Thread: Aoto Body explained..

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Normally you will use whatever gets the job done, so in most cases you will use multiple processes.... Off dolly tends to move the metal around, getting it closer to where it was, but the shrinking is minimal, as compared to the other methods. Next, the donut dolly is a bit more effective, then a shrinking tip is a bit more effective, with the torch shrinking likely accomplishing the most shrinking. But much of this all depends on the panel, what is needed to correct the damage, persons skill/comfort level with different methods, etc.

With your quarter, as the rear side access is challenged, some of your alternatives to off-dolly are to use heat and dent puller combinations or load it full of bondo or cut out the inner panel to provide the needed access for off-dolly. IMO a heating tip and dent puller/stud welder + stud puller combo would tackle about 90% or so of that damage if you did wish to leave the inner panel intact. This would leave a minimal amount of filler required to fix the remaining defects. I doubt you'll be able to get the panel back out where it needs to be with shrinking alone (ie: using pencil torch only), it will need pulling also. Not having a stud welder/dent puller anymore, unless you plan to get one, the option of cutting out the inner panel would seem more appealing....

With rear access provided, you can use whatever works to get the job done. In this scenario, I would suggest some off dolly to bump up the severe low spots, then go with a shrinking method (or if panel is too tight to push outward, some shrinking may be needed first). The Donut dolly method can be accomplished with minimal cost, There is a reducer bushing that would work a bit better than the elbow I showed earlier. A straight through hole in the reducer bushing allows you to use a finger in the hole to locate the dent for positioning the tool. The issue here is likely going to be free and clear access for swinging the hammer, so for tight areas, you may want to use the heating tip or your pencil torch. When you get to a point where you've shrunk enough and need to bump up some low spots, I've found the small shot bag I showed works a bit quicker than trying to use on-dolly hammering to stretch the metal. Of course, using the shot bag on the outside to bump the panel outward would require swinging room for the hammer, so sometimes you'll need to be creative with bumping devices......as long as what you are doing doesn't create more damage.

For the hammers, even though one is "flat", it still has a slight crown, in order that the edges of the hammer will not damage a flat panel by leaving semi-circular marks from the edge hitting the panel. But really, the higher crowned hammer is used where it more closely matches what you are striking, such as the back side of a crowned panel. If the inside of your quarter has such a low crown that the "flat" hammer leaves marks, then you would want to use the higher crowned one. But use it with restraint, as you don't want to pound dents back the other direction.

Regarding hammers, all will shrink, just depends how they are used. Given an on-dolly scenario, all will stretch as well. There are also what I consider "gimmick" hammers that may have a waffle face that are touted as shrinking hammers. In most cases, any waffle face device will take a stretched piece of metal and basically "accordian" the length to pull in any stretch. The reason I call these gimmick devices, is that they really didn't shrink anything, and now that your panel has this waffle shape deformity, you have locked yourself into using body filler to fix the area. Not saying anything is wrong with that, it all depends on your level of finish you are trying to attain. But there are plenty of methods that actually shrink the metal, such as those we've been discussing, that will leave the panel flat/original crown where filler isn't a requirement to cover damage left by the tooling.

As to the hammer used for the donut dollly, it goes back to the springback condition that was described above in the formation of a dent. As we use the donut dolly, the same condition will need to occur. So if you have a flat sheet, and a flat hammer, you'll be there forever as nothing is getting pushed into the hollow of the dolly (the shrinking effect) so nothing is going to happen. If you have a flat panel, such as the bus door shown earlier, then a slightly crowned hammer is needed so that once the metal is forced in the hollow, and the slight bit of springback occurs, our result we are looking for is the return of the flat (original crown). When hammering on an outward crown, such as the outward facing roof dent sample experiment, you can use the flat hammer as is does force the high dent crown down into the hollow. Using a crowned hammer in this case would be like these two surfaces coming together: -------)(--------- , where you will have more chance of creating dents the other direction, so hammer selection will depend on your panel shape and what you are trying to accomplish.

On positioning the donut dolly, hammer strikes against the high side (convex) and dolly supports against the low side (concave)