On Thu, 10 Dec 1998, Brad Kahler wrote:
> I'm in the process of trying to straighten an edge on my front valence. It
> had been pushed in about 1" or so and in the process one edge was bent
> and it stretched the metal that forms the angle on the underside. I've got
> the edge straightened out again but the bottom portion is now buckled up.
> I'm under the impression that you can use heat to shrink metal but I'm not
> sure just how to do that. I've got an oxy-acetylene outfit but I'm a little
> nervous about doing more damage than is already there.
There is a good book by Petersen publishing - the name escapes me - that
has lots of good stuff regarding shrinking and stretching metal.
To shrink metal you can do a number of things:
To shrink a small ding, grab thy oxy-acetylene torch, put a fairly small
tip on and heat the ding to a cherry red. Move the torch in a circular
(concentric) pattern so that the Most Dinged part of the the ding is also
the Most Hot. When it's cherry red, put the torch down (turn off, hand to
beautiful assistant, place on special rack, whatever) and with
hammer-and-dolly, bop the ding down flat. The sudden cooling introduced
by the hammer & dolly will shrink the metal. Or so you hope.
For large wrinkles you can heat shrink. (same as above but more time
consuming). I would be tempted to cut away the wrinkle and lap the metal,
then weld the hell out of it and grind off the excess.
You can also get a shrinking dolly (often cheap dollies have a shrinking
face on them - looks like a meat tenderizer) I'm not sure exactly how to
use these, but I bet it's not the same as a voodoo dolly. Probably some
method of whacking with hammers will force the metal to contract upon
itself; maybe it just corrugates the metal so that you fit more length
into less space, then you break out the Bondo and make it look pretty.
Is the sheetmetal accessible? Can you get it off the car to really start
banging at it? Provided it's not too thin, you won't be able to damage it
further. I'd get the work area red hot anyway, then let it cool in open
air for a long time. That should get rid of any tendency to tear the
metal (result of metal fatigue) and make all the steel molecules smarten
up a bit. Also, it will burn off any bondo, lead, or rust that may be
lurking. Watch those fumes, don't want to inhale anything really nasty.
Or even anything mildly nasty.
-Malcolm
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