On a large automaton of Little Tich, the 19th century music hall performer. The large mainspring was found to have its hole torn out from the barrel hooking. This is a fairly common repair, a result of ‘overwinding’.
The secret to the repair is the process of softening the steel prior to punching and shaping a new hole.
The new end will be curved to fit the shape of the barrel and then the spring cleaned and greased before fitting.
The original hole is torn out so begin by softening the end, note the heat protection for the main coils.
Punch a small hole or dimple
Cut off and reshape tail of the spring. It can also help to reshape the curve to aid hooking.