If this is a one off thing I’d suggest using a cut off disc to start
the channel. Once you’ve got the rough configuration you could widen
it as needed with either a fatter cut off disc or burs. If you try
burs I’d start out with a krause and if needed move to a small bud
or flame bur. You’d be holding the shaft parallel with the groove but
angled up somewhat. As you might imagine the bur will want to jump
out of the groove so you need to move slowly and as much as possible
use the tip of the bur. A back and forth motion, advancing a little
bit more each time will keep jumping to a minimum. If this channel
is to fit around the edge of the flat sheet or however your bangle is
made, you might then need to make the groove with a
square(perpendicular) cross section. After you’re satisfied with the
groove dimensions you could use a small wheel bur to cut the groove
square. Wheel burs tend to really jump because they have corners
that dig in and grab.
If you intend to solder this wire onto the edge to act as a bumper
of sorts, it might be easier to simply use a file to flatten
lengthwise along the wire AFTER forming it to the bracelet and solder
that flat to your bracelet edges. The reason I suggest this is that,
OK you’ve grooved your wire and now you need to form it to the
curvature of your bracelet. I think you’d have problems keeping that
groove in proper alignment during the bending process. I think the
groove would tend to work its way to the outside of the bend.
If you want a groove to primarily act as a locating agent during
soldering you could simplify the process by using a few small tabs or
’dowels’ to lock into corresponding holes instead.
If this any sort of production piece maybe warm up the bracelet with
your torch and use that to gently melt a groove into a wax block,
then carve away til its what you want and cast and mold that,
assuming you can keep the bracelets consistent from run to run.
Generally, I find it most efficient when fabbing a mechanism, to
start with the most crucial aspect of it and work from there. In this
case it would be the fitment of wire to bracelet. And usually the
simplest method works best.
That is, IF I understood the problem correctly.