The length you need is calculated by adding the wire diameter to the
inside diameter, and multiplying the result by PI. So, since 3" =
76.2mm, and the wire thickness is 10mm, the length is 86.2x3.14159 =
270.8mm = 10.66".
If you have a long length of the wire there will be no problem in
bending it round a suitable former and then sawing off one loop, but
if you only have just enough wire then proceed as follows. This is
the way I made a solid 9ct gold bangle from 8mm square wire; 9ct gold
is rather tougher than silver.
Don’t try bending it into a circle straight off. Use a vice with
soft jaws and bend the ends first. Hold about 1/2" to 3/4" in the
vice and then bend each end so it looks rather like a wide flat
staple. Try to avoid sharp bends. Leave the ends straight and then
start bending at various parts between the end bends until the ends
start to meet. You will probably need the vice to help bend the
metal, the objective is to get the two straight ends to meet up, in
line with each other. You can then solder the joint.
With the joint nicely soldered, the next problem is to make it round.
For a mandrel I used a piece of brass tubing with an OD a little less
than the required ID of the bangle. I used the vice to squeeze the
loop at strategic parts until it approximated a circle and could be
forced onto the mandrel (it would be much easier with a tapered
mandrel). I then pounded it with a hide mallet until it was round. I
hope this helps.
Regards, Gary Wooding