Drilling method

A drilling method for drilling a plurality of holes having differing diameters through a plurality of workpieces by horizontally moving a table on which the plurality of workpieces is mounted relative to a plurality of spindles juxtaposed to each other, each spindle arranged relative to a respective workpiece and rotatably holding one drill bit at an edge thereof to align an axial line of the drill bit being held therein with a center position of a part of the respective workpiece to be machined, the method comprising:

• for each spindle, detecting a misalignment of an actual axial center of the drill bit from a designed axial center in X and Y directions before drilling the respective workpiece by rotating the drill bit to be used in drilling with a number of revolutions per minute predetermined based on the diameter thereof;
• checking, with a controller from a drilling program, which hole is a first hole to be drilled with a first drill bit, the first hole being selected from a hole configuration that is to be drilled more than any other hole configuration to be drilled, a hole to be drilled that has a smaller diameter than any other hole to be drilled or a hole to be drilled having higher precision than any other hole to be drilled;
• and
• drilling a reference hole through the respective workpiece by correcting the drilling position of a second drill bit based on a difference in misalignment between the axial center of the first drill bit and the axial center of the second drill bit in the X and Y directions based on the measured result of the misalignment of the axial center of each drill bit.