What are Springback or Spring Back Dimple Dies?

Many aircraft builders ask what the difference is between a Springback and regular dimple die. The concept behind springback dies are that the aluminum is slightly "canned" in the opposite direction of the dimple (about 1-1/2 degrees) which allows the aluminum to "Spring back" into a flat sheet around the dimple. A regular dimple die will 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 that have the illusion that they invented the springback dimple dies, or that they have improved upon them. We have measured and tested all of them. The bottom line is that the spring back dimple dies work on 1/8" or larger diameter countersink holes, and all of them work the same with no noticeable difference in the finished product. However, technique of dimpling also affects the finished dimple and canned effect. On 3/32" rivets we find that a standard die works as well as the spring back dimple die. Many will argue these points, but they will also say that they invented this 1942 tool. The best dimpled hole is one that is dimpled a second time with the actual rivet that will fill the hole and a dimpling block -- see my May 2, 2006 previous post on this subject.