jd750ace, 3003 H14 is the material of choice most tank builders and metal shapers use. I use .090" on all my tanks. Depending on the tank design when using .090" material the majority of my tanks become thicker, to about .115" thickness. My tanks get thicker in the areas that are shaped to compound or reverse compound curves. When you shrink metal (done correctly without actually creating what I would call damage) you are actually gathering metal and making the material thicker. I rarely use english wheels, hammers or plannishing which are all forms of shaping metal by stretching which one would be thinning the material. Welding process and building practices are all important and most reputable builders know what to do and how to do it or they would not be doing what they are doing.
I figured that's what you were using. It's no good in aircraft work, as 3000 series is silicon based and it's highly crystalized structure prevents it from developing repeatable strength properties in wrought sheet form. Car and bike guys like to use it because of it's high malleability. It does work harden, but not to a predictable value. the only practical use of the silicon alloys in aircraft is in casting. The A356 cast alloy is in exceptionally wide use. It is often used in engine cases for bikes as well. It has a very high corrosion resistance, being low in magnesium and having extremely low copper content.
I've been repairing aircraft for 28 years, and have formed thousands of parts. We shrink form parts, but not nearly as common as stretch forming in our industry. Stretching is harder, as things can crack and tear while working them, and maintaining consistent material thickness is a challenge. We seldom cold form anything heavier than 0.063" thick.
When working with structural alloys, the material does not move like 3003. It's quite different. We have to verify our remaining material after forming by ultrasonic thickness testing so we ensure our design mechanical properties are maintained. Below is a pic of the finest forming machine in the world for aircraft parts, the Eckold machine. They can shrink, stretch, planish, cold forge, almost anything, but a machine and a complete set of non-marring dies is around $150K nowadays!! Also is a pic of the aft pressure bulkhead out of the Constellation. It is an 84 inch spherical form. You have not had any fun til you tried to make a slice of a giant bubble out of 0.32" thick 2024 Clad sheet! It took a little bit to get it right, but a fine man from Hungary figured out how to do it repeatedly. This dome must endure flight loads at a pressure of 5.75 pounds per square inch. 84 inches in diameter, and domed, I have no idea what that works out to exactly, but inexactly, it's a whole shit-ton of load on a very thin part!
The last pic is the tailcone section that is 80% new material that I re-built over the course of 100 days. A little different than making motorcycle tanks and fenders. Your tanks look very nice, BTW. Not easy to get them symmetrically assembled.
