8"x1"x0.80mm for the bangle
6"x1"x0.80mm for the bracelet
Anticlastic stake (steel, wood, Delrin - whatever!)
Suitable raising hammer(s) - metal, Nylon or wood.
(saw, torch for annealing & soldering, files etc.)
I'd recommend sawing the profile out rather than cutting it with snips - the snips will result in an edge that needs more filing due to both the serrations it leaves and the bend deformation at the edges. This needs more filing than a saw-cut outline would.
For the bangle, make sure the ends are square (using Dennis' tip for checking with squared paper), bend them together and solder. I've done a quick solder on them, followed by sawing the join & resoldering to make sure that the ends are clean. Make sure that the solder flows completely through the joint - raising puts a fair amount of stress on the join, and any weakness in it may well pull it apart. Pickle, rinse, dry, remove any excess solder from the surface, then mallet the bangle round on a suitable mandrel. Use a leather, rubber, wooden or plastic mallet to avoid deforming it too much; if you're using a tapered mandrel like mine, you'll need to flip the bangle over and do it again to avoid turning your bangle into a frustrum (a truncated cone). Then - anneal and pickle again.
Selecting the smallest curve on the anticlastic stake that the bangle width will fit and a hammer where the curvature more-or-less matches the stake, gently hammer along the bangle. Hammer parallel lines along to start to curve the bangle, turning it along the stake as you go. Once you reach the middle, turn it around and do the other side. As the form progresses, move the bangle to progressively smaller curves until it has the curvature you want. Anneal as you go along if needed, but don't anneal as you approach the final form - the work hardening gives this form a lot of strength.
You can level the edges a little bit by placing the bangle flat on a suitable surface - a surface plate is ideal - and gently tapping any high spots down, but it gives a more consistent curve if you can do this on the stake.
Finally, make sure there are no areas of the bangle need reworking; polish and - in the case of copper anyway - apply a wax polish to avoid it tarnishing too quickly.
The bracelet is similar, but... First of all, I cut it to a tapered oval shape, then bend it to shape on an oval mandrel. There should be a gap slightly over 1" at the ends; this forms the axial curve (the subsequent raising will put in the generator curve). Note that these are not as easy to bend to size after they're formed due to the shape - can be done, but it's more work.
The same applies in forming these as the bangle - work in lines parallel to the centreline of the bracelet, gradually working the shape in. As you do so, you'll find the bracelet is determined to open out again - hold it closed as firmly as you can while hammering it, but you'll have to take it back to the mandrel regularly to reshape it. As you do so, some of the generator curve opens out again. You can put some of the axial curve in as you're hammering by striking over the edge of the stake; it depends upon what you find easiest.
If you want to use reticulated or roll printed silver, then reticulate/pattern it before cutting out, then do use a Nylon mallet to avoid damaging the pattern. Keum boo I'm undecided on - it's easy enough to adhere the gold when the bracelet is flat, but I don't really see why it shouldn't work just as well at the end (and you wouldn't need to do the multiple annealing cycles to start with).
If the solder joint tears on the bangle, you'll need to file the tear, insert a piece of silver and solder that in place to fill it - don't try to fill the tear with solder. Frequent annealing does help avoid the problem altogether; if the repair isn't successful, you could always saw out the soldered area and turn it into a cuff instead.
I've found that - depending upon the amount of raising done - the diameter of the bangles decreases by about 10-15% from the original size, so you can calculate back from that.
Metals Technic, McCreight
Form Emphasis for Metalsmiths, Seppa