Hi Robert

This is how I would do it.

Pre face the workpieces if they are hacksaw cut.

As it is aluminium and fairly easy to turn I would glue the disk to another 10mm smaller diameter disk fitted in the chuck.

There are lots of adhesives Loctite for example, that will release if you heat them.
Jewellers often use shellac

Then:

Drill a 2.5mm hole in the center.
Bore the hole to 3 mm (You will need to make a tiny boring bar from high speed steel).
Face the disk.
If the flywheel is recessed, recess one side.
Turn the edge of the disk to 95mm diameter.
Turn the back 5mm of the edge of the disk, this will assist setting it up to machine the other side later.
If the edges need chamfering do them now.

Then:

Unglue the disk from the mounting disk
Using a 4 jaw chuck remount the disk (protect the turned edge with thick paper)
You can use the two turned edges to set up the piece accurately with a dial indicator.
Face and cut the second recess if needed.

Cheers
John

Hi Robert,

Buy a band saw, and make jaws to hold short parts. You will never regret it.

Hope this helps.

Peter.