Compensating for vortex shedding in a disk drive for modifying the thickness of an actuator arm

1. Field of the Invention A method of designing an actuator arm of a head stack assembly for use in a disk drive is disclosed. The disk drive comprises a disk, the actuator arm for positioning a head over the disk while the disk is rotating at a selected spin-rate. The actuator arm having a leading edge and a trailing edge and a selected thickness, and the head stack assembly having a structural resonance frequency. The disk is rotated such that the disk generates air flow around the actuator arm while the disk is spinning at the selected spin-rate. The actuator arm positions the head over the disk while the disk is spinning at the selected spin-rate, wherein the air flow travels from the leading edge to the trailing edge of the actuator arm such that the air flow causes vortex shedding at a vortex shedding frequency resulting in an undesirable force being applied to the actuator arm when the vortex shedding frequency is aligned with the structural resonance frequency. A perturbing effect due to the undesirable force applied to the actuator arm is measured. The thickness of the actuator arm is then modified and the thickness data stored. The process is then reiterated for a plurality of different actuator arm thickness values. A manufacturing thickness is then selected for the actuator arm from the stored thickness data to compensate for the undesirable force that is applied to the actuator arm due to the vortex shedding.