I apologize, I am not at that house right now. I will try to describe the process...
1. First, use a two part liquid acrylic epoxy, I use West System, but if JB weld is all you can get then it will probably be fine so long as you are using the two part liquid rather than the putty.
2. Insert the set screw or tape up the set screw hole so that the epoxy doesn't leak out. Do any prep to the opening inside of the handle that you need to. You want the epoxy to harden around crevices but you are not trying to fill up the entire handle with epoxy.
3. Put the handles in a clamp or vise so you can pour in the epoxy.
4. Mix up the epoxy and pour it in.
5. After it hardens drill out the hole size recommended by your threaded insert.
6. Heat the insert with a lighter and thread it in.
Here is a video about inserting threaded inserts into hardened acrylic turning blanks (steps 5 and 6).
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I've got COPPER. Decided to keep bronze
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