Method for producing a tapped bore and tap drill bit

A method for producing a tapped bore in a workpiece with a tap drill bit, which, at its drill bit tip, has a primary cutting edge and a thread profile trailing in a tap drilling direction. The method has a tap drilling stroke, in which the tap drill bit is driven into the workpiece with a tap drilling advance in the tap drilling direction and at a tap drilling rotational speed synchronized therewith, and the tool-primary cutting edge produces a core-hole bore, and the thread profile of the tool bit forms an inner thread at the inner wall of the core-hole bore. In the tap drilling stroke, shavings are produced, which are conveyed in a shavings discharge direction, which is oppositely directed to the tap drilling direction, out from the tapped bore and collide here with thread flanks of the inner thread that face the shavings that are discharged.

FIELD

The invention relates to a method for producing a tapped bore, in particular a tapped blind bore, as well as a tap drill.

BACKGROUND

In a so-called percussion tap drilling process, a percussion tap drill bit is used both to create a core bore and to cut an inner thread in a joint tool bit stroke. The percussion tap drill bit has a primary cutting edge at its drill bit tip and a thread profile having at least one thread cutting tooth, this profile trailing in a tap drilling direction. In the method, first of all, the tap drill bit stroke occurs and, subsequently, a reverse stroke occurs in the opposite direction. In the tap drilling stroke, the primary cutting edge of the bit produces, on the one hand, the core-hole bore and, on the other hand, the thread profile of the tool bit produces the inner thread at the inner wall of the core-hole bore until a useable desired thread depth is reached. For this purpose, in the tap drilling stroke, the tap drill bit is operated during a tap drilling advance at a tap drilling rotational speed that is synchronized therewith. In the oppositely directed reverse stroke that follows, the tap drill bit is guided in a reverse direction out of the tapped bore and, in fact, this is done with an oppositely directed reverse feed as well as with a reverse rotational speed that is synchronized thereto. It is thereby ensured that the thread profile of the tap drill bit in the thread path of the inner thread is moved out of the tapped bore without any load.

In the above method, shavings are produced in the tap drilling stroke and are conveyed out from the tapped bore in a shavings discharge direction that is opposite to the tap drilling direction. In this case, the shavings moving in the shavings discharge direction collide with the thread flanks of the inner thread that face the shavings. Therefore, at the thread flanks of the inner thread that face the shavings, abrasion or removal of material can occur and lead to defects in the inner thread. Such defects can, in turn, impair the seating behavior of a screw element that is screwed into the inner thread.

Known from DE 38 80 394 T2 is a combined tool bit for drilling a hole and for cutting a thread. First of all, a core-hole bore is produced using the tap drill bit. Subsequently, the tap drill bit is moved with its tool bit axis in a circular path around the drilling axis and, in fact, this is conducted with rotation of the tap drill bit, as a result of which the thread profile produces an inner thread in the core-hole bore. Essentially the same method is also known from DE 39 39 795 C2 and from U.S. Pat. No. 5,678,962.

SUMMARY

The object of the invention consists in providing a method for producing a tapped bore in a workpiece as well as a tap drill bit with which a permanently operationally secure screw connection is ensured.

The invention is based on the fact that, in the tap drilling stroke, the shavings that are to be discharged collide with the thread flanks of the inner thread that face the shavings and can potentially damage them. Against this background, in accordance with the characterizing part of patent claim1, the thread flanks of the inner thread that face the shavings are not yet produced with a finished dimension in the tap drilling stroke, but rather are produced with a flank material allowance. In this way, at the thread flanks that face the shavings, a collision contour is provided with which the shavings to be discharged collide.

Only in a final processing step, which occurs after the tap drilling stroke, can the flank material allowance of the thread flanks of the inner thread that face the shavings be removed to produce the final dimension. Preferably, this final processing step takes place in the reverse stroke, during which the thread profile of the tool bit that is guided out of the tapped bore in the reverse direction removes material from the flank material allowance of the flanks facing the shavings until the final dimension is obtained.

In the tap drilling stroke, the tap drilling advance and the tap drilling rotational speed synchronized therewith are matched to each other in such a way that the produced thread turn of the inner thread has a predefined tapped-bore thread pitch. Analogously to this, in the reverse stroke, the reverse feed and the reverse rotational speed synchronized therewith are also matched to each other in such a way that a reverse thread pitch is obtained. Depending on the adjustment of the aforementioned parameters, the reverse thread pitch can be identical to the tapped-bore thread pitch or else, if need be, it can be different from it. By way of example, it is possible in the tap drilling stroke to impose a first pitch (that is, a tapped-bore thread pitch) on the inner thread, while, in the reverse stroke, a second thread pitch (that is, a reverse thread pitch), which is different from the first thread pitch, is imposed on the inner thread. The reverse thread pitch and the thread-stroke thread pitch can be adjusted with respect to each other in such a way that, overall, a load-optimized design of the inner thread profile is obtained.

By way of example, in the tap drilling stroke—with the exception of the thread flanks of the inner thread that face the shavings—the inner thread geometry (that is, the thread flanks of the inner thread that face away from the shavings, the radial inner-thread inner crown of the inner thread, and the radially outer thread base of the inner thread) can already be produced in a final dimension. Only afterwards is it possible, in the reverse stroke, to produce the thread flanks of the inner thread that face the shavings to the final dimension.

In a preferred embodiment, the reverse stroke does not immediately follow the tap drilling stroke, but instead there follows a flute-forming step, in which a peripheral flute, which adjoins the inner thread and has no thread pitch and in which the thread profile of the tap drill bit can rotate without any load, is formed. In this way, the tap drilling speed can be reduced to zero, without any breakage of the tool bit or any breaking of the thread profile occurring based on an excessively large cutting load.

The thread profile of the tap drill bit can have thread profile teeth, which are described below, and/or at least one reverse tooth. Both the thread profile teeth and the reverse tooth can be formed respectively as a shaping tooth (with corresponding shaping edges) or as a cutting tooth (with corresponding cutting edges that remove shavings) or as a combination thereof.

As mentioned above, the thread profile of the tap drill bit can rotate free of load in the peripheral flute produced without a thread pitch in the flute-forming step. The provision of the peripheral flute, moreover, makes it possible for the tap drill bit to use a cutting edge to produce a peripheral thread countersink in the opening of the bore. The peripheral thread countersink can therefore be produced during the above flute-forming step.

In a technical implementation, the tap drilling stroke can be extended in the tap drilling direction directly by a flute-forming stroke. In this case, the tap drill bit can be moved beyond the desired thread depth until a desired bore depth is reached and, in fact, done so with a flute-forming advance as well as at a flute-forming rotational speed that are not synchronized to each other and/or are different from the tap drilling advance and from the tap drilling rotational speed.

It is preferred when, at the end of the flute-forming step, the thread profile, as viewed in the axial direction, can rotate completely in the peripheral flute of the tapped bore without any load. The peripheral flute is produced during the flute-forming stroke by use of the primary cutting edge as well as the bit thread profile at the tap drill bit.

When the desired bore depth has been reached, the flute-forming advance is reduced to zero. At the same time, the flute-forming rotational speed is also reduced to zero in order to make possible the reversal in the direction of rotation that is required for the reverse stroke.

At the start of the reverse stroke, the tap drill bit is controlled in such a way that the thread profile of the tool bit cannot be driven in without a load, but rather can be retracted under shaving-removal load into the thread turn run-out that opens into the peripheral flute. Subsequently, the tap drill bit is guided out of the tapped bore in a direction that is opposite to the tap drilling direction and, in fact, is conducted with a reverse feed as well as at a reverse rotational speed synchronized therewith, as a result of which the thread profile of the tool bit can be rotated out of the tapped bore with removal of material (that is, with finishing of the thread flanks facing the shavings to the final dimension).

When the tap drilling stroke, the flute-forming stroke, and the reverse stroke are being carried out, the longitudinal axis of the core bore axis and the axis of rotation of the tap drill bit preferably remain at all times in coaxial alignment with one another.

A tap drill bit for carrying out such a method can preferably have a clamping shank and a tap drill bit body joined to it. At least one shavings groove can extend along the longitudinal axis thereof up to a front-end primary cutting edge at the drill bit tip. At the front-end primary cutting edge, a shavings surface that delimits the shavings groove and a front-end free surface of the drill bit tip converge. As viewed in the peripheral direction of the tool bit, the shavings groove can be delimited by at least one drill bit web. The shavings surface of the shavings groove can transition into a back surface of the drill bit web on the outer peripheral side with formation of a secondary cutting edge. At the back surface of the drill bit web on the outer peripheral side, the thread profile can be formed with at least one thread cutting tooth. The tooth height of the cutting tooth is dimensioned in the radial direction in such a way that the cutting tooth protrudes outward over the primary cutting edge in the radial direction by a radial offset. If need be, the cutting tooth can extend the primary cutting edge outward in the radial direction so that the surfaces are flush with each other. Alternatively and/or additionally, the cutting tooth, as viewed in the axial direction, can be arranged at an axial offset behind the primary cutting edge.

In a preferred embodiment variant, the tap drill bit can have three drill bit webs. Each of these drill bit webs is formed with at least one thread cutting tooth. The thread cutting teeth are preferably not formed with the same cutting geometry, but rather are different in design. By way of example, it is possible to form in the peripheral direction of the drill bit, in succession, a preliminary cutting tooth, a middle cutting tooth, and a finished processing tooth of different cutting geometry at the drill bit. The cutting teeth are formed offset with respect to one another at the tap drill bit in the axial direction. The extents of their offsets are adjusted in such way that, by the tap drilling rotational speed and by the tap drilling advance, a flawless thread cutting is ensured.

In order that, in the reverse stroke, the flank material allowance is removed from the thread flanks facing the shavings in an operationally safe manner (that is, without premature breakage of the tool bit), the thread profile of the tool can preferably have at least one reverse tooth that is formed specially for this purpose. Said tooth can be formed with a thread-flank cutting/shaping edge. In the reverse stroke, the thread-flank cutting/shaping edge can remove the flank material allowance of the thread flanks that face the shavings, said flank material allowance being preserved in the tap drilling stroke, until the final dimension is reached.

The reverse tooth, like the thread profile tooth, is also formed on the back surface of the drill bit web. In a technical embodiment of the tool bit, the reverse tooth can protrude radially outward over the primary cutting corner by a reverse tooth height. The thread-flank cutting edge of the reverse tooth can transition into a reverse cutting edge at a radially inner, cutting inner corner. In this case, the tap drill bit processes not only the thread flanks of the bore-hole inner thread facing the shavings, but, at the same time, also deburrs the thread inner crown thereof. Preferably, the reverse tooth and/or the reverse cutting edge can be constructed in terms of design in such a way that they are active only in the reverse stroke and largely functionless in the tap drilling stroke.

The above-mentioned reverse cutting edge can extend along the longitudinal direction of the drill bit. In this case, it is possible for the back surface of the drill bit web on the outer peripheral side and the shavings surface of the shavings groove to converge. For this reason, the reverse cutting edge and the secondary cutting edge are formed at the longitudinal edges of the drill bit web that lie opposite one another in the peripheral direction of the drill bit.

In order to create a stable thread profile at the tap drill bit, it is preferred when, in the peripheral direction of the drill bit, a tooth web that is formed on the back surface of the drill bit web adjoins the at least one thread profile tooth and/or the reverse tooth. In this way, the thread profile tooth and/or the reverse tooth is or are protected in the tap drilling stroke and/or in the reverse stroke against premature breakage of the tool bit. Preferably, the thread profile tooth and the reverse tooth can be joined to each other via a tooth web formed on the back surface of the drill bit web. The tooth web can have front sides that face away from each other in the peripheral direction of the drill bit, each of which forms the thread profile tooth and the reverse tooth.

The tooth web can have a radially outer web crown surface as well as a web flank surface facing the drill bit tip and a web flank surface facing away from the drill bit tip. In order to reduce the tool load during the tap drilling stroke and/or during the reverse stroke, the above-mentioned web surfaces can be formed at least in part as free surfaces, which, in the tap drilling stroke and/or in the reverse stroke, are essentially functionless.

The web crown surface of the above tooth web can transition at a first peripheral web edge into the web flank surface that faces the drill bit tip. In addition, the web crown surface can transition at a second peripheral web edge into the web flank surface that faces away from the drill bit tip.

In regard to a reduced tool load during the flute-forming stroke, it is preferred when the tap drill bit has a special peripheral flute-cutting edge in order to produce the peripheral flute in the flute-forming stroke. In a preferred embodiment variant, at least one of the two above-mentioned peripheral web edges can be formed as such a peripheral flute-cutting edge, by means of which, in the flute-forming stroke, the peripheral flute adjoining the bore-hole inner thread is formed. In the tap drilling stroke and in the reverse stroke, in contrast, the peripheral cutting edge can be essentially functionless.

As ensues from the above description, the peripheral flute can adjoin the inner thread of the tapped bore. Said peripheral flute fulfills the following dual function: First, when the thread is produced, it is possible to rotate the thread profile of the tap drill bit without any load. Second, when a fastening screw is screwed in, the peripheral flute forms a compensatory space, which compensates for screw length tolerances of the fastening screw. The screw length of such a fastening screw is strongly subject to tolerances owing to manufacture. By use of the peripheral flute, it is possible to screw in the fastening screw, which is subject to tolerances, in a process-secure manner, without needing to increase the thread depth of the tapped bore, as would be required in the prior art.

DETAILED DESCRIPTION

Shown inFIG. 1is a finished tapped blind-hole bore1. The bore1is created with its bore base3to a desired bore depth tBin a workpiece5by means of a so-called percussion bore processing, which will be explained later on the basis ofFIGS. 5 to 8. At its bore opening, the bore1has a peripheral thread countersink7, which, in its further course downward, transitions into an inner thread9. The inner thread9extends along the bore axis A to a useable desired thread depth tG. As further ensues fromFIG. 1, a thread turn15of the inner thread9opens with a thread run-out11into a peripheral flute13. Said peripheral flute does not have a thread pitch and, as viewed in the axial direction, is formed between the inner thread9and the bore base3. The thread turn15has a radially outer thread base17as well as laterally top and bottom thread flanks18,19, which transition radially inward into a thread inner crown21. The top thread flanks19inFIG. 1are the thread flanks that face the shavings and are described later on the basis ofFIGS. 9 and 10, whereas the bottom thread flanks18inFIG. 1are the thread flanks that face away from the shavings.

The tapped blind-hole bore1shown inFIG. 1is produced by use of a tap drill bit23, which is described below on the basis ofFIGS. 2 to 4. In accordance therewith, at its drill bit tip25, the tool bit23inFIG. 2has three front-end primary cutting edges27, which are distributed uniformly around the periphery, as well as a thread profile29trailing in the tap drilling direction I (FIG. 5 or 6).

The tool bit23is constructed with a clamping shank24as well as with a tap drill bit body26adjoined to it, along the bore axis A of which a total of three shavings grooves28, which are distributed uniformly over the periphery, extend up to the respective front-end primary cutting edge27at the drill bit tip25.

At each primary cutting edge27, a shavings surface31, which delimits the shavings groove28, and a front-end free surface33of the drill bit tip25converge. In the peripheral direction of the tool bit, the respective shavings groove28is delimited by a drill bit web35. Overall, the tap drill bit23shown in the figures has three drill bit webs35. The shavings surface31of the shavings groove28transitions here into a back surface37of the respective drill bit web35on the outer peripheral side, with formation of a secondary cutting edge36. The secondary cutting edge36and the front-end primary cutting edge27converge at a radially outer primary cutting corner39.

At the back surfaces37of the three drill bit webs35on the outer peripheral side, each thread profile29has a preliminary cutting tooth41, a middle cutting tooth42, and a finished cutting tooth43. Each of the cutting teeth41,42,43is formed with a radially outer thread-base cutting edge45as well as with thread-flank cutting edges47in order to cut/shape the thread turn15shown inFIG. 1. In this case, the cutting teeth41to43are designed with different geometries and spaced at different axial distances Δa (indicated only inFIG. 5) from the drill bit tip25in order to cut the thread turn15of the inner thread9shown inFIG. 1. In addition, the preliminary cutting tooth41, the middle cutting tooth42, and the finished cutting tooth43have different tooth heights Δr1, Δr2, Δr3in the radial direction (FIG. 2). By way of example, the preliminary cutting tooth41, the middle cutting tooth42, and the finished cutting tooth43can be axially larger in the peripheral direction. The finished cutting tooth43then cuts the entire inner thread contour. Alternatively to this, the finished cutting tooth43can also be designed as a shaping tooth in order to increase the thread strength.

In addition, at the transition between the tap drill bit body26and the clamping shank24, the tap drill bit23has a cutting edge49for formation of the thread countersink7shown inFIG. 1.

Described below on the basis ofFIGS. 5 to 8is the method for producing the tapped blind-hole bore1shown inFIG. 1: In accordance therewith, inFIG. 5, the tap drill bit23is guided in a tap drilling direction I toward the workpiece5, which has not yet been pre-drilled, and a percussion boring is carried out. In a tap drilling stroke G, the main cutting edges27produce a core-hole bore and, at the same time, the trailing thread profile29produces the inner thread9at the inner wall of the core-hole bore. The tap drilling stroke G occurs with a tap drilling advance fGand at a tap drilling rotational speed nGsynchronized therewith in a tap drilling direction of rotation and, in fact, is carried out until the desired thread depth tGis reached (FIG. 6).

Immediately afterwards, a flute-forming step (FIG. 7) is carried out, in which the tap drilling stroke G is extended in the tap drilling direction I by a flute-forming stroke N. In the flute-forming stroke N, in contrast to the thread-forming stroke G, the flute-forming advance fNand the flute-forming rotational speed nNof the tap drill bit23are not synchronized with each other and are different from the tap drilling advance fGand from the tap drilling rotational speed nG.

In this way, the thread profile29uses its preliminary cutting tooth41, its middle cutting tooth42, and its finished cutting tooth43to produce the peripheral flute13shown inFIG. 7, in which the thread profile29can rotate without any load. The flute-forming advance fNand the flute-forming rotational speed nNare established in such a way that an excessively large cutting edge load on the cutting teeth41to43is prevented.

When the desired bore depth tBis reached, both the flute-forming advance fNand the flute-forming rotational speed nNare reduced to zero. Subsequently, for preparation of a reverse stroke R (FIG. 8), a reversal in the direction of rotation occurs. In the reverse stroke R (FIG. 8), the tap drill bit23is guided in a reverse direction II (FIG. 8) out from the tapped bore1and, in fact, is guided with an oppositely directed reverse feed fRas well as with a reverse rotational speed nRsynchronized therewith. These parameters are of such a magnitude that the thread profile29of the tap drill bit23is not free of load, but rather is guided out of the tapped bore1with a shaving-removal load in the thread turn15of the inner thread9. In this way, as will be described later, material is removed from a collision contour53(FIG. 9 or 10), which is still formed at the thread flanks19of the inner thread9.

At the start of the reverse stroke R, the tap drill bit23of the fabrication unit is actuated in such a way that the cutting teeth41,42,43are each driven with shaving-removal load into the thread turn run-out11, which opens into the peripheral flute13. In the further course of the reverse stroke R, the thread profile29of the tap drill bit23is then rotated outward, with shaving-removal load (that is, material is removed from the collision contour53) through the thread turn15of the inner thread9.

InFIG. 9, the tap drilling stroke G illustrated inFIG. 6is shown in detail. In accordance therewith, the tap drill bit23is driven with the predefined tap drilling advance fGas well as at the tap rotational drilling speed nGsynchronized therewith in the tap drilling direction I into the workpiece5. Shavings51are thereby produced, which are forced in a shavings discharge direction S, which is opposite to the tap drilling direction I, out from the tapped bore1. The shavings51that are conveyed in the shavings discharge direction S out from the tapped bore1in this case collide with the thread flanks19facing the shavings of the inner thread5.

In accordance with the invention, in the tap drilling stroke I—with the exception of the thread flanks19that face the shavings of the inner thread9—the complete inner thread geometry is already produced with the final dimension, namely, specifically, the thread flanks18that face away from the shavings, the radial inner-thread inner crown21, and the radially outer thread base17. In contrast to this, the thread flanks19that face the shavings of the inner thread9after the tap drilling stroke I are not yet produced in a final dimension, but rather are produced with an additional flank material allowance Δx (FIG. 9). In this way, at the thread flanks19that face the shavings, a collision contour53is provided, with which the shavings51to be discharged collide.

In the subsequent reverse stroke R, material is removed from the above collision contour53at the thread flanks19facing the shavings until the final dimension is reached. For this purpose, in the flute-forming step, the tap drill bit is positioned in the axial direction in such a way that, at the start of the reverse stroke R, the tap drill bit23is controlled in such a way that the thread profile29is driven under shaving-removal load, that is, with removal of material, into the thread turn run-out11(FIG. 1), which opens into the peripheral flute.

Through corresponding adjustment of the reverse feed fRand the reverse rotational speed rRsynchronized therewith, a reverse thread pitch αRfor the thread flanks19facing the shavings is obtained in the inner thread9in the reverse stroke R. The reverse thread pitch αRof the thread flanks19facing the shavings can be identical to the tapped bore thread pitch αGor can differ from it, in order to achieve, if need be, a load-optimized inner thread design.

In this way, different flank diameters can be adjusted for different alloys of the workpiece5, with the respective flank diameters each being adapted specially to the workpiece alloy used. Beyond this, it is also possible to regrind the thread teeth of the thread profile in the course of a reprocessing of the tool bit. In this case, the axial offset by which the tool bit is to be shifted in the axial direction in the flute-forming step at the start of the reverse stroke R would be enlarged in order to achieve a corresponding material engagement in the thread flanks facing the shavings19.

Described below on the basis ofFIGS. 11 to 15, is the structure and the mode of action of a tap drill bit in accordance with another exemplary embodiment. The tap drill bit shown inFIG. 11fundamentally corresponds to the preceding figures. For this reason, reference is made to the above description. The tap drill bit shown inFIG. 11has, in addition, a reverse tooth57, with which, in the reverse stroke R described below on the basis ofFIG. 15, material is removed from the flank material allowance Δx of the thread flanks facing the shavings19in an operationally reliable manner.

FIGS. 12 to 14relate to different side views of the tap drill bit. InFIG. 12, the preliminary cutting tooth41, the final processing tooth43, and the reverse tooth57are shown. InFIG. 13, the middle tooth42and the final processing tooth43are shown, while, inFIG. 14, the final processing tooth43, the reverse tooth57, and the preliminary cutting tooth41are shown.

InFIGS. 12, 14, 15, the reverse tooth57is formed with a thread-flank cutting/shaping edge59. In the reverse stroke R, the tap drill bit is actuated in such a way that its thread-flank cutting/shaping edge59removes material of the flank material allowance Δx from the thread flanks19facing the shavings to produce the final dimension.

The reverse tooth57, like the thread profile teeth41,42,43, is also formed on the back surface37of the drill bit web. In this case, the reverse tooth57protrudes radially outward over the primary cutting corner39by a reverse tooth height ΔrR(FIG. 11). InFIG. 14 or 15, the thread-flank cutting edge59of the reverse tooth57transitions at an inner corner60of a radially inner cutting edge into a reverse cutting edge61, which is also active in the reverse stroke R. As a result, in the reverse stroke R, not only does a processing (for example, a processing by removal of shavings) of the thread flanks19that face the shavings of the bore-hole inner thread9occur, but, at the same time, also a deburring of the thread inner crown21of the inner thread9occurs, as indicated inFIG. 15. During this deburring, burr formation at the thread inner crown21, which would otherwise result during the processing of the thread flanks19facing the shavings, is prevented.

As further ensues fromFIGS. 12 to 15, at the reverse cutting edge61, the back surface37of the drill bit web on the outer peripheral side and the shavings surface31of the shavings groove28converge. Therefore, the reverse cutting edge61and the secondary cutting edge36both extend along the longitudinal direction of the drill bit and are formed at longitudinal edges K1, K2of the drill bit web (FIG. 14) that lie opposite one another in the peripheral direction of the drill bit.

In order to create a stable thread profile29at the tap drill bit, a tooth web63adjoins each thread profile tooth41,42,43and the reverse tooth57in each case. Said tooth web is formed in each case on the back surface37of the drill bit web. As a result, the respective thread profile tooth41,42,43and the reverse tooth57are protected in the tap drilling stroke G and/or in the reverse stroke R against a premature breakage of the tool bit. As ensues fromFIG. 14, the thread profile tooth43and the reverse tooth57are joined to each other via a tooth web63that is formed on the back surface37of the drill bit web. The tooth web63has a radially outer web crown surface65as well as a web flank surface67that faces the drill bit tip25and a web flank surface69that faces away from the drill bit tip25. In order to reduce the tool bit load during the tap drilling stroke G and/or during the reverse stroke R, the above-mentioned web surfaces65,67,69can be formed at least in part as free surfaces, which are essentially functionless in the tap drilling stroke G and/or in the reverse stroke R.

In accordance withFIGS. 12 to 14, the web crown surface65of the tooth web63transitions at a first peripheral web edge71into the web flank surface67that faces the drill bit tip25. In addition, the web crown surface65in a second peripheral web edge72transitions into the web flank surface69that faces away from the drill bit tip25. In regard to a reduced tool bit load during the flute-forming stroke N, the tap drill bit has a peripheral flute-cutting edge US (FIGS. 12 to 14) in order to produce the peripheral flute13in the flute-forming stroke N. In the illustrated embodiment variant, the peripheral flute-cutting edge US is realized, in particular, by means of the second peripheral web edge72.