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[zaggernut]

After all the flat spot issues talked about here, especially with tops with large bearing ball tips, I have decided to try making my own top from scratch, where I can control all parameters. I would continue the discussion in the other topic, but that one has taken a life of its own.

Anyway, my game plan is to -

   1. Buy some tungsten rod/pipe/sheet and some magnesium alloy rod,
   2. cut/sand the tungsten into a flywheel on a lathe,
   3/4. press fit the magnesium rod into the tungsten flywheel,
   4/3. turn the magnesium rod into a stem and inner disc,
   5. drill a thru-hole in the stem to press fit a short thin tungsten carbide/sapphire cylinder (these can be replaced thanks to the thru-hole),
   6. shape the thin cylinder into a tip,
   7. tap 3 horizontal balancing screws into the magnesium stem and 3 vertical screws into the inner magnesium disc,
   8, friction fit and shape either a carbide or a sapphire tip, and finally
   9. somehow balance the top.

Of course, I plan to prototype shapes to test for aerodynamics first with brass, as it shouldn't be all that density dependent. Sizes are a different matter and I may end up having to make a couple different tungsten flywheels.

Which leads me to the first hurdle, which is in aquiring tools. Will it suffice to use a watchmaker's lathe as opposed to a typical entry level mini-lathe? I only intend to use the lathe for topmaking, nothing more, and I feel like a watchmaker's lathe will have less play in the spindle and also less runout, not to mention it takes up much less space.

The second hurdle lies in aquiring tungsten. For with all my searching, I cannot find sellers of tungsten rod/pipe over 20mm/0.8" diameter without purchasing bulk. Does anyone know places which sell tungsten of 40mm/1.5" or greater diameter (or just sheet tungsten) in reasonable quantities (~500g)? My best bet right now would be to buy an overpriced 1.5" tungsten cube made for element collecters, and then cut it into cylinder shape. Also, would it be at all possible to machine pure tungsten, say by making extremely shallow cuts on the lathe, or simply sanding my way to the desired shape? I have asked a couple of the top EDC topmakers and they nowadays use MT-185 alloy, which apparently doesn't have much or any inhomogeneity and is like 97% W, but there is something special in my mind about using pure tungsten. I have also heard pure tungsten is brittle, and I am worried press fitting the Mg core might cause the flywheel to crack.

[ortwin]

Big plans! Sounds good to me, you seem very motivated. I will try to comment on some points of your plan but there are people around here with a lathe that for sure know more than me.

   1. Buy some tungsten rod/pipe/sheet and some magnesium alloy rod,

Why does it always have to be tungsten?
Platinum has a higher density, plus it is a lot cheaper than gold these days. There are coins available that might have roughly the correct outer size and shape. My guess is that is better to work with on a lathe than tungsten.

Magnesium? I thought that the element is very brittle. But yes, alloys can be different.

   . ...
   7. tap 3 horizontal balancing screws into the magnesium stem and 3 vertical screws into the inner magnesium disc,

The balancing screws in the stem? That can work of course, but there they would have a much smaller "lever" than on the flywheel. But of course you could adjust much finer.

[size=78%]  [/size]
   9. somehow balance the top.

Do you have an idea  already by which method you want to do this?

[the Earl of Whirl]

Good luck with all of this!!!  Sounds intriguing!!!

[ta0]

Why does it always have to be tungsten?
Platinum has a higher density, plus it is a lot cheaper than gold these days.

Platinum would be much easier to work and as you said, more dense that tungsten and even gold.
But, platinum is about 87 times more expensive than tungsten!
Still, platinum is currently about half the cost of gold.
Iridium is even denser than platinum (only osmium is denser) but 2.3 times more expensive than gold. Alloys of 90% Platinum and 10% Iridium are used in the industry, so it should be good for machining.
An EDC top made of platinum/iridium would make a record breaking and pocket breaking top! 

[zaggernut]

Platinum has a higher density, plus it is a lot cheaper than gold these days. There are coins available that might have roughly the correct outer size and shape. My guess is that is better to work with on a lathe than tungsten.

Magnesium? I thought that the element is very brittle. But yes, alloys can be different.

What ta0 said about platinum alloy. Half the cost of gold still isn't very enticing. I am personally more worried about the Mg erupting into flames while machining, but I hope the alloys are less prone to this. Not much against aluminium, it just looks worse.

The balancing screws in the stem? That can work of course, but there they would have a much smaller "lever" than on the flywheel. But of course you could adjust much finer.

3 advantages to doing it this way. One, I won't have to drill threads through tungsten; two, I'll not be taking away from the AMI of the top; and three, the screw holes will be in a position with less velocity wrt the surrounding air, so hopefully it will affect air flow around the top less. And I doubt my starting imbalance will be large enough to require screws placed further out.

Do you have an idea  already by which method you want to do this?

Like I said in my first thread, still no definitive plan. There's the laser plan, the paintbrush plan if I don't use a ball tip, spincake's accelorometer plan. I need the top in my hand first, before I can tell what actually works for me.

... I will try to comment on some points of your plan but there are people around here with a lathe that for sure know more than me.

Please do! Your spoke design is a bit over my paygrade, but we are making tops after all, we will share a lot of the same considerations.

[Jeremy McCreary]

I wish you success in this endeavor!

I'm not convinced that the EDC format is the path to record spin times, so keep an open mind as you choose your test profiles.

The aerodynamically optimal top profile remains elusive and may not be the profile that minimizes critical speed. Expect a tough trade-off and a big test matrix there.

I keep looking for TESTED guidance on rotor aerodynamics in existing machines with high-speed rotors open to the air but have yet to find it in the engineering literature I can access for free. (Industrial rotors are often enclosed, sometimes in vacuum.) Perhaps you'll have better luck.

[Iacopo]

Will it suffice to use a watchmaker's lathe as opposed to a typical entry level mini-lathe? I only intend to use the lathe for topmaking

I wouldn't take one with too little power.  The mine, (a Myford Super 7), is 550 W and it is barely enough for to machine some tungsten alloys. They are hard ! With patience and time, I can machine a 60 mm tungsten 80/copper 20 alloy flywheel. But harder alloys/bigger diameters would be a problem.
Don't take lathes made in China, especially if you like precision, you will be unhappy. It might be better to look for some old lathes, to save some money, and the quality will be better.