Thankyou Mike and Bob, I could have mostly eliminated the warping by making a different bottom die. I should not have just done a narrow perimeter form as that is what created the warp. Instead it should have been the full size of my pressing area as that puts the same pressure everywhere. I guess I was just a bit slack really
. The better way would have been to mill the shape I wanted into a thicker piece of metal as that would cover all areas or plug weld a laser/plasma sheet on the top. Either way it was just lack of support and I knew it would happen but being aluminium it is easier to shrink and stretch.
This is a problem when using bead rollers as that too creates stretching. As I am no panel beater, YouTube is a valuable source of information but I used a rubber mallet to shrink and stretch the material. Not as easy task on steel. The dies I made to press my bottom engine covers were heavy and pressed the entire area of the covers so I got very minimal distortion.
The wire rolled edge certainly stiffens it up and I clamped the whole thing down before I formed the edges. I learn a bit more each time I make things like this.
Oh, and Mike! No I don't have any .50 Vickers ammo boxes�� unfortunately and would be very happy to do a deal with anyone that has some�� Please��