FIELD OF THE INVENTION The invention relates to the field of drill heads.

BACKGROUND OF THE INVENTION

High speed steel drills are optimized for drilling holes in steel. CN107225273A discloses an anti-fracture high-speed steel straight shank twist drill. The anti-fracture high-speed steel straight shank twist drill includes a drilling rod, a drilling bit, a pressure sensor, a spiral rod, a compression head, a compression rod, a spring, a groove, an air pressure chamber, and a steel sleeve; one end of the drilling rod is connected to the drilling bit, and the other end of the drilling rod is connected to the spiral rod; a pressure sensor is arranged in the drilling rod; the air pressure chamber is arranged outside the drilling rod; a surface of the spiral rod is sleeved with the steel sleeve, and a groove is formed in an outer side of the spiral rod; the bottom of an inner wall of the groove is connected to the spring; the top of the spring is connected to the compression rod; and the top of the compression rod is connected to the compression head. While the twist drill is blocked, the pressure sensor detects a torsion force acted on the drilling bit, when the torsion force exceeds a limit value, the compression head is compressed by the air pressure chamber, the spring is compressed, the spiral rod can rotate under drive of a machine, and then the drilling bit can be prevented from being fractured due to super force; and the steel sleeve can protect the spiral rod from damage due to high speed friction, and the service life of the twist drill is prolonged.

A disadvantage of these type of drills is that they wear out rapidly especially when a longitudinal force forces the drill quickly into the steel. SUMMARY OF THE INVENTION

An object of the invention is to mitigate the disadvantages as mentioned above.

According to a first aspect of the invention, a drill for drilling in hard materials, comprising a drill head having a rotational axis, wherein the drill head comprises: a centre point aligned with the rotational axis; main cutting edges radially extending from the centre point, wherein each of the main cutting edges deviates from a radial.

A drill is typically used for drilling holes in an object or workpiece. The centre point of the drill is arranged to a particular or selected location of the object when starting to drill a hole in the object. The centre point is typically the vertex, the most protruding part or the most extended part of the drill and therefore typically contacts the object first at the particular or selected location. The centre point thereafter drills a centring hole in the object when the drill is pushed into the object. This centring hole typically has a small diameter compared to the diameter of the drill as a whole. The centre point after initiating the centring hole snugly fits in the centring hole.

After that the centre point initiated the centring hole and reaches a particular depth, the main cutting edges will come into contact with the object when the drill is pushed further into the object. The main cutting edges remove the main body of material for forming the hole. The diameter of the hole typically snugly fits around the drill; thus, the diameter of the drill is substantially equal to the diameter of the hole. The main cutting edges, during removing the main body of material, may experience side forces or centrifugal forces causing the drill to move, accelerate or jerk sideways. The centre point snugly fitting in the centring hole opposes these forces by pushing off against the centring hole having the technical effect that the drill as a whole is kept at the particular or selected location. This effect is particularly present during first contact of the main cutting edges. The drill when drilling typically has a particular angular velocity. The rotational axis is the axis where around the drill rotates. The distance of a part of the drill from the rotational axis is defined as the radius for this part of the drill. The tangential velocity of a part of the drill depends on the radius of this part multiplied with the revolutions of the drill. Thus, the tangential velocity of a part of the drill linearly increases with increasing radius of the part. Or, the outer part of the drill is having the highest tangential velocity while the part of the drill aligning with the rotational axis is having the lowest tangential velocity.

It is an insight of the inventor that the high tangential velocity of the outer part of the main cutting edges causes increased wear of this part of the main cutting edges. It is a further insight of the inventor that the outer parts of the respective main cutting edges have to travel the longest path when going around thus cut away the larger part of the material along this path causing increased wear of this part of the main cutting edges. It is even a further insight of the inventor that the wear of the outer part of the main cutting edges may be reduced by that each of the main cutting edges deviates and/or curves away from a radial. A radial is defined as an imaginary straight line starting at the rotational axis, wherein the direction of the line is perpendicular to the rotational axis. As the main cutting edges deviates and/or curves away or is not perpendicular to the high tangential velocity or is under an angle with the tangential velocity, the main cutting edge may cut or slice instead of bluntly digging into the material to be cut away. Thus, the feature that each of the main cutting edges deviates and/or curves away from a radial has the technical effect of extending the lifetime of the drill head, and thus the drill.

The outer part of the main cutting edges while rotating cuts away material. The orientation of the outer part of the main cutting edges is, as it deviates and/or curves away, not perpendicular to the tangential velocity of the same outer part of the main cutting edges. It is an insight of the inventor that this not being perpendicular causes instability of the drill head, especially during first contact of the main cutting edges with the body of material. The centre point increases the stability, especially during first contact. Hence, the combination of the centre point and the feature of the main cutting edges not being perpendicular to the tangential velocity has the technical effect of providing a stable drill head, and thus a stable drill, with an extended lifetime. In an embodiment of the drill, the deviation of one of the main cutting edges is defined as that there exists a tangent line tangent to a point of the main cutting edge, wherein the tangent line has a non-zero angle with the radial through that point. This advantageously defines the feature of deviating in other words.

In an embodiment of the drill, each of the main cutting edges comprise at least one section that deviates and/or curves away from the radial. Preferably, the at least one section deviating and/or curving away is arranged distal or away from the centre point. The section deviating and/or curving away may comprise straight stretches of main cutting edge and/or continuously curving stretches of main cutting edge as long as the shape of the main cutting edge is functionally shaped to exhibit the technical effect as disclosed during use.

The shape of the main cutting edges may be considered in a functional cutting plane, which is substantially a plane perpendicular to the rotational axis, or may functionally be projected on a projection plane perpendicular to the rotational axis, for example as shown in figure 1 , for functionally understanding the disclosed technical effect. Typically, the main cutting edges deviating and/or curving away do so within the cutting plane and/or the projection plane to exhibit the technical effect as disclosed during use. In an embodiment of the drill, each of the main cutting edges comprises a convex edge section. The convex edge section is typically substantially arranged in a cutting plane perpendicular to the rotational axis of the drill. A convex edge is defined as an edge that deviates and/or curves away opposite to the direction of rotation with an increasing radius typically viewed in the cutting plane.

A convex edge section causes a part of the section radially closer to the centre point to come in contact with the material to be cut away earlier than a part of the section radially more away or distant from the centre point. This has the effect of creating an outward force on just cut away and loose material forcing this loose material outward to e.g. a flute for being transported away from the drill head. Thus, this convex edge section has the technical effect of improving the transport of loose material. Furthermore, the improved transport causes loose material to come less into contact with the main cutting edge, specifically the convex edge section, reducing wear on the main cutting edge, specifically the convex edge section, thus further improving the lifetime of the drill head. In an embodiment of the drill, the drill head has a drill head circumference and wherein a distal end of each of the convex edge sections ends at the drill head circumference. This has the effect that the material to be cut away faces a cutting edge over the complete diameter of the hole to be drilled. As a cutting edge provides low friction when cutting or slicing, this feature has the technical effect of reducing friction, which in turn reduces wear, which in turn further extends the lifetime of the drill head.

In an embodiment of the drill, the drill has a drill circumference, and comprises at least two guiding lands arranged to the drill circumference and spiralling away from the drill head. Typically, the space between guiding lands form a flute for transporting removed or cut material away from the drill head. Specifically, at least one edge of a flute is formed by the edge of a first guiding land, preferably both opposite edges of a flute are formed by respective edges of guiding lands. Guiding lands provide a surface on the cylindrical circumference of the drill which surface contacts the side of the hole that is drilled while the drill is rotating. The guiding lands typically do not cut away material but provide more a gliding surface for the drill. The guiding lands therefore typically does not increase the diameter of the drilled hole. The guiding lands have the technical effect of stabilizing the drill and/or rotational axis of the drill while drilling the hole in the material. The stabilization causes the drill to rotate with less friction in the drill hole and thus further extends the lifetime of the drill head.

In an embodiment of the drill, the at least two guiding lands start at the drill head circumference. As the guiding lands start at the drill head circumference, this has the technical effect of stabilizing the drill already when the drilled hole is still very shallow. Stabilizing the drill already with shallow drill holes has the further technical effect of extending the lifetime of the drill head.

In an embodiment of the drill, an end of the respective at least two guiding lands is adjacent to a respective distal end of one of the convex edge sections. Thus, the main cutting edge ends at the start of the guiding land. Typically, the main cutting edge and the guiding land join under a clear angle.

The main cutting edge is typically substantially in a cutting plane perpendicular to the rotational axis. The guiding lands typically spiral around the rotational axis along the circumferential surface of the drill from the drill head to the base of the drill. The clear angle is typically substantially a right angle.

As the main cutting edges deviates and/or curve away from the radial, typically providing a convex edge section, the radial forces causing instability are typically in the direction wherein the main cutting edge extends. Having a landing guide at a position where the radial forces are typically the highest or dominant provides the technical effect of improved countering these radial forces and thus results in improved stabilization of the drill head. The improved stabilization leads to less friction and thus extended lifetime of the drill head.

In an embodiment of the drill, each of the main cutting edges comprises a concave edge section. The concave section is another embodiment for a main cutting edge curving away from the radial. A concave section causes a part of the section radially closer to the centre point to come in contact with the material to be cut away later than a part of the section radially more away from the centre point. This has the effect that the part more away from the centre point aggressively cuts into the material. Furthermore, the part more away from the centre point digs first into the material to be cut away. As the part more away from the centre point digs in first into the material, this part becomes stable relative to the material to be cut away and may be seen as a sort of moving anker. The moving anker has the technical effect of providing stability to the drill head. The improved stability leads to less friction and thus extended lifetime of the drill head.

In an embodiment of the drill, the concave edge section is arranged proximal relative to the convex edge section. Thus, the concave edge section is arranged radially closer to the rotational axis compared to the convex edge section. Arranging the concave edge section and the convex edge section according to this embodiment has the technical effect of positively combining the reduced wear on the convex section with the improved stability of the concave edge section.

In an embodiment of the drill, the concave edge section and the convex edge section are adjoining. In this embodiment, the concave edge section and the convex edge section advantageously form a continues main cutting edge extending from the centre point to the circumference. Preferably, the main cutting edge at the circumference adjoins the guiding lands. The feature of the concave edge section and the convex edge section adjoin reduces the friction of the drill head in the material to be cut away. The reduced friction results in less wear and thus a further extended lifetime of the drill head.

In an embodiment of the drill, a proximal end of each of the concave edge sections ends at the centre point. Typically, the centre point comprises centre point cutting edges. Preferably, a respective centre point cutting edge adjoins a respective main cutting edge, more specifically an end of the concave edge section.

The feature of the proximal end of each of the concave edge sections ending at the centre point advantageously provides a continues cutting edge from the centre of the centre point, such as the apex, to the circumference of the drill head. This reduces the friction of the drill head in the material to be cut away. The reduced friction results in less wear and thus a further extended lifetime of the drill head.

In an embodiment of the drill, the centre point protrudes from the drill head for centring the drill head in use. As argued throughout this text, the centre point protruding or extending from the drill head, preferably providing an apex typically aligned with the rotational axis, provides a point of stability after first contact of the centre point with the material to be cut away. The improved stability results in less friction thus less wear and thus a further extended lifetime of the drill head.

In an embodiment of the drill, the hard material is a metal. In an embodiment of the drill, the metal is a hard metal, such as steel. In an embodiment of the drill, the drill is a high-speed steel (HSS) drill. The shape of the drill, specifically the main cutting edges being substantially in a cutting plane substantially perpendicular to the rotational axis, is advantageously well suited to cut into metals, such as hard materials. The shape and/or material of the drill may be typed as an HSS drill with all the advantages provided by an HSS drill.

In an embodiment of the drill, the number of main cutting edges is two, three or four. Typically, the number of landing guides is equal to the number of main cutting edges or the number of landing guides is a multiple, such as two, of the number of main cutting edges.

In an embodiment of the drill, the drill is combined with any of the features of the embodiments specified for the other aspects of the drill, specifically the drill head.

According to another aspect of the invention, a drill for drilling in hard materials, comprising a drill head having a rotational axis, wherein the drill head comprises a centre point comprising: an apex aligned with the rotational axis; centre point cutting edges radially extending and receding from the apex, wherein a first one of the centre point cutting edges and a second one of the centre point cutting edges have a different radius and/or are receding at least for a part at a different rate.

A drill is typically used for drilling holes in an object or workpiece. The centre point of the drill is arranged to a particular or selected location of the object when starting to drill a hole in the object. The centre point is typically the vertex, the most protruding part or the most extended part of the drill and therefore typically contacts the object first at the particular or selected location. The centre point thereafter drills a centring hole in the object when the drill is pushed into the object. This centring hole typically has a small diameter compared to the diameter of the drill as a whole. The centre point after initiating the centring hole snugly fits in the centring hole.

After that the centre point initiated the centring hole and reaches a particular depth, the main cutting edges will come into contact with the object when the drill is pushed further into the object. The main cutting edges remove the main body of material for forming the hole. The diameter of the hole typically snugly fits around the drill; thus, the diameter of the drill is substantially equal to the diameter of the hole. The main cutting edges, during removing the main body of material, may experience side forces or centrifugal forces causing the drill to move, accelerate or jerk sideways. The centre point snugly fitting in the centring hole opposes these forces by pushing off against the centring hole having the technical effect that the drill as a whole is kept at the particular or selected location. This effect is particularly present during first contact of the main cutting edges.

The drill when drilling typically has a particular angular velocity. The rotational axis is the axis where around the drill rotates. The distance of a part of the drill from the rotational axis is defined as the radius for this part of the drill. The tangential velocity of a part of the drill depends on the radius of this part multiplied with the revolutions of the drill. Thus, the tangential velocity of a part of the drill linearly increases with increasing radius of the part. Or, the outer part of the drill is having the highest tangential velocity while the part of the drill aligning with the rotational axis is having the lowest tangential velocity. It is an insight of the inventor that the centre point due to its low angular velocity causes friction, typically the majority of the friction of the drill head when drilling into the body of material. It is a further insight of the inventor that by introducing an additional movement not aligned with the direction of the tangential velocity to the centre point, specifically the apex, the friction of the centre point and thus drill head may be reduced.

The centre point according to the invention has the feature of centre point cutting edges radially extending and receding in an axial direction from the apex. These centre point cutting edges cut away the material for forming the centring hole. The centre point according to the invention may have the further feature of a first one of the centre point cutting edges and a second one of the centre point cutting edges have a different radius. As the radius is different and the centre point cutting edges are receding in an axial direction from the apex, at a particular depth of the centring hole, one centre point cutting edge is still able to cut away material while the other centre point cutting edge is not able to cut away material as this centre point cutting edge has ended. This asymmetry causes instability. This instability causes an oscillation or movement, typically a small oscillation or movement, of the centre point, and thus the drill head. As this additional small oscillation or movement is not aligned and/or in sync with the tangential velocity, it has the effect of letting the apex move, such as in an oscillating or random pattern. As the apex is moving around, one of the centre point cutting edges comes into contact with the material that used to be in front of the apex and cuts this material away. The technical effect is that the introduced oscillation or movement reduces the friction of the centre point, more specifically the apex or the region around the apex, and thus reduces the friction of the drill head as a whole when drilling. This reduced friction allows the drill to drill a hole in an object with less force or pressure applied on the drill. Furthermore, a reduction of friction has also the technical effect of extending the lifetime of the drill head and thus the drill.

Alternatively, the centre point cutting edges are receding at least for a part at a different rate in an axial direction from the apex. As the rate of receding is different, at a particular depth of the centring hole, one centre point cutting edge receding less rapidly is still able to cut away material while another centre point cutting edge receding more rapidly is not able to cut away material as this material is already cut away by the other centre point cutting edge. This asymmetry causes instability. This instability causes an oscillation or movement, typically a small oscillation or movement, of the centre point, and thus the drill head. This oscillation or movement leads to the effect of an extended lifetime of the drill head and thus the drill as described above.

In an embodiment, the feature of a different radius is advantageously combined with the feature of receding at least for a part at a different rate. This has the effect of optimized control over the oscillation or movement as well as that the oscillation or movement may be generated by centre point cutting edges extending radially less far.

In an embodiment of the drill, the centre point cutting edges are angularly evenly distributed around the apex. If the centre point comprises two centre point cutting edges, the centre point cutting edges are arranged around the apex with a radial angle of pi. If the centre point comprises three centre point cutting edges, the centre point cutting edges are arranged around the apex with a radial angle of 2/3 pi radian. If the centre point comprises four centre point cutting edges, the centre point cutting edges are arranged around the apex with a radial angle of pi/2 radian. The angular distribution may be seen from a point on the rotational axis not being the apex, preferably from a point in front of the drill head on the rotational axis. The angularly evenly distributed centre point cutting edges have the technical effect of increasing the stability of the centre point, drill head and thus the drill, as the centre point cutting edges remove the same amount of material from the drill hole apart from the claimed advantageous asymmetry. The advantage is that the amplitude of the oscillation or movement of the apex is therefore balanced between reducing friction of the apex region and providing a stable drill.

In an embodiment of the drill, the centre point cutting edges deviate and/or curve away from a radial. The centre point cutting edges have a tangential velocity around the rotational axis. This tangential velocity is perpendicular to the direction in which the radial extends from the rotational axis. If the centre point cutting edges deviate and/or curve away from the radial, the tangential velocity is not perpendicular to the centre point cutting edge. This allows the centre point cutting edge to slice through the material instead of bluntly cutting. The centre point cutting edge slicing through the material has the technical effect of reducing the friction of the centre point cutting edge and thus the centre point and drill head as a whole.

In a preferred embodiment, the centre point cutting edges deviate and/or curve away in substantially the same manner. This introduces stability in the centre point. The advantage is that the amplitude of the oscillation or movement of the apex is therefore balanced between reducing friction of the apex region and providing a stable drill.

In an embodiment only one centre point cutting edge deviates and/or curves away from the radial. This introduces instability in the centre point, therefore preferably this asymmetry is therefore preferably introduced when the first part of the centre point is already well into material. Thus, the introduced instability in the centre point is preferably arranged at some distance from the apex or rotational axis. In an embodiment of the drill, the centre point cutting edges are convex centre point cutting edges. The convex shape of the centre point cutting edges provide the centre point cutting edges when slicing through the material to be removed with a centripetal force stabilizing the drill head. Furthermore, the convex shape of the centre point cutting edges provide the material just cut away when slicing through the material to be removed with a centrifugal force such that the material is removed from the region where the centre point is in a similar fashion as described for the convex edge sections of the main cutting edges.

This improved removal of material advantageously reduces friction of the centre point.

In an embodiment of the drill, the centre point cutting edges recede from the apex at the same rate. This receding at the same rate provides stability to the centre point. The amount of instability introduced by features of the centre point can be balanced by at least having a same rate of receding of the centre point cutting edges in this embodiment allowing the skilled person to balance the amount of oscillation or movement introduced by the rotating centre point when drilling.

In an embodiment of the drill, the part of the first one of the centre point cutting edges and the part of the second one of the centre point cutting edges having a different rate of receding are arranged distal from the apex. This advantageously allows the centre point to first cut an initial centre hole with a shallow depth enough to provide stability to the centre point, whereafter the asymmetric part of the centre point comes into contact with the object or material for introducing a controlled instability for reducing friction of the centre point. This has the technical effect of only introducing the controlled instability at a point in time when the centre point already provides some stability as it can push sideways onto the shallow initial centre hole.

In an embodiment of the drill, the drill head comprises main cutting edges radially extending from the centre point. The centre point is typically providing stability to the drill head by making a centring hole before the main cutting edges cut into the material. This centre point typically comprises the apex of the drill head protruding the most into the material or object. As the main cutting edges typically cut away the larger part of the material to be removed from the hole, the main cutting edges will experience the largest forces in varying directions when cutting. These forces in varying directions cause instability. The centre point rotating in its centre hole provides stability to the drill head as it may push sideways against the centre hole walls to provide stability in a sideway direction.

The advantage of the main cutting edges radially extending from the centre point is that the main cutting edges substantially cut away material along the same line, such as at the same radial or any deviating and/or curved shape extending from the rotational axis, such that advantageously a discontinuation or step in the cutting edge in a substantially radial plane is prevented. A discontinuation or step in the cutting edge, comprising a main cutting edge and a centre point cutting edge, may cause instability, which is advantageously prevented. In an embodiment of the drill, a proximal end of preferably each of the main cutting edges ends at a distal end of the centre point cutting edges. This embodiment further specifies the absence of a discontinuation or step in the cutting edge. This embodiment specifies that a main cutting edge and a centre point cutting edge are arranged adjoining with their ends. In a preferred embodiment, the main cutting edge proximal end is in line with the centre point cutting edge distal end to form a continues cutting edge.

The main cutting edge proximal end may have a main proximal tangent line substantially in the cutting plane and having a main proximal direction. The centre point cutting edge distal end may have a centre distal tangent line substantially in the cutting plane and having a centre distal direction. The continues cutting edge may exhibit a main proximal direction and a centre distal direction which are different. For example, the main proximal direction and the centre distal direction show a step or abrupt change, while the cutting edge is continuous. This advantageously allows the main cutting edges and the centre point cutting edges to have their individual shapes for performing their respective functions, while preventing the introduction of instability or too much instability. In an embodiment of the drill, the centre point comprises an asymmetric cutting edge arranged between a proximal end of one of the main cutting edges and a distal end of one of the centre point cutting edges; and a proximal end of another one of the main cutting edges ends at a distal end of another one of the centre point cutting edges. The asymmetric cutting edge advantageously allows to bridge the asymmetry introduced between the centre point cutting edges. The asymmetry can be either that the centre point cutting edges have different radius and/or recede at a different rate. This asymmetric cutting edge advantageously allows to have a continuous cutting edge extending from the apex or rotational axis to the circumference of the drill head.

In an embodiment of the drill, the asymmetric cutting edge is extending in a direction different from the direction of the distal end of the one of the centre point cutting edges. This advantageously may introduce the asymmetry into the centre point for obtaining the controlled instability, oscillation or movement of the apex in operation.

In an embodiment of the drill, the hard material is a metal. In an embodiment of the drill, the metal is a hard metal, such as steel. In an embodiment of the drill, the drill is a high-speed steel (HSS) drill. The shape of the drill, specifically the main cutting edges being substantially in a cutting plane perpendicular to the rotational axis, is advantageously well suited to cut into metals, such as hard materials. The shape of the drill may be typed as an HSS drill with all the advantages provided by an HSS drill. In an embodiment of the drill, the number of centre point cutting edges is two, three or four.

In an embodiment of the drill, the number of centre point cutting edges is two and the two centre point cutting edges form an S-shape with the apex as rotational symmetric point. This embodiment advantageously combines several features as specified in other embodiments for balancing the reduction of friction of the centre point due to the instability, oscillation or movement and the stability provided by the centre point as it is able to counter any random forces having an orientation substantially lying in the cutting plane by the centre point pushing sideways onto the walls of the centre hole. In an embodiment of the drill, the drill is combined with any of the features of the embodiments specified for the other aspects of the drill, specifically the drill head. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which:

Figure 1 schematically shows a top view of a drill head; Figure 2 schematically shows a side view of a drill head;

Figure 3 schematically shows a perspective side view of a drill; and Figure 4 schematically shows a top view of a second drill head.

The figures are purely diagrammatic and not drawn to scale. In the figures, elements which correspond to elements already described may have the same reference numerals.

LIST OF REFERENCE NUMERALS

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Figure 1 schematically shows a top view of a drill head 150 of a drill 100. The drill rotates around a rotational axis R. The drill rotates around this rotational axis in the direction D. The viewpoint of this figure is on the rotational axis, which causes the rotational axis, being a line, to be depicted as a dot in the centre of the drill. To introduce stability to the drill head and also the drill as a whole, the centre of rotation or rotational axis is aligned or at least substantially aligned with the centre line or elongated axis of the drill. The rotational axis further more may define a radial Rad. The radial Rad may be a line starting at the rotational axis and extending perpendicular from the rotational axis. The radial may be defined as radially extending from the rotational axis. Typically, the radial is the shortest way of reaching the circumference of the drill head starting from the rotational axis. The rotational axis further more may define a radial plane. The radial plane may be defined as a plane perpendicular to the rotational axis.

The drill head comprises main cutting edges 160, 160’. The main cutting edges have as a function to cut away the main part of the material from the object wherein a hole is to be drilled. The drill head has a circumference C, which is typically or substantially circular. The main cutting edges typically extend to the circumference of the drill head. The main cutting edges are typically substantially arranged in a radial plane thereby defining the cutting plane or main cutting plane which is a radial plane intersecting the rotational axis at a particular point. This particular point may be found by virtually extending the main cutting edges toward the rotational axis.

The drill head comprises a centre point 180. The centre point is typically protruding from the drill head. Thus, the centre point is protruding towards the viewpoint of Figure 1. The centre point functionally cuts a centre hole into the object or material wherein a hole is to be drilled. The centre point has as function that it should counter any forces having an orientation substantially in a radial plane. These forces are typically introduced by the main cutting edges when cutting, slicing and/or removing away the larger part of the material from the drill hole. These forces may be introduced by imperfections, granules, veins in the material to be removed. These forces are countered by the centre point pushing sideways onto the centre hole and thereby holding the drill head and thus the drill stable in a radial plane. The technical effect of this is that the centre point provides for a smooth entry of the main cutting edges into the material to be cut away by the main cutting edges. Further, the technical effect of this is that the centre point promotes a straighter drill hole having less deviations or sideway imperfections and may prevent a tortuous drill hole. It may be deduced from the previous that the centre point is typically protruding from the drill head to fulfil its function.

The centre point may comprise an apex 182. The apex is the most protruding part or point of the centre point. The apex typically protrudes towards the viewpoint in Figure 1. The apex is typically substantially aligned with the rotational axis. The apex is typically also substantially aligned with the centre line of the drill. This alignment of the apex typically enhances the stability of the drill head and thus the drill as a whole. Stability of the drill head may be defined as the amount of movement of and/or forces acting upon the drill relative to the object or material wherein a hole is to be drilled and/or while drilling.

The main cutting edges are typically arranged radially outward from the centre point. The main cutting edges may be arranged adjoining to the centre point. The drill head may comprise several main cutting edges, such as three, four or two as shown in Figure 1. The main cutting edges are typically radially distributed evenly for minimizing radial forces generated by the cutting main cutting edges.

Each of the main cutting edges 160, 160’ may comprise a convex edge section 165, 165’. The convex edge section deviates and/or curves away from the radial in a radial plane with increasing radius. The convex edge section curve deviates and/or curves away in a direction opposite to the direction of rotation D or away from the material to be cut.

The drill head while rotating provides a tangential velocity to the main cutting edge. The tangential velocity increases linearly with increasing radius. Thus, the outside or radially most extending part of the main cutting edge will experience the highest tangential velocity. Also, the outside or radially most extending part of the main cutting edge will cut away the most material as it travellers the longest distance when going around. These two reasons may cause increased wear of the outside or radially more extending parts of the main cutting edges compared to parts of the main cutting edges arranged inside or radially less extending parts of the main cutting edges. Parts of the main cutting edges experiencing more wear will become quicker blunt compared to parts experiencing less wear. A blunt cutting edge will cause increased friction when drilling. Furthermore, the increased friction will further increase wear of that part of the blunt cutting edge further worsening the friction of that part of the main cutting edges.

The main cutting edges 160, 160’ may comprise convex edge sections 165, 165’. The edge section having a convex shape arranges the edge section under a non-perpendicular angle with the tangential velocity. This advantageously allows the convex edge section to slice through the material to be removed instead of bluntly and frontally cutting into the material to be removed. The slicing motion of the convex edge section reduces the amount of wear on the convex edge section. A further effect of the convex edge section is that the edge section may be longer compared to extending along the radial while ending at the same radial distance from the rotational axis. The longer edge section means that more edge length is available to cut away material near the circumference of the drill head. Thus, the wear of the main cutting edge near the circumference of the drill head is spread out more, hence reducing the wear of the convex edge section. This effect may also be reached in an embodiment having a concave edge section arranged near the circumference of the drill head. Thus, the lifetime of the drill head may be extended by main cutting edges symmetrically radially extending from the centre point wherein each of the main cutting edges deviates and/or curves away from the radial.

The part of the main cutting edge close to the circumference of the drill head is preferably convex shaped. The material may comprise imperfections or other irregularities such as granules. The convex shape allows for forces experienced from these imperfections typically to advantageously translate into centripetal forces. Furthermore, the convex shape advantageously causes an outward or centrifugal force on the material just cut away. The centripetal and centrifugal forces or any other forces having a direction in a radial plane, such as the cutting plane, may be countered by the centre point snugly fitting in the centre hole. The centre point thus advantageously stabilizes or counters the instability caused by the main cutting edges curving away.

The drill may comprise guiding lands 190, 190’, 191, 191’. A drill may be seen as a cylinder. The drill head is arranged to one end of the cylinder. The shank is arranged to the other end of the cylinder. The drill head is the part of the drill contacting the object or material first wherein a hole is drilled. The shank typically has a fitting for fitting into a drilling machine. Guiding lands are arranged along the surface of the cylinder and spiral from the drill head to the shank.

Flutes are arranged between the guiding lands for transporting cut material away from the drill head towards the shank and thus out of the drill hole. The upper edge of the wall on each side of the flutes may be formed by edges from the guiding lands. Guiding lands may stabilize the drill when the drill is far enough inside the drill hole for the guiding lands to be able to push onto the sides of the drill hole.

The convex edge sections 165, 165’ may comprise distal ends 166, 166’. The convex edge section of a main cutting edge typically ends at the circumference of the drill. Preferably, the convex edge section ends at a guiding land. More preferably, the convex edge section ends at an edge of the guiding land 190, 190’. As the edge of the guiding land is typically also the upper wall of the flute, the material just cut away is advantageously directly inserted in the channel created by the flute and the side of the drilled hole for transport away from the drill head. This improves transportation of material just cut away. The material cut away is thus less likely to come an additional time into contact with the main cutting edge reducing the wear of the main cutting edge. Furthermore, the pressure of the material just cut away is lessened further reducing the change of material cut away to come an additional time into contact with the main cutting edge. Thus, this has the technical effect of reducing wear, hence, improving lifetime of the main cutting edge, drill head and drill.

The main cutting edges may comprise concave edge sections 170, 170’. Typically, if also a convex edge section is present, the concave edge section is arranged radially closer to the axis of rotation and/or apex compare to the convex edge section. In other words, the concave edge section is arranged proximal relative to the convex edge section.

The convex edge section may have a proximal end 167, 167’ which is proximal relative to the rotational axis R. The concave edge section may have a distal end 171, 17T which is distal relative to the rotational axis R. The proximal end of the convex edge section may be adjacent or adjoining to the distal end of the concave edge section for forming a continuous main cutting edge.

The centre point 180 may comprise centre point cutting edges 181 , 18T. The centre point cutting edges typically extend from the apex 182. The centre point cutting edges typically start out to extend relatively inside a radial plane, which may be typed as a centre point cutting plane, from the apex.

Thereafter the centre point cutting edges at a particular radius recede to form a sharp ridge 184 with the apex in the middle of the ridge, as shown in Figure 2. This typically sharp receding at the ends of the ridge cause a centre hole while drilling, which centre hole has a relatively steep sidewall. This steep side wall allows the centre point arranged in the centre hole to counter any forces in a radial plane caused by the drilling and causing instability of the drill head by the centre point being pushed against the sidewall of the centre hole. Due to the steep side wall of the centre hole, these forces may even make a slight angle with the radial plane.

The apex is typically aligned with the rotational axis of the drill. From the apex the first centre point cutting edge 181 being part of the ridge 184 extends a first radius r1. Also, from the apex the second centre point cutting edge 18T being part of the ridge 184 extends a second radius r2. The first and the second radius are different in Figure 1. This difference in radius from the apex and/or the rotational axis causes a slight instability during drilling, which instability reduces the friction encountered by the centre point. The concave edge section may comprise a proximal end 172, 172’.

The proximal end of the concave edge section typically ends at the centre point 180. The centre point may comprise centre point cutting edges 181, 18T. The centre point cutting edges may be adjacent or adjoining to the proximal end of the concave edge section for forming a continuous cutting edge with the main cutting edge. Thus, a centre point cutting edge and a main cutting advantageously form a continuous cutting edge for allowing material to be cut away starting from the apex up to the circumference of the drill.

Due to the different radius of the centre point cutting edges in the embodiment of Figure 1 , one of the centre point cutting edges may be extended by an asymmetric cutting edge 183, as shown in Figures 2 and 4. The asymmetric cutting edge links the centre point cutting edge to the proximal end of a main cutting edge for advantageously forming a continuous cutting edge.

Figure 2 schematically shows a side view of a drill head 150. The drill head comprises main cutting edges 160, 160’ and a centre point 180. The main cutting edges extend from the centre point and slightly recede with an increasing radius. The receding may be under an angle in the range of up to pi/4 radian, preferably less than pi//5 radian, more preferably less than pi/6 radian. The receding main cutting edge may still be considered to be substantially arranged in a radial plane, such as a main cutting plane. The drill head may comprise guiding lands 190, 191, 19T for providing a means for the drill to push against the side wall of the drill hole for creating stability. Furthermore, between the guiding lands the flutes 192, 192’ are formed for transporting removed material from the drill head towards the shank of the drill.

The slight receding of the main cutting edges has the technical effect of improving the transport of just cut material towards the circumference for enhancing the transportation of just cut material away from the centre point and/or centre of the drill head and towards the outside of the drill head and/or the flutes. The enhanced transportation reduces the friction of the drill head while drilling.

The centre point 180 may comprise centre point cutting edges 181 , 18T. The middle of the centre point is formed by the apex 182. The centre point cutting edges extend from the apex and/or rotational axis for a specific radius relatively level and thereafter start to recede sharply thereby forming a ridge 184. As the ridge may extend radially different in different directions, and the preference to form a continuous edge with the main cutting edges, the centre point cutting edge 181 ’ providing the part of the ridge extending radially less may be extended by an asymmetric cutting edge 183 for filling the gap towards the end of the main cutting edge for advantageously forming the continuous cutting edge.

Figure 3 schematically shows a perspective side view of a drill 100. The drill comprises a drill head 150 and may comprise a shank 110. The drill head and the shank are arranged on opposite ends of the drill. The shank may be shaped to be gripped by gripping means of a drilling machine. The shank is typically shaped such that the drill may be easily replaced in the drilling machine. The drill typically rotates around a rotational axis R. The drill may rotate around the rotational axis in a rotational direction D.

Figure 4 schematically shows a top view of a second drill head 150. Figure 4 shows the same features as in Figure 1. This figure further shows a larger difference in the ending of the centre point cutting edge, hence the asymmetric cutting edge 183 is more clearly present in Figure 4. According to the invention, the diameter of the drill may be in the range of 2 mm to 100 mm, preferably 4 mm to 80 mm, more preferably 6 mm to 60 mm, even more preferably 8 mm to 40 mm, most preferably, 10 mm to 20 mm.

According to the invention, the diameter of the centre point may be a fraction of the diameter of the drill, the fraction may be in the range of 0.5 to 0.01 , preferably 0.4 to 0.04, more preferably 0.3 to 0.06, even more preferably 0.2 to 0.08, most preferably around 0.1.

According to the invention, the centre point cutting edges may be asymmetric. The asymmetry may be by a different rate of receding especially at some radial distance from the apex and/or rotational axis. The difference in rate of receding may be expressed as a ridge extending from the apex and/or rotational axis with different radius. The asymmetry in the ridge may be expressed as a different radius from the apex and/or rotational axis for the ridge. The difference in radius may be in the range of 2 mm to 0.005 mm, preferably 1 mm to 0.01 mm, more preferably 1 mm to 0.05 mm. The asymmetry may also be by extending to a different radius from the apex and/or rotational axis. The difference in radius may be in the range of 2 mm to 0.005 mm, preferably 1 mm to 0.01 mm, more preferably 1 mm to 0.05 mm. The gap in the asymmetry may be filled up or bridged by an asymmetric cutting edge.

According to the invention, the asymmetry from the centre point causes a movement or an oscillation or movement during drilling. The amplitude of the oscillation, motion or movement is typically a fraction of the diameter of the centre point. The fraction may be in the range of 0.5 to 0.01 , preferably 0.4 to 0.02, more preferably 0.3 to 0.03, even more preferably 0.2 to 0.04, most preferably around 0.05. Examples of hard materials are metals, preferably certain metals, such as iron and copper, and alloys containing metals, such as steel, bronze and brass.

According to the invention, the centre point protrudes from the drill head. The length of the protrusion of the centre point, more specifically the apex, may be expressed as a ratio relative to the diameter of the centre point. The ratio may be in the range of 0.7 to 0.05, preferably 0.6 to 0.1 , more preferably 0.5 to 0.15, even more preferably 0.4 to 0.2, most preferably around 0.3. In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the scope of the invention as set forth in the appended claims. For example, the shapes may be any type of shape suitable to achieve the desired effect. Devices functionally forming separate devices may be integrated in a single physical device.

However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ or ‘including’ does not exclude the presence of other elements or steps than those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or as more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.