David Randolph was faced with a choice: buy an expensive plasma cutter or build a cheaper version at home. He chose the latter. Download files and build them with your 3D printer, laser cutter, or CNC. Thingiverse is a universe of things.
It's simple to use: mount the tongue of the outer frame (approximately 3/8" square) in your lathe's tool post. Then, swing the handle to rotate the cutting tool bit in a smooth arc. Use for making universal couplings, decorative ball-ends on handles, and much, much more. Cuts ball-shapes up to 3/4" diameter. Includes high speed steel tool bit.