I made one loosely based on a design by the late Steve Bedair. I believe details are still available online. Downside of the design is you really need a collet chuck as a three jaw gets in the way. Simple to make and very robust, mine is used every few weeks putting large radius on bolt heads for my motorcycle work.

Warco sell a ball turner device for the ML7

Bert

I made the Radford spherical turning attachment which was subsequently improved by George Thomas. I believe similar designs are now produced by our Asian cousins but I suspect any purchase of one of these devices would be money down the drain. The reason being that if the device does not rotate on an axis very precisely at the lathe centre height all it will produce is egg-shaped monstrosities. Clearly, the only way to get the axis at the precise height is to bore the body of the device in the lathe on which it is to be used.

My device produces spheres that are perfectly satisfactory as ball handles etc. where cosmetic appearance is all that really matters. However, I have recently made the Radford worm-wheel hobbing attachment, the design of which called for universal joints rotating around a sphere rather than a 'spider'. Although the balls I produced looked perfectly spherical to the naked eye, I found that they were not as accurate as expected when rotated in the U/J casings and had to be mounted on a spigot and eased with a file in the lathe to effect a fit without any binding or rubbing.