Dear cdgoldin,

I checked my Statics and Strength of Materials to see if there was a formula
for bending sheet metal around a curve. The best that was there were the
parabolic deflection beam formulas. I don't think they apply. However, with a
distributed load on a straight beam, the apex of the parabola does have a
computable radius after the material gets bent.

So let's say the Young's modulus of your stainless is known. Use the Young's
modulus calculator, the bend radius, and the sheet thickness in:

http://www.allmeasures.com/Formulae/...gs_modulus.htm

to get the force required to hold the material in a 16 inch diameter circle.
Apply an adjustable strap, slowly working up to that much tension in the strap,
more or less, and your desired bend radius. The strap should be right down the
middle. Use one of those endless hose clamps, available in lengths of up to 10
feet, if you don't have a two ladder lock buckles and a 5 foot length of nylon
webbing. Use your judgement.

Then apply something a little stronger and resistant to heat, like two pieces
of 3 mil aluminum tape 2 inches wide, and at least a foot long, along the
edges, over the joint. The extra length is so the adhesive at the ends remains
strong while the brazing or welding is done. Remove the center strap, if you
used nylon, or leave the endless hose clamp in place. Either way, your choice.

Then, tag weld the seam, be it lapped or butted, one half the way from the
center to the edge. Two weld nuggets about 1/8 inch diameter should do. I don't
weld much at all. I am probably not as good a welder as you.

If having the seam lapped and then having the upper layer stubbornly remain,
say, 1/16 inch from the lower, preventing a sound weld, is a problem, then
clamps must be applied to a bar over the seam, leaving the weld area free, and
using a more or less identical bar diametrically opposite. For instance, I'd
think two pieces of 1x1 inch steel 18 inches long with a 1/4 inch hole through
at each end 3/4 inch from the end would do, in combination with two pieces of
1/4-20 threaded rod about 18 inches long, and four matching nuts.

Once two tag welds are made, you can make several more to hold that edge down
if it is a lap joint, or a few more if it is a butt joing, and then grind them
all smooth. After that, my choice would be to braze rather than weld. Handy &
Harman will provide a small sample of stainless compatible braze filler, about
3/16 inch diameter, which is an excellent color match and very strong. You'd
use a hell of a lot of flux for stainless and try to work quickly, because the
chromium in the steel becomes chromium oxide, a ceramic, at brazing
temperatures, and even a large amount of, say Anti-Borax brand flux can only
dissolve so much chromium oxide before turning black and forming an insoluble
glass. This is an indication that the flux has been "burned". The material is
very tough.

If you finish the joint and the flux is insoluble, you can add lots more flux
and reheat the work to dissolve the chromium oxide. Then, soaking the seam in a
tub of hot water overnight will dissolve all the flux. If necessary, set up a
tray with vinegar and water or a solution of hydrochloric acid. This will
dissolve the remaining flux.
Be careful with HCl, you already know it's dangerous ****.

Now to finish this, you can use a sanding belt to smooth the braze and remove
oxides from the metal that got hot but wasn't protected by the flux, and you're
done.

I switched to decaf all day yesterday, at well, did a little work, and felt OK.
I'd still like to know if when you read my first post in reply to your original
post, whether you got the impression I had had too much coffee?



Yours,

Doug Goncz (at aol dot com)
Replikon Research

Replikon Research researches replikons, which are self-reproducing
configurations of non-living matter in environments that support replication,
analogous to organisms living in ecologies.