Disc clamp shim for a rigid disc drive

In a disc drive data storage device including at least one disc secured to a hub of a spindle motor using a disc clamp, the disc clamp including a circumferential contact surface near its outer periphery, the contact surface engaging the disc near its inner diameter, the disc clamp fastened to the hub by a plurality of screws equally spaced about a circle spaced radially inward from the contact surface of the disc clamp,

• a shim, interposed between the disc clamp and the hub, comprising
• a plurality of radially extending arms equal in number to the number of screws, the radial extent of the arms being slightly larger than the radius of the contact surface,
• the arms thus forming contact points where the radius of the contact surface meets the sides of the arms, and
• alignment means for positioning the radially extending arms equidistantly between adjacent screws,
• the width of the arms selected such that the contact points divide the angular displacement between adjacent pairs of screws into thirds, with contact between the contact surface, contact points and disc serving to evenly distribute a clamping force from the screws through the disc clamp and shim to the disc.