Abstract:
A toolholder ( 1 ) for clamping a cutting insert ( 6 ), the toolholder including a rigid base jaw ( 2 ), an upper clamping jaw ( 3 ) defining with the base jaw a longitudinally extending insert receiving slot for releasably receiving the cutting insert in a predetermined position, the upper clamping jaw tapering towards a leading nose portion ( 12 ) so shaped and dimensioned to initially urge the cutting insert to the predetermined position prior to its clamping in the insert receiving slot.

Description:
FIELD OF THE INVENTION 
     This invention relates to toolholders for releasably receiving one or more cutting inserts. 
     BACKGROUND OF THE INVENTION 
     In U.S. Pat. No. 4,580,930 to Zinner, there is illustrated and described a toolholder having a rigid base jaw and a tapering clamping jaw defining a longitudinally extending insert receiving slot for releasably receiving a cutting insert which is clamped therein by a clamping force transversely directed to its major clamping surfaces. Irrespective of how tightly a cutting insert is clamped in an insert receiving slot, it can be undesirably and forcibly extracted therefrom during a cutting operation by outwardly directed unseating forces acting co-directional with the slot. To prevent such unseating, the toolholder is provided with a stopping member ( 28 ) received in a recess ( 27 ) formed in the cutting insert&#39;s lower clamping surface (see FIG.  12 ). However, this complicates the toolholder&#39;s construction and requires suitably formed cutting inserts. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a toolholder for clamping a cutting insert, the toolholder comprising: 
     a rigid base jaw, 
     an upper clamping jaw tapering towards a leading nose portion, 
     said base jaw and said clamping jaw defining therebetween a longitudinally extending insert receiving slot for releasably receiving the cutting insert in a predetermined position, 
     a stopping member for engaging an auxiliary clamping surface of the cutting insert to prevent its outward longitudinal displacement from said predetermined position during a cutting operation, 
     characterized in that 
     said stopping member being constituted by said leading nose portion so shaped and dimensioned to initially urge the cutting insert to said predetermined position prior to its clamping in said insert receiving slot. 
     In accordance with the present invention, a clamping jaw&#39;s leading nose portion initially urges a cutting insert inward to its predetermined position in an insert receiving slot prior to its otherwise conventional clamping and thereafter it reacts against the outwardly directed unseating forces prevailing during a cutting operation to positively secure the cutting insert in its predetermined position. Such clamping necessarily involves elastic deformation of substantially the entire clamping jaw which in turn entails that its leading nose portion also undergoes elastic deformation from an initial unclamping state to a final clamping state. 
     By virtue of the present invention, the proposed modification to an otherwise conventional toolholder facilitates the secure clamping of preferably conventional double ended cutting inserts. In addition, the proposed modification to an otherwise conventional toolholder can be readily implemented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the different aspects of the present invention and to show how the same can be carried out in practice, preferred embodiments will now be described, by way of non-limiting examples, with reference now made to the accompanying drawings, in which: 
     FIG. 1 is a partial side view of a toolholder according to the present invention before clamping a cutting insert; 
     FIG. 2 is a partial side view of the toolholder of FIG. 1 after clamping a cutting insert; 
     FIG. 3 is an enlarged side view of the leading nose portion of the toolholder&#39;s clamping jaw designated A in FIG. 1; 
     FIG. 4A is an enlarged side view of the leading nose portion of the toolholder of FIG. 1 before the clamping of a cutting insert; 
     FIG. 4B is an enlarged side view of the toolholder&#39;s leading nose portion at an intermediate stage during the clamping of the cutting insert in which the toolholder&#39;s actual position is shown in solid lines and its initial position (FIG. 4A) is shown in dashed lines; 
     FIG. 4C is an enlarged side view of the toolholder&#39;s leading nose portion after the clamping of the cutting insert in which the toolholder&#39;s actual position is shown in is solid lines and its intermediate position (FIG. 4B) is shown in dashed lines; and 
     FIG. 5 is an enlarged side view of a toolholderes leading portion with a replaceable nose portion. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to the drawings, FIGS. 1 and 2 show a toolholder  1  comprising a jaw member  1 ′ having unitary construction with a rigid base jaw  2  and an upper clamping jaw  3  defining a longitudinally extending insert receiving slot  4  for receiving a double ended cutting insert  6 , for example, as illustrated and described in U.S. Pat. No. 5,156,502. The cutting insert  6  has an upper surface  10  which comprises has a central upper major clamping surface  7 , a leading inclined auxiliary clamping surface  8  and a trailing inclined auxiliary clamping surface  9 . As seen in FIG. 1, the auxiliary clamping surfaces  8 ,  9  are inclined in opposite senses and separate the upper major clamping surface  7  from corresponding front cutting edges  8   a ,  9   a , respectively. 
     The upper clamping jaw  3  has a tapering major leading portion  11  terminating in a leading nose portion  12  constituting a stopping member of the toolholder  1 . The upper clamping jaw  3  has an underside surface  13  with a major component surface  14  associated with the major leading portion  11  and a minor component surface  16  associated with its leading nose portion  12 , the major and minor component surfaces  14  and  16  being separated by a longitudinally extending recess  17  (see FIG. 3) and respectively adapted to abut against the cutting insert&#39;s major clamping surface  7  and auxiliary clamping surface  8 . 
     The major component surface  14  is substantially co-directional with the base jaw&#39;s upperside surface  18  and in practice is slightly rearwardly diverging at an angle of about 1° such that its leading portion  14 A contacts the cutting insert&#39;s clamping surface  7  before its trailing portion  14 B during the clamping of the cutting insert  6 . The minor component surface  16  is forwardly and downwardly directed with respect to the major component surface  14  towards the base jaw&#39;s upperside surface  18  at an obtuse angle necessarily less than the obtuse angle between the cutting insert&#39;s major clamping surface  7  and its auxiliary clamping surface  8 . The height of a leading portion  4   a  of the insert receiving slot  4  is a minimum at the leading nose portion  12 , namely, h 1  is less than h 2 .Thus, h 1  defines the height of the insert opening  4 ′ of the insert receiving slot  4 . 
     In this case, h 1  is less than the cutting insert&#39;s height h 3 , namely, the toolholder  1  is normally closed in the sense that it has to be opened for insertion of the cutting insert  6 . Thus, the leading nose portion prevents insertion of the insert into the insert receiving slot  4 , in the absence of a force enlarging the insert oppening  4 ′. The opening of the insert receiving slot  4  can be facilitated by, for example, an insert receiving slot opening key illustrated and described in U.S. Pat. No. 5,697,271, whose prongs are inserted in throughgoing bores  21  and  22  respectively formed in the base jaw  2  and the upper clamping jaw  3 . Thus, upper clamping jaw  3  is resiliently displaceable relative to the rigid base jaw  2 , upon application of a force. In order to reduce the opening force required to open the insert receiving slot  4 , a rearward extension  19  is provided in the toolholder  1 . 
     The clamping of the cutting insert  6  is now described with reference to FIGS.  4 A- 4 C. After insertion of the cutting insert  6 , the opening force as effected by the insert receiving slot opening key is relaxed, the minor component surface  16  abuts against the cutting insert&#39;s auxiliary clamping surface  8 , whereupon the natural resiliency of the leading nose portion  12  urges the cutting insert  6  against a back stopper  23  formed in the trailing portion  4   b  of the insert receiving slot  4 , thereby locating the cutting insert  6  in a predetermined position. Once stopped, the minor component surface  16  still abuts against the cutting insert&#39;s auxiliary clamping surface  8  whilst the major component surface  14  non-contactingly overlies the cutting insert&#39;s major clamping surface  7  (see FIG.  4 A). 
     Clamping of the cutting insert  6  is achieved by a clamping screw  24  received in a clamping screw bore  26  (shown in cross section in FIGS. 1 and 2) having an unthreaded portion  27  formed in the upper clamping jaw  3  and a threaded portion  28  formed in the base jaw  2 . On initial application of a clamping force by the clamping screw  24 , the leading nose portion  12  undergoes a slight elastic deformation whereby its minor component surface  16  is forcibly slided down the cutting insert&#39;s auxiliary clamping surface  8  until the major component surface&#39;s leading portion  14 A contacts the cutting insert&#39;s major clamping surface  7  (see FIG.  4 B). On continued application of the clamping force, the upper clamping jaw  3  undergoes a slight elastic deformation whereby its major component surface  14  is brought, at least along a major portion thereof, into clamping contact with the cutting insert&#39;s major clamping surface  7  (see FIG.  4 C). In this position, the leading nose portion  12  prevents the outward longitudinal displacement of the cutting insert  6  from the insert receiving slot  4  during a cutting operation by outwardly directed unseating forces acting co-directional with the slot  4 . 
     While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention can be made without departing from the scope of the claims appended hereto. For example, a leading nose portion  12  may be formed on an elongated member  29  secured to a clamping jaw&#39;s major leading portion  11  by a fastening screw  31  (see FIG.  5 ). Also, the invention can be applied to different types of toolholders without restriction to the manner in which a clamping force is applied, for example, it can be applied to a lathe toolholder illustrated and described in U.S. Pat. No. 5,697,271, a circular saw, and the like. Also, a toolholder can be normally open as opposed to normally closed, namely, a cutting insert can be normally inserted without application of an opening force.