Method for reducing disk thermal expansion effects while writing reference spiral servo patterns to a disk of a disk drive

A method for reducing disk thermal expansion effects while writing spiral reference patterns on a disk of a disk drive, the disk drive comprising control circuitry and a head disk assembly (HDA) comprising the disk, an actuator arm, a head connected to a distal end of the actuator arm, and a voice coil motor for rotating the actuator arm about a pivot to position the head radially over the disk, the method comprising:

• using an external servo writer to control a radial location of the head for writing a plurality of the spiral reference patterns between an inner circular seed track at an inner radial location and an outer circular seed track at an outer radial location, each spiral reference pattern being written based on a head velocity profile controlled by the external servo writer during writing of the respective spiral reference pattern, wherein thermal expansion of the disk during writing of the plurality of spiral reference patterns may increase a radial distance between the inner and outer circular seed tracks, and the external servo writer adjusts the head velocity profile for writing each respective spiral reference pattern to account for thermal expansion of the disk;
• and
• using the head internal to the disk drive to read the spiral reference patterns in order to write product servo bursts to the disk.