It depends on the size, material, tolerances, surface finish, any distortion during machining, Forces being produced, Chip issues, how you are processing them (inside & outside in the same setup?) and what the blank shape is.
Could create a plug and/or a nest (or a A/B load), might be able to use vacuum, or even a bladder, or tabs that get machined off after. Sometimes you can use Glue. Might even have to move clamping points during processing, production quantities, Lots of options with lots of issues to determine priority and direction to go in.