[Boatanchors] How to repair stripped panel threads

[Kim Herron]

Yup, Heli-Coils work in thicker stock, but in the case of the Navigator,
it's sheet metal.  Helicoils won't work in sheet metal.  If memory serves,
that rig (and many others) use #6 sheet metal screws.  The easy fix is to
put #8's in place of them all.  The more difficult fix (ant probably better
) is to use threaded inserts in the holes.  You need the special tool to
install the inserts and then you've got to use machine screws.  The kind of
insert I'm talking about is found in Collins gear and there about 5 or 6
different systems out there to do just this kind of repair.  The quick and
dirty way to do this is to epoxy a nut to the back side of the case.  Let it
set for a while (day or two) and then use machine screws.  Don't over
tighten them.  If the cabinet flange is wide enough, you can use a speed
nut.  It slides over the flange, and the sheet metal screw threads into it.
But on the Johnson (and Heath) gear, there usually isn't enough room to do
that.  The top side of the speed nut sticks out beyond the edge of the
panel. 
 
 

Kim Herron W8ZV
www.goldenradioservice.com
kim.herron at sbcglobal.net
1-616-677-3706 

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of WA5CAB at cs.com
Sent: Saturday, December 13, 2008 1:39 AM
To: texasroadrunner at comcast.net; boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] How to repair stripped panel threads


John's reply later in this thread is absolutely correct.  The helicoil is
the preferred method in industry and the military for repairing stripped
threads.  I've used them successfully down to #2-56 UNC.  The helicoils
themselves are cheap, and in each thread size come in several lengths.  The
dollars are in the special tap and the installer and drive tang breaker.

A helicoil is a length of almost (*) square bar coiled up such that the ID
is slightly greater than the original thread's minor diameter.  The special
tap has the same pitch as the original thread but a pitch diameter equal to
the original plus the radial diagonal dimension of the bar.  You drill out
the original tapped hole with the correct diameter bit, run the special tap
through the hole, and screw the helicoil into it.  The helicoil has a drive
tang bent across the inner end that must be broken off after insertion.  If
the length of the helicoil exceeds the panel thickness, it is best to cut
the excess off with something like a Dremel tool and abrasive disk.

(*) The bar is actually a "Squashed" square, as standard V-form threads are
60, not 90 degree.

There are some other methods.  Usable in sheet metal is the nut-sert, which
is somewhat similar to a hollow pop-rivet.  The drawbacks are that it takes
a relatively large diameter hole and leaves what amounts to a flat washer on
the outside surface.  Two others come to mind but are generally only usable
in aluminum or brass castings and wood.

In a message dated 12/12/2008 11:30:44 PM Central Standard Time,
texasroadrunner at comcast.net writes: 


I'm sure this subject has come up before, but couldn't find any hits via 
google groups.
Wondering what folks on this list have used to repair stripped threads? 
I've experienced way too many over tightened fasteners which attach BA 
panels to their chassis.  Currently I have a bunch of panel screws on a 
Navigator- some are too loose due to over tightning.    One gent suggested 
dipping and curing toothpicks in Devcon epoxy and then placing them into the

hole before screw insertion.  Short of welding (JB?) a nut on the back end 
of the threads, looking for other ideas out there.




Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480 

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