Drilling tool assembly with centre drill and cup shape drill

Abstract: A center drill used for machining a hole in a work piece which is adapted to be partially enclosed in a cup shape drill member in a side view thereof, includes a drill portion provided on a leading end of the center drill, and a dust extractor radially outwardly extending from a portion of the center drill which is enclosed in the cup shape drill member.

Description: BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT This invention relates to a drilling tool assembly including a center drill and a cup shape drill used for forming a circular hole in a work piece. The invention also relates to a cup shape drill. One conventional example of the drilling tool assembly of the above-mentioned type is illustrated in Fig. 12A. This type of the tool includes a tool holding portion 90, to a middle portion thereof a center drill 92 is detachably mountable, and a tubular body 94 which is coaxially mounted onto the holding portion with the center drill. The center drill is provided with a drill portion at the leading end thereof. The tubular body 94 is provided with a plurality of cutting tips 93 on the forward end thereof. The tip of the drill portion is set to project forward from the end of the tubular body 94. With the aforementioned type of the drilling tool assembly, the drilling operation is carried out in the following manners: At first the drilling portion is driven at high speed and a leading end of the center drill 92 is pressed onto the work piece (such as a wall member) and a guide hole is being machined with the center drill 92. And subsequently a circular path around the guide hole of a radius approximately equal to the tubular member (also referred to as a cup shape drill member) is machined with the plurality of tips formed on the leading end of the tubular member as the drilling tool assembly is further pressed onto the work. Then at the end a circular opening with a diameter substantially equal to an outer diameter of the tubular body is formed in the work. However, at some point after an initiation of drilling operation, a space formed between the tubular body 94 and the center drill 92 is being filled with fragments and dust as shown in Fig. 12B. At this point it requires to extract the dust filling this space to carry on the next drilling operation. Conventional methods of extracting the dust accumulated in the space are described in the following. a) As shown in Fig. 13, through holes 97 of a relatively small diameter are formed in the base portion of a tubular member and a pair of extracting rods 98 are inserted through these holes and dust accumulation 95 in the space can be pushed out of the tubular member 94; b) Not only is the center drill 92 detachable from the tool holding portion 90 but also the cup shape drill member 94 is designed to be detachable from the tool holding portion 90. The drilling tool assembly thus constructed can extract the dust accumulated in the inner space of the cup shape drill member as the cup shape drill member 94 being disassembled from the drill tool assembly. In the case of structure in the above a) to withdraw dust accumulation out of the cup shape drill member, it requires to use such as a pushing rod 98 as shown in Fig. 13 which can only be used for this purpose thereby rendering an increase of the necessary tools for the drilling operation. In addition, the base portion of the cup shape drill member is formed with a pair of holes (or alternately a single hole) thus it in some degree lessens the mechanical strength of this base portion against a certain directional force applied thereto. In case of the structure described in the above b), it requires to dismount the cup shape drill member which has a significantly larger diameter than the center drill. It therefore takes a greater effort to conduct such a dismounting work thereby lowering the productivity of the drilling operation. In fact there has been conducted various kinds of modifications in an attempt to ease such dismounting operation. Such modifications were aimed to design an attaching structure which enables dismount of the cup shape drill member from the tool holding portion with ease; however, such attaching structure necessitates complicated machining steps performed on both the tool holding portion 90 and the cup shape drill member. Thus an increase in an initial cost of the drilling tool assembly has been unavoidable. It is known in prior art to provide a cup shape drilling tool having a tubular body including a plurality of cutting tips provided on a periphery of a leading end of the tubular body. Such a cup shape drilling tool is known e.g. from WO-A-89 10815 and DE-U 91 10 056. However, if the cutting tips have all the same shape, only the first cutting tip at the lead end in a rotating direction is always subject to maximum stress and the rest of the tips follow the cutting path of the first tip. Such cutting condition will produce an uneven cutting stress, causing the first cutting tip to be worn out quickly. In order to overcome the above problem, US-A-5 417 526 discloses a hollow crown drill having an axially extending support or carrier member (1) with a plurality cutting members (2-4; 6-9), wherein cutting faces (2a-4a; 6a-9a) of the cutting members (2-4; 6-9) have a width (b) increasing counter to the rotational direction (D) of the serially spaced cutting members (2-4; 6-9). Further, the part (7, 9) of the cutting members (6-9) following counter in the rotational direction may be offset upwardly by a height (h) measured parallel to the axis of the crown drill with respect to the leading cutting members (6, 8). It is the object of the invention to provide a cup shape drilling tool and an assembly thereof having an improved dust extraction capability. This object is fulfilled by a cup shape drilling tool having the features disclosed in claim 1 and by a cup shape drilling tool assembly according to claim 4 and 7. Preferred embodiments are defined in the dependent subclaims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side view illustrating a drilling tool assembly not according to the invention, wherein the drilling tool assembly comprises a tool holding portion 10 and related features as well as a flange member 50 and related features being preferred features of the invention according to the claims; FIG. 2 is a cross sectional side view illustrating a holding mechanism of a center drill of the drilling tool assembly; FIG. 3 is a cross-sectional side view taken along line III-III shown in FIG.2; FIG. 4A is a cross sectional plan view illustrating a state where dust accumulates in a cup shape drill member; FIG. 4B is a cross sectional side view illustrating a state where the center drill together with the dust accumulation is pulled out of the cup shape drill member; FIG. 5A is a cross sectional side view showing an alternate form of a flange member; FIG. 5B is a cross sectional side view showing another form of a flange member; FIGS. 6A - 6D each is a side view showing an alternate form of a radially projected member other than the above mentioned flange member; FIG. 7 is a cross sectional side view illustrating a drilling tool assembly according to the invention; FIG. 8 is a plan view of the drilling tool assembly right after completion of the drilling operation; FIG. 9 is a fragmentary side view seen from a point B indicated in FIG. 8; FIG. 10 is a cross sectional side view illustrating drilling operation with the drilling tool assembly according to the invention; FIG. 11 is a cross sectional side view illustrating a state where a dust accumulation is extracted out of the cup shape drill member; FIG. 12A is a cross sectional side view illustrating a conventional drilling tool assembly prior to the initiation drilling operation; FIG. 12B is a cross sectional side view illustrating a state of dust accumulation in a cup shape drill member with the conventional drilling tool assembly; and FIG. 13 is a cross sectional side view illustrating a state where the dust accumulation in the cup shape drill member of the conventional tool assembly is extracted with an extracting rod member. Next a drilling tool assembly not covered by the claims is described with reference to FIGS. 1 to 4, wherein features and advantages thereof in particular with respect to a tool holding portion 10 and related features as well as a flange member 50 can be preferably used in connection with the invention as defined in the claims. The drilling tool assembly ( or also referred to as a tool assembly ) is provided with a tool holding portion 10 as shown in the FIG.1. The tool holding portion 10 has a base portion ( left end in FIG. 1 ) and a tool connection portion 12 which is fixed onto the base portion. The tool holding portion 10 has an opposite end ( right end in Fig. 1 ) to which a center drill 102 and a base plate 40 of a cup shape drill member 101 are to be coaxially mounted. Provided that the tool connecting portion 12 is connected to an unillustrated drive source, the tool holding portion 10, the center drill 102 and the cup shape drill member 101 are driven together in an integral form. A leading end of the aforementioned tool holding portion 10 for mounting the center drill 102 is formed with a mounting hole 18 having a circular cross sectional shape extending along a center axis of the tool holding portion 10. At the innermost end of the hole 18 an insertable hole 20 with non circular cross section is formed. The center drill 102 has a drill portion on the leading end and a circular shaped mounting portion 24 on the other end which can be fit into the mounting hole 18. At the end of the mounting portion 24, there is also provided a non-circular shaped projection 26 which can be fit into the insertable hole 20. Because of the fitness of non-circular shaped projection 26 into the corresponding non-circular shape insertable hole 20, it is made possible to fix a relative angular position of the center drill 102 with respect to the tool holding member 10. At the halfway along the lengthwise direction of the mounting portion 24 of the center drill 102, there is formed a circumference groove 28 extending around the circular mounting portion. On an inner circumferential surface of the holding hole 18, there is formed an engaging portion 30 for engagement with the groove 28. In more details, there are provided two through holes 32 allowing communication between an exterior of the tool holding member 10 and the holding hole 18 and a ball 34 having a proper diameter engaging the groove formed around the outer surface of the holding portion of the center drill is placed into each through hole 32. In addition, around the outer surface of the tool holding member 10 and at the through hole 32 in the lengthwise direction, there is formed a circumferential groove 36 and a C shaped expandable member 38 is fit into the groove 36. Due to this elastic restoration force into a radially contracting direction, the balls 34 each is biased radially inward thereby being maintained is the state of engagement between the balls 34 and the circumferential groove 28, i.e. an engagement state of the centering drill 102. A construction of the removable structure is not limited to the certain type described above, thus it could be in the form such as a hollow tool holding portion having a transverse through threaded hole on the side surface thereof with a screw bolt engaging through the threaded hole and the leading end of the screw bolt pressing the chucking portion of the center drill against the inner surface of the tool holding portion. The cup shape drill member 101 has a donut shape base portion 40 and a tubular member 42 extending from the outer periphery of the base plate in an axial direction. The tubular member 42 forms a plurality of cutouts 44 at the distant end thereof and a plurality of cutting tips ( see FIGS 7 and 8) that are provided around the respective cutouts 44. The base plate 40, the tubular member 42 and the cutouts 44 and respective cutting tips 45A constitute a cup shape drill member 101. Since the inner thread 46 is provided on the inner surface of the donut shaped base member 40 and the outer thread 48 mating with the inner thread 46 is formed on the leading end of the tool holding portion 10, the cup shape drill member 101 is engageable with the tool holding portion 10. The length of the center drill is set such that when the cup shape drill member 101 is securely fastened to the holding portion 10, the drill portion 22 of the center drill 102 projects (rightward direction in Fig. 1) further away from the tip portion of the tubular member 42. The significant character of this drilling tool assembly 100 is to equip a flange portion 50 on the center drill 102 as shown in FIGS. 1 and 2. Such flange 50 is formed in the donut shape with a hole 51 in the middle thereof fitting onto the outer surface of the chucking portion of the center drill 102. The diameter of hole 51 is set such that it is slightly smaller than the outer diameter of the neck portion 23 of the center drill 102 and slightly larger than the chucking portion 24 of the center drill 102. The fixing structure of the center drill 102 includes a stepped portion 52 of a diameter smaller than that of the leading end of the center drill 102 and an axial width substantially equals to the thickness of the flange 50 at adjacent to the chucking portion of the center drill 102 and another stepped portion 54 (or referred to as a circumferential groove) of a smaller diameter than the stepped portion 52 at axially adjacent to the stepped portion 52. With this structure, the flange member 50 is fitted onto the center drill 102 from its chucking end and traversed axially towards the leading end of the center drill 102 till the inner edge of the flange member 50 comes into contact with an outer edge of the stepped portion 52 and then a C-shaped stop ring 56 is fitted onto the stepped portion 54. As a result, the flange 50 is securely mounted onto the chucking portion of the center drill 102. Next an operation of the drilling tool assembly 100 is hereinafter described. First of all, a drilling tool assembly 100 as a whole is rotated at a high speed through connection of a drive connecting portion 12 to the unillustrated drive mechanism then the drilling tool assembly is pressed against the work piece such as a wall. The drilling portion 22 or 22a of the center drill 102 starts machining a surface of the wall first and proceeds a drilling operation. Then the cutting tips 45A formed around the cup shape drill 101 begin drilling operation as the center drill 102 advances into the wall. Thereafter the wall is formed with the hole of a diameter approximately equal to the outer circumference of the tubular member 42 of the cup shape drill 101. After the drilling operation with this drilling tool assembly, the fragments and dust (hereinafter referred to as a dust accumulation) 60 of the wall is found stuck in the tubular member 42 as shown in Fig. 4A. At this stage, with a conventional drilling tool as shown in Fig. 12, to remove the dust accumulation out of the tubular member 42 by pulling out the center drill from the tubular member 42, it is likely to cause difficulty since there exists no projection on the center drill which can function as a dust extractor as it could engage the stuck chips. However, with the drilling tool having the flange 50 provided on the center drill 102, as the center drill 102 is pulled out from the tool holding member 10 by overcoming the resistance force generated by the balls 34 and the elastic member 36, the dust accumulation 60 is removed from the tubular member 42 as shown in FIG.4B. Thus it facilitates a preparation for the next drilling procedure. While technically speaking, the dust accumulation in the tubular member 42 can also be extracted therefrom by removing the cup shape drill member 101 from the tool holding member 10; however, such removing operation of the cup shape drill member 101 requires a heavy task owing to its structure of larger diameter. As can be imagined, taking out of the center drill 102 from the tool holding member 10 only requires to overcome the resistance force generated by the elastic member which clamps a chucking portion of the center drill. Thus this removal operation of the center drill is much more easier than the removal operation of the cup shape drill member 101. As a result, it significantly improves a workability of the drilling operation for it could minimize a time required to clean up the cup shape drill 101. The diameter of the flange 50 may be set such that it is smaller than the inner diameter of the tubular member 42 and should be larger than the drilling portion 22 of the center drill 102 in order for the flange portion 50 to function as a dust extractor against the dust accumulation 60. In fact it will suffice to equip a flange member 50 on the center drill 102 whose diameter is slightly larger than the diameter of the drill portion 22 of the center drill 102 to extract the dust accumulation 60 out of the cup shape drill member 101. On the other hand, it would be also possible to extract the dust accumulation 60 out of the tubular member 42 with a flange 50 mounted on the center drill 102 whose diameter is only slightly smaller than the inner diameter of the tubular member 42 (i.e., only a slight clearance is formed between the outer diameter of the flange 50 and the inner diameter of the tubular member 42 ). However, the another advantage with this structure is to keep much of the fine dust produced during the drilling operation on the outer side of the flange member 50 for much of the dust unlikely moves through the small clearance; therefore, the much of dust also could be extracted from the tubular member 42 as the center drill 102 is removed from the tool holding member 10. Alternately, the flange 50 can be formed in the shapes shown in such as FIGS 5A and 5B; a forward opening concave shape and a flange with a wall member 58 forwardly extending around an outer periphery of the flange member 50 respectively. These structures of the flange member have a common feature that both form a forward opening recess portion and the clearance between the outer periphery of the flange and the inner surface of the tubular member is set small thus the fine dust produced during the drilling operation can be more securely deposited in the respective concave portions. In fact, to merely achieve the principal object that the dust and chips accumulated (dust accumulation) in the tubular member 52 are easily extracted along with the removal operation of the center drill 102, the shape of the flange 50 is not limited to the circular shape but could be in the oval, rectangular, triangular, or arbitrary polygon shape. In the extreme case, merely placing the radially extended projection onto the neck portion of the center drill 102 will sufficiently extract the fragments accumulated in the tubular member 42. For instance, eliminating the flange member 50 from the center drill 102 and leaving the stopper ring 56 whose outer diameter is slightly larger than the diameter of the neck portion of the center drill 102 will do the extraction of the dust accumulated in the tubular member 42 along with the removal operation of the center drill 102 from the tool holder 10. Thus anything projecting radially outwardly from the neck portion of the center drill 102 function as a dust extracting member. Having mentioned about the principal feature of the dust extracting member, another form thereof is shown in FIGS. 6A to 6D. As shown in FIGS. 6A and 6B, the dust extracting member takes the shape of a pin 62 or a rectangle 64. In the case of pin 62 for the dust extracting member, merely placing the standard sized pin member to the through hole provided in the neck portion of the center drill 102 will suffice. The common feature of the dust extracting members shown in FIGs. 6C and 6D is a ring member attached to the neck portion of the center drill 102. The ring members 66, 68 used for this purpose are preferably to have a cut out portion along the circumferential path of the ring such that opposite ends of the ring member can be separated from each other when placing the ring onto the neck portion and then inserted into the through hole provided on the neck portion of the center drill 102. Then the both ends of the ring are to be mated with each other in the middle of the through hole of the neck portion of the center drill 102. Such ring member can be set to pivot around the pin hole on the neck portion of the center drill 102 or firmly placed in the pin hole so that no pivot movement occurs. In either case, substantially the same effect can be achieved thus it is a matter of design choice how tight the fitness between the ring member and the pin hole in the neck portion. Furthermore, an axial position of the dust extracting member along the center drill 102 is preferably set such that it is close to the innermost of the tubular member 42. Because it could earn sufficient axial distance from the leading end of the tubular member 42 to the dust extracting member and such axial distance is an indication of the maximum thickness of the wall (as a work piece) to be drilled with the drilling tool assembly 100. A member to securely hold the flange member (a dust extracting member ) 50 onto the center drill 102 is not limited to the aforementioned structure. For instance, the flange could be welded onto the center drill 102. However, in the case of the replacement of the tubular cutter 101 for the drilling operation with a different diameter, the flange member 50 more suitable for this different cutter may be required for easing the dust extracting operation. For adapting this situation, the replaceable flange member 50 and replaceable structure provided on the center drill 102 would be demanded. Thus the structure previously mentioned with reference to FIG. 2 including the two stepped configuration of the neck portion of the center drill 102 best suits for this demand as it allows a replacement of the another flange member 50 with a specified inner hole which adequately fit outside of the stepped portion 52. The present invention is hereinafter described with reference to FIGS 7 to 11. In the invention, cutting tips 45A, 45B each is arranged on the edge of respective cut out portions 44 formed at the leading end of the tubular member 42. These cutting tips 45A, 45B each is formed to project forward and radially from the leading end of the tubular member 42. These cutting tips are also protruding inwardly and outwardly in the radial direction from the leading end of the tubular member 42. As shown in FIG 8 in particular, three of cutting tips 45B are provided within the circumferential area of an angle less than 180 degree on the leading end of the tubular member (in this particular figure, the angle is about 90 degree). And the number more than the cutting tips 45B of another form of cutting tips 45A are provided in the other circumferential area of the leading end of the tubular member. It should be noted that the radially projected amount of the cutting tip 45B (also referred to as an inwardly protruding cutting tip) to the center of the tubular member is greater than that of the cutting tip 45A (also referred to as a non-inwardly protruding cutting tip) so that a radius Rb (FIG. 8) of the inscribed circle formed by the cutting tip 45B is smaller than a radius Ra of the inscribed circle formed by the cutting tip 45A as the tubular member 42 is driven. Furthermore, the leading end of the cutting tip 45A projects forward from the leading end of the cutting tip 45B in the axial direction of the tool by an amount (T) as shown in FIG 9. In other words, the cutting tip 45B is positioned backward relative to the cutting tip 45A by an amount (T) in the axial direction. These cutting tips 45A and 45B together with the aforementioned tubular body 42 constitute a cup shape drill member 101 for this invention. In addition, the cup shape drill member 101 and the aforementioned center drill 102 and the tool holding assembly 10 for holding the latter and the former constitute a drilling tool assembly 100 of this invention. Moreover, the drilling assembly 100 in the assembled state is set such that the leading end of the center drill 102 projects forward from the leading end of the cup shape drill member 101. The drilling operation using the above mentioned drilling tool assembly is hereinafter described. As described, first of all, the drilling tool assembly 100 is pressed against the work piece such as a wall, then the leading end of the center drill 102 begins drilling the center of the hole required to be formed. As the center drill 102 advances its drilling operation, the forward end of the cup shape drill member 101 contacts on the surface of the wall and begins drilling operation to make a hole whose diameter substantially coincides with the outer diameter of the tubular portion of the cup shape drill member. As the cup shape drill advances its drilling operation by an amount little more than the thickness of the wall, it leaves a hole in the wall with the specified diameter. What actually happens in more details at the leading end of the cup shape drill member 101 when it had made contact with the wall surface is that the forward end of the cutting tips 45A first machines annular groove on the wall and subsequently the forward end of the cutting tip 45B machines with the outer surface of an inner wall of the annular groove formed by the tips 45A since the tips 45B project radially inward than the tips 45A. Thereafter the annular grove 52 of a width (W1) coinciding substantially with the radial width of the cutting tip 45B is left on the wall as shown in Fig. 10. The annular groove 52 formed in the wall to some extent functions as a passage for the cutting dust produced by the drilling operation to flow into the enclosed space S formed between the tubular member and the surface of the wall. Moreover the leading end portion 22a of the center drill 102 is set larger in diameter than the other drill portion 22 thus a clearance 54 is formed between the center drill and the drilled surface of the wall as shown in FIG 10. After advancing the drill tool assembly 100 in the axial direction by more than the wall thickness, it leaves a hole with a specified diameter and at this stage the drilling operation thus is completed. After the completion of drilling operation, when the drilling tool assembly is pulled out from the wall, the cylindrical shape dust accumulation 60 is expected to be formed in the tubular member 42 as shown in FIG 4A. The dust accumulation 60 is initially stuck to the inwardly protruding cutting tips 45B, however, it can be shifted radially by a specified amount to the side opposing to where the cutting tips 45B lie by tapping the drilling tool assembly 100 since there is formed a clearance 54 (see FIG. 10) between the outer surface of the center drill and the inner diameter of the dust accumulation 60. The specified amount is determined by comparison of the width W2 and the width W3. For instance, in case that W2 is larger than W3, then the specified amount corresponds to W3. In other words, with reference to FIG 8 the dust accumulation 60 in a solid line can be shifted radially away from the side of cutting tips 45B to be positioned as shown by the dash and double dotted line. Once it is successfully shifted to the opposite side of the cutting tips 45B in the tubular member 42, as there exists more space in this side due to the smaller radial thickness of the cutting tips 45A, the accumulated dust can be easily extracted from the cup shape drill member 42 as the center drill 102 is removed from the tool holding member 10. Please see FIG. 11. In this form, since the cutting tips 45A are projected forward from the cutting tips 45B, the drilling operation by the cutting tips 45A comes ahead of the operation by the cutting tips 45B. Furthermore, the cutting tips 45B are further projected inward from the cutting tips 45A, thus the drilling operation by the tips 45A substantially makes a subsequent drilling operation by the cutting tips 45B loadless towards an axially advancing direction of the drilling tool assembly. Thus only the drilling operation carried out by the cutting tips 45B is a machining of the surface of the inner wall of the annular groove already made by the cutting tips 45A to secure the clearance noted by W2 shown in FIG 10. Once again this clearance generally noted by 52 in FIG 10 enhances a dust flow into the enclosed space S thereby enabling to increase a drilling speed to some extent. Furthermore, the number of the inwardly protruding cutting tips 45B is preferably less than a half of total number of the tips including all the cutting tips 45A, 45B. Technically speaking only one cutting tip in the type of 45B with the rest in the type of 45A will do the extracting operation. As long as the inwardly protruding cutting tips 45B lie within the half of circumference of the tubular member 42, any possible arrangements of tips therein would not deteriorate the performance of this drilling operation. As maybe obvious by this stage, the inwardly protruding cutting tips 45B should not be dispersed beyond 180 degree apart among each other since the accumulated dust could not be radially shifted by the specified amount to the other side of the cutting tip 45B if there were another cutting tip 45B on the other side. It may be preferable to dispose a plurality of the cutting tips of 45B in the circumferential area of smaller angle so that the dust generated by the drilling operation flows easily through the clearance 52 thereby improving a drilling operation. Furthermore, with this arrangement a radial shifting operation of the accumulated dust in the tubular member 42 after completion of the drilling operation just before extracting the center drill 102 out of the tubular member 42 is made easier. It should be noted that in case that the center drill 102 has a leading end with a diameter of substantially equal to the other drill portion (i.e., there is created almost no clearance 54 between the center drill 102 and the drilled hole of the wall) then the center drill can be pulled out of the tubular member 42 at the middle of the drilling operation or after completion of the drilling operation to leave the dust accumulation in the tubular member 42. Thereafter the accumulated dust 60 left behind in the tubular member 42 can be shifted radially to be easily pulled out from the tubular member. Although the present invention has been fully described by way of examples with reference to drawings, it is to be understood various changes and modifications will be apparent to those skilled in the art without departing from the scope of the present invention. Accordingly, the invention should not be limited by the foregoing description but rather should be defined only by the following claims.

Claims: A cup shape drilling tool (100) comprising: a tubular body (42) including a plurality of cutting tips (45A, 45B) provided on a periphery of a leading end of the tubular body (42), characterized in that the tubular body having a plurality of inwardly protruding tips (45B) which project further radially inwardly of the rest of the cutting tips (45A) by the same amount and all the inwardly protruding tips (45B) lie in an arc of 180 degree at one end of the tubular member (42). A cup shape drilling tool (100) according to claim 1, wherein the cutting tips (45A, 45B) include a plurality of the inwardly protruding tips (45B) and the plurality of inwardly protruding tips (45B) are successively arranged on the leading end of the tubular member (42). A cup shape drilling tool (100) according to claim 1 or 2, wherein a leading end of the inwardly protruding tip (45B) is set backward of a leading end of the other cutting tips (45A) in an axial direction of the drilling tool (100). A cup shape drilling tool assembly (100) comprising: a cup shape drill tool according to one or more of the preceding claims; a center drill (102) partially enclosed in the cup shape drill member (101) in a side view thereof; and a tool chucking device (10) for securely holding the center drill (102) at a middle of the cup shape drill member (101) in a plan view. A cup shape drilling tool assembly (100) according to claim 4, wherein the center drill includes: a drill portion (22, 22a) formed on a leading end of the center drill (102), a dust extractor (50; 62; 64; 66; 68) radially outwardly extending from a portion (14) of the center drill (102) lying in the cup shape drill member (101). A cup shape drilling tool assembly (100) according to claim 5, wherein a diameter of the drill portion (22, 22a) is set larger than that of an axially rearward portion (14, 24, 28) of the center drill (102). A cup shape drilling tool assembly (100) comprising: a cup shape drill member (101) including a plurality of cutting tips (45A, 45B) provided on a periphery of an opening end of the cup shape drill member (101), a center drill (102) partially enclosed in the cup shape drill member (101) in a side view thereof, including: a drill portion (22, 22a) formed on a leading end of the center drill (102) projects axially outwardly from the opening end of the cup shape drill member (101); a tool chucking device (10) for securely holding the center drill (102) at a middle of the cup shape drill member (101) in a plan view; characterized in that the cup shape drill member having a plurality of inwardly protruding tips (45B) which project further radially inwardly of the rest of the cutting tips (45A) by the same amount and all the inwardly protruding tips (45B) lie in an arc of 180 degree at one end of the cup shape drill member (101). A cup shape drilling tool assembly (100) according to claim 7, wherein the center drill (102) is detachably attached to the tool chucking device (10). A cup shape drilling tool assembly (100) according to claim 7 or 8, wherein a diameter of the drill portion (22, 22a) is set larger than that of an axially rearward portion (14, 24, 28) of the center drill (102).

Inventors: AJIMI KUNIO, AJIMI TSUNEYOSHI, AJIMI, KUNIO, AJIMI, TSUNEYOSHI
Applicants: HOUSE BM CO LTD, HOUSE B.M. CO., LTD.
Application year: 1996
Main classification: B23B51
IPC codes: B23B51