3 Head Sphere Machine - coring process added

So you're saying the probably thousands of spheres made using the the single cup sphere setup for old flat laps don't exist?

That's kind of like saying if I hold a lathe bit in my hand against my piece while the lathe bit in the tool post is cutting that the bit in my hand is somehow doing something important.

On review it is clear that the upper "cup" is a measuring tool, and is doing ZERO material removal.

Tonight, I'm hoping tonight to make core cuts to make a preform. Will make images for this thread.

Regarding cup size.

I have not experimented with different sizes but this concept intrigues me.

Today if my sphere is 5" the circumference is 15 so I use 4" cups leaving approximately 3/4" between each cup. Bigger cups won't fit and bang into each other too much smaller they cut slower and the rough ball pops out easier.

ETA

Might be smart to try a 3" cup in that trio. I can visualise better random motion.

Excellent! Thank you Scott!

Your very brief stop just a tad north east of St. George Utah paid off in a future nice sphere.

And the price was right.

You might consider ALSO adding your images to the first post so the whole story is told in one place for new viewers.

Sorry Rob. I missed this.

No, accessories not included

I think what 1dave is saying that without some other interaction, simply placing a preform on a single cup and spinning it, is going to do nothing but spin it like a top. You require a second interaction, hands or device to cause the off axis rotations needed to true a sphere. You notice in the video that the upper cup tilts back and forth to cause the sphere to rotate in different axis's. It is also used to apply weight to enhance the polishing action as can be seen when the optician adds a weight to it.

Also there have been several "perfect" sphere's made over time for different purposes.

In the video posted, they were making a kilogram reference using a single head at first (hands did the perturbations) and then a two head machine for polishing. However you want to define the role of the upper head, you can see him adding polishing compound so unless the upper cup is made from a perfectly frictionless material, they both have to contribute to the polishing action.

Two four-head machines were built and used to make "perfect" spheres for the Gravity Probe B Experiment (GP-B) at Standiford. They had a peak to trough average of less than 25 nanometers.

I'm just stating an opinion here, but I'd suppose a primary difference between 2-head and 3-head designs would be more support from more directions resulting in trapping the sphere better and reduced tendency to ejects a sphere (which happens). I would also imagine that 3-head would tend to average out errors better in the same way you use 3 flat laps against each other in turn to average out the errors in any one of them, 2 laps tend to mirror each other more. You can check that in any tool and die manuals. Yes, the more heads, the more cost and maintenance is true too, but you probably have to replace 2-heads slightly more often than 3-heads.
For that matter, make a 6 head machine to capitalize on triangular stability, averaging, entrapment and speed.

Kevin

One trick I have heard of for a jig for core drilling is to use a piece of pvc pipe cut in half legnth wise to hold your stone for the 2nd, 3rd, ect. Cuts. Your pipe I.D. would need to be the diameter of your core.

The bigger the better for coring. Up to the torque limits of the motor. Mine says up to 8" cores.

They are diamond.

As for ball size: it will be marginally smaller than the inside diameter of core bit.