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.