PURPOSE: To bore perpendicular or lateral holes, which intersect respective circumferential parts of the frame body at precise right angles in order to insert strings therein, by a mechanical method even when the frame body or the like has a shape of the combination of square parts and circular arc parts.

CONSTITUTION: In order to bore the holes perpendicular to the frame body 1, guide holes 7 are provided on the face part of a former stand 2 in a line close to and parallel to the peripheral edge of the former stand at predetermined intervals. A guide needle 8 corresponding to the hole 7 is disposed in an array to a vertical drill 5. Desired perpendicular holes 6' are continuously and precisely bored by sequentially inserting the guide needle 8 in the guide hole 7. In order to bore the holes laterally, the guide holes 7' are provided laterally in order to apply the drill 5 horizontally.