RE: [PSUBS-MAILIST] Re:Stainless in aluminum

["Gregory B. Snyder" <snyder@mnrad.com>]

Vance -
I always lear a lot from your posts.
Thanks-
Greg

-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of
VBra676539@aol.com
Sent: Sunday, August 29, 2004 5:17 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Re:Stainless in aluminum


Brian,

Maybe Hugo will catch this question and help me out here with some
product 
names, but I can tell you that the answer to your question is yes and
no.

At HBOI, we used a stainless steel insert which was threaded inside and
out. 
Bore the hole to the insert size, tap, screw the insert itself into the 
aluminum with a mandrel and then hammer in the locking dogs. The insert
should be 
well bedded in one of the super whammydine Loctites (or epoxy or
something) in 
an effort to exclude seawater from the outer threads. It's going to
become a 
permanent fixture anyway (as you might well imagine) so you might as
well nail 
it in there the best way you know how.

The inserts come in all sizes, so that their inside thread size will
match 
whatever bolt you have in mind. The trick to using them successfully is
to 
grease the bolt with nonsoluble grease every time you install it, and I
mean grease 
it GOOD!!! Otherwise, and as I remember it, about the only otherwise we
ever 
found, was that salt would creep in there and build on the
threads--which gave 
you a twisted off bolt head, more often than not, when you tried to pull
it 
later.

One more hint: Don't use machine threads for this kind of application.
1/4 20 
is about as fine as you'd want to risk. The coarser threads, when being 
reluctant on removal, are easier to rock back and forth, thus easier to
persuade 
out into the light.

We used Almag hatches in the early days at Perry and had to fight
corrosion 
quite a bit, and as I have said somewhere (somewhen?) else on this page,
we 
used magnesium anodes on the aluminum dive planes and rudder assemblies.
I have 
actually WATCHED them corrode, with fumes streaming off and little bits
of 
metal flaking into the water, when a DC circuit shorted to ground.

You can, of course, bolt straight into aluminum, but the damage will
happen 
on the aluminum end, and you probably won't see it until it gets pretty 
bad--and it won't be pretty--just pretty bad. Beware. Some days it's
like diving in 
battery acid. A single dive with a pesky short can cause some BIG
problems.

Best Regards,
Vance



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