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HCCA Forums • Brass Restoration Tips
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Brass Restoration Tips

Posted: Sat Nov 16, 2013 8:12 pm
by MochetVelo
In brass-era cars, brass restoration is a common job. Here are some tips:

Annealing is necessary to shape and re-shape sheet brass. Over time, and through stretching and shaping in manufacture, brass hardens and become stiff and springy (called "work-hardening"). To reverse this condition involves heating the metal with a torch (propane is fine) until it glows a dark red. A darkened room is helpful to observe the color change. Don't go to a "bright" red or you may blow a hole in your work. The brass can then be left to cool naturally or quenched with water. The result: rigid, inflexible brass become softer and more pliable. The same metal can be re-annealed after prolonged tapping and shaping. Failure to anneal may result in split and broken brass.

This same process can also be used on aluminum sheet. A trick here: use an acetylene torch with large flame held away from the metal so it deposits a black layer of soot. Switching to a hotter flame, heat the metal again. When the soot burns off, the aluminum has been annealed and is ready to work. I should note here that sheet steel does not work-harden in the same was as brass and aluminum.

Brass instrument shops use all sorts of odd-shaped tools to tap out dents. Basically, you want a shape the follows the contour you want to repair. Sandbags ("shotbags") like those used in panel beating and regular body-shop dollies can be used also. Special forms can be made of wood to hammer against. By "hammering", I mean controlled tapping only on the area you wish to move. Some dents can be massaged back into shape by rubbing with smooth hardwood or metal tools you make yourself. Tool handles, toy blocks, even drumsticks make good rubbing tools.

TIP: A low-temperature alloy (containing bismuth) such as "Cerrolow" can be melted as low as 117-degrees F. Say you have a dented headlamp rim. You find a good spot on the rim and melt the alloy on it. Use aluminum foil or even cardboard to contain the metal. When it hardens, you pop it off and use it as a mold to tap out the dents. Here is a link to this alloy: http://www.mcmaster.com/?error_redirect ... ys/=peu1yq

I'll add more things, but feel free to post your own tips and methods for restoring brass-era automobiles!

Phil

Re: Brass Restoration Tips

Posted: Sun Nov 17, 2013 1:25 pm
by mojoe59
Can you tell me how to repair small cracks/tears in brass lights? Also, are the Bismuth alloys re-usable for other molds
Thanks,
Joe

Re: Brass Restoration Tips

Posted: Sun Nov 17, 2013 1:49 pm
by MochetVelo
Cracks can be repaired with brazing rod. These come in different alloys, the color depending on the copper/zinc ratio. You would first anneal the brass and smooth out the split, then braze in the repair. Finally, the repair is smoothed by filing, sandpaper and buffing wheel. The result will not be invisible, but will no longer attract the eye like a crack will. Brazing can be tricky, so you may find a welder who can do it for you. If the metal is badly split or damaged, the only recourse is to replace it. There are still metal spinning shops that do this type of work. You may find one with a wood form that will work, otherwise one must be made. Another repair is to "skin" the part if it is not too complex. That is, form a cylinder (say for a carbide generator) and solder it atop your messed up section. It sounds hokey, but can look acceptable if done carefully.

I've gotten lamps and horns repaired professionally. This costs around $500-$700 each if they are complete and not terribly deformed. You should be able to do minor repairs yourself, however.

Phil

Re: Brass Restoration Tips

Posted: Sun Nov 17, 2013 4:51 pm
by mojoe59
Brazing rod seems thick in diameter to melt onto thin sheet brass like a light. Do they make a fine brass wire that wouldn't take as much flame to braze the crack on a light. I was thinking of something like the wire on a mig welder but am not sure if that is available in brass. Also, what would you suggest as a flux if using a thin wire as noted.
Thanks,
Joe

Re: Brass Restoration Tips

Posted: Sun Nov 17, 2013 5:49 pm
by MochetVelo
I don't think you can braze with a MIG welder, at least on a budget. You can buy brazing rod 3/64" diameter, which is pretty slender. You want to build it up and grind off the excess. The flux you use doesn't vary with wire thickness. Go to a welding supply store and see what they have.

Phil