JB Weld ball mount antenna thread repair

[Jeff Liebermann]

I have a friend with a problem. He has a rather heavy duty ball mount
on his van, with a 6ft long fiberglass HF antenna of some sorts
attached. No spring between the ball mount and the antenna.
Unfortunately, the antenna unscrewed itself and he was driving around
with the antenna flopping about for many weeks. The result was that
the antenna beat up the 3/8-24 threads in the ball mount end to where
the threads are now stripped out. Fortunately, the antenna end
threads seem intact.

The original plan was to drill out the threads in the ball mount and
install a Helicoil to repair the threads. The problem is that the
Helicoil 3/8-24 kit costs as much as a new ball mount.
<http://www.ebay.com/itm/400302414654> ($32 for the kit)
Either way, he doesn't want to spend the money.

So, instead of rethreading the ball mount, I propose to insert a 1"
long 3/8-24 piece of threaded rod into the ball mount and secure it
with JB Weld, which allegedly contains metal particles. My tests show
that it's still an insulator when hardened, mostly because the metal
particles do not overlap. However, the close fit of the
threads may be sufficient to get some manner of connection.
<http://www.youtube.com/watch?v=9gKYfgIGMlE>

Silver loaded conductive epoxy might provide a better connection, but
the stuff is fairly weak at 900psi compared to JB Weld at 3900psi. It
may not be sufficiently strong to survive the flopping antenna.
<http://www.mgchemicals.com/products/8331.html>

Will JB Weld work?
Or will it get hot due to IR^2 losses due to antenna currents?
Will adding steel filings help?
Is there a better way to do this?
Is there a better adhesive?

--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Paul Drahn]

Hi, Jeff.
The antenna part threads are ok because it is stainless steel, while the
ball part is some type of pot metal, primarily zinc. The Heicoil will
eventually rust and cause no end of problems.

the correct repair method is to drill and ream the ball part to a known
larger size, perhaps even 1/2 inch. Then press in a stainless steel rod
and cut it flush with the top of the original hole.

Then drill and tap the pressed in piece for 3/8X24 threads.

In California where it never rains, an aluminum rod may be used, but
won't last forever. You may also want to seal the top of the plug/ball
with a little RTV to ensure car wash water can't get in.

I suppose a clever person could drill and tap the rod 3/8x24 before
pressing it into the ball. Might be easier to do the drilling and
tapping using a lathe.

Paul, KD7HB

[Dave Platt]

In article <1arjv7lqob37ke2fl...@4ax.com>,

Jeff Liebermann <je...@cruzio.com> wrote:

>Will JB Weld work?
>Or will it get hot due to IR^2 losses due to antenna currents?

I suspect it will behave like a high-dissipation-factor capacitor in
series with the antenna current. There will probably be both
resistive loss, and some reactance in the connection... how much of
each I can't predict, and the amounts may not remain stable with time.

>Will adding steel filings help?
>Is there a better way to do this?
>Is there a better adhesive?

Can you separate the "mechanical connection" and "electrical
connection" aspects?

You could use JB Weld, as you intend, to rebuild the mechanical
connection at the base of the whip. Either before or after doing
this, drill a small hole in the ball, and use this to connect a
flexible jumper wire (either solder the wire into the hole, or tap the
hole for a small screw) and connect the other end of the wire to the
base of the whip... in effect a very short, flexible "flying lead".

Another thought... if you under-size the hole you drill for the
threaded rod, you might be able to achieve an interference fit between
the threaded rod and the hole, so that have to press-fit the rod into
place (e.g. with a vise) and you have actual metal-to-metal contact
between the rod and the metal of the ball. You could use some JB Weld
to reinforce the connection, but the Weld would tend to be squeezed
out of the actual contact reason when you force the rod into place.
If you've got a clean metal-to-metal interference fit between rod and
ball, the presence of the JB Weld in the other areas will be
irrelevant... it will be "shorted out" by the direct metal contact
areas. The JB Weld would act both as a structural reinforcement, and
to exclude oxygen from the interference-fit contact surfaces and help
keep the resistance low over time.


--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
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