I have seen different versions of radius turning tools all over the net, I have pretty much all tools to do just about anything possible, The one thing I didn't have was one of these, I probably want use it very much but never the less I made one to fit my Clausing 14" X 48 Lathe.
I have made allot of knobs and things of that nature from time to time whenever there was a call for it, and I would always make a knurled straight knob, So I wanted to be able to make a lot of variations of handles and ball knobs.
The main body was made from O-1 Tool Steel, The tool bit holder was made from 5/8" 303 stainless steel and so was the turning handle and radius adjusting screw.
There is an aluminum knurled knob on top of the radius adjustment screw, and the pivoting handle has an aluminum ball on the end of it which I made with this tool.
The main body has 45 degree male and female dovetail slides with 6-32 screws on the side for take up which works effortless, the radius adjusting screw is 3/8"-24 for a fine adjustment,
The lever collar was made from 2" bar stock, 4140 Heat treated, I used my BXA boring bar holder from my quick change tool post for the pivoting shaft to turn in, which was made from 3/4" 4140 Heat treated bar stock.
I didn't do any drawings or anything just rough sketches on paper here in the shop, but with a little imagination and maybe some trial and error you can make one just as good or better.