need help, first sphere

I'll bump a slow thread because I'm interested in it. And I'll echo DirtCleaner's request for pics. I really don't know what HP's machine looks like or how it is set up, so pics would be pretty cool. And how are you determining roundness?

On my homemade toy machine I've found that too much grinding pressure or springs or bungees or gravity or whatever can encourage selective grinding of soft areas. Or the case where the rock is not uniform but nearly equally hard, there is a tendency to grind lobes into the sphere. It is a 3-headed machine, so maybe preferentially grinding a 3-lobed shape is understandable. So I measure the rock with calipers, find the high lobes, and grind them on the diamond wheel, then return to the sphere machine. For diametral tolerances I'm happy with plus/minus 0.010" which can't really be seen.

So, yes, pics please.

And DirtCleaner's mention of preform quality is spot on. It is tough to make a sphere from an egg. Or a 3" thunderegg - a hidden gas bubble, apparently filled with a deep blue agate, in basalt, covered in baked mud and gravel, shaped like a potato - a current project.

Good luck with your spheres and HP machine.