Robert Swinney wrote:
Leo sez:
". . . I've never actually done this*, but it seems to me that it would be
helpful

to countersink both sides also--this would give the excess metal room to
expand and form a "head" on each end. . . ."


Countersinking would drill away metal in the center that could be better
expanded to the outside. IMO, it is better to begin striking the center
area(s) first with the ball peen, thus forcing that metal to the edges.
..snip..

uh Bob,

I think that Leo was referring to the hole what was to be filled, not
the plug material. In fact it would be a good idea, but too often the
material is so thin anyway that countersinking would be difficult to do
without opening the hole beyond all help.

As for drilling the plug material, it does make it easier to expand but
weakens the plug for exactly the reason you state.

George Vigneron