Patent Publication Number: US-2004045425-A1

Title: Fixing for a saw blade of a jigsaw

Description:
[0001] The present invention relates to a fixing for a saw blade of a jigsaw, comprising a fixing element with a receiving cavity for receiving the end of the saw blade for fixedly clamping and clamping means which engage on the saw blade and which are situated between the saw blade and a wall of the receiving cavity running obliquely in the direction of the saw blade, and which means have a substantially circular cross-section.  
       [0002] Such a fixing is connected to the reciprocating drive rod of a jigsaw.  
       [0003] A fixing of the above stated type is known from EP 0 792 713 A2. The clamping means are formed herein by a pin which engages on an edge of the saw blade and which lies between the saw blade and the oblique side of the receiving cavity in order to receive the end of the saw blade. A self-clamping force is generated using such a construction. In order to release this clamping force and remove the saw blade from the fixing, a lever engaging on the pin is tilted counter to the bias of springs engaging on the pin. During tilting of the lever the pin is displaced along the obliquely running wall of the receiving cavity away from the saw blade. For release of the saw blade the sliding friction resulting from the clamping force must be overcome.  
       [0004] The object of the present invention is to provide a fixing of a saw blade for a jigsaw with an improved construction. For this purpose the fixing is characterized in that the clamping means consist of two pairs of clamping members with a substantially cylindrical cross-section which lie at a mutual distance and each of which is situated on either side of the saw blade. This ensures that the saw blade is also retained in the fixing element transversely of its wide sides. In addition, the one pair of clamping members can take over the clamping action of the other pair of clamping members when this latter is elastically deformed by tensile strain and pressure load on the saw blade. This is a self-clamping construction, i.e. the greater the force exerted on the saw blade during sawing, the greater the clamping force. An additional effect is that to release the saw blade the user only has to overcome a relatively small friction force resulting from rolling friction on either side. It is noted that a fixing for a saw of a fretsaw is known from JP 05-253738. The fixing contains two rollers which co-act with a V-shaped groove to clamp the saw. The saw is clamped at both ends in such a fixing. The saw is placed with bias in the fretsaw and is only placed under strain of tension during sawing.  
       [0005] The clamping members preferably engage on the wide sides of the saw blade. In addition to the surface pressure on the saw blade being relatively low, use can be made of the standardized dimension in width direction of the wide sides of commercially available saw blades. The saw blade is retained in width direction in the receiving cavity, while the difference in thickness can be offset by the clamping member displaceable along the oblique wall of the receiving cavity.  
       [0006] In preference the clamping members of a pair are further situated at the same height relative to the fixing element so that the saw blade is not under strain of bending by the clamping members, and the chance of the saw blade breaking is minimized.  
       [0007] In a particularly advantageous embodiment according to the invention, the fixing element for receiving the or each pair of clamping members comprises a V-shaped groove which defines the oblique walls of the receiving cavity. Both clamping members are hereby clamped on both sides of the saw blade between a wall running obliquely to the saw blade and the saw blade, which results in a favourable symmetrical load on the saw blade.  
       [0008] Unlocking means are preferably further provided for removing the clamping means from the saw blade. In a preferred embodiment the unlocking means comprise an actuating element under bias which can be displaced relative to the fixing element for co-displacement of the clamping members.  
       [0009] The clamping members are preferably formed by pins.  
       [0010] The invention finally relates to a jigsaw provided with a fixing for a saw blade according to the present invention. 
     
    
    
     [0011] The invention will be further elucidated with reference to the annexed drawings. In the drawings:  
     [0012]FIG. 1 shows a perspective view of a jigsaw provided with a fixing for a saw blade according to the present invention;  
     [0013]FIG. 2 shows a detail view of a fixing according to a first embodiment of the invention;  
     [0014]FIG. 3 shows a detail view of a fixing according to a second embodiment of the invention, and  
     [0015]FIG. 4 shows a detail view of a fixing according to a third embodiment of the invention. 
    
    
     [0016] The jigsaw shown in FIG. 1 is provided with a housing  1 , a part of which is broken away in the drawing to provide a view of the interior of the jigsaw. In housing  1  is arranged an electric motor  2  for driving a drive rod  3  which bears on its lower end a fixing  4  for a saw blade  5 . Electric motor  2  is provided with a motor shaft  6 . Between motor shaft  6  and drive rod  3  for saw blade  5  are arranged converting means  7  for converting the rotating movement of electric motor  2  into a reciprocating movement of saw blade  5 . Converting means  7  comprise a gear transmission  8  consisting of a first gear wheel  9  connected to motor shaft  6  and a second gear wheel  10  co-acting therewith, and an eccentric  11  arranged on second gear wheel  10 . Eccentric  11  co-acts with drive rod  3  to transmit the rotating movement of the second gear wheel  10  as a reciprocating movement of saw blade  5 .  
     [0017] The second gear wheel  10  is supported rotatably in housing  1  by means of a gear shaft  12 . Gear shaft  12  is rotatably mounted in bearings  13  on either side of second gear wheel  10 . Gear shaft  12  herein extends through an opening  14  arranged in drive rod  3 .  
     [0018] The fixing  4  for a saw blade  5  situated on the lower end of drive rod  3  comprises a fixing element  15  with a receiving cavity  16  for receiving the end of saw blade  5  for clamping, clamping means  17  engaging on saw blade  5  and an actuating element  18  with which clamping means  17  can be removed from saw blade S. Actuating element  18  can slide relative to fixing element  15 . The construction and operation of fixing  4  will be further elucidated with reference to different embodiments shown in FIGS.  2 - 4 . Corresponding components in FIGS.  2 - 4  are designated with the same reference numerals.  
     [0019] In the first embodiment of fixing  4  as shown in FIG. 2, clamping means  17  are formed by one pair of clamping members in the form of pins situated on either side of saw blade S. Pins  17  have a cylindrical shape and engage on the wide sides of saw blade  5 . The edges of saw blade  5 , i.e. the short side of saw blade  5 , are retained between walls  19  of fixing element  15 . The receiving cavity  16  for receiving the end of saw blade  5  for clamping is located on the one hand between walls  19  and on the other between two walls  20  running obliquely toward saw blade  5 . Receiving cavity  16  has a V-shaped cross-section, which is manifested in the V-shaped grooves  30  in each wall  19  of fixing element  15 . Pins  17  extend on both sides through a V-shaped groove  30  in fixing element  15  into a longitudinal groove  21  of actuating element  18  extending transversely of the operating direction. The slidable actuating element  18  lies around fixing element  15  and serves to hold pins  17  transversely of saw blade  5  as well as for release thereof.  
     [0020] Fixing  4  is further provided with retaining means  22  for retaining saw blade  5  in a direction transversely of the wide sides thereof. In the embodiment according to FIG. 2, these retaining means  22  are formed by a retaining element  23  with a V-shaped recess  24  for receiving the outer end  27  of saw blade  5 . In addition, saw blade  5 , which is commercially available with different thicknesses, is centered in the V-shaped recess  24 . By means of a spring  25  arranged in fixing element  15  the retaining element  23  is pushed into contact with the outer end of saw blade  5 .  
     [0021] A compression spring  26  is further arranged between actuating element  18  and fixing element  15 . This compression spring  26  ensures that pins  17  in V-shaped groove  30  of fixing element  15  are pushed to saw blade  5  via actuating element  18 . The bias generated by spring  26  must be so great that the forces of inertia during sawing are overcome in order to hold pins  17  against saw blade  5 . Saw blade  5  is loaded by a downward directed force during sawing. Pins  17  will hereby move further in the V-shaped groove  30  toward saw blade  5  and therein clamp saw blade  5  with a greater clamping force in fixing element  15 . For release of saw blade  5  the actuating element  18  must be displaced upward relative to fixing element  15  counter to the spring force of compression spring  26 . Because the pins  17  lying on either side of saw blade  5  have a circular cross-section, only a rolling friction resulting from the clamping force need be overcome. Rolling friction is equivalent to a low coefficient of friction wherein low friction forces are the result of normal forces, or in the present case clamping forces.  
     [0022] In order to be able to clamp saw blades of both the “T-shank” type and the “U-shank” type in the fixing  4 , which types of saw blades otherwise have practically the same standardized width, two recesses  27  for the protrusions of the “T-shank” type of saw blade are arranged in walls  19  of fixing element  15 .  
     [0023]FIG. 3 shows a second embodiment of fixing  4  according to the present invention. The difference of this embodiment from the first embodiment is that two pairs of pins  17   a ,  17   b  are provided at a distance from each other. The pins  17   a ,  17   b  of each pair lie on either side of saw blade  5 . The one pin  17   a  of each pair of clamping members  17   a ,  17   b  is herein arranged between saw blade  5  and the wall  20  of receiving cavity  16  running obliquely to the saw blade, while the other pin  17   b  of each pair of clamping members  17   a ,  17   b  is arranged rotatably but not displaceably in fixing element  15 . The longitudinal grooves  21  in actuating element  18  and transverse grooves  31  in fixing element  15  co-act for this purpose. In this embodiment the above stated retaining means  22  are formed by the pairs of clamping members  17   a ,  17   b  placed at a mutual distance. A retention transversely of the wide sides of saw blade  5  is hereby ensured.  
     [0024] In the final embodiment of fixing  4  according to the invention shown in FIG. 4, the difference from the embodiment shown in FIG. 3 is that each pair of clamping members  17  lie in a V-shaped groove  30  of fixing  4  and that each pin  17  therefore co-acts with an inclining wall  20  of receiving cavity  16 . A symmetrical load on saw blade  5  is herein obtained. The one pair of clamping members  17  takes over the function of the other pair of clamping members  17  when this latter deforms elastically due to load on saw blade  5 . In the third embodiment is further ensured that the middle of the saw blade comes to lie on the same sawing line. Conversely, in the embodiment of FIG. 3 one of the two wide sides of the saw blade forms the reference plane. Finally, no additional means  22  are required relative to the embodiment of FIG. 2 for retaining saw blade  5  in fixing element  15  transversely of the wide sides, now that tilting in this direction is prevented by the pairs of pins  17  placed at a mutual distance. Centring of saw blades  5 , which can have a relatively differing thickness, is carried out with this embodiment.  
     [0025] It is further noted that in the shown embodiment the fixing element  15  is formed together with drive rod  3  from one piece of plate material which is given the desired form by folding. On the upper side the plate part is provided with a cavity  28  (FIG. 1) for receiving the eccentric  11 . The opening  14  for passage of gear shaft  12  is situated in cavity  28 . On the underside the plate part is bent to form fixing element  15 . The plate part then extends further upward and is bent once again to form a stop  29  for compression spring  26 .  
     [0026] The clamping members shown in the figures have a circular cross-section. According to the invention however, any clamping member with a substantially circular cross-section, for instance elliptically shaped cross-section, can be applied as long as the clamping member can roll along a certain distance of its periphery.  
     [0027] It must be noted that it is in principle possible to have an embodiment wherein a pair of clamping members are not located at the same height, this in contrast to the shown embodiments. Such a construction does however have the drawback that the saw blade is under strain of bending by the clamping members. The chance of the saw blade breaking is not inconsiderable here.