Even if you don't have a lathe or milling machine, 1/4 inch aluminum is soft enough to be machined with wood working tools.
There was an article in "Fine wood working" magazine about
12 years ago on how to use a router with a carbide blade.

A circle cutter on a drill press would also work, but there are considerable safety issues.


The easiest way to cut a disk out of aluminum plate is on a metal
cutting badsaw with a thin blade. Drill a center hole and bolt the blank to a flat piece of scrap, so the blank can pivot into the blade.

Saber saws will also work on 1/4 inch plate, work slowly and pause often to allow the blade to cool.
The newer spiral blade saws I see on TV are advertized as being able to cut metal. but I don't know if they're suitable.

The rougher the initial cut, the more sanding and filing to get the final shape. You did want ROUND wheels?