When you've gotten things as straight as possible with the hammers and dollies, can you heat stretched areas and small dings and touch them with ice to shrink them back down a bit? An old body man told me long ago (he's no longer with us), that he did that to remove hail dents from cars. I'm just wondering how well it might work on hammered metal. I want to use as little Bondo as possible.
We've had a lot of hail in our area and alot of people use a hair dryer or heat gun on lower temp and then place a zip lock bag of ice on the heated dent, and most times the dent disappears. I have seen it done on sheet metal that has set in the afternoon sun and then the ice bag applied.
If the metal has already been worked with a hammer and dolly, I'm not sure if that will work, but it will not cost anything but time to try. Good Luck
It's not difficult to describe but requires practice to perfect but here we go. You use an acetylene torch to heat a nickle size spot cherry red. Put your dolly under the spot and use a flat surface hammer (I always used a standard pick hammer) to lightly drive the metal around the spot toward the center, working your way around the spot. Quench with water and feel for contour. If done correctly you'll feel a flat spot where you just worked. Continue until the stretched area is at the desired contour. If necessary you can use hammer-on-dolly to re-stretch if you shrink it too much. BE CAREFUL with the heat! Too much can warp a panel beyond repair.
A side note: Off dolly work is most time far more effective in straightening sheet metal because you're not stretching it more than it's already stretched. Most folks do a lot of on dolly hammering which stretches the metal a bit every time you strike. Off dolly is pushing against the low spot with the dolly while working around the low spot with the hammer, not hammering directly on the dolly.
To shrink metal were it is stretched (on flat pnl) you have to determine "ground zero" first then gently bring it up to a head so to speak till there is no more "oil canning" in and around the surrounding area. Do your best to feel with a flat hand. Then as said heat that spot till cherry red but NOT to burning point of when the metal sparkles and if you can get a flat dolly under it quickly smack it flat and quench with cold water. If you can not get access with a dolly carefully work it down with just your hammer and quench. Do not "Konan" or over kill when hammering. I would use a flat end and not the pick end. I have to warn you this takes years of practice and a shrink in the wrong place could be disastrous and very laborious to fix.
To stretch the metal you merely need to hammer and dolly it. The more you hit it the more you will stretch it but take care here too.
If you have any concerns feel free to send me a P\M.
Thanks for the info guys. I learned a lot of that when I was young, but that was around 45-50 years ago. I still have my hammers and dollies and lots of tools, so I don't have to start from scratch. I do need to buy a torch set, though. Hoping I'll be able to do that next week.
Years ago when I helped at a local body shop the metal guy would use a torch to heat the area, then quench it with a water soaked rag and then use a flat 14" vixen file on the area. This was in the mid 70's when the tin was getting flimsy, he would on occasion use a hammer and dolly but always said the metal was junk to begin with and wouldn't take it and would stretch and have to be replaced. The flatter the panel the harder it is to work it. Don
There is a relatively new product out that removes a lot of the risk factor of heating and shrinking with a torch. It's called a "shrinking disk," and they are sold by a number of body work outfits. It's typically an 8 or 9" metal disk with a particular configuration on the surface that causes friction, i.e., heat to build on the portion you're grinding. You mount it on a high speed hand held grinder. It's use is fairly simple--you apply it on the stretched area until heat builds up, then quench with a water-soaked rag. You can continue to hammer/dolly on and off dolly (as Tiny describes) in between applications, after, etc. Over the past couple years, I have used both the torch method and the heat disk on many panels, etc. The heat disk might take a little more patience, but the risk factor is lowered considerably and the results are remarkable. I have brought back to near perfect many panels that seemed hopeless when I began. It works especially well with flat panels that are "oil canned." The disks run typically something like $50-100 and last a good long time. Just a couple weeks ago, I had to weld in a patch on a rear 37/38 pickup fender. The welding process caused some of the surrounding metal to warp. I went at it with hammer/dolly and the heat shriking disk and within about 20 minutes had the contour of the fender about perfect.
I say all of this stressing that I am NOT a professional body man, but entirely self-taught through books, videos, and trial and error. I must say that I've been able to save a lot of metal and restore things to near perfect WITHOUT the use of bondo by using the disk and the other typical hammers, dollies, spoons, etc.
Jim Do you have more info on the "shrinking disc"? That sounds like a better method than the oxy, less chance of blowing a hole.
I am not a fully trained panel man though I have had some training where I learnt the oxy torch method. There also is a carbon rod type heater unit available that works nearly as well as the oxy but price prohibitive for the part time user.
Another option for heating the metal is MAPP. It looks much like a propane torch setup but gets to higher temperatures. Does not cost nearly as much as oxy-acetylene to buy and much more portable. Works great for panel shrinking, heating rusted fasteners, etc.
I've used the disc and it is a lot easier to control than the torch. You run it across the high spots and blow air to cool. You don't end up with the leopard spots all over the metal. I got my disc on an ebay site but can't recall exactly what I searched under. Seems it was kinda wierd but I would start with body and fender tools or some such. If you can't find it let me know I can dig deeper.
Here's a pretty neat youtube video of the process:
Take a look--it really works well. I got my disc from an outfit called Sunchaser in California. It doesn't appear that they're selling the disc anymore. You can google "metal shrinking disc" and you'll get lots of results.
Good luck. I think you will find it a pretty easy process.
