Boring a large diameter hole in a lathe

[batt]

Sharpen the boring tool like a knife tool for aluminium, flat top for brass, and set tool flat against face of job ... should be able to take at least 3 mm cuts ... not too heavy a feed ... should peel the metal of easly.
If need be can send a image of tool set up.
Batt

 

[cjtoombs]

You may not have the equipment, but I'd do a 5" hole in the mill with a rotary table. Or even CNC. Use an endmill to just cut a slot.

This is how I would probably do it, since I have the equipment, but if you do, ensure that you either bolt the center section down or leave it attached and do the final cut manually. When the center waste portion comes loose, it WILL break your end mill. You will also need to clear the chips some way or another, as gravity won't help you on a mill. One could also rough cut it with a bandsaw, if you have a way to solder or weld the blade.