A large number of lathes and chucks either come with an indexing facility or like the Axminster chucks you can buy one as an add on. The only problem with these is that they usually only give you 24 points, this is fine if you are doing clocks or anything that needs 2, 3, 4, 6, 8, 12 or 24 holes. If you do not have this facility or you want a different number of points then you either have to buy one, usually from America, or make one which is the option I chose.
Below is how I went about making one using tools found in most turners workshops, I am not an engineer but the ring I made is accurate enough for my needs, if you are doing segmented turning you have to be very accurate when making it or buy one in.
A word of warning this ring must only be used on the lathe with the lathe turned off, never use it with the lathe spinning.
I started with a square piece of 2mm thick poly carbonate which was small enough to allow it to turn over the bed but large enough to allow me several different numbers of holes. I used this because I had some but any thin rigid material up to about 4mm can be used.
The first thing to do is find and mark the center.