Machining Tungsten

On that earlier link I saw Molybdenum alloys, which are apparently used and not as expensive as tungsten.

I think it goes without saying unless you know you've got the gear to handle it, you should always go for a relatively well machining material.

Michael W

In that case maybe Andrew should consider a Showman's conversion

Exactly my experience. Professional sources state carbide drills but HSS cobalt taps. Certainly I 'drilled' the tungsten with no problem using a carbide endmill. Time to move onto another material.

Iridium is denser than platinum, and both are cheaper than gold. But at about $1000 per ounce that'd be $12000 for the two engines. And then some scumbag would nick 'em. No idea about machining platinum or irdium, but I would expect gold to be poor, much too malleable.

A futher search on Ebay has located a 87WNiFe alloy from Israel and W80Cu20 from China. Both are over £100, which is a bit risky if they don't machine as well as expected. I'll see if I can get a smaller sample to try.

Andrew

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.

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

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

I've never had a bad finish on platinum

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

N.

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".

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**

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

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.

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.

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

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

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

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

Thanks Rod, very generous.

Andrew

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

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

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

Ed.

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