Machining Tungsten

As a precursor to making heavy half balls (for a Pickering governor) I bought a short length of 8mm diameter pure tungsten from Ebay recently. I've had a go at machining it this afternoon.

Turning with an insert intended for aluminium was fine. Swarf came off as particles, like cast iron. The finish was smooth, but dull. I suspect that to get a shiny finish one would need to grind. Drilling and tapping was another matter. Trying a HSS centre drill resulted in the end of the bar fracturing. Another attempt with a HSS spot drill resulted in the drill fracturing.

'Drilling' with a 4mm centre cutting carbide endmill was fine. But when I tried to tap 2BA the tungsten fractured again:

I shouldn't be surprised; it's pretty much what the books say. Tungsten alloys machine well, albeit rather abrasive, but pure tungsten is tricky as it is brittle.

I can buy the required size of pure tungsten on Ebay, but it's $300. On this showing I think it's going to be a nightmare machining job. So I'll probably revert to an alloy. Most likely tungsten/copper as I can get it on Ebay. If possible I'll buy a sample before committing large dollars for the required size.

Andrew

Edited By Andrew Johnston on 12/08/2017 14:52:46

Yes , Pure tungsten is a bit of a swine to machine,. My friends big Tesla coil uses tungsten rods as electrodes in the rotary spark gap. Fine to face the electrodes up with a TC tip, but forget anything else. The Tungsten /Copper alloy is a much better bet for machining, but unfortunately the copper evaporates from the alloy in a rotary spark gap (60 amps at 11,000V AC)! It makes a right mess!

Andrew.

Another result; the tungsten was easily marked with a file, although hardness seems to be around 50Rc.

Andrew

Why not buy a couple of tungsten balls and silver-solder them inside hollow steel shells?

N.

I had to use "heavymetal" for a MOD project many years ago. These people make a machineable version.

https://www.plansee.com/en/products/components/balancing-weights.html

I have only ever machined tungsten once with a quite different experience to Andrew.

Years ago, a chap I used to know gave me a set of tungsten darts (dart board darts that is) to "thin down" as he complained that they were to heavy and chunky. I half expected that they would be to hard to turn so I was quite surprised that my bit of HSS had no trouble at all in attacking the grey coloured metal and reducing the diameters to the required dimensions.

It was very similar to turning gun metal and left a lovely brass like finish. Now the strange bit - within seconds the lovely brassy finish oxidised and turned to a matt grey.

That's a bit different to your stuff Andrew - what?

Rik

PS - Talking about heavy metal, has any one ever machined depleted uranium? What's it like? I'm thinking crossbow sabot versus local vermin. Wonder if Reeves stock it?

Rik

These people sell some really nice chemicals!  http://www.unitednuclear.com/index.php?main_page=index&cPath=16_17_69 

Edited By vintagengineer on 12/08/2017 18:36:36

I hope that was tongue in cheek. Machining uranium has the slight problem that the swarf is prone to catching fire, and most fire extinguishers won't put it out. It is also very mildly radioactive. If you even try to obtain some you'll have MI5 at your door. It's not even the densest element, although probably the densest commonly occuring. For that you need osmium. Reeves definately don't stock that! If you're rich enough you could use Gold, which is nearly as heavy as Tungsten, and machines very nicely. It could well be cheaper than osmium, and will keep its value. You can also buy tungsten powder. Make a thin shell and fill it with powder.

Edited By duncan webster on 12/08/2017 18:49:53

Edited By duncan webster on 12/08/2017 18:50:52

"These people sell some really nice chemicals!"

I notice they have sold out of yellowcake. I 'spect there is quite a demand for the stuff just lately from what I am reading in the papers - I'll get me tin hat then!

Rik

Hello Duncan,

Your material was either a matrix including tungsten or a tungsten alloy, usually with copper. They both machine with consummate ease. Pure tungsten can be machined with tungsten carbide or with greater difficulty HSS. In my experience you need plenty of coolant.

As for drilling or tapping it with normal kit, forget it, you will find that it will usually shatter, or break the tooling. Maybe a tungsten carbide drill might work, but I don't know if tungsten carbide taps are available!

Andrew.

"I hope that was tongue in cheek -- you'll have MI5 at your door"

Not to worry Duncan I am not in the market for yet more uranium and as for Osmium - we still have two cases of their excellent 100w light bulbs to see us through. Tongue in cheek? Me? Never!

Rik

I've just been called by someone with professional experience of these things. In case anyone was seriously considering it, don't start machining depleted uranium.

There may be a frisson to having a DU paperweight, but any uranium dust from machining is very toxic (mostly in a heavy metal way as well as alpha radiation) and you really don't want the swarf catching alight and filling your workshop and lungs with uranium oxide dust.

Even exposure to contamination from the use of armour piercing DU rounds appears to have caused health issue.

en.wikipedia.org/wiki/Uranium#Human_exposure

I note the source above sells three pellets approximating 3g for $69 and warns:

"Caution: Use normal safety precautions (wear a filter mask/respirator and gloves) when working with Uranium metal. Accidental inhalation or ingestion of Uranium particles can be dangerous. Machining will produce particles that can spontaneously ignite producing radioactive smoke. Note: adult signature required upon delivery"

Neil

DU has been used commercially. Sailing boat keels have been made from it. Conspiracy theorists got very excited by the 1992 crash of the El Al 747 in Amsterdam because some residual radiation was discovered in the wreckage. What they didn't know was that, in those days, some 300kg of DU was used for balance weights in 747s. I believe that they use tungsten heavy alloy now.

Rod

Andrew,

May I suggest you spark erode the hole after turning your sphere, Fit the supporting shaft then spark erode a taper pin hole through the assembly. I have not spark eroded tungsten but I have an Xray target a will experiment on it if you like.

Regards, John

Yes, DU was used in the earlier Boeing 747's for elevator and aileron balance weights - not sure when they changed to the tungsten. At work, we used to have a DU storeroom - very clearly marked and always locked - I always made sure that I walked on the opposite side of the corridor when passing it.

Many years ago I saw the machining facilities at the place where uranium of the fissile variety (U235) was machined to make warhead components. If you think DU is bad then you should have seen this!

Andrew.

It looks as though the heaviest safe material is gold?

Platinum is denser than tungsten and much easier to machine

Neil

Depleted Uranium is extremely dense and heavy, when I was an NDT technician our radio active isotopes used for gamma radiography, (Cobalt and Iridium) were carried in containers encased in depleted uranium which was excellent for absorbing the emitted gamma radiation until we took the isotope out for radiography. The containers were extremely weighty, especially if you had to carry them up to any appreciable height. Glad I don't do that anymore and contrary to expectations I do not glow in the dark from all the radiation that I absorbed.

Dave