Kyle Boatright wrote:

A 1/8" dimple die won't fit in a #40 hole, which is roughly 3/32.

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Dear Kyle (and the Group),

I believe my cited comment had to do with using poppers. The 100
degree dimpling sets use a steel mandrel -- typically, a finishing nail
with the point clipped off -- that you replace periodically as the work
progresses.

When using thin/soft metal, using the popper-type dimpling dies tends
to enlarge the hole. Come back to set (pull) the rivets and they're
liable to pull right through the hole, leading to the Conventional
Wisdom that countersunk-head poppers don't work. They do -- at least
for aluminum poppers -- but only if the hole is the proper size.

Start with a pilot hole that is smaller than the intended rivet size --
and select a pulling mandrel to fit. Anything that fits will work. (I
think I used 4d finishing nails.) Just make sure your puller can grip
the shank and that the head of the nail is large enough to not pull
through the die. A pneumatic puller will give you more uniform
results. You will need to ream/drill the hole to size prior to setting
the rivet but the result is a tight, symmetrical dimple.

If you have a lathe, dimpling dies for poppers are easy to make.
(Hint: For the male die, grind the angle into your tool bit. For the
female, simply grind a drill bit to 100 degrees. They may be used
as-made but will last longer if case-hardened.) 100 degree dimple die
sets for poppers are also available from AirParts, ATS and so on.

-R.S.Hoover