"JJ" wrote in message
...
Has anyone had to specify or repair smaller threaded holes (8-32) in
aluminum that have been heli-coiled? How about the difference better
regular heli-coil and the "locking" heli-coil that has the
circumference slightly deformed triangularly so there is extra
gripping by those 3 sides with the fastener. This sounds like a
pretty good idea and I wonder if it eliminates the need for thread
locking fluid. There isn't a lot of vibration or heavy load
(application is an industrial keyboard/control panel)

The manufacturer seems to have specified heli-coil (1 "diameter" long)
as part of the original design/construction because of concern about
stripping out more due to the fastener being inserted and removed
rather than the load being secured.

I'm curious to know if we'd be better off in this application with a
stud going into bare aluminum (no heli-coil at all) and probably using
an aggressive thread locking fluid. (red) This way there would be
practically no insertion/removal in that threaded hole, just the
torque/stress from removing the retaining nut. (probably nyloc)



In the semiconductor manufacturing equipment I help design, Heli-coils are
used in aluminum not just to protect threads from damage where a screw is
frequently removed, but also to prevent generating particles during
fabrication. I have not used the locking heli-coil. However, if a screw is
not in a environment with a lot of vibration, impact or temperature
extremes, then a locking device is really not necessary if the screw is
fully-torqued. A fully torqued-screw is stretched just below its yield
point, and the friction between the material and the head and threads of the
bolt is enough to keep it in place except in extreme conditions (although
what often happens in practice is that small screws are over-torqued and
large ones a under-torqued). There are some cases where you do not want to
fully torque a bolt, so then a locking device is absolutely necessary.

As for protruding studs versus screws; a stud and nut is uglier and there is
some risk the exposed threads of the stud can be damaged. On the other hand,
studs can be convenient to hang a vertical panel when fastening.