Head stack and actuator arm assemblies including a bobbin to stiffen the coil portion of an actuator of a hard disk drive and disk drives including the same

A disk drive includes a disk and a head stack assembly for reading and writing to the disk. The head stack assembly includes a body portion defining a through bore that defines a pivot axis; an actuator arm cantilevered from the body portion and a head gimbal assembly coupled to the actuator arm. A coil portion is cantilevered from the body portion in an opposite direction from the actuator arm. The coil portion defines first and second actuator fork members and includes a coil supported by the first and second actuator fork members. A bobbin is configured to stiffen the coil portion, and is attached to an inner periphery of the coil. The bobbin may define a first truss and a second truss that crosses the first truss. An adhesive is disposed between the bobbin and the wound coil.