What ancillary item, requiring repeatable and accurate construction, did Whitney also design and patent?

Answer

An early version of the staircase machine

Whitney applied his internalized principles of precision tooling to other areas, including designing and patenting an early version of the staircase machine used for cutting wooden stair stringers.

What ancillary item, requiring repeatable and accurate construction, did Whitney also design and patent?
inventioninventortechnologymachineMechanic