Pi is a constant which can be traced back to ancient Egypt and Babylon. Call it 3.14, multiply it by the diameter of a circle and you have the circumference, or in our case the length of metal needed to make a ring.
Now come the iffy bits. If the metal is 2mm thick, do you take the inner or the outer diameter? Well most people would work out the mean, by adding the thickness of metal to the inner diameter. However to get a good joint you may have to pass a saw blade through, possibly more than once. At every pass you will reduce the ring by about a quarter of a size.
The upshot is that I skip all that, but I do bear in mind that most rings need between 55mm and 65mm of metal. Anneal the metal, make it round so that the ends overlap side by side and slide it up my ring stick until it is about one size too small. Then mark where to cut with a waterproof pen, cut, adjust and solder. Put it on the ring stretcher, which will round it and slowly stretch to size. There will be no damage to any surface texture, or major cleaning up of hammer marks.
You will have noticed that so far I have glossed over the crucial part, which is how to bend up the ring shank. So here goes.
In my early days I used some ring pliers, with the beaks made safe by pushing on short lengths of tightly fitting polythene tubing which you can buy in ironmongers. This was still a struggle because the metal quickly becomes too stiff to bend further.
My life was turned around when I finally bought a ring bending tool. This looks like stubby pliers, but easily forces the metal around a central drum to make it ring shaped. The name varies according to supplier, and the price varies widely too. It soon became apparent that while the drum did not mark the inside of the ring too badly, The outer surface would need protecting. This is done by positioning a short piece of leather cut from an old belt or luggage strap on the stubby jaws. Should you find it difficult to keep in place, some double sided adhesive tape will do the trick.
I have found that starting with only a little excess metal to save waste, it is best to bend up the ends first and then work on the centre. Once you have adjusted the size and cut to the right length the metal can again be annealed and the ends made to meet more closely using the same tool. Dennis
Below: Ring bending tool with leather in place and a heavy ring made by this method.