On Mon, 05 May 2008 17:44:58 +0000, etpm wrote:

On Mon, 5 May 2008 09:43:26 -0700 (PDT), Jim Wilkins
wrote:

On May 5, 8:20=A0am, stryped wrote:
I finally got my garage door working in my shed. Now the next problem:
these doors were given to me and there is a panel or two that has
dents in them. I fooled with taping them from behind but to no avail.
Is there a way to get these dents out?

You need better tape, like the aluminum kind used to patch rust holes in
cars you want to get rid of quickly.

The metal in dents is usually stretched and can't be flattened anyway,
unless you can heat it red hot and hammer from either side.
I've seen dents in painted soft steel sheet and aluminum being removed
with just a heat gun and a wet rag. just heat and cool the streched
part. The dents must have a large radius. If you want to tap out the
dents from the back side you should use a soft hammer on the protruding
side and a hard surface to back up the hollow side of the dent. The soft
hammer lets the metal flow back together while a hard hammer just tends
to push the metal.
ERS

The idea behind heat shrinking metal is that you get it hot and it (a)
expands and (b) gets weaker. This tends to push the edges in toward the
center. When you hit it with the wet rag it gets strong and pulls the
whole panel in toward the center of the hot spot.

My dad used to take care of wows in large, lightly contoured panels using
an air sander with a dull disk. He'd play the disk over an area to heat
it up just right, and it'd pull in when he was done. I don't remember
any cooling being applied, although it may have been part of the mix.

There are shrinking hammers that draw the metal together when they hit.
There used to be things called "slapping files" that did basically the
same thing, only they looked like files rather than hammers.

I've never thought of the soft-faced hammer trick, the next time I'm
shrinking sheet metal I'll have to give it a try.

No matter what you do, you're not going to end up with a perfectly flat
panel.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html