I cup props using a cuping anvil or some times at the pond pliers with a ball bearing welded to one side, bar cut is to notch the trailing edge against the hub to help a prop unload and spin up. Works very well when you do not want to back cut because of the reduced lift but need to unload it some.
Google it and there is a wealth of info out there
Google it and there is a wealth of info out there
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