Abstract:
A bit assembly includes a bit having a bit head and a bit shank, a mounting sleeve being held in the region of the bit shank, and a support element that comprises a guidance region being associated with the bit. To allow the bit to be easily deinstalled from the bit receptacle and allow it, if applicable, to be easily installed again, provision is made that the support element comprises, in the region of its underside facing away from the bit head, a deflection segment.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a bit, in particular a round shank bit, having a bit head and a bit shank, a mounting sleeve being held in the region of the bit shank; and having a support element that comprises a guidance region. 
         [0003]    2. Description of the Prior Art 
         [0004]    A bit of this kind is known from DE 37 01 905 C1. The mounting sleeve is embodied here as a clamping sleeve that is constituted from a resilient material, for example sheet steel. It comprises a longitudinal slot that is delimited by sleeve edges. The mounting sleeve diameter can be varied by means of the longitudinal slot, in which context the sleeve edges are to be moved toward one another (smaller diameter) or spaced farther apart from one another (larger sleeve diameter). Different clamping states can be achieved in this fashion. The support element, embodied as a wear protection disk, is pulled onto the mounting sleeve. This support element has a circular cross section and is penetrated by a bore. The bore is dimensioned such that the mounting sleeve is held, as compared with its slackened state, in a preloaded state having a decreased outside diameter. The outside diameter thereby generated is selected so that the clamping sleeve can be slid with little or no energy expenditure into a bit receptacle of a bit holder. The sliding-in motion is limited by means of the support element. Upon further insertion of the bit shank into the bore, the support element is moved into a region of the bit shank not surrounded by the clamping sleeve. The mounting sleeve then springs open radially and braces itself in the bore of the bit holder. The round shank bit is thereby held in axially captive fashion, but freely rotatably in a circumferential direction. For deinstallation of the bit, it is driven out of the bit receptacle by means of a mandrel acting on the back side of the bit shank. 
         [0005]    There are application instances in which the bit can no longer be used for certain milling purposes when it is partly worn away. It is then dismantled, and new unworn bits are installed. The partly worn bits are, however, then still suitable for coarse processing tasks. Because the support element has already been slid away from the mounting sleeve, however, installation then becomes more complicated. Separate clamping tools are used, with which the clamping sleeve can be preloaded in forceps fashion. The bit can then be inserted into the bit receptacle without energy expenditure. The clamping tool is taken off while the bit is in a partly inserted state, and the bit is then driven completely into the bit receptacle with a hammer. 
         [0006]    DE 10 2005 042 663 A1 discloses a further bit. A wear protection disk is likewise used here as a support element which holds the mounting sleeve in a preloaded state. The support element can be shifted toward the bit head until the mounting sleeve springs back radially. The support element then engages with protrusions into receptacles of the mounting sleeve, resulting in a non-rotatable bearing point between the mounting sleeve and the support element. Non-rotatable bearing points of this kind have proven to be disadvantageous, since they cause intensified and inhomogeneous wear. 
         [0007]    EP 1 427 913 B1 discloses a bit in which a support element can once again be slid off from a mounting sleeve. The support element comes to rest between the bit head and the free end of the mounting sleeve. The support element has, on its side facing toward the mounting sleeve, a peripheral protrusion. The clamping sleeve can become wedged in place on this extension as the bit is driven out, with the result that the clamping sleeve becomes unintentionally spread. Deinstallation then becomes difficult and laborious. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the invention to create a bit of the kind mentioned above that enables easy reuse after it is deinstalled from a bit holder. 
         [0009]    This object is achieved in that the support element comprises, in the region of its underside facing away from the bit head, a deflection segment. 
         [0010]    Upon deinstallation of the bit from the bit receptacle, the mounting sleeve can be brought into effective engagement with the deflection segment. The mounting sleeve is thereby brought into the mounting sleeve segment constituted by the guidance region. The mounting sleeve is then once again in a clamped state that enables facilitated deinstallation of the bit from the bit receptacle. This clamped state then also makes it possible, however, to insert the bit into a bit receptacle, in the context of re-use, with little or no energy expenditure. For initial installation, the bit is preferably already configured in such a way that the guidance region holds the mounting sleeve in a clamped state. 
         [0011]    According to an inventive alternative, the mounting sleeve can be moved by means of the deflection segment out of a slackened position into a clamped position. This is advantageous, for example, when the support element has unintentionally been slid away from the mounting sleeve and is in its working position facing toward the bit head. It is then easily possible, by means of the deflection segment, to reestablish an installation position by sliding the support element onto the mounting sleeve. The deflection segment can also serve to bring the mounting sleeve out of a partly clamped position into a clamped position. The partly clamped position exists, for example, when the bit is installed in the bit receptacle and acts with a residual clamping force on the bore wall of the bit receptacle. 
         [0012]    To ensure reliable conveyance of the mounting sleeve into the deflection segment, one conceivable inventive variant is such that the support element comprises an introduction region that transitions indirectly or directly into the deflection segment. The mounting sleeve can then, with a segment facing toward the support element, be threaded into the introduction region and brought by way of it into the deflection segment. It has proven to be particularly advantageous in this context if provision is made that the mounting sleeve comprises a guide that is held in the region of the introduction region. A spatial association between the mounting sleeve and the support element is then already arrived at in the installation position. The result of this overlap between the mounting sleeve and support element is to produce a labyrinth-like closure that reduces the risk of dirt penetration. The rotational behavior between the bit and the support element is thereby improved. It is also conceivable for the guide to be at a distance from the introduction region in an axial direction of the bit. The introduction region should then be dimensioned so that the guide of the mounting sleeve can be reliably introduced upon deinstallation. Wear-related deformations of, for example, the mounting sleeve in its region facing toward the support element can, in particular, also be accounted for in this context. 
         [0013]    A particularly preferred inventive configuration is such that there is arranged, in the transition region of the bit head into the bit shank, a centering segment that is embodied on its outer circumference in such a way that it forms a rotary bearing point together with the guidance region. The rotary bearing point enables the support element to rotate independently of the mounting sleeve. A wear-optimized design of the bit as a whole is thereby achieved. In addition, this rotary bearing point creates a centered orientation of the bit with respect to the support element, which results in an improvement in the milling result and a decrease in rotational wear. 
         [0014]    A bit according to the present invention can be such that the support element comprises on its upper side, facing toward the bit head, an introduction enlargement that transitions indirectly or directly into the guidance region. This introduction enlargement simplifies initial installation of the bit. In this context, firstly the mounting sleeve is placed onto the bit shank; then the support element is slid onto the slackened mounting sleeve, the introduction enlargement serving as a threading-in aid. 
         [0015]    A particularly simple design results from the fact that the guidance region and the introduction region are each constituted by a bore; and that the bore constituting the introduction region has a larger diameter than the bore constituting the guidance region. 
         [0016]    As already mentioned earlier, an essential structural criterion for bits is a wear-optimized design. The intention is that the least possible wear occur on the cost-intensive bit holder into which the bit is inserted. It is therefore advantageous if the support element exerts as little rotational wear as possible with respect to the bit holder. At the same time, however, the bit should rotate as readily as possible so that it becomes worn away homogeneously over its entire circumference. To ensure this, provision can be made in accordance with a variant design of the invention that the support element comprises, on its upper side, a recess in which a facing region of the bit head is received; and that the bit head is braced with a contact surface on a support surface of the recess. The recess and the facing region of the bit head form a labyrinth-like closure that impedes the penetration of removed material. Good rotatability of the bit with respect to the support element is thereby maintained. It has become apparent that it is disadvantageous if the support element is immobilized nonrotatably with respect to the bit holder, since it can then, as a result of impact loads, work inhomogeneously into the facing contact surface of the bit holder. For this reason, relative movability of the support element with respect to the bit holder needs to be maintained. To ensure this, in accordance with an inventive variant the support element is equipped with recesses on its radially externally located circumferential region. These recesses constitute catch regions for removed material, which then introduces a circumferential force into the support element. It thus induces a rotational motion of the support element. A centered alignment of the support element with respect to the bit holder can be achieved by the fact that the support element comprises a protruding centering projection on its underside. Said projection can engage into a centering receptacle of the bit holder. A kind of seal is once again constituted between the centering projection and centering receptacle, preventing the penetration of removed material. A further wear-optimized bit design is achieved when provision is made that the centering projection comprises a centering surface, extending in inclined fashion with respect to the longitudinal center axis of the bit, that transitions via a set-back recess into a circumferential seating surface extending radially with respect to the longitudinal center axis. The set-back recess forms a kind of stress-relieving throat. In addition, this recess leaves the associated edge region of the bit holder exposed, resulting in improved free rotatability. 
         [0017]    A bit according to the present invention can be characterized in that the mounting sleeve comprises one or more holding elements that engage into a circumferential groove of the bit shank to form a rotary bearing point. This guarantees free rotatability of the bit in a circumferential direction with respect to the mounting sleeve. It is particularly advantageous in this context if provision is made that the holding elements are divided out from the mounting sleeve along two separating edges extending in a circumferential direction; and that the separating edges of the holding elements are located respectively opposite the groove side walls of the groove. The holding elements can be stamped out of the sleeve material, and coordinated with the groove width, in highly dimensionally accurate fashion. A slight axial clearance of the bit shank with respect to the mounting sleeve is left. Depending on the location of the bit, the separating edges constitute linear abutting edges against the facing groove side walls. This configuration enables exact guidance of the bit shank, resulting in improved rotation properties. 
         [0018]    The invention will be explained in further detail below with reference to an exemplifying embodiment depicted in the drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  shows a bit in a prepared initial position; 
           [0020]      FIG. 2  is a side view of the bit depicted in  FIG. 1 , in an installation position; 
           [0021]      FIG. 3  shows a detail labeled “III” in  FIG. 2 ; 
           [0022]      FIG. 4  is a perspective view of a support element shown in  FIGS. 1 to 3 ; 
           [0023]      FIG. 5  is a side view of the bit shown in  FIGS. 1 to 3 , in its installation position on a bit holder; 
           [0024]      FIG. 6  shows a detail labeled “VI” in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION  
       [0025]      FIG. 1  shows a bit  10  that is embodied as a round shank bit. It comprises a bit shank  11  that constitutes substantially a cylindrical geometry. A circumferential groove  15  is recessed into the bit shank. Bit shank  11  is attached via a centering segment  12  to a bit head  13 . Bit head  13  comprises, at its end facing away from bit shank  11 , a bit tip  14  made of hard material, for example hard metal. A cup into which bit tip  14  is soldered is recessed for this purpose into the end of bit head  13 . As is evident from  FIG. 1 , bit head  13  possesses a collar  13 . 2  in the attachment region to centering segment  12 . Collar  13 . 2  constitutes a downwardly directed contact surface  13 . 1 . Bit  10  is embodied, with its bit shank  11 , its bit head  13 , and its bit tip  14 , rotationally symmetrically with respect to the longitudinal center axis extending through bit tip  14 . A mounting sleeve  20  is arranged in the region of bit shank  11 . Mounting sleeve  20  is produced from a planar material, for example sheet steel. Holding elements  21  are stamped out of the planar material and pushed out into the region surrounded by mounting sleeve  20 . Holding elements  21  are cut out along two stamping edges that extend in a circumferential direction of mounting sleeve  20 . Mounting sleeve  20  is rolled up in such a way that a circular cross section results, leaving a clamping slot  23 . 
         [0026]    A support element  30  is slid onto mounting sleeve  20 . Support element  30  is of disk-shaped configuration. The conformation of support element  30  will explained in further detail below with reference to  FIG. 3 . As this drawing shows, support element  30  comprises, on its side facing toward the bit head, a cup-shaped recess  31  into which bit head  13  can be set with its collar  13 . 2 . In that context, bit head  13  rests in planar fashion, with its contact surface  13 . 1 , on a facing support surface  31 . 1  of recess  31 . Facing away from recess  31 , support element  30  comprises a seating surface  33  that is arranged plane-parallel to support surface  31 . 1 . This seating surface  33  transitions via a recess  35  into a centering step  34 . Recess  35  is embodied in this context in the shape of a concave fillet in order to achieve a stress-optimized transition. The centering surface, adjacent to recess  35 , of centering projection  34  is arranged in inclined fashion with respect to the longitudinal center axis of bit  10  and, like seating surface  33 , extends annularly around the longitudinal center axis of bit  10 . 
         [0027]    As is further evident from  FIG. 3 , a bore that constitutes a guidance region  36  is recessed centeredly into support element  30 . Introduction region  36  transitions into support surface  31 . 1  via an introduction enlargement  36 . 3  developed in rounded fashion. Adjacent to guidance region  36 , facing away from introduction enlargement  36 . 3 , is a deflection segment  36 . 1 . Deflection segment  36 . 1  is constituted by a draft that extends in inclined fashion with respect to the longitudinal center axis of bit  10  and the longitudinal center axis of support element  30 . This inclination can be constituted by a linear segment or by a curve segment. An introduction region  36 . 2  is adjacent to deflection segment  36 . 1 . Introduction region  36 . 2  is in turn constituted by a bore, the bore diameter being greater than the diameter of the bore generating guidance region  36 . Introduction region  36 . 2  is transitioned into guidance region  36  via deflection segment  36 . 1 . 
         [0028]    In the installation position, as illustrated in  FIGS. 2 and 3 , bit head  13  is inserted with its collar  13 . 2  into recess  31  of support element  30 . Centering segment  12  of bit shank  11  is in this context associated with guidance region  36 . The result is to create a rotary bearing point between guidance region  36  and centering segment  12 . Care must be taken in this context that the outside diameter of the cylindrical centering segment  12  is coordinated with the inside diameter of guidance region  36  in such a way that free rotatability between support element  30  and centering segment  12  is retained. The clearance between these two components should be selected so that the least possible lateral offset (transversely to the longitudinal center axis of the bit ( 10 )) occurs. 
         [0029]      FIG. 3  shows that bit shank  11  comprises a fillet region  12 . 1  that transitions from a reduced-diameter shank region into the enlarged-diameter region of centering segment  12 . Mounting sleeve  20  is arranged in the reduced-diameter region. In its end region facing toward support element  30 , mounting sleeve  20  constitutes an end-located guide  22 . This guide  22  is terminated by a bevel  22 . 1 . In the installation position, guide  22  is arranged in the region of introduction region  36 . 2 . The association is such that a clearance remains between the outer wall of mounting sleeve  20  and introduction region  36 . 2 . This clearance should be selected to be larger than the clearance between centering segment  12  and guidance region  36 , thus avoiding contact between mounting sleeve  20  and support element  30  in the installation position. Centering segment  12  and guidance region  36  then therefore take over clearly defined rotational mounting. 
         [0030]      FIG. 4  shows support element  30  once again, in isolation. As this depiction illustrates, recess  31  is delimited by a circumferential rim  31 . 2  into which recesses  32  are set. Recesses  32  are embodied as radially extending grooves. The depiction in  FIG. 4  also makes it apparent that support element  30  is embodied rotationally symmetrically with respect to its longitudinal center axis. 
         [0031]      FIGS. 5 and 6  depict the association of bit  10  with a bit holder  40 . As these drawings illustrate, bit holder  40  comprises a base part  41  onto which is shaped an insertion projection  42  protruding on the underside. Base part  41  furthermore carries a holding projection  43 , shaped on integrally, into which a bit receptacle  46  is introduced as a cylindrical bore. Bit receptacle  46  is embodied as a through bore that is open at both of its longitudinal ends. A driving-out mandrel (not depicted) of a driving-out tool can be introduced through that end of bit receptacle  46  which faces toward insertion projection  42 . This driving-out tool then acts on the free end of bit shank  11 . The end of bit receptacle  46  facing away from insertion projection  42  opens into a cylindrical segment  44  of holding projection  43 . This cylindrical segment  44  comprises an annular contact surface onto which seating surface  33  of support element  30  is set. As  FIG. 6  clearly illustrates, centering projection  34  of support element  30  is inserted into a correspondingly shaped centering receptacle of bit holder  40 . 
         [0032]      FIG. 6  further shows that introduction enlargement  36 . 3  of support element  30  is embodied in such a way that the associated edge region between collar  13 . 2  and centering segment  12  is left open (throat  12 . 2 ), so that good rotatability of bit  10  with respect to support element  30  is retained. It is further evident from  FIG. 6  that recess  35  leaves open the associated edge region of bit holder  40 , thus guaranteeing that seating surface  33  rests in planar fashion on the associated support surface of bit holder  40 . 
         [0033]    A deinstallation tool, as already mentioned earlier, can be used to deinstall bit  10  from bit holder  40 . This deinstallation tool comprises a supporting segment that is braced at the front side on rim  31 . 2  of support element  30 . A driving-out mandrel of this tool can be moved at the back side through bit receptacle  46  so that it acts on the free end of bit shank  11  and pushes it out of bit receptacle  46 . The supporting segment of the driving-out tool holds support element  30  in its position. The result is that guide  22  of mounting sleeve  20  is slid into the region of deflection segment  36 . 1  of support element  30 . Deflection segment  36 . 1  then clamps the end of mounting sleeve  20  constituted by guide  22  radially inward, achieving a reduction in the diameter of mounting sleeve  20  at least in this region. As a consequence of a further displacement of bit  10 , mounting sleeve  20  travels with its enveloping region into guidance region  36  of support element  30 . This sliding motion can be continued until, for example, the position of support element  30  achieved in  FIG. 1  is produced. Bit  10  can then be lifted out of bit receptacle  46  with little or no energy expenditure. It is then available for re-installation.