Clamping device for a jigsaw

The invention relates to a clamping device (8) for connecting a saw blade (12) to a reciprocating rod (6) of a jig saw, in particular a hand-operated compass saw (2), comprising a mounting (20), which is connected to the reciprocating rod (6) and has a recess (22) for receiving a head end (10) of the saw blade (12), a locking sleeve (30), which can be turned about the axis (40) with respect to the mounting (20) against the force of a torsion spring (60) to lock the head end (10) of the saw blade (12) in a locking position in the recess (22) and to allow removal of the saw blade (12) in a removal position. It is intended that a stop (78) interacts with a part (80) of the torsion spring (60), in order to prevent movement of the locking sleeve (30) beyond the removal position.

The present invention relates to a clamping device and to a jig saw within which the clamping device is included.

Clamping devices designed to clamp a saw blade in a jig saw serve to connect the saw blade in a fixed manner with a motor-driven reciprocating rod of the jig saw, the objective being to lock the saw blade in position with as little movement as possible and in a defined position relative to the holder, to attain a good and precise sawing result.

RELATED ART

A clamping device of the type described initially is made known in EP 1 236 530 B1. This clamping device makes it possible to replace the saw blade quickly and easily, and to immobilize saw blades of different thicknesses in a defined position in the slot-shaped recess of the holder, since the rotatable locking sleeve—which is referred to as a blade guide in EP 1 236 530 B1—reaches behind two lateral projections of the saw blade when rotated out of the release position and into the locked position, thereby preventing the saw blade from moving out of the holder recess, and also ensuring—via the action of the curved surface of the cam element on the contact element inserted in a guide opening of the holder—that the contact element is pressed against a broadside of the saw blade, in order to press the saw blade via its opposite broadside against the adjacent boundary wall of the recess, thereby ensuring that the saw blade is fixed in position, regardless of its thickness.

With the known clamping device, the cam element of the locking sleeve is provided with stop regions on both end faces of the curved surface, each of which is formed by an end section of the cam element that is bent inward in the shape of a hook, the cam element being located radially inwardly from the cylindrical torsion spring in an annular intermediate space between the cylindrical outer circumferential surface of a part of the holder and the inner side of a cylindrical outer wall of the locking sleeve. The two inwardly bent end sections of the cam element, which serve as stop regions, impact—from opposite sides—an outwardly pointing, thicker top part of the contact element when the locking sleeve is in the release position or a home or starting position, in which a saw blade is not located in the holder and the user is not applying any force to the locking sleeve. In this manner, the locking sleeve may be prevented from rotating past these two end positions.

This design has two disadvantages, however: When a user rotates the locking sleeve into the release position using a swiveling lever and presses on the swiveling lever with a great deal of force, one bent end section of the cam element of the locking sleeve impacts the top part of the contact element with strong force, due to the lever effect. This may cause the end section to become bent or the contact element to become tilted in the guide opening of the holder. The risk that the end section will bend is increased further by the fact that, in the release position, the distance is greatest between the curved surface and the top part of the contact element, so that the bent end section—in the radial direction—must extend relatively far inward beyond an adjacent section of the cam element, so that it impacts the top part. The relatively large overhang of the bent end section may also result in its becoming jammed in the annular gap between the outer circumferential surface of the holder and the inner circumference of the cylindrical torsion spring.

The object of the present invention, therefore, is to improve the known clamping device such that the locking sleeve is prevented from being rotated past the release position, without the risk of the contact element becoming tilted, and without the risk of damage occurring to the cam element with the curved surface.

DISCLOSURE OF THE INVENTION

This object is attained according to the present invention in that the stop interacts with a part of the torsion spring to prevent the locking sleeve from rotating past the release position.

Preferably, the part of the torsion spring that interacts with the stop abuts an end face of the torsion spring inserted in a recess of the holder. The part that interacts with the stop extends radially outwardly past the holder and passes through the annular gap surrounding the holder.

This has the advantage that the same end section of the cam element with the curved surface may be used to prevent the locking sleeve from rotating in a direction past the release position, and to prevent the locking sleeve from rotating in the opposite direction past the home or starting position, in which the locking sleeve is rotated by the torsion spring when a saw blade is not located in the recess of the holder. As with the clamping device made known in EP 1 236 530 B1, when in the home or starting position, the end section advantageously impacts a side of the thicker head part of the contact element to prevent the locking sleeve from rotating past the home or starting position. In other words, the stop regions, which limit the angle of rotation in both directions, only need to be placed on or near an end face of the cam element with the curved surface.

In addition, the end face of the cam element does not need to be bent in order to form the stop region that comes in contact with the torsion spring, thereby making it possible to improve its deformation resistance. Particularly strong resistance is attained when the end face of the cam element is extended slightly past the stop region that impacts the top part of the contact element when in the home or starting position, and it is also somewhat thicker in design, this end face then forming the stop region that impacts the torsion spring. Since the end face is essentially oriented in the direction of motion of the cam element when it impacts the torsion spring, the cam element has great rigidity in the direction of impact.

The angular position in which the end face of the cam element impacts the torsion spring may be attained by changing the angular orientation of the opening in the holder—which serves to receive the end face of the torsion spring—and/or by extending the end face of the cam element past the section that serves as stop region when in the home or starting position.

As an alternative, it would be feasible, however, to use the opposite end face of the cam element in the home or starting position as the stop for limiting the rotary motion of the locking sleeve by extending the cam element at this end so far that, in the home or starting position, it impacts—from the opposite side—the part of the torsion spring that serves as the stop for the cam element in the release position.

EMBODIMENT OF THE INVENTION

Hand-guided compass saw2shown inFIG. 1includes—in a known manner—a housing4, an electric motor with a not-shown transmission located inside housing4, a reciprocating rod6that is driven in a linear motion by the electric motor via the transmission and that may be moved back and forth and up and down, a clamping device8located on the free end of reciprocating rod6for clamping a top end10of a saw blade12, and a support roller unit16located between clamping device8and an adjustable base plate14of compass saw2for supporting a saw blade back18of saw blade12.

As shown best inFIGS. 3 through 8, clamping device8includes a holder20, which is rigidly connected with the lower free end of reciprocating rod6. Holder20is provided with a recess22that has a rectangular cross section, is open toward the bottom, and is slot-shaped, into which top end10of saw blade12may be inserted from below and then locked in place in holder20.

To this end, as shown inFIG. 2, top end10of saw blade12is provided with two diametrically opposed lateral projections24and a narrower neck section26beneath projections24, so that, after top end10of saw blade12has been inserted in recess22of holder20, projections24may be gripped from underneath by lower end face28of a locking sleeve30that encloses holder20, in order to hold top end10of saw blade12in position in recess22such that it is fixed in position in the axial direction.

Holder20also has an upper part32with a larger diameter, and a lower part34with a smaller diameter, and it is largely enclosed—except for an upper dust-protection cap36—by locking sleeve30, which is hollow-cylindrical and stepped in design, and which is attached to holder20using a snap ring38such that it may rotate around a longitudinal axis40of reciprocating rod6between two defined end positions.

The first end position, which is shown inFIGS. 3 and 4and is referred to as the home or starting position, is the position in which locking sleeve30is located when a saw blade12has not been inserted in recess22and no rotary force is being applied by a user to locking sleeve30.

The second end position, shown inFIGS. 5 and 6, is the release position, in which a rectangular slot opening42in lower end face28of locking sleeve30is aligned with recess22—which has a rectangular cross section—in holder20so that top end10of saw blade12, including projections24, may be inserted into recess22from the bottom through slot opening42.

The locked position shown inFIGS. 7 and 8is located between the home or starting position and the release position. In the locked position, diametrically opposed edges of slot opening42in lower end face28of locking sleeve30reach behind the two projections24of saw blade12, as shown best inFIG. 2, thereby preventing saw blade12from moving axially out of recess22.

A guide opening44oriented transversely to longitudinal axis40of reciprocating rod6is located in the lower part of holder20, in which a contact bolt46is inserted such that it is displaceble transversely to longitudinal axis40. Contact bolt46serves to press top end10of saw blade12—when inserted in recess22and in the locked position—against a boundary wall48of recess22that is diametrically opposed to contact bolt46, in order to hold top end10of saw blade12in a defined position against boundary wall48, regardless of its thickness, thereby ensuring that saw blade12is positioned evenly and precisely. To this end, contact bolt46must be slid into recess22that much further, the thinner saw blade12is.

Contact bolt46with the rectangular cross section has a bevel50on the underside of its inner end that extends into recess22, so that, when top end10of saw blade12is inserted into recess22, it is displaced outwardly until top end10of saw blade12may pass between the free end of contact bolt46and boundary wall48, and into recess22.

Contact bolt46also includes an expanded top part52, which extends into an annular intermediate space54between a cylindrical circumferential surface56of lower part34of holder20and the inner side of outer wall58of an expanded top part of locking sleeve30.

A helically coiled torsion spring60is located in intermediate space54, whose end face62is bent radially inwardly and, opposite to the free end of contact bolt46, is inserted into a radial receiving opening64in lower part34of holder20, and whose other end face66is bent radially outwardly and is inserted into a receiving opening68of a hollow projection70that projects radially outwardly beyond the outer side of locking sleeve30. Torsion spring60serves to rotate locking sleeve30in the home or starting position, or in the locking position when saw blade12, in the release position, is removed from recess22of holder20, or when it has been inserted in recess22of holder20, and when a release lever (not shown) that is used to rotate locking sleeve30into the release position and that acts on one side of projection70has been released by the user.

Intermediate space54also serves to receive a cam element72, which is connected as a single piece with locking sleeve30, and which extends between torsion spring60and10circumferential surface56of lower part34of holder20from below into intermediate space54, as shown best inFIGS. 3,5, and6. Cam element72is shaped nearly as a semi-spiral winding, and it has a curved surface74on its inner side facing holder20. The distance between curved surface74and circumferential surface56of lower part34of holder20decreases in the counter-clockwise direction. As a result, contact bolt46is moved by curved surface74of cam element72that acts on its top part52into recess22, and it is pressed with via free end against the adjacent broadside of top end10of saw blade12that has been inserted in recess22, saw blade22then being pressed via its opposite broadside against the adjacent boundary wall48of recess22when locking sleeve30is rotated by torsion spring60into the locked position in the counter-clockwise direction, i.e., in the direction of the arrow inFIG. 4.

To prevent locking sleeve30from rotating in the counter-clockwise direction past the release position shown inFIGS. 5 and 6when the user replaces saw blade12, cam element72has an elongated end face78on the other side of stop region76, the length of which is selected such that it impacts a part80of torsion spring60when in the release position. Part80of torsion spring60abuts end face62of torsion spring60inserted in receiving opening64and extends radially outwardly past holder20, extending transversely through intermediate space54.

To prevent locking sleeve30from rotating in the counter-clockwise direction past the release position shown inFIGS. 5 and 6when the user replaces saw blade12, cam element72has an elongated end face78on the other side of stop region76, the length of which is selected such that it impacts a part80of torsion spring60when in the release position. The part80of the torsion spring60that interacts with the end face78extends transversely into the intermediate space54.

By changing the length of end face78of cam element72that extends past stop region76, it is possible to select a desired angle of rotation of locking sleeve30between the release position and the home or starting position.

To change this angle of rotation, it would also be possible to locate the end face62of the torsion spring60at a location other than directly across from the guide opening44of contact bolt46—at an angle to the guide opening44relative to axis40.

It is also possible to eliminate stop region76and extend end face82of cam element72—which is diametrically opposed to end face78—so far that it impacts the opposite side of part80of torsion spring60(not shown) when in the home or starting position.