Turning a perfect sphere (how to)

[Kathy Marshall]

This is a step by step for turning a perfect sphere as demonstrated by Keith Gotschall.

The 1st step is to turn a blank to a cylinder. Start with a piece a little longer (about 1 - 1 1/2") than the diameter.
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After turning it round, measure the diameter with calipers (this will be the final diameter of the ball).
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Add about 1/32" to the diameter measurement. That will give you just enough extra to give a little fudge factor and still work with a jamb chuck. If you add too much, you'll have a hard time getting it to hold in the jamb chuck.
Take that measurement and transfer it to your cylinder, then find the exact center point and run a pencil line around the cylinder. Don't do what I did and scratch it in :eek: (really, I don't know what I was thinking, but at least I made it a very shallow scratch).
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Use a parting tool to define the ends, then start roughing out a sphere shape, being careful not to remove too much. I parted it down in stages so I'd have more support in the initial roughing. Part down the waste to a small enough diameter to be easily sawed off, but not so small that it will easily come apart before you're ready.

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Remove from the lathe and saw or cut off the waste.
Next you'll need to turn a jamb chuck. Turn a cylinder then mount in a chuck. Then turn a hole a little smaller that the diameter of the ball, it should be deep enough that the ball doesn't bottom out and the sides should taper in (ball shaped).

Continued.......

[Kathy Marshall]

Test for fit as you're hollowing the jamb chuck. It should be a snug fit so it holds and the ball should go in to about 1/8" less than the halfway mark (you should be able to see the centers where you cut off the waste, on the outside of the jamb chuck). The positioning should be 90 degrees from how it was turned as a cylinder (the cut ends should be perpendicular to the ways).
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When you have a good fit, use the point of the live center in the tailstock to line up the center line. Don't touch the live center to the line, just get it very close to visually line it up. If you have a good snug fit, when you turn the lathe on (slowly), you should see just a dot at the spot where the tailstock would touch. If you see a small circle, then it's not lined up just right.
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For the next step, I used a small cut off from a pen blank so I could use the tailstock to apply just enough pressure so the ball wouldn't pop out for this step.
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Use a parting tool and cut a groove in the middle. Take small cuts and take it down until you just touch the pencil line, don't go deeper than the line. The groove will match the diameter from the pencil line, giving you the final depth.
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Move the tailstock out of the way (you won't be needing it again), then turn the ball 90 degrees so that the pencil line is running perpendicular to the ways. You'll need to turn some length off of the jamb chuck (the hole will be too big now) and maybe deepen the hole. Adjust the hole as needed until you have a good snug fit, it will be the only thing holding the ball for turning. The pencil line should be out about 1/8" out from the jamb chuck.
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Once you've got a good fit, and the the groove is running parallel to the ways, start turning the diameter of the ball down to the bottom of the groove. Take fine cuts, you don't want to pop the ball out and you don't want to turn below the groove. When I got very close to the groove bottom, I used a small square scraper to take very fine cuts until the groove marks were gone.
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Switch the ball end for end and turn down the other half. You should end up with no lines except for the original pencil line which will get sanded off.

Start sanding and keep repositioning the ball so the entire surface gets sanded (move it randomly rather than all 90 deg turns), repeat with each grit until you're happy with the finish.
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Hope I explained it well.
Have fun and I look forward to seeing some perfect spheres posted!

[Faust M. Ruggiero]

Kathy,
Thanks for taking the time to show us the technique. There is a nice feeling about rolling a smooth sphere around in your hands, especially one made from a dense wood. I'll give it a try.
faust

[mickey cassiba]

Thank you for the great tutorial Kathy. With no local turners to speak of, and no time to make it to the 'big city' for classes, I have to rely on articles like this and utube videos for pretty much all of my instruction.

[Fred Belknap]

Kathy like Mickey I rely almost completely for inspiration and information on the internet. You did a great job showing how it is done. I wonder how large a sphere you can make with this set up. I also need to find a way to hollow them as a larger sphere would likely crack or distort quite a bit. Looks like one could leave one of the tenon on and hollow it out then put it in the ball chuck. I made a couple by eye and they ended up not quite the same and not quite round either.

[Baxter Smith]

Thanks Kathy. Well done!