Turning a ball on a lathe

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ML_Woy

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I just finished building a ball turning attachment to mount on the cross slide of my 12" Craftsman lathe. My first attempt to turn a ball turned out less than I expected. I need some assistance in the proper way to set up the tool to make the cuts. Oh, the tool cut great, was centered perfectly,but the radius did not turn out correctly. I had trouble getting the tool to clear the stock on the left side cuts, maybe the material needs to be relieved so to provide tool clearance when it rotates, not sure.

So could a forum member lay out the steps for proper set up, say for turning a 1" ball from 1.25" stock.

Thanks
 
Well, just from doing it by hand on a wood lathe, you don't want to try to do it all at once if you want it to be accurately round. You want to go in steps from square corners to round. Like trimming a circle from a square piece of paper. Snip off the corners to make an octagon. Then the corners between to make a 16 sided then those corners to make 32 sides. Keep going and it will finally be round.

Since you are cutting unsupported stock, you want to do it in halves. Do the half at the un-supported end first because want more stock to support you when you are turning that end to minimize deflection. Make a rough cuts until you get it mostly shaped but not quite round. Now move to the other end of the sphete to be. Make a plunge cut just past the length you want that is about 1/3 the way in. Nibble it out wider and wider to make clearance for the tool. Then you can come in bit by bit to make the other side more round.

When you get it close, back out far enough to clear everything and come in slowly taking small bites on the full stroke around the piece until you get down to the final shape.
 
you need to get the ball turning tool pivot point in line with the center of the ball, as well as the tool being on center.
 
I would say trim back the vertical post a bit more to get more clearance at the sides of the insert.

Did you dovetail the sliding bar in? I can't see from the picture. I was thinking about putting a t-slot on mine instead of grub screws on the side.
 
Many years ago I built a ball turning attachment to turn 3-3/4" and 4-3/4" diameter balls made of Delrin plastic. Anyway you do it, its a two operation job to turn a "round" ball. As one member stated above, your pivot point of your ball turning attachment has to be on "exact" center of the work you are about to turn a "ball" on.
The ball turning attachemnt I built had a slot for a 3/8" square tool bit. It also server a purpose to mount a 1" travel dial indicator that I used to center the fixture. How it worked was you set the fixture as close as you can eyeball it in respect to your work OD. Set your dial indicator, take a reading in front of your work, next rotate the fixture to the back side of your work and take a reading. Compare the two readings and adjust the cross slide until it reads "0" on both sides. Lock your cross slide from moving. If you don't get the fixture exactly on center, you will not turn a perfect ball or sphere. The roundness of the ball will be off. Oh, BTW- set your compound at 90 deg. to the cross slide and lock the gib in place. Do this before adjusting the cross slide.
Next, remove your dial indicator and place your tool bit in place. use a "square" nose tool with the corners chamfered at around 30 deg. The blunt nose or square nose is crucial in te forming the sphere. Adjust the tool bit in the holder to about the radius you want. Keep it on the plus side and adjust later. Again do not move your crosslide or compound! The only way to adjust the radius is to move the tool bit in or out the holder.

Use carriage movement to take cuts. Use a dial indicator to keep track of carriage movement. Only cut 1/2 of the sphere in this operation. Do not go past top dead center.

I'll add more in another post on getting the rest of your ball or sphere. I have to think how I DID THIS thirty years ago.
 
David Kirtley said:
I would say trim back the vertical post a bit more to get more clearance at the sides of the insert.

Did you dovetail the sliding bar in? I can't see from the picture. I was thinking about putting a t-slot on mine instead of grub screws on the side.
Click to expand...

I did not dovetail the sliding bar. I just used an end mill and made a snug fit. There are three set screws which secure the tool post. The reason for not using a dovetail cut was two, first I do not have a dovetail cutter but more I wanted to have the ability to adjust the height of the cutting tool so I put four set screws in the tool post to allow me do dial in the insert.

As for more side clearance, I have been giving that a lot of thought, that may be my first modification.
 
newbie asking a stupid question... but once you 'round' then end of your piece of barstock, how do you turn the other side of the sphere?
(no thread hijack intended)
 
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