Newsgroups: alt.autos.antique
Subject: Re: Brazing up sheet metal
From: rdb@local.host
Date: 12 Aug 92 07:35:33 -0600
Reply-To: rdb@local.host
Organization: Organization, City, State, etc.


SIn article <1992Aug11.203718.27708@mlb.semi.harris.com>, jws@billy.mlb.semi.harris.com (James W. Swonger) writes:
> As many of you are probably tired of hearing, I'm brazing new sheet metal
>onto my project car. I've just completed the first large-area patch and will
>describe the process. 
>
> First off, let me advise you to bite the bullet and get a MIG instead. The
>results are very ugly and will require serious fill work. I experienced 
>some severe emotional distress as I watched exterior panels warp before my
>eyes. Spare yourself; get the right tool.
>
> I found a parts car way back and had the quarters cut off along with pulling
>the other sheet metal. Hoping to minimize the damage, I decided to cut away
>the minimum amount of rust from the rear wheel rim, cut a fitting patch 
>from the donor quarter and braze it in.
>
> I separated the two layers and first installed the wheel well/lip. This went 
>fairly well, actually; the molded shape of the wheel well lent enough
>strength that warpage was controllable. The donor piece had a nice line -
>which will at least give a chance of getting the final shape right.
>I then tucked the outer skin piece inside the original quarter after trimming
>it to shape. I did this so that I would be filling into the repair, not
>bringing up the surrounding panel.
>
> The smooth outer panel warped badly - no rigidity. I have found that brazing
>requires the pieces to be tightly overlaid to get a good joint. You want 
>capillary action to draw the brass in. Unfortunately the metal had a tendency
>to warp away from the flame, and I then had to chase the top piece down 
>with a hammer. Consequently the seam is depressed about 1/2". The warping
>also tended to make the pieces meet at an angle instead of flat. More heating
>and hammering and rebrazing gave me a strong seam but an ugly one. 
>
> One thing that really disturbed me was that I began to find all sorts of
>cracks in the steel. The sheet metal has a narrow zone where it can be 
>hammered nicely. Above that heat (medium orange) the metal becomes softer
>but sort of brittle as well; striking it sharply will cause it to crack
>rather than bend. I did not expect this, and may pay for it later. I took
>to damage control by recessing the cracked areas some more and filling
>generously with brass to contain the stress. Thin brass will crack too.
>
> I found that brass can be worker sort of like lead to fill holes and to build
>up areas. It is lighter, stronger and more expensive. Some of the technique
>is similar to lead. You can deposit and build up brass by simulataneously
>heating the rod and the surface. Maintain a small wet patch but don't heat it
>deep enough to run. Keep pressing the rod into it and let the heat of fusion
>keep the temperature right at slump.Balancing the flame and rod can let you
>build up fairly thick brass shapes, fill holes, etc. If the metal looks wet
>you are past slump and close to run. Varying the flame distance varies the 
>depth and spread of the heat. You want the surface wet but the body still 
>solid. Every once in a while I had to pull back and let the heat spread out
>to keep the whole thing from slumping. Periodically (about avery 1/16" of
>buildup I would stop adding and just go over the work area with the cone of
>the flame, locally remelting the brass to ensure it became one continuous
>piece. I would heat a small spot to the run point (almost), and the high spots
>would pull back and merge into the surrounding metal. I used this as my cue.
>Moving over the area in this way I got the deposited lumps merged into a unit.
>
> I filled a couple of small rot holes this way, reconnected the seam in the
>wheel well where it had rusted apart and also used this method to restore the
>fender flare lip somewhat. At the far end of the patch I ended up with an
>angular mismatch as well as some inward warping near the lip, and with this
>method I built up the proper form in brass. I expect this to be more durable
>than lead or plastic filler; the brass is much harder than either. I stopped
>slightly short of the final surface because I don't know yet how well it
>grinds out.
>
>
>rebuild the fender flare lip where my patch panel came up a bit short and
>off in angle; it now has a thick, continuous brass lip rather than 
>-- 
>##########################################################################
>#Irresponsible rantings of the author alone. Any resemblance to persons  #
>#living or dead then yer bummin. May cause drowsiness. Alcohol may inten-#
>#sify this effect. Pay no attention to the man behind the curtain. Billy!#
 Speaking from experience you will find that brass is not the way to go. 
nothing but lead will stick to brass. I mena nothing!  Plastic won't stay and
primer won't stay.  After a while they will flake and fall off.  All body work
should be welded with  mig or torch.  Brazing will only work if lead is put
over it for primer to stick to it.