Patent Publication Number: US-7909314-B2

Title: Device for extending the clamping width for a clamping tool and combination of clamping tool and device for extending the clamping width

Description:
The present disclosure relates to the subject matter disclosed in German application number 10 2007 036 406.9 of Jul. 27, 2007, which is incorporated herein by reference in its entirety and for all purposes. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a device for extending the clamping width for a clamping tool. 
     The invention further relates to a combination of clamping tool and device for extending the clamping width. 
     Commercially available clamping tools and, in particular, clamps such as screw clamps, lever clamps or one-hand-operable clamps usually have a clamping width which may be too small for certain applications. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a device for extending the clamping width for a clamping tool is provided, which allows the clamping width of the clamping tool to be increased. 
     In accordance with an embodiment of the invention, a first rail is provided, to which a first workpiece abutment element is fixed, a second rail is provided, to which a second workpiece abutment element is fixed, a first bracket is provided, on which the first rail and the second rail are mounted for sliding displacement, and a second bracket is provided, on which the first rail and the second rail are mounted for sliding displacement, and the first bracket and the second bracket serve for engagement of the clamping tool thereon. 
     The first bracket and the second bracket each provide bearings and, in particular, slide bearings for the displaceable mounting of the first rail and the second rail. A clamping width as distance between the first workpiece abutment element and the second workpiece abutment element can be set by positioning the first rail and the second rail relative to each other. 
     The clamping tool engages the first bracket and the second bracket and clamps these to each other. The clamping of the first workpiece abutment element and the second workpiece abutment element to one or more workpieces lying between the first workpiece abutment element and the second workpiece abutment element is thereby achieved. An extension of the clamping width of the clamping tool is, in effect, achieved; the clamping tool need only have the clamping width for clamping the first bracket and the second bracket. The total clamping width with which one or more workpieces are then acted upon is the distance between the first workpiece abutment element and the second workpiece abutment element. The first bracket and the second bracket, which are clampable to each other, are force-introducing elements via which the clamping force of the clamping tool can be introduced into the extending device. The forces that are introduced are transmitted via the first rail and the second rail to the workpiece abutment elements. The forces can be passed out there in order to clamp one or more workpieces between the workpiece abutment elements. 
     It is expedient for the first rail and the second rail to be aligned parallel to each other. A mounting and guidance for displacement on both the first bracket and the second bracket are thereby achieved in a simple way. In particular, the first bracket and the second bracket can then be of the same design, so that the number of components required is minimized. 
     It is further expedient for the first rail and the second rail to be positioned next to each other at least over a portion thereof. This results in a simple and compact structure. 
     A distance between the first workpiece abutment element and the second workpiece abutment element is determined by the position to which the first rail and the second rail are displaced relative to the first bracket and the second bracket. These positions are adjustable, and, therefore, the clamping width is also adjustable. 
     It is provided that the first bracket and the second bracket are positioned between the first workpiece abutment element and the second workpiece abutment element. A “clamping width extension” is thereby achieved. The clamping width required for clamping the first bracket and the second bracket is smaller than the resulting clamping width of the extending device with which one or more workpieces are clampable. 
     In particular, an order of sequence is first workpiece abutment element, first bracket, second bracket, second workpiece abutment element. The aforementioned elements follow one after the other. 
     It is expedient for the first bracket to comprise at least one guide opening via which the first rail and the second rail are mounted for sliding displacement on the first bracket. A mounting, in particular, a mounting for sliding displacement, of the respective rail (in particular, second rail) on the first bracket is thereby achieved in a simple way. Furthermore, a blocking of the first bracket relative to the first rail is achieved in a simple way. 
     For the same reason it is expedient for the second bracket to comprise at least one guide opening via which the first rail and the second rail are mounted for sliding displacement on the second bracket. A mounting of the first rail for sliding displacement on the second bracket is thereby achieved. Furthermore, a blocking of the movability of the second rail on the second bracket is achieved. 
     In particular, the at least one guide opening of the second bracket and the at least one guide opening of the first bracket are orientated in alignment with each other. As a result, the device for extending the clamping width can be constructed in a simple and compact way. The first bracket and the second bracket can then basically be of the same design, so that the number of components required is minimized. 
     It is quite particularly advantageous for the first rail to comprise at least one blocking element which by abutting on the second bracket prevents the second bracket from being able to become detached from the first rail. The second bracket is thereby secured against loss. 
     In particular, the at least one blocking element is arranged at or in the proximity of an end of the first rail that faces away from the first workpiece abutment element. A maximization of the clamping width is thereby achievable. 
     It is then similarly expedient for the second rail to comprise at least one blocking element which by abutting on the first bracket prevents the first bracket from being able to become detached from the second rail. The first bracket is thereby secured against loss. 
     To obtain a large clamping width it is expedient for the at least one blocking element to be arranged at or in the proximity of an end of the second rail that faces away from the second workpiece abutment element. 
     In an advantageous embodiment, the first workpiece abutment element has an aperture by means of which an end of the second rail is able to be brought behind the first workpiece abutment element. An arrangement is thereby achieved, in which the end of the second rail is followed by the first workpiece abutment element and then the first bracket. A clamping width is thereby obtainable, which is smaller than the length of the second rail (less a corresponding length of the second workpiece abutment element). The device for extending the clamping width is, therefore, designed for variable use, and clamping widths can be infinitely set, which range from the sum width of the first bracket and the second bracket to almost the sum length of the first rail and the second rail less the sum width of the first bracket and the second bracket. 
     In particular, the aperture is a through-opening through which the second rail is adapted to extend. The second rail can then also be guided on the first workpiece abutment element if the clamping width is below a certain limit. 
     For the same reason it is expedient for the second workpiece abutment element to have an aperture by means of which an end of the first rail is able to be brought behind the second workpiece abutment element. When this end lies behind the second workpiece abutment element, the order of sequence is then end of the first rail, second workpiece abutment element, second bracket. 
     In a corresponding manner, this aperture is then advantageously a through-opening through which the first rail is adapted to extend. 
     It is expedient for the first rail and/or the second rail to be fluted on an upper side and/or lower side. A blocking effect is thereby achieved in a simple way in cooperation with a blocking device of the first bracket and the second bracket by canting of a corresponding blocking element (in particular, a blocking plate). 
     In a variant of an embodiment, a fixing device is arranged on the first workpiece abutment element for fixing the second rail to the first workpiece abutment element. For example, the fixing device is designed as clamping device. A clamped position of the extending device can thereby be secured. 
     For the same reason, a fixing device may be arranged on the second workpiece abutment element for fixing the first rail to the second workpiece abutment element. 
     It is quite particularly advantageous for the first bracket to have a blocking device by means of which the displacement of the first bracket away from the first workpiece abutment element on the first rail is blockable. Accordingly, the movement of the first bracket towards the second bracket is blockable by the blocking device. As a result, upon exerting a clamping force between the first bracket and the second bracket, the first workpiece abutment element and the second workpiece abutment element are clamped to one or more workpieces lying between these. 
     In particular, the blocking device is so designed that its blocking action is releasable. A clamped position can thus be released. 
     It is further expedient for the blocking device to be so designed that the second rail is freely displaceable on the first bracket, more particularly, in any position of the blocking device. This enables, upon exerting a clamping force on the first bracket and the second bracket, by means of which these are pressed towards each other, a corresponding displacement of the second rail in order to press the second workpiece abutment element against a workpiece. 
     It is further expedient for the blocking device to be so designed that it has no blocking effect for the movement of the first bracket towards the first workpiece abutment element. This results, for example, in a simple adjustability of the bracket position. 
     For the aforesaid reasons it is then advantageous for the second bracket to have a blocking device by means of which the movement of the second bracket away from the second workpiece abutment element on the second rail is blockable. In particular, the blocking device is so designed that its blocking action is releasable. It is then further advantageous for the blocking device to be so designed that the first rail is freely displaceable on the second bracket. 
     For the aforesaid reasons it is then also purposeful for the blocking device to be so designed that it has no blocking effect for the movement of the second bracket towards the second workpiece abutment element. 
     In a constructionally simple embodiment, the blocking device has a blocking plate with an opening through which the respective rail extends. A blocking of the movability of the corresponding rail at least in one direction is then achieved by correspondingly inclining the blocking plate. It is possible for both the first rail and the second rail to extend through the opening. 
     In particular, in a blocking position the blocking plate is so inclined towards the respective rail and in canted engagement with it that the corresponding movability of the respective rail is blocked. A blocking of the movability in one direction is thereby obtained in a simple way. The movability in the other direction is not blocked by this. The blocking position can be released in a simple way by altering the inclination. 
     It is further expedient for the blocking plate to be so arranged for movement on the respective bracket that its inclination towards the respective rail is adjustable. For example, the blocking plate is arranged for pivotal movement. A blocking position can be released in a simple way by adjusting the inclination and, in particular, by reducing an angular position with an acute angle to the corresponding rail. 
     It is expedient for the blocking plate to be acted upon by a spring, the force of which presses the blocking plate into a blocking position, and for the blocking plate to have to be moved against the force of the spring in order to release the blocking position. A blocking position is thereby automatically secured by the action of the spring. The spring force must be overcome in order to eliminate the blocking force. 
     In terms of construction and manufacturing technology it is expedient for the first opening to have a first region for the first rail and a second region for the second rail, and for that region which serves to block the movability of the corresponding rail to have smaller height dimensions. A compact structure is thereby obtained. Both the first rail and the second rail extend through the opening and by corresponding design of the blocking plate a blocking action is achieved for only one of the rails, while the other rail is freely movable relative to the respective bracket. In particular, the first rail is freely movable on the second bracket, and the second rail is freely movable on the first bracket. The blocking device on the first bracket acts upon the first rail, and the blocking device on the second bracket acts upon the second rail. 
     It is expedient for the first bracket to have a first abutment surface, and for the second bracket to have a second abutment surface, with the first abutment surface and the second abutment surface facing away from each other. In a simple way, a clamping tool such as a clamp can then act upon the first bracket and the second bracket and clamp these to each other and hence bring about a clamping of the first workpiece abutment element and the second workpiece abutment element on one or more workpieces. 
     It is further expedient for the first workpiece abutment element to have a first abutment surface and for the second workpiece abutment element to have a second abutment surface, with the first abutment surface and the second abutment surface facing each other. One or more workpieces can then be clamped between the first abutment surface and the second abutment surface. 
     It is expedient for abutment surfaces of the first workpiece abutment element and the second workpiece abutment element and abutment surfaces of the first bracket and the second bracket to lie on different sides in relation to the rails. Consequently, the clampability of the first bracket and the second bracket on a clamping tool is not impeded by the abutment of the abutment surfaces of the workpiece abutment elements on one or more workpieces. 
     In an advantageous embodiment, the first bracket and the second bracket each have openings which are open on three sides and are orientated towards each other. In particular, the openings are open upwards (in a direction away from the rails) and open forwards and rearwards (in a direction parallel to a longitudinal direction of the rails). Consequently, a profiled rail or a slide rail of a clamping tool can be inserted into the openings. The clamping tool is thus secured at the sides against slipping when it exerts a clamping force on the first bracket and the second bracket. 
     In accordance with the invention, a combination of clamping tool and device for extending the clamping width is also provided. This comprises a clamping tool and a device according to the invention for extending the clamping width. 
     The clamping width of the clamping tool can be increased by the solution according to the invention. 
     In particular, the clamping tool is a clamp. Different clamps such as screw clamps, lever clamps, one-hand-operable clamps, etc. may be used. 
     It is expedient for the clamping tool to be operable with one hand. With one-hand-operability, the necessary clamping force can be exerted with one hand by, for example, a lever being operated with one hand. This makes it easy to use. 
     The following description of preferred embodiments serves to explain the invention in greater detail in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective representation of an embodiment of a device according to the invention for extending the clamping width; 
         FIG. 2  shows a sectional view of the device according to  FIG. 1  for extending the clamping width; and 
         FIG. 3  shows the device according to  FIG. 1  for extending the clamping width with a clamping tool positioned thereon. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of a device according to the invention for extending the clamping width, shown in  FIGS. 1 to 3  and designated therein by reference numeral  10 , comprises a first rail  12  and a second rail  14 . The first rail  12  and the second rail  14  are basically of the same design. They have a cross section which has an essentially rectangular envelope. The first rail  12  and the second rail  14  each have opposed broad sides  16   a ,  16   b  and opposed narrow sides  18   a ,  18   b  (upper side and lower side) orientated transversely and, in particular, vertically thereto. In one embodiment, they have a fluting  19  on each of the narrow sides  18   a ,  18   b . The first rail  12  and the second rail  14  each extend in a longitudinal direction, to which the broad sides  16   a ,  16   b  and the narrow sides  18   a ,  18   b  run parallel. The first rail  12  and the second rail  14  are straight. 
     The first rail  12  and the second rail  14  are made, in particular, from a metallic material. They serve as slide rails, as will be explained in greater detail hereinbelow. 
     A first workpiece abutment element  20  is fixed to the first rail  12 . In principle, it is possible for the fixing to be releasable, so that the fixed position of the first workpiece abutment element  20  on the first rail  12  is adjustable. Preferably, the first workpiece abutment element  20  is fixed at or in the proximity of a first end  22  of the first rail  12 . 
     The first workpiece abutment element  20  serves for abutment on a workpiece. It is of bracket-shaped construction and projects with a first abutment surface  24  for a workpiece away from the narrow side  18   b . If the narrow side  18   a  is regarded as upper side and the narrow side  18   b  as lower side of the first rail  12 , then the first workpiece abutment element  20  projects with the first abutment surface  24  downwards. 
     The first workpiece abutment element  20  is made of, for example, a plastic material. It comprises an abutment element body  26  which has a bent outer side  28 . An opposed inner side  30  is, in particular, of flat construction. Arranged on the inner side  30  is an abutment portion  32  on which the first abutment surface  24  is formed. The abutment portion  32  is, for example, pushed onto the abutment element body  26 . 
     An aperture  34  is formed on the abutment element body  26 . The first rail  12  extends in this aperture and is fixed to the first workpiece abutment element  20 . A corresponding fixing device described further on in conjunction with the fixing of a second workpiece abutment element  36  to the second rail  14  is provided for this purpose. 
     The abutment element body  26  has a further aperture  38  which, in particular, is constructed as through-opening. The second rail  14  is adapted to extend through this aperture  38  and to be guided on the first workpiece abutment element  20 . The aperture  38  serves for mounting the second rail  14  for sliding displacement on the first workpiece abutment element  20 . 
     The aperture  34  by means of which the first rail  12  is fixed to the first workpiece abutment element  20  and the aperture  38  for guiding the second rail  14  lie parallel next to one another. 
     The second rail  14  is positioned parallel to the first rail  12 . It also has narrow sides  40   a  (upper side) and  40   b  (lower side). The narrow side  40   a  is arranged in alignment with the narrow side  18   a  of the first rail  12 . The narrow side  40   b  is arranged in alignment with the narrow side  18   b . Furthermore, the second rail  14  has broad sides  42   a ,  42   b  which run substantially parallel to one another and parallel to the broad sides  16   a ,  16   b  of the first rail  12 . 
     The second workpiece abutment element  36  is basically of the same design as the first workpiece abutment element  20 . It has a second abutment surface  44  which faces the first abutment surface  24 . A connecting line between the first abutment surface  24  and the second abutment surface  44  lies parallel to the first rail  12  and to the second rail  14 . 
     The second workpiece abutment element  36  is fixed to the second rail  14  by means of a fixing device  46 . This comprises, for example, a clamping screw by means of which the second rail  14  is clampable to an abutment element body of the second workpiece abutment element  36 . 
     The second workpiece abutment element  36  also has apertures corresponding to the apertures  34  and  38 . The second workpiece abutment element  36  is arranged mirror-symmetrically with the first workpiece abutment element  20  in relation to a center plane. Accordingly, the apertures  34  and  38  on the first workpiece abutment element  20  are arranged mirror-symmetrically with the corresponding apertures on the second workpiece abutment element  36 . 
     The first rail  12  is adapted to extend through an aperture on the second workpiece abutment element  36  corresponding to the aperture  38 . If it extends through this, it projects with a second end  48  facing away from the first end  22  beyond the second workpiece abutment element  36 , i.e., projects behind this. Consequently, the second workpiece abutment element  36  is then arranged between the first end  22  and the second end  48  of the first rail  12 . The corresponding aperture is of such construction that the first rail  12  can be pulled out of the corresponding aperture on the second workpiece abutment element  36 . Depending on the position of the first rail  12  and the second rail  14  in relation to one another, the first rail  12  extends through or does not extend through the second workpiece abutment element  36 . 
     The second rail  14  is fixed at or in the proximity of a first end  50  on the second workpiece abutment element  36 . (In principle, the fixing may be releasable, so that the position of the second workpiece abutment element  36  on the second rail  14  is alterable.) With a second end  52  located opposite the first end  50 , the second rail  14  can extend through the aperture  38  on the first workpiece abutment element  20 . This position is shown in  FIG. 1 . In this case, the first workpiece abutment element  20  lies between the first end  50  and the second end  52  of the second rail  14 . 
     It is also possible, depending on the position of the first rail  12  and the second rail  14  relative to each other, for the second rail  14  to project out of the aperture  38  of the first workpiece abutment element  20  and to lie between the first workpiece abutment element  20  and the second workpiece abutment element  36 . 
     In the event the first rail  12  extends in the corresponding aperture of the second workpiece abutment element  36 , the latter forms a slide bearing for the first rail  12 . In the event the second rail  14  extends in the aperture  38  of the first workpiece abutment element  20 , the latter forms a bearing for the second rail  14 . 
     The first rail  12  is linearly displaceable in a direction of displacement/opposite direction  54  relative to the second workpiece abutment element  36  and on (if it extends in it) the second workpiece abutment element  36 . This direction  54  is parallel to the longitudinal direction of the first rail  12  (and the second rail  14 ). 
     Furthermore, this direction  54  is transverse and, in particular, vertical to the first abutment surface  24  and the second abutment surface  44 . The second rail  14  is linearly displaceable in a direction of displacement/opposite direction  56  relative to the first workpiece abutment element  20  and on (if it extends in it) the first workpiece abutment element  20 . This direction  56  is parallel to the direction  54  or coincides with it. 
     Arranged, in a variant of an embodiment, on the first workpiece abutment element  20  is a fixing device by means of which the second rail  14  is releasably fixable (not shown in the drawings) to the first workpiece abutment element  20 . For example, the fixing device is constructed as clamping device. By means of this, a certain position of the second rail  14  relative to the first workpiece abutment element  20  or a certain position of the first workpiece abutment element  20  and, in particular, a clamped position, can be secured. Alternatively or additionally, it is also possible for a fixing device to be arranged on the second workpiece abutment element  36  to releasably fix the first rail  12  on the second workpiece abutment element  36 , in particular, in order to secure a clamped position. 
     Arranged on the first rail  12  and the second rail  14  are a first bracket  58  and a second bracket  60 . The first bracket  58  and the second bracket  60  are positioned between the first workpiece abutment element  20  and the second workpiece abutment element  36 . The order of sequence is first workpiece abutment element  20 , first bracket  58 , second bracket  60 , second workpiece abutment element  36  in relation to a longitudinal direction of the first rail  12  or the second rail  14 . 
     The first bracket  58  and the second bracket  60  are force-introducing elements. Via these, a force and, in particular, a clamping force can be introduced by means of a clamping tool. This introduced force, which is transmitted via the first rail  12  to the second rail  14 , can then be passed out via the workpiece abutment elements  20  and  36  to one or more workpieces in order to clamp these. 
     The first bracket  58  is formed by a bracket body  62 . The second bracket  60  is basically of the same design as the first bracket  58  and is arranged mirror-symmetrically with the first bracket  58 . The bracket body  62  of the first bracket  58  and the second bracket  60  is preferably made of a plastic material. 
     The first bracket  58  has a first abutment surface  64  for a clamping tool  66  ( FIG. 3 ). The second bracket  60  has a second abutment surface  68  for the clamping tool  66 . The first abutment surface  64  and the second abutment surface  68  face away from each other. The first abutment surface  64  faces the first end  22  of the first rail  12 . The second abutment surface  68  of the second bracket  60  faces the first end  50  of the second rail  14 . 
     The first abutment surface  64  and the second abutment surface  68  are preferably of flat construction. 
     With their respective bracket body  62 , the first bracket  58  and the second bracket  60  extend on a side, in relation to the first rail  12  and the second rail  14 , that faces away from that side in which the first workpiece element  20  and the second workpiece element  36  extend. The first abutment surface  64  and the second abutment surface  68  lie on a different side than the first abutment surface  24  and the second abutment surface  44  of the first workpiece abutment element  20  and the second workpiece abutment element  36 . Accordingly, the first abutment surface  64  and the second abutment surface  68  lie on an upper side of the device  10  for extending the clamping width if that side on which the first abutment surface  24  and the second abutment surface  44  lie is a lower side. 
     The first abutment surface  64  and the second abutment surface  68  lie transversely and, in particular, at least approximately vertically, to the first rail  12  and the second rail  14 . On a side  70  opposite the respective abutment surface  64 ,  68 , the first bracket body  58  and the second bracket body  60  are of inclined configuration, and this side lies at an acute angle to the first rail  12  or the second rail  14 , which is, for example, in the order of magnitude of between 10° and 20°. 
     The first bracket  58  has a first bearing device  72  for slidable mounting of the first rail  12  and the second rail  14 . In a corresponding manner, the second bracket  60  has a second bearing device  74  for slidable mounting of the first rail  12  and the second rail  14 . (The bearing devices  72 ,  74  may also be seen as slide bearing devices for slidable mounting of the first bracket  58  and the second bracket  60  on the first rail  12  and the second rail  14 .) 
     To form the first bearing device  72 , the first bracket  58  has a guide opening  76  through which the first rail  12  and the second rail  14  extend. In a corresponding manner, the second bracket  60  has a guide opening  78  through which the first rail  12  and the second rail  14  also extend. In the described embodiment, a common guide opening  76  is provided on the bracket body  62  of the first bracket  58  for the first rail  12  and the second rail  14 . The guide opening  78  on the second bracket  60  is of the same design as the guide opening  76  on the first bracket  58 . It is also possible for separate guide openings to be provided for the first rail  12  and the second rail  14 . 
     A blocking element  80  is arranged on the first rail  12  at or in the proximity of the second end  48 . This is formed, for example, integrally on the rail  12  by an elevation. The blocking element is so designed that upon striking the second abutment surface  68  of the second bracket  60 , it blocks the further movability of the first rail  12  with respect to the second bracket  60  towards the first bracket  58 . As a result, the first rail  12  cannot be drawn completely through the guide opening  78  of the second bracket  60  and cannot extend completely out of it. The second bracket  60  is thereby prevented from being pulled off the first rail  12 , and the second bracket  60  is secured against loss on the first rail  12 . 
     The aperture on the second workpiece abutment element  36  corresponding to the aperture  38  is so configured that the first rail  12  can be pushed through with the blocking element  80 , i.e., the blocking element  80  does not abut on the first workpiece abutment element  20 . 
     The aperture on the second workpiece abutment element  36  which corresponds to the aperture  34  and via which the second workpiece abutment element  36  is fixedly secured to the second rail  14  may have smaller height dimensions (between the narrow sides  40   a  and  40   b ) than the aperture corresponding to the aperture  38  so as to enable a firm holding of the second workpiece abutment element  36  on the second rail  14 . 
     In a corresponding manner, the second rail  14  has a blocking element  82  which extends beyond the narrow side  40   a  to such an extent that, when the blocking element  82  abuts on the first abutment surface  64  of the first bracket  58 , a further sliding displacement of the first bracket  58  and the second rail  14  (in relation to a direction of movement of the first bracket  58  away from the second bracket  60 ) is blocked. The first bracket  58  is thereby secured against loss. 
     As explained hereinabove in conjunction with the second workpiece abutment element  36 , the aperture  38  is so configured that the second rail  14  can extend fully with the blocking element  82  through the aperture  38 . 
     The first bracket  58  and the second bracket  60  each have a blocking device  84  by means of which the displaceability of the first bracket  58  and the second bracket  60  in a certain direction is blockable. The blocking devices  84  of the first bracket  58  and the second bracket  60  are basically of the same design, and the blocking directions are opposed to each other. By means of the blocking device  84  of the first bracket  58 , its movement towards the second bracket  60  on the first rail  12  and the second rail  14  parallel to the direction  54  or  56  is blockable. By means of the corresponding blocking device of the second bracket  60 , its movement towards the first bracket  58  along the direction  54  or  56  is blockable. The blocking device  84  is so configured that the blocking is releasable. The respective bracket  58  or  60  is displaceable on the first rail  12  and the second rail  14  without any blocking action (blocking effect) in the direction opposite to the blocking direction. 
     The blocking device  84  comprises a blocking plate  86  which is arranged for movement and, in particular, pivotal movement on the bracket body  62  of the first bracket  58 . The blocking plate  86  has an opening  88  configured as through-opening. The first rail  12  and the second rail  14  extend through this opening  88 . The opening  88  is so configured that by means of the blocking plate  86  a blocking action is achievable for the movement of the first bracket  58  towards the second bracket  60 , but the second rail  14  is freely displaceable (so long as the blocking element  82  does not abut on the first abutment surface  64 ) in each position of the blocking plate  86  on the first bracket  58 . The opening  88  has a first region  90   a  and a second region  90   b  for this purpose. The first rail  12  extends through the first region  90   a , and the second rail  14  extends through the second region  90   b . The first region  90   a  has a smaller height than the second region  90   b . The heights may be so selected that in a blocking position the blocking plate  86  is in canted engagement with the first rail  12  via its fluting  19  so as to block the movement of the first bracket  58  towards the second bracket  60 . The second region  90   b  is so configured that irrespective of the position of the blocking plate  86 , the second rail  14  is freely displaceable on the first bracket  58 . 
     A channel is formed in the solid material of the bracket body  62  to produce to the guide opening  76 . In the area of the blocking plate  86 , this channel is open at the sides via an opening  92 . As a result, the first rail  12  (and also the second rail  14 ) is not covered by channel walls in the area of the opening  92 , and the blocking plate  86  can act upon the first rail  12 . 
     The blocking plate  86  is acted upon by a spring. For this purpose, a pressure spring  94  is arranged beneath the first rail  12  and the second rail  14  on the first bracket  58 . The pressure spring  94  is arranged, in relation to the first rail  12  and the second rail  14 , on that side on which the first abutment surface  24  of the first workpiece abutment element  20  is also located. 
     The pressure spring  94  is aligned at least approximately parallel to the first rail  12  and the second rail  14 . It exerts a pressing force on the blocking plate  86 , by means of which the blocking plate  86  is pressed in a direction away from the second bracket  60  against an abutment region  96 . This abutment region  96  is orientated obliquely at an acute angle to the longitudinal direction of the first rail  12  and the second rail  14 . A typical order of magnitude of an angle  98  ( FIG. 2 ), in which a blocking position is reached, is, for example, 15°. The angle depends upon the surface structure of a rail and the point at which the force is introduced. 
     In an abutment region  100 , the blocking plate  86  abuts on the bracket body  62 . Formed at the abutment region  100  in the bracket body  62  is a slot-shaped opening  102  through which the blocking plate  86  extends and projects beyond the side  70  of the first bracket  58 . Via the projecting portion, the blocking plate  86  has an operative portion  104  to which an operator has access. 
     The blocking plate  86  is shown in a blocking position  106  in  FIGS. 1 to 3 . The blocking plate  86  is orientated at the angle  98  at an incline to the first rail  12  and is in canted engagement with it. The movement of the first bracket  58  towards the second bracket  60  is thus blocked. The second rail  14  is freely displaceable in relation to the first bracket  58 . 
     To release the blocking position, the blocking plate  86  is moved and, in particular, pivoted towards the first bracket  58  by pressing on the operative portion  104 . As a result, the blocking plate  86  moves in the area of the opening  88  in a pivoting direction  108  ( FIG. 2 ). The canting of the blocking plate  86  on the first rail  12  is thereby released, and the first bracket  58  can be displaced on the first rail  12 . 
     A blocking device of the second bracket  60  is basically of the same design as the blocking device  84 , and this blocking device  110  of the second bracket comprises a blocking plate  112 . This blocking plate  112  is designed in analogy with the blocking plate  86 , and the blocking plate  112  has a corresponding opening which ensures that in a blocking position the blocking plate  112  is in canted engagement with the second rail  14 , and the second bracket  60  is unable to move towards the first bracket  58 . In each position of the blocking plate  112 , the first rail  12  is freely movable. In a blocking position of the blocking plate  112 , the blocking plate  112  is orientated at an angle of the same amount in relation to the second rail  14  as the blocking plate  86  in relation to the first rail  12 . However, the sign of the angle is reversed. Accordingly, to release the blocking position, the blocking plate  112  must be pressed in the direction of the second bracket  60 , which causes the corresponding opening to be pivoted in the pivoting direction  114 , which is the opposite direction to the pivoting direction  108 . 
     The blocking plates  86  and  112  are, for example, flat metal strips. 
     The device according to the invention for extending the clamping width operates as follows: 
     The clamping width S 2  of the device  10  for extending the clamping width is the distance between the first abutment surface  24  and the second abutment surface  44 . This distance is set by the position of the first rail  12  and the second rail  14  relative to each other. The first rail  12  and the second rail  14  are mounted on both the first bracket  58  and the second bracket  60 . These provide the corresponding slide bearings for mounting the first rail  12  and the second rail  14  for sliding displacement. The rails  12  and  14  are permanently mounted so as to lie next to each other on the first bracket  58  and on the second bracket  60 . Owing to the blocking elements  80  and  82 , the first rail  12  and the second rail  14  are unable to become detached from the first bracket  58  and the second bracket  60 . 
     If the clamping width is below a minimum limit (distance between the first abutment surface  24  and the second abutment surface  44 ) the first rail  12  may also be guided for sliding displacement on the second workpiece abutment element  36  and/or the second rail  14  may be guided for sliding displacement on the first workpiece abutment element  20 . 
     When the blocking position of the first bracket  58  and the second bracket  60  is set, the alteration of the clamping width is then carried out by setting the relative position of the rails  12  and  14 , the distance between the first abutment surface  24  and the second abutment surface  44  being determined by the distance of the second end  48  of the first rail  12  from the second workpiece abutment element  36  and the distance of the second end  52  of the second rail  14  from the first workpiece abutment element  20 . 
     The settability of the relative position between the first rail  12  and the second rail  14  can be impeded by the first bracket  58  and/or the second bracket  60  when the blocking element  82  abuts on the first bracket  58  and/or the blocking element  80  abuts on the second bracket  60 . 
     The position of the first bracket  58  and the second bracket  60  is, in principle, freely adjustable on the first rail  12  and the second rail  14 , the outer limits to the one side being the first workpiece abutment element  20  or the blocking element  82 , depending on whether the first workpiece abutment element  20  or the blocking element  82  lies closer to the first bracket  58 , and to the other side the second workpiece abutment element  36  or the blocking element  80 , depending on whether the workpiece abutment element  36  or the blocking element  80  lies closer to the second bracket  60 . 
     The position of the first bracket  58  and the second bracket  60  relative to each other and hence the distance S 1  (taken as the distance between the first abutment surface  64  and the second abutment surface  68 ) is, in principle, optionally adjustable within the aforesaid limits. The movement of the first bracket  58  towards the second bracket  60  is blocked and the movement of the second bracket  60  towards the first bracket  58  is blocked by the respective blocking device  84  and  110  when these are in their respective blocking position. 
     In one embodiment, the blocking devices  84  and  110  are so configured that the movement of the first bracket  58  away from the second bracket  60  and the movement of the second bracket  60  away from the first bracket  58  are not blocked. 
     The clamping tool  66  can engage the first bracket  58  and the second bracket  60  with a clamping width S 1  ( FIG. 3 ). The clamping width S 1  may be smaller and, in particular, considerably smaller than the clamping width S 2 . (For illustrative reasons, S 2  is shown only slightly larger than S 1  in the Figures.) In the solution according to the invention, a larger ratio of S 2  to S 1  is achievable than that shown. In a concrete embodiment, a maximum clamping width S 2  of approximately 1.80 m is achievable with a minimum clamping width S 1  of approximately 10 cm. An “extension transmission ratio” in the order of magnitude of 20 is thereby obtained. 
     The first abutment surface  24  and the second abutment surface  44  are placed against one or more workpieces which are to be clamped together. To do so, the first rail  12  and the second rail  14  (guided via the first bracket  58  and the second bracket  60 ) are displaced relative to each other such that the workpiece or workpieces is or are clamped between the first workpiece abutment element  20  and the second workpiece abutment element  36 . The first bracket  58  and the second bracket  60  are brought into position (or have previously been brought into position) on the first rail  12  and the second rail  14 . Via a first abutment element  116  of the clamping tool  66 , which is placed against the first abutment surface  64  of the first bracket  58 , and a second abutment element  118  of the clamping tool  66 , which is placed against the abutment surface  68  of the second bracket  60 , a clamping force is exerted, which endeavors to move the first bracket  58  and the second bracket  60  relative to and towards each other. The second workpiece abutment element  36  is pressed by this clamping force against a workpiece. Upon movement of the second bracket  60  towards the first bracket  58 , the second rail  14  with the second workpiece abutment element  36  fixed thereto is taken along if the blocking device  110  is in its blocking position. Via a movement of the first bracket  58  towards the second bracket  60  the first rail  12  with the first workpiece abutment element  20  is also taken along by the clamping force, and the first workpiece abutment element  20  is pressed against a workpiece. By securing the clamped position of the clamping tool  66  the clamped position of the first workpiece abutment element  20  and the second workpiece abutment element  36  is secured. 
     Owing to the relative movement of the first bracket  58  and the second bracket  60  towards each other being blocked, a clamping force that has been introduced (with the brackets  58  and  60  as force-introducing elements) can be passed through the intermediary of the first rail  12  and the second rail  14  by the workpiece abutment elements  20  and  36  onto one or more workpieces. 
     The clamping tool  66  is, in particular, a clamp. This may comprise a slide rail  120  on which the second abutment element  118  is guided for sliding displacement. A corresponding mechanism ensures provision of the clamping force. 
     It is advantageous for the clamping tool  66  to be designed as a one-hand-operable clamp which is actuatable with one hand with a hand grip  122  for actuation of the clamping force. 
     In the embodiment shown, the clamping tool  66  has a counter grip  124  which is orientated at least approximately along the slide rail  120 . The slide rail  120  may be mounted for sliding displacement on the counter grip  124 . 
     Such a clamping tool is described in DE 10 2004 013 066 B4, to which reference is explicitly made. Furthermore, a corresponding clamping tool is shown in Community designs Nos. 000300009-0001 to -0008. 
     It may be provided that the first bracket  58  and the second bracket  60  each have a slot-shaped opening  126   a ,  126   b . The profiled rail and, in particular, slide rail  120 , of the clamping tool  66  may be placed in these slot-shaped openings  126   a ,  126   b , which extend from the respective abutment surface to the opposite side  70 . The clamping tool  66  is thereby secured against slipping sideways. (A position in which the slide rail  120  is not placed in the openings  126   a ,  126   b  is shown in  FIG. 3 .)