How To Use a Hammer and Dolly
Working out a dent or wave in a body panel is not easy. It requires a deft hand, a sharp eye, and the ability to feel the imperfections in the panel itself. That should not stop you from trying, as no one is born knowing how to do those things. The art of the hammer and dolly is as unique as the person holding the tools, everyone does it a little differently. Before you start whacking that fender, you need to know what you are using. There are many different types of hammers and dollies for metal work, and choosing the wrong one can make the job harder than it has to be.
You should not be using a claw hammer for metal work, so just put that one down immediately and step away. Instead, you need specialty body hammers. These have different shaped heads that are typically flat, though not always. Your basic body hammer set comes with the following:
The round head is flat for smoothing, while the pick side is called a strawberry crown, which is used for working very small dents. You can also use the pick to knock down high spots.
One round head and one wide chisel point, the chisel hammer is really handy when you need to reach into the a tight corner to work a dent or crease out of the panel.
One head is round, the other is square. The bumping hammer is your general purpose body hammer, good for working dents large and small. The square head is best for working in corners.
The head of a shrinking hammer has raised sharp points all over the surface. Some people swear by them, while other hate them.
These are great for smoothing rough surfaces. This is a good tool used in shrinking metal.
The dolly is the backup device, used to support the metal behind the hammer. There are many different shapes and sizes, but the most common are the heel, wedge or “comma”, utility, toe, and egg shapes. The first four are commonly included in body hammer kits.
The name says it all, a heel dolly looks like the heel of a shoe. It has a long radius across one side and a flat edge on the other. One face has a slight dome, and the opposing face is flat.
Similar to the heel dolly, the toe dolly is about twice as long with a shorter radius on one corner, with 3 sharp corners. The top domed and the bottom is flat.
Also called a “comma”, the wedge dolly is shaped like a comma. The long skinny edge is great for working tight corners and edges.
This one looks like a rounded anvil, and the compact nature of it makes it good for tight spaces.
This one is not included in many sets. There are multiple edges, angles and curves on an egg dolly which makes it very versatile.
Working A Dent
The best way to learn is to practice. Unless you really want to start on your car, we suggest taking a scrap fender, hood, or even just a piece of 18-gauge sheet metal and start there. Use a hammer to make a small dent about the size of a quarter, about ¼” deep. This is a great place to start without being overly complicate with creases and multiple impact points.
Selecting the right hammer and dolly is critical. While most dents can be worked with a round flat faced hammer, the dolly is very important. The curve of the panel dictates the dolly you need. Match the shape of the panel as best you can.
To start, the hammering is done from the inside of the panel, with the dolly on the outside. Start by lightly tapping the deepest part of the panel with the hammer, slowly working the dent out to the dolly. Do not make big hits, light taps are better.
As the dent is reduced in depth, switch positions of the tools, the dolly goes to the inside, and the hammer is used on the outside of the panel. This is the smoothing portion of the job, taking the high spots even with the rest of the panel. Push the dolly against the panel and lightly tap the dented area until it is smooth.
How you strike the hammer and how you hold the dolly all affects the results of the work. Hold the dolly tight to the panel maximizes the hit, a loose hold allows the dolly to bounce, reducing how much the metal stretches. Every dent is the result of stretched metal. While most small dents can be worked without shrinking, big dents usually need some form of shrinking. Shrinking metal is a special technique, and there are many ways to do it. The best is to use heat, a wood hammer, and a dolly. Any time you hit sheet metal with steel hammer against a steel dolly, it stretches. Using wood, you eliminate one of those hard points, so the metal can move without stretching. A wood hammer is a good way to go, but sometimes you need a wood dolly or buck. You can make these to whatever shape you need. To shrink stretched metal, you need a wood hammer, a dolly, a torch, and a wet rag.
Use a permanent marker to mark the area you need to shrink, this is critical as once you get going, you can easily lose the spot.
Begin by heating the area with the torch. Oxy acetylene is best as you can control the heat easily and apply it quickly, whereas propane takes a long time to get sheet metal hot enough to shrink. If you are asking “doesn’t heat make metal expand?”, the answer is yes, it does. However, when you strike the hot metal with a wood hammer, you end up folding it over a little, which shrinks the area.
The area should be orange hot, not red or white hot, and the center will pull out in a nipple-like dome. This is where you strike. Wearing welding gloves, place the dolly behind the peak and strike the peak with the wood hammer. A couple of good hits should do the job.
Once you have knocked it down, apply the wet rag. This will cool the metal and contract the molecules, further shrinking the metal. You don’t want to do this over and over again, as it will harden the steel, making brittle.
If you are working a large panel with lots of stretched metal, you will likely want to use a slap spoon to smoothing out the shrinking work. This is a heavy paddle with a curved dome. This is where the light hold of the dolly is important. The dolly is held loosely behind the panel and the spoon is slapped over the surface, being careful not to use the edge (which will cause creases). A few slaps can make a big difference in a wavy, bumpy panel.
The hammer and dolly process takes a lot of time and patience, but the results are well worth it. You will use less body filler, spend less time sanding, and get a better paint job in the end. Don’t rush it, take your time and learn the process. After you work out a few small dents, you can start tackling the bigger jobs, and that just feels good knowing that you did it yourself.
Check out all the tools & equipment available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to use a hammer and dolly, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.