Spheres and Lathes

Is your lathe manual or numerically controlled?

The best method using a lathe..... is to use a CNC lathe .... but from your post I doubt you have access to one. The best method on a manual lathe is with a ball turning attachment. Ref. attached.

http://www.gadgetbuilder.com/BallFixture.html

http://www.youtube.com/watch?v=f4pwUw0G3RQ

Neither will create a "perfect" sphere but a CNC lathe that is well maintained will do a good job. You can buy very accurate spheres and balls pretty cheap.

Check out Bal-tec at http://www.precisionballs.com/

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An image of one of the most accurate man-made spheres, as it refracts the image of Einstein in the background. This sphere was a fused quartz gyroscope for the Gravity Probe B experiment, and differs in shape from a perfect sphere by no more than 40 atoms of thickness. It is thought that only neutron stars are smoother. It was announced on 1 July 2008 that Australian scientists had created even more perfect spheres, accurate to 0.3 nanometers, as part of an international hunt to find a new global standard kilogram.^[3]

To make half circle HSS forming tool as per your required dimension.

i can't concieve any way of making a sphere with a lathe...........

I did this once with a manual lathe. The idea is to step the cut in accordance with the relationship r*sin(theta).

1. Determine the diameter of the sphere you want to cut. Divide this number by 2.

2. Draw a quarter circle on a piece of paper and divide this in to sections of equal width- assuming the horizontal axis is equivalent to the turning axis, then the lines dividing the sections should be vertical. The higher the number of sections, the more accurate the surface of the sphere, but this will be limited in practice by the shape of your cutting tool. We will call the distance between the equally-spaced vertical lines "delta".

3. Draw a line from the center of the quarter circle to the point where each vertical line crosses the circumference. Determine the angle of this line from the horizontal. Calculate the sine of the angle with your handy calculator (if you select the right display mode). Make a table (you can use Excel for this) listing all of the results.

4. Multiply each of the sines from step 3 by the radius of the sphere. Subtract the result from the radius and record this as the "cut depth". Now you have a spreadsheet that has the first column the "delta" number, the second column the sine of the angle, the third column r times the sine, and the forth column the cut depth.

5. Mount your stock into the lathe, turn the diameter down to the desired diameter + about 0.010 inches (the excess material will be worked off during the finishing stage). Note the point along the stock that you want to be the center of the sphere.

6. Your first cut will be one delta away from the center line. Be sure to account for backlash when setting the start of this cut. Cut away from the center line. Cut enough length to be sure you can get the tool in close to the turn axis as the job progresses.

7. Repeat step six, beginning cut 3 two delta from the center line, cutting to the depth from your table. Continue in this manner till half the sphere has been cut.

8. Now, repeat the same process on the other side of the centerline, but do not do the final cut just yet, because you need to do some finishing first.

9. After You have done all the cuts, file the steps lightly with a machinist's file to smooth out the steps. Don't over-do it, or you will distort the shape.

10. Cut the sphere from the stock, hand touch the cut-off point, then put the sphere in your handy rock polisher with various grits (here, you will have to consult other sources, because I don't know what material you are working with). Several steps of finer grit should give you a pretty nice sphere, but most likely not as round as the gyroscope sphere, or even a typical ball bearing, but pretty impressive when you tell people you did this on a lathe...

Hi,

perfect spheres are not an easy job. So what do you really need?

Balls for precision ball-bearings or any other material are mass produced by ball-mills.

Highest precision available is grade 3, that is 3 microinch out of roundness and 6 microinch tolerance of diameter within one batch. Not for inexperienced people and not available for export without end-user certificate. Try with grade 5 if near your needs.

Highest precision glass balls: spheres or partial spheres for optical lenses and mirrors - any shape, utmost tolerances. High cost and highest precision.

Highest precision in metallic hollow spheres some cm in diameter: ask the atomic bomb producers in your country - they know or should know.

So please be a bit more specific: diameter, tolerances of roundness and diameter and roughness, material, how much to be produced ...

RHABE