How can I fuse copper wire to a copper cuff
It would be a lot easier and more accurate to solder the wire. It can be done with lots of practice and a hot torch using either oxy propane or oxy acetylene and small torch tips. I use a Smith little torch with oxy acetylene. You have to get the heaviest piece close to melting before bringing the wire in. Even so the bigger piece is so hot the wire if very light will melt first. Have fun! Sometimes the disasters turn out to be the most beautiful.
If you really want to fuse it then it has to be in contact,which makes it quite difficult as its a curved surface.
Soldering is much ,much easier as AuroraClarke has said,there is a technique but its troublesome it involves glueing the wire down with a mixture of gum tragacanth,copper carbonate and borax.
When dry heat from the rear with a reducing flame .The chemistry is the same as granulation , I created a piece for my graduation show in 1975 and havent bothered since as it was such a pain.