Re: [VACList] Rivets re:bucked tail diameter, etc

["T Meeker" <tmeeker@xxxxxxxxxxxxxxx>]

Dick,

There truly are "round hed" and "dome head" types of rivets.  These were old
style compared to what is mainly used today.  That was part of the reason
for developing the "universal head" rivets that have a very minute flatened
area on the very top of those type rivets.

But rivet shavers can also make some "designer" rivets, too.  If you ever
look closely at some rivets and they have concentric swirl marks on the
rivet head you can bet they were "shaved" down to the level of the skin.  At
times this is necessary but it could also mean that the countersink was not
deep enough to consume the head of the rivet and shaving was done for
cosmetics.  If it was done for cosmetics you can also bet that there
shouldn't be too many done like that over a prescribed area.

Rivets are designed to be at full strength when properly installed.  What is
properly installed?  Well, that depends. ;)  Make a countersink too deep and
you risk having to enlarge the hole up to the next size fastener; if you
have room inside and outside to do so.  Will the rivets then be spaced too
closely for government work?  Maybe.  If that is the case you may have to go
to another type of fastener for that screwed up hole.  Maybe on the inside
where you intended to have this first fastener that was countersunk too much
the rivet tail would be interfering with the radius of a stringer or rib.
You are not supposed to have rivet tails or any other fastener in the
radiused area of ribs and stringers or other things like that.  See what I
mean?  It all depends on the particular situation you are trying to fix.
Nothing is impossible; it's just that the impossible takes longer to get
done. ;)

In cases where a rivet won't work because you can't buck it then you have to
go to another type of fastener, maybe an interference fit fastener where the
nut being screwed onto the threaded portion actually pulls the fastener into
the hole until a set torque is reached.  At this point the hex head part of
the nut would break off.  This would achieve maximum strength at that point
for that particular fastener but those types are either made of coated steel
or stainless steel.  Coated steel here would be magnetic and stainless
wouldn't be magnetic.  Too close to electrical wires where the steel could
interfere with magnetic functions of instruments?  Can't use steel there so
you'd have to go with stainless steel that doesn't have as much iron in it
which is what causes things to become magnetic.  Cheap stainless can be
magnetic and it can also rust if there's not enough nickel in the mix.

I know this is more than you ever wanted to know but to me it's fascinating
stuff. ;)

Tom