I need to tap out a 1/4" hole in my mast to 5/16" 18 (no threads in
there right now) and put a machine screw in there.

I have some options in terms of metal types and there have been a
number of discussions about corrosion and so on with SS in contact
with aluminum and how really useless the isolating compounds are in a
sal****er environment etc etc

So what's the metal of choice? I'm seeing brass, SS, silicon bronze,
zinc plated steel.. what's optimal for the aluminum (non-)interaction?
These other discussions don't have a consistent conclusion. (And no
rivets, this is a small job, I really do need the machine screw).

This is a freshwater boat and has been for a long time. However I
wouldn't rule it out of taking it down the east coast one day.

Thanks for any comments,

-CB

Use stainless, preferably 316 and a teflon anti-seize goo.

"CB" wrote in message
ups.com...

I need to tap out a 1/4" hole in my mast to 5/16" 18 (no threads in
there right now) and put a machine screw in there.

I have some options in terms of metal types and there have been a
number of discussions about corrosion and so on with SS in contact
with aluminum and how really useless the isolating compounds are in a
sal****er environment etc etc

So what's the metal of choice? I'm seeing brass, SS, silicon bronze,
zinc plated steel.. what's optimal for the aluminum (non-)interaction?
These other discussions don't have a consistent conclusion. (And no
rivets, this is a small job, I really do need the machine screw).

This is a freshwater boat and has been for a long time. However I
wouldn't rule it out of taking it down the east coast one day.

Thanks for any comments,

-CB

The stainless is more noble than aluminum, hence the stainless will
corrode the aluminum. But, since the bolt is so small compared to the
mast the damage done by the corrosion will be very, very, very slight
and the damage will not be localized at the hole, but over the entire
volume of the aluminum. At least, that is what I've been told and how
I've done similar work on my mast. Use the goo though.

On 22 May 2007 19:59:46 -0700, CB wrote stuff
and I replied:

I have a serious concern about a machine thread in the relatrively
thin wall of an almmunium mast. Al does not takew threads well, and
then not fine threads, adn then most thin metals a happier with
coarser threads.

Use a reivet if at all possible. Ironically, even self-tappers of
reltatively coarse thread, with large flutes, are better in thin
sections.

Apart from that, use 316 and some sort of insulator. It's worked on
many boats.


I need to tap out a 1/4" hole in my mast to 5/16" 18 (no threads in
there right now) and put a machine screw in there.

I have some options in terms of metal types and there have been a
number of discussions about corrosion and so on with SS in contact
with aluminum and how really useless the isolating compounds are in a
sal****er environment etc etc

So what's the metal of choice? I'm seeing brass, SS, silicon bronze,
zinc plated steel.. what's optimal for the aluminum (non-)interaction?
These other discussions don't have a consistent conclusion. (And no
rivets, this is a small job, I really do need the machine screw).

This is a freshwater boat and has been for a long time. However I
wouldn't rule it out of taking it down the east coast one day.

Thanks for any comments,

-CB

CB wrote:
I need to tap out a 1/4" hole in my mast to 5/16" 18 (no threads
in there right now) and put a machine screw in there.

I have some options in terms of metal types and there have been a
number of discussions about corrosion and so on with SS in contact
with aluminum and how really useless the isolating compounds are in
a sal****er environment etc etc

So what's the metal of choice? I'm seeing brass, SS, silicon
bronze, zinc plated steel.. what's optimal for the aluminum
(non-)interaction?

Don't even consider brass if you want any strength. It has none and
is even worse in a salt water environment as it will lose the zinc
that is compounded with copper to make brass.


--

dadiOH
____________________________

dadiOH's dandies v3.06...
....a help file of info about MP3s, recording from
LP/cassette and tips & tricks on this and that.
Get it at http://mysite.verizon.net/xico

CB,
It is correct to consider the dissimilar metal as an issue, but in this
application, it isn't the major one. This is so because the fastener will
not be subjected to immersion, only wetting. So, in application, the problem
is not so different than on a motocycle case or an aircraft. Stainless in an
anti-seize grease is fine. The bigger issue is the thin wall of the mast.
Rivets are much better and if removing the fastener periodically is an
issue, you should use an aluminum riv-nut riveted in place and then use a
316 screw.
Steve

"CB" wrote in message
ups.com...

I need to tap out a 1/4" hole in my mast to 5/16" 18 (no threads in
there right now) and put a machine screw in there.

I have some options in terms of metal types and there have been a
number of discussions about corrosion and so on with SS in contact
with aluminum and how really useless the isolating compounds are in a
sal****er environment etc etc

So what's the metal of choice? I'm seeing brass, SS, silicon bronze,
zinc plated steel.. what's optimal for the aluminum (non-)interaction?
These other discussions don't have a consistent conclusion. (And no
rivets, this is a small job, I really do need the machine screw).

This is a freshwater boat and has been for a long time. However I
wouldn't rule it out of taking it down the east coast one day.

Thanks for any comments,

-CB

On Fri, 25 May 2007 00:14:06 +0800, OldNick
wrote:

On 22 May 2007 19:59:46 -0700, CB wrote stuff
and I replied:

I have a serious concern about a machine thread in the relatrively
thin wall of an almmunium mast. Al does not takew threads well, and
then not fine threads, adn then most thin metals a happier with
coarser threads.

Aluminum riv-nuts are easily obtained, easily fitted, and reasonably
replaceable when the time comes. Screw a SS screw into a riv-nut

Brian Whatcott Altus OK

On 24 May 2007 06:42:50 -0700, Todd wrote stuff
and I replied:

This does not sit well with me. I thought that localisation was why
stainlless screws ended up in powdered aluminium and came loose. The
way I learnt it, the actual corrosion was across the boundary of the
two.

The stainless is more noble than aluminum, hence the stainless will
corrode the aluminum. But, since the bolt is so small compared to the
mast the damage done by the corrosion will be very, very, very slight
and the damage will not be localized at the hole, but over the entire
volume of the aluminum. At least, that is what I've been told and how
I've done similar work on my mast. Use the goo though.

On 22 May 2007 19:59:46 -0700, CB wrote stuff
and I replied:

Your geting replys Cb. Hows it goin'g


I need to tap out a 1/4" hole in my mast to 5/16" 18 (no threads in
there right now) and put a machine screw in there.

I have some options in terms of metal types and there have been a
number of discussions about corrosion and so on with SS in contact
with aluminum and how really useless the isolating compounds are in a
sal****er environment etc etc

So what's the metal of choice? I'm seeing brass, SS, silicon bronze,
zinc plated steel.. what's optimal for the aluminum (non-)interaction?
These other discussions don't have a consistent conclusion. (And no
rivets, this is a small job, I really do need the machine screw).

This is a freshwater boat and has been for a long time. However I
wouldn't rule it out of taking it down the east coast one day.

Thanks for any comments,

-CB

On Fri, 25 May 2007 18:40:03 +0200, "Steve Lusardi"
wrote stuff
and I replied:

I disagree with ther first bit. If the boat is to be used
_exclusively_ in FW environments, then you may get away with it. But
the OP did mention possible marine trips. Also, a boat by its spidery
nature (don't want to climb the mast) and less industry pressure
compared to even automotive, will tend to get less inspection in
whatever setup.

Also, actual constant immersion can sometime be better than moist
environments....less oxygen and other acids etc.

CB,
It is correct to consider the dissimilar metal as an issue, but in this
application, it isn't the major one. This is so because the fastener will
not be subjected to immersion, only wetting. So, in application, the problem
is not so different than on a motocycle case or an aircraft.


Stainless in an
anti-seize grease is fine. The bigger issue is the thin wall of the mast.
Rivets are much better and if removing the fastener periodically is an
issue, you should use an aluminum riv-nut riveted in place and then use a
316 screw.
Steve

"CB" wrote in message
oups.com...

I need to tap out a 1/4" hole in my mast to 5/16" 18 (no threads in
there right now) and put a machine screw in there.

I have some options in terms of metal types and there have been a
number of discussions about corrosion and so on with SS in contact
with aluminum and how really useless the isolating compounds are in a
sal****er environment etc etc

So what's the metal of choice? I'm seeing brass, SS, silicon bronze,
zinc plated steel.. what's optimal for the aluminum (non-)interaction?
These other discussions don't have a consistent conclusion. (And no
rivets, this is a small job, I really do need the machine screw).

This is a freshwater boat and has been for a long time. However I
wouldn't rule it out of taking it down the east coast one day.

Thanks for any comments,

-CB