Metal Stress
By: Ray Stalnaker


First of all, one of the most important aspect of large dent and some smaller dent repair is stress relief. If there is still stress on the panel, the dent is not 100% repaired. Now I am mainly talking about collision and other severe damage, but some of what I am saying will apply to large door dings and hail. Stress—or a crown—comes from a dent being so big that the metal has nowhere to go but out. The term "crown" is generally used when describing the ring of stress that surrounds large round dents such as large hail. Another way for stress to occur is for the dent to be in an area close to a body line, or an edge, or some other restricting area. I like to remove stress in steps: Push or glue pull the dent a little. Then start relieving the stress until you feel you can push some more. Continue like this until the repair is complete. The reason we push first is to give the stress somewhere to go. If you try to knock the stress out first, it will likely lock the dent in. What we want to do is lock it out.

Most of the time, after the bulk of the dent is removed, the last 20% or so is going to be a large, shallow, low area. There is still stress on the panel that needs to be relieved. When relieving stress, I like to use a knock-down that is a little blunt, but not too large. I almost always use plastic of some kind--never metal or rubber. The only time I might stray from that rule is if there is a huge amount of stress and very good access behind the panel to clean up the mess. Then I might use a large rubber knock-down. Let me explain: If a very large knock-down is used, you will sometimes end up with a very textured look everywhere that a large amount of stress was removed. Sometimes this is inevitable, but minimize this as much as possible. If there is great access to get a tool behind the area, then you can clean this up. If you do not, however, you must be very careful, because what you put in is not coming back out. Generally, the knock-down indentions are too small and sharp to glue pull. Now there are times when a flat knock-down will do the job better than anything else--the reason being that it will not make those little indentions. In my opinion, the only time this is the case is where there is a small, very tightly stressed area. Using a highly polished body hammer to tap out stress is somtimes a great time saver on very large stressed areas, you will have to go back and clean up the area with your knockdown after you have gone over it with the body hammer. And then of course finish it off with a rod behind the panel. The main thing to remember when using your knockdown is that there is very little differance in working the metal from the outside and working it from the inside. Sometimes I will even push with my knockdown on the high spots, and I have tapped on the back side of a panel to push the metal up. You just have to keep in mind what every good trainer has been known to say: "Slower is faster."

The slower you move the stress, the cleaner the finished repair will be. A lot of light taps is better than just banging away at it. The exception to this of course is very large collision type damage. I like to use the black, weighted knock-down sold by PDR Gear.  The aluminum knock-down from DentCraft that has the interchangeable tips also works very well, this tool gives you a wide variety of choices on your knock-down tip.  Another great tool for stress relief is the DentCraft Dent Dollie Set. They come in a set of 3 with different curvatures on each working surface. These nylon blocks are invaluable for de-stressing the edges of panels (roofs, quarters, dog legs, etc.). You will also find many other uses for these awesome little tools as you use them.

Now I have just laid out some guidelines. Every dent is different, and every tech is different, so you will have to use your own judgment in each given case. The main thing to remember is: Always read the metal and your light. Read the stress!