I don't mean to come off as an ass on this, but don't do it...
tension rings are fickle beasts, they are actually really easy to
make, any one with a gold wedding ring and a jewelers saw could do
But, they are VERY hard to make right.
When I go to make a ring I start out designing the ring in
solidworks, and then using software to do a strength analysis (called
FEA) then I careful select a piece of material, I make the ring, I
measure it to make sure it's exactly like the measurements I have
designed. Then I harden the ring, but not to hard, just the perfect
level of hardness/flexibility, which is all based on the gem type,
size of the gem, size of the ring, ect....
Then when the ring is done, I have to test it, I have quite a few
pieces of hardware that are used specifically for that task. Almost
all of them custom made by me for my uses.
I have seen a few jeweler try to make tension rings, people that are
fantastic jewelers and craftsman, and not one of them has been
successful. they don't understand the fundamental physics behind
designing/making a tension ring.
I will even say this, I only make tension rings, I could probably
not even make the most simple of prong engagement rings, I've never
even learned to solder gold. The best I can do is clean and polish.
But when it comes to tension rings, I think I'm pretty decent.