Center hole formation in an information storing disc

Apparatus for providing a centrally apertured disc with a replica disc center hole edge locator concentric with a spiral information groove, said apparatus comprising:

• a turntable for receiving a centrally apertured disc and causing rotation thereof;
• inscribing means, mounted with respect to said turntable so as to be subject to engagement with a surface of a disc during rotation thereof by said turntable, with said engagement being maitnained at a fixed distance from the center of rotation of said disc so that said inscribing means serves to cut, in a region of said disc surrounding and spaced from the central aperture thereof, a closed circular groove of a predetermined depth and a first diameter, centered about said center of rotation of said disc;
• and
• means, subject to radial motion with respect to said turntable during said rotation of said disc, for forming an information storing groove in said surface of said disc in a spiral configuration centered about said center of rotation of said disc, with all of the convolutions of said spiral groove having a greater diameter than said first diameter and with the maximum depth of said information storing groove being small relative to said predetermined depth.