I was not too keen on the solid flywheels that are shown in the photos of other engines so decided to go for a spoked one along the lines of what's on the Wall Wizzard with heavy spokes and rim and a large hub that the starter cord pulley could be screwed to. I ordered a piece of EN3, but the colour suggests I got EN8.  I started by roughing it down to size on the lathe from the 105mm dia purchased to 100mm finished dia. I have a couple of holders that allow the two ‘unused’ corners of CCMT inserts to be used and find them ideal for this type of work.

The middle section was recessed on both sides to loose some of the waste material and then some holes drilled and bored so that the milling cutter could enter easily and not have so much work to do.

With the flywheel held in a 3-jaw chuck mounted to the CNC's table the initial adaptive clearing cut was done leaving the stepped finish below

A ‘steep & Shallow’ cut was then taken with a 6mm ball ended cutter before flipping the flywheel over and doing the same two operations to the other side,

There were a few ridges due to some backlash which has now been traced to an overtight head gib strip so the spokes were given a light tickle with THE Dremel before adding the pulley screw holes and broaching the keyway.

Part four here   Part six here