Punch that has an outer drill and drill inside, inside drill has a cutting flute of a plurality of pairs, flute pair forms a centering pyramid

摘要

Trepan with (46) outside drill that surrounds the inner drill inside and drills (44) is (40). By (42), drills are adapted to the rotating head. The inner drill flute pairs that are arranged symmetrically is formed. The center of the inner drill, two flutes of these (146, 150), form a (169) pyramid which is used to open the pilot hole. Flute of the remaining (148 and 152) is spaced apart from the pyramid.