Looks like I'm accepted, thanks Will
Thanks for the input Mark. I have done zero spinning before apart from viewing Youtube videos and imagining how it's done LOL. My metal lathe is pretty big so should be fine for seeing how mild steel sheet responds to spinning. Time to read some of the spinning books I've collected too.
After reading your post I messaged a spinning mob and have asked for a quote on two 900mm diameter, 3mm thick hemispheres. Should be interesting.
I would guess tank heads would be more expensive than a thinner spun sheet. Aren't the tank heads sort of roll pressed with powerful hydraulic forming machines.
Keith.