Patent Publication Number: US-2019184473-A1

Title: Metal drill

Description:
The present invention relates to a drill bit for hand-guided drilling of a blind hole into a metal workpiece. 
     Drill bits are known which have a shank that defines a drilling direction and has a cutting edge and a stop shoulder, the distance of which from one other defines a blind hole depth. Usually, the shank has an enveloping circle diameter between the cutting edge and the stop shoulder, which enveloping circle diameter is as large as a blind hole diameter defined by the cutting edge. In hand-guided drilling, the drill bit may be unintentionally pivoted, causing the shank to expand or damage the blind hole during drilling. 
     The object of the invention is to provide a drill bit which reduces the risk of widening or damaging the blind hole. 
     The object is achieved by a drill bit for hand-guided drilling of a blind hole, having a blind hole diameter and a blind hole depth, into a metal workpiece, the drill bit comprising a shank that defines a drilling direction and has an axis of rotation oriented in the drilling direction, the shank having a cutting edge at the end thereof facing the drilling direction and a stop shoulder at a distance from the cutting edge that defines the blind hole depth and is measured against the drilling direction, the cutting edge defining the blind hole diameter by rotation about the axis of rotation, the shank having an enveloping circle diameter which varies along the axis of rotation and which is larger at the stop shoulder than the blind hole diameter, the shank having a first shank portion which is arranged between the cutting edge and the stop shoulder and extends as far as the stop shoulder and in which the enveloping circle diameter is smaller than the blind hole diameter. Preferably, the shank has two or more cutting edges at the end thereof facing the drilling direction, which cutting edges together define the blind hole diameter by rotation about the axis of rotation and are preferably arranged symmetrically about the axis of rotation. 
     An enveloping circle diameter within the meaning of the invention is the diameter of the smallest possible circle which still completely envelops the shank with a circle center on the axis of rotation. In other words, for each point along the axis of rotation, the circular area of the envelope circle is the area that the shank covers when it rotates about the axis of rotation. In the case of a circular circumferential line, the enveloping circle diameter is equal to the diameter of the circumferential line, i.e. the shank diameter. Inward deviations of the circumferential line from the circular shape do not affect the enveloping circle diameter; outward deviations, however, increase the enveloping circle diameter. 
     In a preferred embodiment, the shank has a second shank portion arranged between the cutting edge and the first shank portion, which second shank portion extends as far as the cutting edge and in which the enveloping circle diameter is constant and equal in size to the blind hole diameter. Particularly preferably, the second shank portion extends towards the first shank portion. 
     In a preferred embodiment, the first shank portion extends towards the cutting edge. 
     In a preferred embodiment, the first shank portion and the cutting edge are made of the same material and integral with one other. 
     In a preferred embodiment, the enveloping circle diameter in the first shank portion increases in regions, in particular continuously, in the drilling direction. Particularly preferably, the enveloping circle diameter in the first shank portion increases linearly, thus forming a conical enveloping. The conical enveloping surface is inclined with respect to the drilling direction at a cone angle which is preferably between 2° and 10° and particularly preferably at least 5°. 
     In a preferred embodiment, the enveloping circle diameter in the first shank portion is constant in regions, particularly preferably continuously constant, thus forming a circular cylindrical enveloping surface. 
     In a preferred embodiment, the shank has, at the end thereof facing the drilling direction, a centering point through which the axis of rotation extends. 
     In a preferred embodiment, the stop shoulder has a stop face oriented perpendicularly to the axis of rotation and facing the drilling direction. 
     In a preferred embodiment, the shank has, at the end thereof facing away from the drilling direction, an attachment portion for temporary attachment to a hand-guided drill bit. Particularly preferably, the attachment portion is an insertion end. 
    
    
     
       The invention is explained in greater detail below with reference to the drawing. 
       The drawing is a side view of a drill bit  10 , which is suitable for hand-guided drilling of a blind hole into a metal workpiece (not shown). The drill bit  10  comprises a shank  20  that defines a drilling direction  30  and has an axis of rotation  40  oriented in the drilling direction  30 . At the end thereof facing the drilling direction  30 , the shank  20  has a cutting edge  50  and a further cutting edge (not shown) which are arranged opposite one other and symmetrically about the axis of rotation  40  and together define a blind hole diameter of the drilled blind hole by rotation about the axis of rotation  40 . In a to the cutting edge  50 , the shank  20  comprises a stop shoulder  55  having a stop surface  60  that is oriented perpendicularly to the axis of rotation  40  and faces the drilling direction  30 . When the blind hole is being drilled, the stop shoulder  55  strikes a surface of the workpiece, such that the distance, measured against the drilling direction  30 , of the stop face  60  from the cutting edge  50  defines a blind hole depth of the drilled blind hole. At the end thereof facing away from the drilling direction  30 , the shank  20  has an insertion end  80  for temporary attachment to a hand-guided drill bit. 
     
    
    
     The shank  20  has an enveloping circle diameter that varies along the axis of rotation  40 . In a first shank portion  41  of the shank  40  that is arranged between the cutting edge  50  and the stop shoulder  55 , the enveloping circle diameter d 1  is smaller than the blind hole diameter. In a second shank portion  42  of the shank  40  that is arranged between the cutting edge  50  and the first shank portion  41 , the enveloping circle diameter d 2  is constant and equal in size to the blind hole diameter. At the stop shoulder  55 , the enveloping circle diameter d 3  is larger than the blind hole diameter. When the first shank portion  41  is directly connected to the stop shoulder  55 , the second shank portion  42  is directly connected to the first shank portion  41  and to the cutting edge  50 . 
     The enveloping circle diameter d 1  in the first shank portion  41  linearly increases continuously in the drilling direction  30 , such that a conical enveloping surface is formed. 
     The conical enveloping surface is inclined with respect to the drilling direction  30  by a cone angle a of 5°. The enveloping circle diameter d 2  in the second shank portion  42  is continuously constant, such that a circular cylindrical enveloping surface is formed which protects the cutting edge  50  from excessive wear if necessary. 
     Furthermore, the shank  20  has a centering point  70  at the end thereof facing the drilling direction  30 , through which centering point the axis of rotation  40  extends. The entire shank  40 , including the cutting edge  50  and the centering point  70 , is formed in one piece, so that the stop shoulder  55 , the first shank portion  41 , the second shank portion  42  and the cutting edge  50  are made of the same material, preferably a metal or an alloy, particularly preferably a steel. 
     In order to remove metal shavings produced during drilling from the cutting edge  50  and the further cutting edge, the shank  20  has two helical grooves  90  which extend through the stop shoulder  55 , the first shank portion  41  and the second shank portion  42  and are delimited by the cutting edge  50  and the further cutting edge, respectively. 
     The invention has been described with reference to the example of a metal drill bit. However, it should be noted that the drill bit according to the invention is also suitable for other purposes.