"john B." wrote in message
...
On Wed, 1 Jun 2011 10:26:17 -0400, "Ed Huntress"
wrote:


"john B." wrote in message
. ..
On Wed, 1 Jun 2011 08:45:34 -0400, "Ed Huntress"
wrote:


"john B." wrote in message
m...

I'm in the process of rebuilding a bicycle frame and am left with some
minor dings and scratches which I want to fill and fair. The tubes are
rather remarkably thin and I really do not want to use a file to clean
them up. My idea is to use lead solder as a filler and my problem is
that I have no idea what to use for flux.

The reason for using a metal filler is that the frame will eventually
be powder coated and the preparation used here is a good glass bead
blasting and I don't think that conventional painting fillers would
stand that, or the high temperature baking.

I do remember my uncle having a bottle of some sort of acid with zinc
(I think) strips in it that he used for flux but other then that I
don't have a clue.

Anyone help?
Cheers,

John B.

Zinc chloride flux. You can buy it already mixed, or make your own. Get
some
muriatic acid (dilute hydrochloric) from a building supply place, where
they
sell it for etching concrete. Dilute it with an equal amount of water.
Muriatic usually is sold as 31.45% hydrochloric; you want around 15%.

Drop in some small pieces of zinc, letting the solution work until it
stops
bubbling. Do this out of doors or you'll rust any steel in the vicinity
from
the acid vapor that goes off with the hydrogen bubbles. Then add some
more
zinc until the solution is saturated. Leave it overnight. It's standard
practice to leave a few zinc pieces in the solution to be sure it's
saturated.

Zinc pieces can be obtained from the shell of a carbon-zinc battery, the
cheapos sold in discount stores.

FWIW, I personally would not apply soldering heat to the middle of a
bicycle
frame tube. Unless it's a real cheap, heavy frame, it depends on the
hardness obtained from drawing the tube for strength, and it's easily
weakened with heat. This is less of a problem at the tube ends, which is
how
they get away with brazing the frames together.

As you say a "lugged" frame built with butted tubes has already been
heated to a red heat in order to braze the tubes, but even the best
frame makers seem quite happy to braze fittings anywhere on the tubes.

That's true. I've seen some discussion about it, including speculation
about
the integrity of a frame with those features, but I've not seen any actual
test results.

Certainly heating a stressed tube could have an effect but I doubt
that in the case of a bicycle frame it is a major problem. Given that
in metal bikes (can't speak for fiber) the main problem is stiffness
it is likely that tubes either thick enough or large enough in
diameter to be stiff enough may well be able to stand a little heat in
the middle and the more modern frames are likely built of something
like Reynolds 631 or better that are air hardening.

The frame makers who have been building for many years are not
reluctant to add braze-ons where you want them.

Braze-ons for bottle mounts on the down tube, brake posts on the forks
and seat stays, cable guides on the top tube and shifter mounts on the
down tube, to name a few, and all brazed at a red heat. My thoughts in
using lead was that it could be done at quite a bit lower temperature
- sort of fail safe thinking :-).

Note that the loads on the down tube are mostly compressive; cable guides
are (or were) typically located near the ends of tubes, where bending
loads
are low; and so on. Also, the two real racing bikes I have owned -- a
Frejus
road bike in double-butted Reynolds 531, and a Cinelli track bike in
Columbus tube -- had no such brazed fittings on main frame tubes.


Actually, the down tube - runs from the head tube to the bottom
bracket - is the most highly stressed tube in the frame - in tension.

Whoops! I forgot the terms. It's only been about 45 years. g Yes, that
tube is certainly loaded in tension.

Think of a really fit racer mashing down on the pedals while pulling
up on the handle bars to beat Lance Armstrong up a hill :-)

I suggest that while your racing bikes may not have had braze-ons most
road racing bikes do. At least for a water bottle on the seat tube and
more then likely for cable guides on the top, down, and R.H. chain
stay tubes.

Bikes in normal use are not stressed enough to test the actual strength of
the tubing. They're generally well within the elastic range, because a
frame
that flexes a lot, in racing, at least, is a very inefficient frame. I
owned
one, which I kept for about two weeks. g

So I'm not saying that you're courting disaster to heat a frame tube in
the
middle. If it's straight carbon tubing, even soldering heat will seriously
compromise the strength. But it's very rare that any bike in normal use
would ever approach the strength limits of the tube. Consider, though,
that
enough local load was once applied to your bike to create those dents.

Reynolds 531 has been around for 100 years or more and certainly has
had an effect on the better grade of bicycle frames. I doubt that many
medium or high priced frames still exist that were built with straight
carbon steel tubes.

It wasn't clear what type of bike you were talking about. My 30-year-old
bike, which is one of my two general-purpose road bikes and which was
medium-priced (Schwinn Super LeTour), is 1020 straight carbon, which
surprised me at the time.

Anyway, it wasn't clear.



I was sorta aware that body lead was different then solder but since
I'm just filling small blemishes - think a 30 year old bike - and I
had hoped that a bit of flux and a glob of solder and a little filing
and polishing and I'd have a smooth tube. I hope :-)


Good luck. If you don't have a body-shop supply where you can buy body
solder, plumber's wiping solder is almost the same thing. But I doubt if
any
of that has been sold for at least 30 years. d8-)

I live in a country that uses plastic pile exclusively for plumbing. I
doubt that one could find a stick of plumbing solder in the whole
country :-)

Let us know how it works out.