On Wed, 1 Jun 2011 08:45:34 -0400, "Ed Huntress"
wrote:


"john B." wrote in message
.. .

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.
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 :-).

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 :-)