I find it somewhat odd that nobody else has mentioned what I am about to mention, both because I've found it to be quite useful
and because it is a nearly fundamental rule of bonding
anything to a metal surface, from paint to solder. . . using a fine file or sand paper, lightly scuff the two metal surfaces to be bonded. Glue, solder, and other liquid-like adhesives bond better to
rough surfaces.
For example, when I connect a bit (e.g., hand, weapon, etc) to a larger 25mm mini, I typically use a round jeweler's file to 'rough up' receiving receptacles (i.e., depressions or holes) and an emory board or fine filing board to do the same to the nub, pin, or other adjoining piece that will rest in aforementioned receptacle. It takes an extra two minutes tops and I've never had it result in anything less than a perfect bond.
[Edit: Oops! I guess that Pogre did mention it

]