Patent Publication Number: US-2003226694-A1

Title: Core drill bit with geometrically defined cutting elements

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention is directed to a core drill bit with geometrically defined, flatsided cutting elements with end face cutting edge surfaces, preferably for cutting brittle materials such as concrete and masonry.  
       [0002] An axial rake angle and a radial rake angle of zero is used for a core drill bit driven rotationally about an axis of rotation and having defined, flat cutting elements, whose surface normal runs with cutting edges along the path of movement of the cutting elements. The orientation of the axial rake angle is positively defined, in the case of tilting of the cutting elements, with an offset of the end face cutting edges in the direction of the path of movement. The orientation of the radial rake angle is also defined, in the case of tilting of the cutting elements, with an offset of the radial outer cutting edges in the direction of the path of movement.  
       [0003] In addition, when core drilling, for example in concrete and masonry, hard or tough inclusions, such as reinforcing bars, must also be severed.  
       [0004] According to DE3407427, a core drill bit for brittle material has geometrically defined, flat PCD (polycrystalline diamond) cutting elements with an exclusively negative axial rake angle relative to the axis of rotation. According to DE4242465 a core drill bit with geometrically differently defined, flat PCD cutting elements that geometrically undercut each other with end face cutting edges and an exclusively negative axial rake angle. An exclusively negative axial rake angle is not optimized for imbedded tough material.  
       [0005] Furthermore, according to DE4341054, a core drill bit has axially and radially inclinedly projecting, geometrically defined, pin-shaped cutting elements. Cutting elements in the form of pins have a surface with cutting edges and thus consequently no rake angle as defined above.  
       SUMMARY OF THE INVENTION  
       [0006] The primary object of the invention is an extension of the optimized area of application of a core drill bit to imbedded tough material.  
       [0007] Essentially, a core drill bit has at least two geometrically defined, flatsided cutting elements, wherein at least one first cutting element and a second cutting element of different axial rake angles and/or radial rake angle, or wherein at least one cutting element with a radial rake angle is present.  
       [0008] By the exclusively negative axial rake angle being absent at least in some cutting elements optimized relative to brittle materials, the core drill bit is extended to tough material imbedded in brittle materials, in virtue of these cutting elements with positive axial rake angle and/or a radial rake angle not equal to zero, because their cutting face edges have an improved cutting performance and the load on the cutting edges is reduced.  
       [0009] Advantageously, at least one cutting element has both an axial rake angle and a radial rake angle not equal to zero, wherein a smooth cut is made possible through the imbedded tough material.  
       [0010] In one embodiment, at least one cutting element has at least one positive axial rake angle and a positive radial rake angle, whereby only minimal cutting forces are required in the case of the tough material; however, wear also increases.  
       [0011] In another advantageous embodiment, at least one cutting element has a negative axial rake angle as well as a negative radial rake angle, wherein the strength of the cutting elements increases; however, high cutting forces are required in the tough material.  
       [0012] In a further advantageous arrangement, at least one cutting element has a positive axial rake angle as well as a negative rake angle, whereby a practical rational compromise is possible relative to the higher strength of the cutting element and lower required cutting forces in the tough material.  
       [0013] Advantageously, at least some different cutting elements have different axial rake angles in the axial rake angle range of between −20° to +20°, or more specifically between −10° to +5°, wherein a practical rational compromise is possible.  
       [0014] Further advantageously, at least several different cutting elements have different radial rake angles in the radial rake angle range of between −20° to 20°, or more specifically between −10° to +10°, wherein a practical rational compromise is possible.  
       [0015] In another advantageous embodiment different cutting elements are stepped in the axial rake angle range [−5°, 0°, +5°] as well as in the radial rake angle range [−5°, +5°] or [0°, +5°], wherein a practical rational compromise is possible.  
       [0016] In still another advantageous arrangement, different cutting elements with different axial rake angles and/or radial rake angles are arranged peripherally asymmetrically, wherein oscillations are prevented and a round cut is produced.  
       [0017] Advantageously, the cutting elements are formed as PCD cutting elements, which are very resistant to wear. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018] The invention will now be more completely described with reference to an advantageous exemplar embodiment, wherein:  
     [0019]FIG. 1 represents a core drill bit in perspective view;  
     [0020]FIGS. 2 a ,  2   b  diagrammatically represents a variant in cross-section viewed from the top;  
     [0021]FIGS. 3 a ,  3   b  diagrammatically represents a further variant in cross-section viewed from the top; and  
     [0022]FIGS. 4 a ,  4   b  diagrammatically represents a still further variant in cross-section viewed from the top. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0023] According to FIG. 1, a core drill bit  1  with a tubular axially extending cutting element support is rotatable about its axis and has three geometrically defined, flat PCD cutting elements with a first cutting element  2   a  with a different axial rake angle α 1,2  relative to a second cutting element  2   b  and a radial rake angle β 1,2 . Accordingly, the cutting element  2   a  has both an axial rake angle β 1  not equal to zero. A third cutting element  2   c  has an axial rake angel α 3  and a radial rake angle β 3  of, for example, 0 degrees. The peripherally asymmetrically arranged three different cutting elements  2   a ,  2   b ,  2   c  have axial rake angles in the axial rake angle range of −10°&lt;=α&lt;=+5°, stepped in [−5°, 0°, +5°] and radial rake angles in the radial rake angle range −10°&lt;=β&lt;=+10°, stepped in [−5°, 0°, +5°]. The cutting elements  2   a ,  2   b ,  2   c  have flat end cutting surfaces.  
     [0024] According to FIGS. 2 a ,  2   b ,  3   a ,  3   b ,  4   a  and  4   b  the core drill bit variants have:  
     [0025] a) a cutting element  2   a  with a positive axial rake angle α 1  and a positive radial rake angle β 1  (FIGS. 2 a ,  2   b );  
     [0026] b) a cutting element  2   a  with a negative axial rake angle α 1  and a negative radial rake angle β 1  (FIGS. 3 a ,  3   b );  
     [0027] c) a cutting element  2   a  with a positive axial rake angle α 1  and a negative radial rake angle β 1  (FIGS. 4 a ,  4   b ).