Drill with a hard material drilling head

Abstract

A one-piece drilling head ( 4 ) which is to be secured, in a material-locking manner, at an end of a helical shaft of a drill, is formed of hard material and includes four radially extending, in a cross-shaped manner, legs ( 5 ) forming, respectively, two diametrically opposite main cutting edges ( 6 ) and two auxiliary cutting edges ( 7 ), with the main cutting edges ( 6 ) and the auxiliary cutting edges ( 7 ) extending proceeding from a drilling head drilling head tip ( 8 ), monotonously and strictly axially up to a radially outer edge, and with an envelope surface ( 9 ′) of the auxiliary cutting edges ( 7 ) lying completely within an envelope surface ( 9 ) of the main cutting edges ( 6 ) and contacts the same only at the drilling head tip ( 8 ).

1 . A one-piece drilling head ( 4 ) for a drill and formed of hard material, comprising four radially extending, in a cross-shaped manner, legs ( 5 ) forming, respectively, two diametrically opposite main cutting edges ( 6 ) and two auxiliary cutting edges ( 7 ), and a drilling head tip ( 8 ) wherein the main cutting edges ( 6 ) and the auxilially cutting edges ( 7 ) extend, proceeding from the drilling head tip ( 8 ), monotonously and strictly axially up to a radially outer rim, and an envelope surface ( 9 ′) of the auxiliary cutting edges ( 7 ) lies completely within an envelope surface ( 9 ) of the main cutting edges ( 6 ) and contacts the envelope surface ( 9 ) of the main cutting edges ( 6 ) only at the drilling head tip ( 8 ). 
   
   
       2 . A drilling head according to  claim 1 , wherein an angular difference of radial standardized ridge angles of the envelope surface ( 9 ) of the main cutting edges ( 6 ) and the envelope cutting surface ( 9 ′) of the auxiliary cutting edges ( 7 ) lies in a range between 2° and 10°. 
   
   
       3 . A drilling head according to  claim 1 , wherein the main cutting edges ( 6 ) and the auxiliary cutting edges ( 7 ) extend axially linearly. 
   
   
       4 . A drilling head according to  claim 1 , wherein the main cutting edges ( 6 ) form, proceeding from the drilling head tip ( 8 ), a straight line in an axial projection. 
   
   
       5 . A drilling head according to  claim 1 , wherein the auxiliary cutting edges ( 7 ) form, proceeding from the drilling head tip ( 8 ), in an axial projection, a convexly curved line facing a following main cutting edge ( 6 ). 
   
   
       6 . A drilling head according to  claim 5 , wherein the auxiliary cutting edges ( 7 ) are uniformly curved. 
   
   
       7 . A drilling head according to  claim 1 , wherein a leg ( 5 ) of the main cutting edge ( 6 ) forms, at the outer radial rim on a side thereof facing in the rotational direction (ω), a tangential ramp surface ( 10 ) axially spaced from the main cutting edge ( 6 ). 
   
   
       8 . A drill, comprising a helically shaped shaft ( 2 ); and a one-piece drilling head ( 4 ) formed of a hard material and secured on an axial end ( 3 ) of the shaft ( 2 ) in a material-locking manner, the drilling head including four radially extending, in a cross-shaped manner, legs ( 5 ) forming, respectively, two diametrically opposite main cutting edges ( 6 ) and two auxiliary cutting edges ( 7 ), and a drilling head tip ( 8 ), wherein the main cutting edges ( 6 ) and the auxilially cutting edges ( 7 ) extend, proceeding from the drilling head tip ( 8 ), monotonously and strictly axially up to a radially outer rim, and an envelope surface ( 9 ′) of the auxiliary cutting edges ( 7 ) lies completely within an envelope surface ( 9 ) of the main cutting edges ( 6 ) and contacts the envelope surface ( 9 ) of the main cutting edges ( 6 ) only at the drilling head tip ( 6 ).