# Need precise and perfectly balanced balls fabricated, any ideas where?

I am working on a hobby project. I need 2 perfectly spherical, perfectly balanced, pure metal (ie. pure titanium, aluminum, etc.) balls made, and then I need one (the larger one) to be precisely drilled through the center. It is essential that everything is done in an extremely accurate manner. I don't really know of any places to look or even get started. I am no professional engineer, but I am a chemistry major with minors in math and physics and specialization in thermodynamics that loves to tinker. However, most metal fabricators don't have the means to be quite as accurate as I need them to, at least the ones I have looked at. Any help is, as always, appreciated and thank you for your time.

jasc15
No such thing as perfect. How precise do you need? There are commercially available balls which are precise to within 0.0001" of a 'perfect' sphere.

Haha sorry, forget with engineers you go to crazy decimals. I would consider that more than accurate enough. Are they balanced? I basically need the small balls center to go through the large balls center. Its just a piece for a project I have been working on for a while, but all parts of the whole are essential in this case :) Thanks for the help.

Homework Helper
By balanced you mean they have a uniform density?
Then yes most metal ball bearing will be good to parts-per-million.

The main question is how big do you need them?
0.25in diamter steel ball bearings accurate to 0.0001in are available in your local bike shop for nothing.
A 10m diameter telescope mirror will cost a little more!

Drilling a hole through the center of a hard metal with a precision lathe to 1/1000in isn't too difficult

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Sorry yes I do mean uniform density, as to cause the ball to be completely balanced. The size of the ball isn't quite as important as its mass, which is of course reliant upon the density of the metal used. I would need a ~25kg large ball and a ~5kg small ball. The small ball needs to pass through the hole in the large ball with the distance between the center of mass the 2 objects (why it needs to be balanced or have uniform density) being less than .00001m. Anyone know where I could get something like this.

Homework Helper
A 25kg ball of say steel is about 18cm diameter, a 5kg one about 10cm.
For a surface finish of 0.01mm (10um) you are probably ok polishing it - you don't care about exactly what diameter you end up with as long as it's smooth.
You could bore a hole with a 10um accuracy - might need to diamond turn the inner surface to get that finish.