I'm trying to epoxy two pieces of metal together, I'm mixing the epoxy the right way but once it hardens the piece breaks off, any suggestions? I'm gluing this flat piece of metal to the nut that's glued on the viewfinder. The nut stays on the viewfinder with the same epoxy so I'm confused about why the other metals won't adhere, should I sand the pieces first? By the way I photographed the wrong side of the flat piece, the side showing has prongs, the other side is flat, the flat side gets glued to the nut. This is a viewfinder from an old Mamiya press camera, not sure what kind of metal it is.