Drilling tool set, drilling tool and indexable drill bit therefor

A drilling tool comprising a basic body defining a center axis, the body having a center insert pocket and a peripheral insert pocket formed in a front end thereof;

• and two chip channels extending from respective ones of the pockets;
• a peripheral cutting bit insert and a center cutting bit mounted in the peripheral pocket and the center pocket, respectively;
• the peripheral bit and its respective pocket being separated from the second bit and its respective pocket by a first plane containing the center axis, the center bit including an active cutting edge intersected by a second plane oriented perpendicularly to the first plane, the intersection forming an angle of at least 60° and no more than 75°.

Indexable drill bit having a quadrangular basic shape and four similar cutting edges, wherein each of the cutting edges comprises first and second part edges transforming into each other via a transition edge portion, the four cutting edges being tangent to an inscribed circle having a diametrical plane defining a reference plane extending parallel to a second part edge and dividing the bit into two mirror-image halves;

• the first part edge being at least partially positioned at a greater distance from said reference plane than the second part edge;
• the transition edge portion defined by a convex curve adjacent to the first part edge as well as a concave curve adjacent to the second part edge, a straight line disposed tangent to both of those curves forming an angle of at least 10° and at most 30° to the reference plane.