Abstract:
A clamping device ( 1, 25, 35 ) for releasably clamping an insertion member ( 9, 27, 38 ) with a shank portion, the clamping device comprising a clamping member having an insertion bore ( 11, 26, 40 ) formed by the union of an access bore portion ( 19 A,  31 A,  41 A) and a gripping bore portion ( 19 B,  31 B,  41 B) for the free sliding insertion into and withdrawal from the shank portion in respect of the access bore portion and its clamping by a clamping surface of the gripping bore portion on its forced displacement thereinto from the access bore portion, the access and gripping bore portions having longitudinal axes ( 20 A,  20 B;  32 A,  32 B;  43 A,  43 B) spaced apart at least along a portion thereof.

Description:
FIELD OF THE INVENTION 
     The invention relates to clamping devices for releasably clamping an insertion member. 
     BACKGROUND OF THE INVENTION 
     A common application of clamping devices is the releasable clamping of a cutting tool (constituting an insertion member) in a toolholder (constituting a clamping device). In JP Unexamined Patent Publication 7-9212, there is illustrated and described a side lock toolholder having an insertion bore formed by the union of an access bore portion and a gripping bore portion, the access bore portion and the gripping bore portion sharing a common longitudinal axis and respectively having, a radius r′ and a radius r where r′&gt;R&gt;r and R is the radius of a cutting tool&#39;s right circular cylindrical shank. The access bore portion extends over an arc angle of almost 180° such that the cutting tool is freely slidingly insertable thereinto and withdrawable therefrom, the cutting tool being forcibly displaceable from the access bore portion to the gripping bore portion. Such a toolholder has a disadvantage that the arc angle of the gripping bore portion is less than 180° which reduces the gripping capability of the gripping bore portion which impairs stability during a cutting operation. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a clamping device for releasably clamping an insertion member, the clamping device comprising a clamping member having an insertion bore formed by the union of an access bore portion and a gripping bore portion for the free sliding insertion into and withdrawal from of the shank portion in respect of said access bore portion and its clamping by a clamping surface of said gripping bore portion on its forced displacement thereinto from said access bore portion 
     characterized in 
     said access and gripping bore portions having longitudinal axes spaced apart at least along a portion thereof. 
     In accordance with a first mode of implementation of the present invention, an insertion bore can be formed by the union of a pair of circular cross section access and gripping bore portions respectively having longitudinal axes which are parallel and offset one from another whereby an insertion member is sideways forcibly displaced from its access bore portion to its gripping bore portion. Preferably, an access bore portion has a right circular cylindrical shape whilst a gripping bore portion can have either a right circular cylindrical shape or a right circular frusto-conical shape. 
     In accordance with a second mode of implementation of the present invention, an insertion bore can be formed by the union of a pair of circular cross section access and gripping bore portions respectively having longitudinal axes which are intersecting whereby an insertion member is pivotally forcibly displaced from its access bore portion into its gripping bore portion. Preferably, an access bore portion has an inclined circular cylindrical shape whilst an gripping bore portion has a right circular cylindrical shape. 
     In both modes of implementation, the access bore portion has a diameter D 1  whose minimum value is greater than the diameter D 0  of an insertion members shank portion whilst the gripping bore portion has a maximum value D 2  which is less than D 0 . In addition, in the former mode of implementation, the two longitudinal axes are spaced apart at a distance D 3  whilst in the latter mode of implementation, the two longitudinal axes are inclined at an inclination angle γ. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to understand the invention and how it is used, preferred embodiments will now be described by way of non-limiting examples only, with reference to the accompanying drawing in which: 
     FIG. 1 is a partially cut-away perspective view of a toolholder clamp fixture for releasably clamping a toolholder; 
     FIGS. 2 and 3 are respectively transverse cross sectional views of the toolholder clamp fixture along a line I—I in FIG. 1 showing a toolholder in its initial insertion and subsequent clamped positions; 
     FIG. 4 is a perspective view of a toolholder for releasably clamping a cutting tool; 
     FIG. 5 is a top view of the toolholder of FIG. 4; 
     FIG. 6 is a longitudinal cross sectional view of the toolholder along a line II—II in FIG. 4; 
     FIG. 7 is a perspective view of a part of a toolholder and a wrench for releasing and tightening a clamping nut of the toolholder; 
     FIG. 8 is a perspective view of the wrench of FIG. 7; 
     FIGS. 9A-9C are respectively longitudinal cross sectional views of the wrench of FIG. 7 along lines III—III, IV—IV and V—V respectively in FIG. 8; 
     FIGS. 10A and 10B are respectively perspective and longitudinal cross sectional views of the wrench and toolholder of FIG. 7 with the toolholder in its initial insertion position; 
     FIGS. 11A and 11B are respectively perspective and longitudinal cross sectional views of the wrench and toolholder of FIG. 7 with the toolholder in its subsequent clamped position; and 
     FIGS. 12A and 12B are longitudinal cross sectional views of a side lock toolholder taken along a line II—II of FIG. 4 for radially and axially clamping a toolholder. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In FIGS. 1-3, a toolholder clamp fixture  1  (constituting a clamping device) includes an L-shaped mounting fame  2  having a horizontal mounting member  3  adapted for mounting the toolholder clamp fixture  1  on a workbench  4  by means of a pair of mounting screws  5 A and  5 B and an upright support  7  on which is mounted a toolholder clamp  8 . The toolholder clamp  8  is adapted for releasably clamping a toolholder  9  (constituting an insertion member) which can be any one of a wide range of different types of toolholders, for example, an HSK-type toolholder, having a right circular cylindrical shank portion  10  of diameter D 0 . The toolholder clamp  8  has an insertion bore  11  formed with an intermediate support shoulder  13  on which rests a lower abutment surface  14  of the shank portion  10 . The toolholder  9  is secured in an upper holding portion  15  of the insertion bore  11  atop the support shoulder  13  by means of a securing device  16  having a sleeve  17  for bearing against the shank portion  10 . 
     As shown in FIGS. 2 and 3, the upper holding portion  15  is formed by the union of right circular cylindrical access and gripping bore portions  19 A and  19 B respectively adjacent and remote from the securing device  16 . The access and gripping bore portions  19 A and  19 B respectively have diameters D 1  and D 2  and parallel longitudinal axes  20 A and  20 B offset one from the other by an offset distance D 3 . The inner surfaces of the access and gripping bore portions  19 A and  19 B intersect at junction lines (not shown) delimiting a generally semi cylindrical clamping surface  21  of the gripping bore portion  19 B having an arc angle greater than 180°. 
     In use, the securing device  16  is initially screwed outwardly from the toolholder clamp  8  such that the toolholders shank portion  10  can be readily slidingly inserted into its access bore portion  19 A (see FIG.  2 ). Thereafter, the securing device  16  is screwed into the toolholder clamp  8  such that its sleeve  17  presses against the toolholders shank portion  10  whereby it is clampingly received by the gripping bore portion  19 B on its forced expansion. Once clamped, a new cutting tool can be clamped into the toolholders cutting tool receiving bore  22  or, alternatively, a worn cutting tool can be replaced. Finally, the securing device  16  is screwed outwardly and the toolholder  9  is manually forced back into the access bore portion  19 A from which it can be readily slidingly withdrawn. Passage back into the access bore portion  19 A is typically evidenced by a click as the toolholder  9  passes past the junction lines between the access and gripping bore portions  19 A and  19 B. 
     With reference now to FIGS. 4-6, there is shown a side lock toolholder  25  (constituting a clamping device) of a two-piece construction with an outer tubular portion  25 A and an inner tubular core portion  25 B formed with an insertion bore  26  for releasably clamping a cutting tool  27  (constituting an insertion member) having a right circular cylindrical shank  28  by means of a transversely directed clamping screw  29  bearing thereagainst. The portions  25 A and  25 B are made of different materials so as to substantially dampen tool chatter, for example, the portion  25 A can be made from steel whilst the portion  25 B can be made from cast iron. 
     The insertion bore  26  is similar to the insertion bore  15  in that it is formed by the union of an access bore portion  31 A and a gripping bore portion  31 B respectively having longitudinal axes  32 A and  32 B parallel and offset to one another (see FIGS.  5  and  6 ). However, since the insertion bore  26  is closed at one end, its open end is more susceptible to forced expansion than its closed end such that if gripping bore portion  31 B is cylindrical in shape, then the gripping force as imparted thereby would not be uniform. In order to ensure that the right circular cylindrical shank  28  is gripped uniformly along the entire length of the gripping bore portion  31 B, the gripping bore portion  31 B has, instead of a cylindrical shape, a right circular frusto-conical shape. The cross-section of the gripping bore portion  31 B, taken perpendicular to the axis  32 B, is greater at its closed end than at its open end. The inner surfaces of the respective access and gripping bore portions  31 A and  31 B, intersect at junction fines  33 A and  33 B. By means of the frusto-conical shape described above, the same gripping capability is achieved along the entire length of the gripping bore portion, such that its clamping surface  33  has an equal arc angle at both ends when the cutting tool  27  is clamped in the gripping bore portion  31 B. 
     The use of the toolholder  25  for clamping a cutting tool  27  is similar to that of the toolholder clamp fixture  1 . By way of example, a toolholder  25  for use with a cutting tool  27  having a shank diameter D 0 =20.00 mm has an insertion bore  26  defined by the following insertion bore triplet D 1 =20.07 mm, D 2 =19.985 mm to D 2 =19.995 mm, D 3 =1 mm. In this case, when the cutting tool  27  is clamped in the gripping bore portion  31 B, the arc angle of the clamping surface  33  is about 181° at both ends of the gripping bore portion  31 B. 
     With reference now to FIGS. 7-11, a wrench  35  (constituting a clamping device) includes an elongated arm  36  terminating in a wrench head  37  adapted for releasing and tightening a right circular cylindrical clamping nut  39  (constituting a shank portion) of diameter D 0  of a toolholder  38  (constituting an insertion member). The wrench head  37  has an insertion bore  40  formed by the union of a right circular cylindrical gripping bore portion  41 B of diameter D 2  and an inclined circular cylindrical access bore portion  41 A of diameter D 1  whereby their respective longitudinal axes  43 B and  43 A define an inclination angle γ (see FIGS. 8 and 9A) therebetween. The longitudinal axes  43 A and  43 B intersect at the midpoints of the respective access bore portion  41 A and the gripping bore portion  41 B such that their surfaces intersect at a pair of crescent shaped junction lines  44 A and  44 B thereby defining a pair of crescent shaped surfaces  45 A and  45 B of the access bore portion  41 A. 
     In use, the wrench  35  is initially inclined relative to a vertically held toolholder  38  so that it can be slided thereonto so that the clamping nut  39  is nested within the access bore portion  41 A (see FIGS.  10 A and  10 B). Thereafter, the wrench  35  is rotated clockwise, as shown by the dashed arrow in FIG. 10B, relative to the toollholder  38  to forcibly insert the clamping nut  39  into the gripping bore portion  41 B, thereby clamping the wrench  35  on the clamping nut  39 . In this position, the wrench  35  is rotated around the axis  43 B thus releasing the clamping nut  39  (see FIGS.  11 A and  11 B). A worn cutting tool can then be replaced by a new cutting tool and the clamping nut  39  is tightened by a counter direction rotation of the wrench  35  relative to the toolholder  38  around the axis  43 B. Upon re-tightening the clamping nut  39 , the wrench  35  is counter clockwise rotated in a direction opposite to that shown by the dashed arrow in FIG.  10 B. As a result, the contact between the clamping nut  39  and the gripping bore portion  41 B is released and the wrench  35  can be upwardly removed from the toolholder  38 . 
     Various modifications and changes may be made in the configuration described above that come within the spirit of the invention. The invention embraces all such changes and modifications coming within the scope of the appended claims. For example, the longitudinal axes of an insertion bore&#39;s access bore portion and gripping bore portion do not have to lie on a single plane as long as an insertion member can be displaced therebetween. 
     In addition, as shown in FIGS. 12A and 12B, a side lock toolholder  25  is used with a cutting tool  42  formed with a recess  42 A having an inclined surface engaged by the toolholder&#39;s clamping screw  29  for simultaneously forcibly displacing the cutting tool  42  from its access bore portion  31 A to its gripping bore portion  31 B, by means of the radial component F ST  of the screw&#39;s clamping force F S , whilst axially urging the cutting tool  42  against the toolholder&#39;s leading abutment surface  30 , by means of the axial component F sa  of the screw&#39;s clamping force F S , thereby securely clamping the cutting tool  42 . The recess  42 A can be either relatively shallow (see FIG. 12A) whereby F 2 &gt;F 1  suitable, for example, for a turning cutting tool or, relatively deep (see FIG. 12B) whereby F 2 =F 1  suitable, for example, for a drilling or a milling cutting tool, where F 1  and F 2  are the axial abutting forces.