Method of electric discharge machining a cathode for an electron gun

A method of machining a cathode used in an electron gun, comprising the steps of:

• placing an object to be machined, which is a material of the cathode, and a machining electrode in an electrically insulating oil;
• applying a discharge current to the machining electrode;
• and
• machining the object to be machined to have a shape corresponding to the shape of the machining electrode by means of electric discharge machining of the machining electrode,
• wherein the machining electrode includes a disk, a plurality of recesses provided on a front surface of the disk and arranged regularly in X and Y directions, a protrusion provided on a back surface of the disk, and a hole for mounting a lead wire for applying discharge current to the machining electrode, and wherein a plurality of bumps corresponding to the shape of the recesses of the machining electrode are formed on the object to be machined by means of electric discharge machining.