Flywheel, 3" Diameter, 6 Heavyweight Straight Spokes

The flywheel casting is oversize so you can finish it to the specified diameter. This flywheel has a rim width of 0.755", a rim thickness of 0.271", a hub diameter of 0.728", and an overall hub length of 1.265".

All Martin Model & Pattern castings are fully annealed for easier machining.
When molten iron is poured into a sand mold, it cools very quickly where it contacts the cold sand. Quick cooling being the formula for hardening iron, this results in a very hard surface, or skin, on the casting. It's commonly known that you must address this hard skin when you start machining a casting.
But Martin Model castings go through another heat treat process. After the castings have cooled, they are once again heated to a high temperature, but this time they are cooled slowly. This ensures that the castings are evenly soft throughout, and that there is no hard skin on the surface