Machining

Three features on the drive wheel require separate machining steps.

The OD of the two rims are turned.
Three chucking pads are designed into the ID of the rims for the turning operation.
The ID of the center bore is turned.
The keyway in the center bore is broached.

The machining operation is done before the austemper heat treatment.
Austempered ductile iron is a work-hardening material and it is easier to machine before the austempering heat-treatment.
The austempering heat-treatment produces a volume change in the part which has to be considered in the machined tolerances.