Machining Tungsten

[jacques maurelParticipant @jacquesmaurel42310]

Surch for DENAL on the web it's an alloy 93% tungsten with iron nickel and cobalt I used it for making boring bars (for low vibration) it's machinable while tungsten is not, but you must use TC taps (I killed HSS ones in this stuff).

J Maurel

[Neil WyattModerator @neilwyatt]

Posted by Andrew Johnston on 13/08/2017 20:29:57:

PS: In constrast to our esteemed editor Johnson Matthey state that platinum is very poor for machining, resulting in significant tool wear which in turn creates a poor finish.

I've never had a bad finish on platinum

BTW remember Tubal Cain says no more than 50% thread engagement for Uranium

N.

[VicParticipant @vic]

I know a guy who used to work with Tungsten Copper. Very heavy stuff but easy to machine apparently. Most of the guys where he worked had their own home made darts made from "offcuts".

[duncan webster 1Participant @duncanwebster1]

Posted by Andrew Johnston on 13/08/2017 21:01:07:

Posted by John Ockleshaw 1 on 13/08/2017 03:32:09:

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.

Great idea, but the half balls fit on each side of a thin leaf spring. It's a very long time since I played with a spark eroder, so I'm not sure how they would cope with a slot 5/16" wide but possibly only a few thou deep.

Irrespective of that it would be interesting to see how well a spark eroder worked with tungsten due to its extremely high melting point.

Andrew

You can wire erode tungsten, or at least you could if you had a wire edm machine. I believe SMEE are making one, but there are plenty around for those with deep pockets. You probably need to machine the ball but leave it on the end of a spigot to give them something to get hold of. Give these people a ring

**LINK**

[JasonBModerator @jasonb]

Andrew would it be worth turning up a temporary sleeve to slip over the rod while you tap it to resist the materials want to burst. Or even slip your turned end into a collet. Another option would be to dril larger and silver solder in a bronze insert that could then be threaded.

As for the EDM you could do a "top hat" shaped cut to slice the ball in half and the spring recess in one pass so would not be cutting a few thou off an edge

Edited By JasonB on 14/08/2017 09:51:22

[Neil WyattModerator @neilwyatt]

May I make a suggestion?

Do a mock up with lead balls – they can be stumpy cylinders on the outside to give greater mass.

Experiment to see discover the force/movement/speed relationship.

Reduce the amount of lead as much as you can while still keeping sufficient movement/force.

You can then replace the lead with something else, if necessary or you may prove that even super dense balls wouldn't work.

Seems likely to be the most cost effective route to me.

[richardandtracyParticipant @richardandtracy]

While I've never machined tungsten, I have put threads in some horrible, brittle plastics at temperatures well below their glass transition temperature.

In these it was vitally important to put the threads in with as much support as possible around the thread. This meant doing the threading into an un-machined bar, supported fully over the area being tapped with an exceedingly fiercely tightened collet. This put the bar in radial compression, and induced tangential compression, so reducing the possibility of the brittle material getting into tension (which is what tends to fracture them). After drilling, re-tighten the collet just in case there has been any relaxation of the compression, then tap. A sharp tap was vital and make sure the cutting faces don't cause any flowing of the metal as this can burst brittle materials (some taps have zero or negative rake which seem to be there to do this). After putting the thread in, the outside of the bar could be carefully reduced to the desired diameter.

This method may be worth testing with Tungsten,

Regards,

Richard.

[Anonymous]

Posted by JasonB on 14/08/2017 07:29:19:

Andrew would it be worth turning up a temporary sleeve to slip over the rod while you tap it to resist the materials want to burst.

Yep, thought of that. But for the real balls it may not be a problem as it'll be a 6BA (or M3) tapped hole in a 3/4" diameter slug.

Andrew

[duncan webster 1Participant @duncanwebster1]

I guess the 6ba is to clamp the half spheres onto the spring? Can you drill through 6ba clear, then counterbore from the outside and glue in a steel or brass nut, then you don't have to tap the tungsten

[Anonymous]

Posted by Neil Wyatt on 14/08/2017 08:38:32:

May I make a suggestion?

Feel free!

I don't think I need to experiment at this stage. A mathematical analysis is fine for calculating the forces and it is clear that the heavier the balls the better. Scaling really works against one here. I then need to design the springs to oppose those forces. I can also calculate the force on the valve operating spindle. The key parameter there will be the friction on the gland between the steam passages and the outside world. I have a design in mind using a PTFE bush. I may need to experiment to confirm friction values.

Another key design feature is the valve itself; it really needs to be balanced. Courtesy of a fellow forum member I have a design for a balanced valve that I can modify and work into my particular cylinder casting.

Once I've finished the governor I can then measure operating force versus speed to see if the sums are correct and check for friction effects.

Andrew

[Roderick JenkinsParticipant @roderickjenkins93242]

I got some Tungsten heavy alloy from the surplus market (either Whiston or Crew) many years ago. I needed to try to improve the balance of this over square crankshaft.

The weights are rivetted into countersunk holes.

I've been looking for an easy source of this stuff ever since. This is what I've got left, together with some tungsten fishing weights that I bought from ebay.

The 1/4" diameter alloy bar has a density of 14.8 which suggests it's about 60% W (assuming the rest is Fe or similar density metal). The weights have a density of c.19 which suggests pretty much pure W, which is disappointing from a machining point of view (but good for ignition points!).

Andrew, I'll pop one of the little slugs in the post and you can play with the machinability, it certainly cut and rivetted with no problems, much like mild steel. The 80/20 copper alloy from China looks like it might be a good choice.

cheers,

Rod

[Anonymous]

Posted by Roderick Jenkins on 14/08/2017 11:16:42:

Andrew, I'll pop one of the little slugs in the post and you can play with the machinability, it certainly cut and rivetted with no problems, much like mild steel.

Thanks Rod, very generous.

Andrew

[jacques maurelParticipant @jacquesmaurel42310]

The DENAL density is 17.5 (19.3 for pure tungsten). The copper/tungsten alloy (used for EDM electrodes) density is only 14.

J Maurel

[Anonymous]

I've had a go at machining the sample kindly provided by Rod. I went carefully, and the tapping was a bit bottom clenching, but I managed to drill and tap M3 without breaking anything:

So whatever it is, it isn't pure tungsten. The drills and tap were all HSS.

In a fit of enthusiasm I've ordered some tungsten alloy from Israel, via Ebay. It's about 1" diameter and 4" long, so should allow me to experiment with real balls. Not bad for £27, including P&P.

It's a tungsten, iron, nickel and cobalt alloy, so similar to DENAL? When I get the material I'll make an estimate of it's density.

Andrew

[Ed DuffnerParticipant @edduffner79357]

Would it be possible to make a sintered structure of tungsten carbide powder and lead?

Ed.

[Nick HulmeParticipant @nickhulme30114]

For problematic materials and parts I default to thread milling, it works even where the material tends to fail or flex with a tap,

– Nick

[MikeParticipant @mike89748]

When lead shot weights used by coarse fishermen were made illegal, I was invited totour a factory researching a material using tungsten powder embedded in plastic. I think it was one of the companies which were previously part of the Royal Ordnance group. They were also involved in making the bodies for tungsten darts, and tungsten penetrators for armour-piercing artillery shells. I saw tungsten items being turned and tapped with conventional machine tools, and when I enquired about the machinability of the metal I seem to remember being told that they never used pure tungsten, but a tungsten-nickel-iron alloy with a density of around 17. They gave me a set of tungsten darts with bodies slim enough to get three in the treble 20, but not being a player I gave them to a pal who was. The tungsten matrix material wasnt a success, and neither has it been a success as a substitute for lead shotgun shot.

[Raymond AndersonParticipant @raymondanderson34407]

Just noticed Andrew's post The brother has machined Tungsten but not for a few years and it was done on a Bohringer lathe that had a heating source to raise the temp up to approx. 200c The Carbide tools had 0 deg top rake and 8-10 deg side rake and quite a large nose radius. After turning the parts [ some of which started at 70mm Ø] they went for finish grinding. Were for parts of "fishing tools " [Oil]. Alll drilling was done using Titex Carbide drills [ which Titex had modified]. Hope this has been of some use.

[Raymond AndersonParticipant @raymondanderson34407]

Should have added that the Tungsten was not very tolerant of any stress risers Careful design and surface finish was paramount.

[Anonymous]

My tungsten alloy bar arrived last Thursday:

I've had a go at machining it this evening. It machines very well, no issues with facing and turning. The finish looks a little rough, but I was using a 0.2mm radius insert at 0.1mm/rev. So no doubt I could improve on the finish:

I measured the surface roughness at six points around the circumference; the average was 2.09µm Ra. Surprisingly that's comparable to what I achieve on other metals so not bad.

Sadly drilling and tapping proved to be more problematic. I managed to get a M6 tapped hole produced, but it wasn't easy. Once I'd started a hole using a carbide slotdrill (removing the broken HSS drill in the process) HSS drills opened up the hole without a problem. Tapping proved difficult, although my M6 taps are far from sharp. More research is needed and I feel a tooling order coming on.

Parting off was simple at 4 thou/rev feed and a conservative 260rpm, giving a good finish:

The centre tab was easily removed by filing.

The next exercise is to use the hydraulic copy unit to produce a hemisphere.

Andrew

[JasonBModerator @jasonb]

Andrew might be worth investing in one of the colour coded taps, maybe a red ring ?

[Anonymous]

Yep, I was reading about the issues last night. The problem seems to be that tungsten has a high Young's modulus so it tends to grip the tap and contract rather than flow slightly. From what I can see a blue or green ring tap may be better as these are intended for materials that close up slightly. The question is do I go for blue, intended for tough stainless steels and tool steels, or green which is intended for tough non-ferrous materials, which of course includes tungsten. Ideally taps would be two flute and have extra relief ground. Or should I just use red, as they are intended for tough steels. Decisions, decisions!

Andrew

[Anonymous]

More progress, forwards and backwards. I've had another go at drilling and tapping tungsten alloy, and drilling small holes. I still don't seem to have the tapping sorted. Even with spiral flute and spiral point ring taps I managed to break one. And that was with a thread engagement of about 30%. Although it was my fault, I think I put a bending load on the tap when trying to back it off. This stuff seems to grip the tap like a boa constrictor. The spiral point tap seemed best, even then it looks like the black finish has worn away after one hole.

On the plus side I found that slow helix carbide drills cut the stuff like butter, beautiful. Still at £11 for the 3.6mm drill I'd have been might upset if it hadn't worked. I also had a go at drilling 1.2mm holes, as I will need these for the 18swg hoops that stop the balls flying off if the governor springs break. Here's the result, two 1.2mm holes 6mm deep, no problem:

The drills are 4-facet so I didn't centre first, just straight in at 2500rpm, using WD40 as a lubricant.

Andrew

[Roderick JenkinsParticipant @roderickjenkins93242]

Looking promising. What density is this stuff?

Cheers,

Rod

[duncan webster 1Participant @duncanwebster1]

can you not drill all the way through, counterbore the back and glue in a nut. Tapping this stuff looks like self imposed purgatory

[Author]

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