Grant Erwin wrote:
Picture the little aluminum disk riveted to the top of a Weber kettle. It
closely matches the profile of the domed kettle top.

I want to make something similar in concept, but with different
dimensions.
I find I have no idea how to shape e.g. a 4" soft aluminum circle so it
will lie close to the OD of a rounded 3D surface like a tank end.

This is for making a smoker vent ..

Grant

I've done both hand raising and metal spinning but these days I do
metal spinning as it's so much quicker for doing round objects. If you
can turn up a blank to match the inside of your piece then you should be
good to go. For a one off very simple tools can be used depending on
your quality requirements. I would be inclined to join and post here
about details to start with
http://metalspinningworkshop.com/forum/upload/index.php . You can use
traditional spinning tools or for things like spinning a tank end I have
used a cam follower roller bearing mounted on what amounts to a radius
turning attachment. See

http://www.metal-arts.co.uk/~djb/Rol...rollertool.jpg
http://www.metal-arts.co.uk/~djb/Rol...rtoolfront.jpg
http://www.metal-arts.co.uk/~djb/Rol...ertoolside.jpg

I have recently done this on the same lathe, Harrison M300, upto 12"
diameter and may try at max 18" using the face plate as a former.