Re: Holes

On Apr 30, 7:44 pm, Jeff Liebermann <je...@xxxxxxxxxx> wrote:
On Sat, 30 Apr 2011 16:18:10 +0700, J. D. Slocomb

<jdsloc...@xxxxxxxxxxx> wrote:
The bike I am re-building has a lugged steel frame. Most of the
smaller tubes - chain & seat stays, brake bridge, etc., have small
vent holes. As all brazing has been accomplished does anyone see any
problem in plugging these holes to prevent water ingress. I had in
mind something like epoxy filler.

As others have mentioned, plugging the holes is a bad idea.  The only
way you can make something water tight is to also make it air tight
and pressurize the insides (hermetically sealed).

In a past life, I spent my time designing marine radios.  Salt water
incursion was a major hazard.  Not only did we have to limit points of
entry, but we also had to deal with providing an exit path.  For
example, horizontal printed circuit boards had drain holes drilled at
many locations to prevent puddling of water on the board.  Coaxial
cables with an air dielectric, were all presurized with dry/dried air.

Over the years, designers would need to relearn the same lessons
again.  One leading GPS manufacturer decided to advertise that their
GPS was water resistant.  They also ignored all the waterproofing
tests and specs:
<http://www.lakemartin.com/BoatingWaterproofSpecs.asp>
When I complained, and they were finding corrosion damage, I was asked
to explain the failure mechanism.  It was simply Boyle's gas Law.  
<http://en.wikipedia.org/wiki/Boyle's_law>
Take the sealed GPS and get it nice and warm in the sun.  Now, dunk it
into a cold water river.  The air inside drops in temperature,
contracts, and creates a partial vaccuum inside the unit.  That sucks
in the water through even the smallest entry point.  Repeat the sun
heating, water cooling, cycle a few times, and a substantial amount of
water will be pumped into the unit.  The same can happen to any
bicycle component that is sealed.

Extra credit goes to another manufacturer that sealed their LCD
display, and was wondering why they were rotting out from the inside.
Same problem.  This is one reason you don't want any liquids around
the edges of an LCD display.  Also, if sealed with something hard,
changes in atmospheric pressure can create really strange patterns on
the display.  I recommended they replace their epoxy seal with a piece
of porous tape.

More on corroded bottom brackets:
<http://www.bikeforums.net/showthread.php/375798-Opened-up-my-bottom-b...>
<http://www.bikeforums.net/showthread.php/512128-Picture-of-my-bottom-.......>
Argh.  I don't quite agree with the 2nd article where one author
claims that there is very little condensation inside the bicycle
tubing.  That's true, but condensation is NOT where most of the water
comes from.  It's from puddling and collecting at component junctions,
and sucked in by partial vacuum, by wicking through gaskets, or by
capillary action.  In radios, I've drained far more water from inside
that could possibly be explained by condensation.
<http://en.wikipedia.org/wiki/Capillary_action>

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

after rain riding, tilt cycle forward up against wall so the chain and
seat stays drain. there's hole there right ? a fan out in the garage
is AAA. like a Wal fan.
and the GPS/Marine VHF waterproof standard whatever best place is a
waterproof bag. Waterproof standards are for accidents not deliberate
use IMO. I see group leaders using the VHF naked direct from a Pdf
holster but they get paid for it. and it does look cool, in
charge....dumb.

its raining octupi and marmots, the kayaker pulls out his WP 8 GPS to
assess the situation, and he sez "its waterproof"
'it is ? who told you that? '
he sez "the guy who sold it to me stupid"
'OK' where are we.
he sez " i dunno...."
.

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