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?
If your door is flat, Lloyd has spoken. If it is contoured, get one of those multifingered molding gauges, jigsaw profiles for each side of the door and get a helper to hold one while you pound the other.
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.
Auto body repair manuals have lots on removing dents from sheet metal panels, check the local library. A skilled craftsman can do it so there's little evidence left of the crease or dent. The skill development curve is pretty long, though, and I'm not one of the elite that can do such. If the dents are small dings, they can be knocked back and filled with body filler. Creases can be unlocked at the proper points and flattened out. You need dinging hammers and dolly blocks to do it and some idea of what to do with them. Big suction cups can pull out shallow creases, too. It's complicated by the fact that the metal has stretched and it'll have to be shrinked down at some point to get a semi-flat surface. The body manuals have all the procedures for it, you get to experiment. There's a reason that there's a constant demand for straight body panels from the auto wrecking yards, replacement is a whole lot easier than unbending dents.