Don't get the concept of "stretched" metal? Try pushing a very large dented area back out to its former profile. Much of the time you'll push the dent out, and it will spring back into the dented configuration. This is "oil canning," and it happens because the impact of the accident has stretched the metal over a large area. The corrective method for this type of injury is to heat-shrink the panel, which we'll learn later, but the important thing now is to realize that if you don't use patience, you're screwed. So take it slowly.
See there," said Roy, pointing to a crushed place on the roof of my formerly rusty-but-straight BMW coupe. "That's where the chain came across the top...and after I told 'em not to." I'm having real trouble controlling a couple of urges: I want to sit down in the middle of Roy's dirty concrete floor and cry over my trashed classic...and at the same time I want to hitch every employee in the damn place to their own chain hoist and dunk them in those gawdawful paint-stripping pickling tanks for a few hours. Not too long, just until the bones show.
I must now confess. When I suggested that sending a car to the paint stripper was an alternative preferable to doing the dirty work yourself, I was speaking from a position of total ignorance. Now I know different. Now I have deduced how this paint-stripping game works. Apparently, from the looks of my coupe, the method these people use is to chain the car to a large construction crane, hoist it 306 feet in the air, then drop it onto a large concrete slab. This process is repeated for several hours, until every scrap of paint has been slammed loose from the unrecognizable ball of metal that used to be your classic car. The cretinous swine who perpetrated this atrocity have struck before, and they will strike again. Beware. If anyone suggests that you trust your car to the heinous thugs running a paint stripatorium, run away. Run away fast. But if you took my initial advice and sent your irreplaceable sheetmetal masterpiece to such a facility, never mind. It'll probably be just fine. Sure it will.
After I finish agonizing over whether or not to do the humane thing and crush what's left of the coupe, I decide that I might as well go through the rustproofing motions, just in case. Know that if you've stripped paint from the car with a chemical stripper, you have about 6 seconds to treat it with rust preventative before it turns brown and disintegrates. So, with great dispatch, I trailer the remains home, purchase a gallon of phosphoric acid (otherwise known as naval jelly) and use a garden sprayer to hit every square inch of the coupe with this vile liquid. After the phosphoric acid spraydown, I rinse the car off. I now have approximately 13 seconds to get the thing primed before...yup: brown, rusty disintegration. After I prime it, I will spend about six hours walking 'round and 'round my poor beast before I sigh, shake my head and get back with the program.
At any rate, what we have in my case is, in military terms, a retrograde movement. Sometimes we need to retreat in order to advance, see, and that's just what I've done. The time I would have spent in this piece rhapsodizing on the joys of welding will now be consumed in a discussion of the joys of bodywork. After all, there is no better time to attend to the minor dents and dings caused by an end-over-end flip or a paint-stripping place. I have every panel that can be exposed in full view, with no distractions like a drivetrain or interior or trim or electrical geegaws to obstruct my whamming the hell out of aforementioned panels. So let's go to work.
The first rule of straightening that precious sheetmetal is to have patience. Never use one blow of the body hammer when ten will do, or a hundred, or a thousand. Because, you see, if you use too much force, you'll do the exact opposite of what you're trying to do and stretch the metal in the opposite direction.