Many of our RV Aircraft builders have ask what the difference is between a Springback and regular dimple die. The concept behind springback dies are that the aluminum is "canned" in the opposite direction of the dimple (1-1/2 degrees) which allows the aluminum to "Spring back" into a flat sheet around the formed dimple. A regular dimple die may leave a slight can around the dimple, in the same direction as the dimple. Springback dimple dies were developed by the Aluminum Company of America in 1942 under contract for the National Advisory Committee for Aeronautics. Since that time there are a few tool companies put out the false illusion that they invented the springback dimple dies, or that they have significantly improved them. We have measured and tested all of these dimple dies and the bottom line is the springback dimple dies work pretty well on 1/8" or larger diameter countersink holes, and all of them work the same with no noticeable difference in the finished product. The technique of dimpling also affects the finished dimple and "canned" effect. On small Number 40 rivets we find that a standard die works as well as the springback dimple dies. Many will argue these points, but they will also say that they invented this 1942 tool. The best dimpled hole is one that has the rivet "set" with the actual rivet that will fill the hole. Use a dimpling block to set the rivet just before driving and bucking it.
To make a dimpling block, simply drill a hole slightly larger than the rivet diameter in a piece of steel or a bucking bar. Next, countersink the steel so that the dimpled skin will lay against this countersunk hole. Then, Install the rivet, hit it 2 or 3 times with the rivet gun lightly to set the rivet into the skin. Buck the rivet. This process gives you a perfectly set flush rivet every time. This is the way the many commercial manufacturers install flush rivets to make commercial airplanes flawless.