Just my two cents worth. Putting partial cuts in the surface of the elevator horn will induce stress risers which, under extreme vibration, will potentially end up with metal fatigue and a catastrophic failure. Don't do that!! Better to lightly sand the surface with fine (400 grit at most) wet-or-dry sandpaper. This will provide sufficient "tooth" on the surface for the epoxy to bond to. Better yet, use silver solder.

Regards, and good luck. Nice looking aircraft.

Revver #142