After 2 arduous sessions, I finally managed to get the frame 98% back to bare metal. I used a wire brush and some 120 grit decorator's roll. Here is what I learned.
1. If you want your frame back to bare metal take it to a firm that can carry out sandblasting/shot blasting - using wire brushes and sandpaper
a) is extremely time-consuming,
b) potentially dangerous when the bristles fly off in all directions,
c) does not reach every crevice on the frame and the finish is uneven,
d) creates a lot of airborne dust in the environment where you are working.
e) it is possible all too easily to mark the frame by catching the wire brush arbor or the drill chuck whilst trying to reach another part of the frame.
2. If you still want to do it yourself then:
a) degrease the frame at least twice before starting, I did it once but caught some residual grease which stops the wire brush from working and clogs the sandpaper terminally
b) wherever possible use a wire brush with bristles pointing forward rather than at 90 degrees to the chuck axis as these are less likely to shed dangerously
c) pressing hard on the wire brush only succeeds in shredding the bristles or scoring the finish on the frame
d) you will need multiple shapes and sizes of wire brush to reach the various crevices on the frame and I guarantee you will not get to all of them.
I shall not be repeating this exercise. Ever again.
