Shrunken metal is the same way—it can only shrink so much before it begins to bulge outward. That’s why oftentimes when you feel a dent, the outer ring actually protrudes from the surface because the metal has simultaneously shrunk (created a protruding ring) and stretched (creating a dent). A good way to remember things, is typically when dents are concave they stretched, and when they are convex they are a shrunk.
By using the tip of an oxyacetylene...
By using the tip of an oxyacetylene torch, and then immediately cooling the area with water, one can shrink a severely stretched piece of sheetmetal. Again this approach is something only one can attain though practice; therefore you should practice on a junk fender to see how the sheetmetal reacts.
In a nutshell, that’s metal. All forms of metalworking are based on the premise of either shrinking or stretching to restore or alter a piece of sheetmetal’s composition. The real key to mastering the craft of metalwork is identifying what areas are shrunk and stretched, and at that point deciphering what method will correct the area. As there are plenty of ways (and even more tools!) to accomplish this feat, we’re going to keep things at the very basics and stick to the methods of hand tools.
The beginning of every metalworker’s career begins and ends with the hammer and dolly. The ironic thing about the hammer and dolly is the correlation to the work they perform. It is a complete oxymoron to the simplicity of the tools. By all accounts, the tools are as simple as it gets—one is a hammer with a face, and the other a small handheld anvil. However, mastering the two to work as one is one of the most complex tasks in the book.
Here is a close-up look at...
Here is a close-up look at the hammer on dolly approach. Notice how the dolly is directly under the high spot, and how the hammer will fall atop the dolly to correct the dent.
Let’s begin with hammers. For starters, they come in all shapes and sizes. Each has a different purpose, but in reality most metalworkers will stick to two or three basic hammers. Only in select occasions will an oddity of a hammer be employed. When looking upon body hammers under a keen eye, one would notice that the faces are actually convex and the diameters vary slightly.
Body hammers usually have a face diameter that ranges somewhere between 1¼-2 inches. Depending on the user’s preference, consistently a 1½-15⁄8-inch hammer is a good all-purpose body hammer. The next hurdle to overcome is determining the curvature of the hammer’s face. A general all-purpose body hammer with a low-crown has a radius somewhere around the 20-inch mark. This crown on the face is great for all-purpose hammer work as it gives the user a larger striking area for consistent and gradual blows.
Some hammers can have a radius of up to 2 inches! Hammers of the medium and high-crown variety are used to get inside curvaceous cavities, where only the high point of the crown will make contact with the sheetmetal for very precise blows. When it comes to bodywork, a flat-faced hammer is very rarely used. Hammers like your ordinary ball peen or claw have a flat face, and unless you hit the metal 100-percent flat, the leading edge of the face will leave a smiley face. Hence the reason why those styles of hammers aren’t used for bodywork!
If you look close, you will...
If you look close, you will notice the circle around the dent. With the dolly placed at the lowest point of the dent (marked with an “X”) I will hammer around the circle to raise the dent in this hammer off dolly approach. My blows will always remain within an inch of the dolly; if not you’ll lose the energy of the blow and defeat the purpose.
The last thing to remember in terms of hammers is quality. A good quality hammer with high-grade steel will make all the difference. You want to make sure the hammer is harder than the sheetmetal because you want the hammer to shape the material, not for the hammer to be shaped! (Same goes for dollies.)
Cheap sets of hammers and dollies are OK for initial practice, but that’s about it. As you continue to use them you’ll notice the hammers and dollies won’t stay true to their original form. They will begin to distort, which means you’re not getting the most out of your tools. Even worse than that is the fact that they will nick and scratch, and when sandwiching sheetmetal between a nicked hammer and dolly, the metal will instantly become dyed with that shape, a big no-no.
When it comes to dollies, things are in line with hammers. Dollies come in various shapes, sizes, and weights. Again though, you’ll find that most stick to a few of their favorite dollies, such as a heel dolly, egg, or a loaf. One thing to keep in mind about dollies is a good-weighted dolly is key. A quality dolly for general use will weigh somewhere around 2-3 pounds, which is right on the money.
A few months back I attended a Ron Covell beginning/advanced sheetmetal weekend class. One of the things Ron discusses is basic hammer and dolly work, and removing dents; here is the process. Ron whacked this piece of metal with a pipe. The red circle at the marker is the first point of contact, whereas the rest of the highlighted area is what ensued after that initial contact. When working a large dent you want to work backwards, meaning first correct the last affected area.