starting the tip shape in rubbish wire though.

2. NaNO2 - Spall tungsten off red hot wire on near-melted stick of sodium nitrite. https://www.youtube.com/watch?v=WvepYAwiKU8
Takes a bit of practice and really good for thick, low-grade wire. Bullies the shape onto it. Not good for thin wire (for me). Better than grinding for starting a thick wire point.

3. Electrolysis - the best. Loads and loads of nuances, but principle is super straightforward. I use this now. Less than 30 seconds from cutting wire off the spool to having a finished and polished, fine point. This is a good starting point, there are other similar articles.

http://www.mccroneinstitute.org/uploads ... 996273.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2555190/

Pic here is one of my first "working" needles done by electrolysis, but I hadn't learnt (any) nuances then. Bit rough, but makes a prettier picture

[Macro_Cosmos]

It's quite amazing how much these needles cost, they are for sure expensive. Great results, I'll try making some when I can legally muck around outside to get stuff.

[rjlittlefield]

Is some special chemical characteristic of tungsten needed to make this work?

Or is tungsten used only for its high physical strength (109000 psi yield)?

Could I make a really soft one out of, say, annealed copper (4830 psi yield)?

--Rik

[Beatsy]

Is some special chemical characteristic of tungsten needed to make this work?

Or is tungsten used only for its high physical strength (109000 psi yield)?

Could I make a really soft one out of, say, annealed copper (4830 psi yield)?

--Rik

Pretty sure tungsten isn't special in the way it's converted to a salt and pulled off the wire by electrolysis. No reason other metals wouldn't work too - given the right electrolyte. But I've not tried it and can therefore only assume that the physical properties are reason for choosing it.

[Smokedaddy]

You always have interesting ideas. I just finished a project using rust removal by electrolysis. The .PDF you linked is very similar to what I did. Looks like that's definitely the best route. I was amazed how well it worked, like magic. Thanks.

Once upon a time I was a certified welder (still am). Years ago I used Chem Sharp to sharpen tungsten. I assume it's similar to what you've mentioned, heat the tungsten and dip. I didn't care for it but it worked fine. Not that it matters, they make a tungsten sharpener too, that's what I use when TIG welding. They're expensive but do the trick. Most welder chuck up a piece of tungsten in a cordless drill then sharpen it on a grinding wheel (usually a diamond wheel on more critical work). Trouble is, in your application the smallest diameter I've ever used is 1.57mm (hand weld not compurtized). If that wasn't a typo you said 0.25mm.

-JW:

Updated: corrected tungsten size to 1.57mm.

[Smokedaddy]

So what was the diameter of the tungsten wire in the image you posted?

[Beatsy]

So what was the diameter of the tungsten wire in the image you posted?

Thanks for your comments. The pic over on the other thread was a needle made from 0.25mm wire. No typo. This one was 0.1mm (also no typo ).

Thicker 0.5mm wire makes better dissecting needles (much stiffer) but I only got some sub-standard rough wire at that size (From Ukraine). Splits and grooves all over - and the electrolysis follows those so you can't get a decent tip shape. It was 10x more expensive than other wire I got from a Chinese vendor and that was superb - bright shiny and smooth. Makes excellent points first go.

I don't think I could envisage manhandling needles made from "38mm" rod though

[Smokedaddy]

So Steve, do you meaning something like this?



-JW:

[Beatsy]

Yes, but check purity if you can (the good one I got claimed 99.5%). I bought the last that seller. had I guess you won't know the state of the dies used to pull the wire until you get it. Bur not much fun (or use) to work with if it's all grooved. Perhaps you can ask about that before buying.

[Smokedaddy]

Since I never thought about looking at the point of my TIG tungsten under a microscope. here is what my tungsten sharpener does to my welding tungsten. I probably could have gotten a little finer point. It has a 30um flat on the end now. I realized it's OOF. Hopefully you see the small horizontal red line just below the tip where Imagej measured its width.



-JW:

[NikonUser]

I looked at the ref. for the needles you bought: 1 pound for 10 ??
FST in America is asking $95.75 for 10 with 1 micron tips

Are yours really just about $1.50 for 10, even for 1 that would be cheaper than over here

[Beatsy]

I looked at the ref. for the needles you bought: 1 pound for 10 ??
FST in America is asking $95.75 for 10 with 1 micron tips

Are yours really just about $1.50 for 10, even for 1 that would be cheaper than over here

No. First link have them for over £100 + VAT for ten. Second are £72-ish plus VAT (20%). I got those. I don't regret buying them as they proved a very useful reference point in a sea of "know nothing" at the start. I wouldn't buy more though - ever!

[Beatsy]

I've been manipulating diatoms using tungsten needles ever since I discovered how to make them. One thing that slightly irked me was the excessive length of the taper to the point. This appreciably thins the wire from the original diameter of 0.25mm, making the tip weaker and more prone to bending (e.g. if pressed too hard on the glass when picking). With thousands of hours of manipulating under my belt I rarely had a problem with that, but folk with less hands-on practice have reported frustration because of it. Needles are easy enough to straighten, or re-make, but it would be nice to minimise the effort (and time) spent doing that.

The obvious solution is to make the taper shorter by not dipping the wire so deep into the electrolyte when forming the point. I tried to do that, of course, but it never worked properly. The (shorter) tapering tip would always take on a bullet-shaped profile rather than a straight-sided isosceles triangle (allowing a needle to come in at a lower angle - necessary when using high-power, close WD objectives). In fact, if you look at the pic at the top, and the one in the linked thread (Spiked), you'll see their tip profiles are slightly convex-sided too, even though they are relatively long tapers.

As I said, I've had no problem with this and I got over the "low angle" need by bending the very tip of the needle after sharpening. Then the main shank can lead in at a steeper angle with the bent bit reaching in between objective and slide at a shallower one. But it still irked me that the tip didn't have straight tapered sides as I thought it should. So I recently took a closer look to see why it happens. An "aha" moment ensued.

When the end of the wire is dipped in the electrolyte, surface tension causes a meniscus to leap up the wire much faster than the "dipping velocity". Similarly, when the wire is retracted, the meniscus sticks to it for a while before suddenly letting go. This means the very tip gets more "all over" electrolysis than the rest of the taper which kills the linearity of the smooth in-out dipping motion. Hope that makes sense. It's not that noticeable with long tapers, but it really shows a lot on short ones - and makes very short tapers (<2mm) practically impossible.

The solution? A few drops of non-ionic surfactant in the electrolyte to break the surface tension! I used Rinse Aid, a dishwasher additive. Jet Dry will likely do the same. There is still some meniscus, but it's much smaller and 2mm tapers are easy to do. They are *way* more robust than I expected too. In fact, it's quite hard to bend the tips, even by pressing on the glass. There's an added bonus in that sharpening goes a lot faster as there's less tungsten being burnt off. Win, win, win!

Here's a couple of needles done with 0.25mm wire and Rinse Aid in the mix (two macro snaps composited into one). The tapers are about 2mm long. They're more aesthetically pleasing too, IMO. That's not an essential property though, but a pleasing one all the same.

[Smokedaddy]

Sweet. I was just reading an old email today where you and I were discussing this. I wonder what diameter pinhole this would punch in a piece of thin aluminum foil?

[Beatsy]

Sweet. I was just reading an old email today where you and I were discussing this. I wonder what diameter pinhole this would punch in a piece of thin aluminum foil?

Easiest thing to do is make a stack of tinfoil, poke a needle down into it then riffle through the stack for the last hole (if you want the smallest). The points on these needles easily approach sub-micron.