1990-09-07
1992-11-24
Watts, Douglas D.
Cutlery
Cutting tools
Saw
30394, B23D 4904
Patent
active
051651734
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a jigsaw, and, more particularly, to a jigsaw including a blade retention system which permits the blade of the saw to be changed without the use of any tool external to the structure of the jigsaw itself.
In known jigsaw structures, the blade is fixed to the reciprocating drive shaft either by means of fixing screws that engage lateral surfaces of the blade to clamp the blade in position as shown, for example, in U.S.-A-3665983, or by means of a combined bayonet and fixing screw system, as shown in G.B.-A-1173172, in which the blade is provided with bayonet lugs which are held, in use, in corresponding retention grooves provided in an end cap of the drive shaft by a screw which engages the end of the blade.
Both of these systems have the disadvantage of requiring the use of an external tool (a screwdriver) in order to change the blade. Not only is this inconvenient, but also there is the danger that an inexperienced or careless operator may either damage a retaining screw in the process of changing a blade, or may inadequately tighten a fixing screw with the result that the blade may inadvertently be released from the drive shaft in use.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a jigsaw with a blade retention system which permits the saw blade to be changed without use of any separate extra tool.
This object and others is attained in a jigsaw a body having a bayonet fitting at the end thereof for receiving a blade having bayonet lugs, and locking means for engaging the blade to maintain the lugs in retention grooves of the bayonet fitting during use of the jigsaw. The locking means is movable to a release position in which the bayonet lugs can be moved out of the retention grooves to permit removal of the blade and insertion of a fresh blade according to the present invention the locking means is movable to its release position by a release device without using a tool separate from the jigsaw itself.
Accordingly, the disadvantage of the prior art, namely that a screwdriver is needed to release the retention screw or screws is avoided.
Preferably the locking means is movable to its release position by the release device incorporated within the jigsaw and permanently connected to the locking means. With such an arrangement, damage to the locking means caused by partial or incorrect engagement of the release device is avoided. Further, the release device preferably incorporates a manually graspable release member for operating the release device, the release member being arranged so that it does not move during normal reciprocation of the drive shaft.
In one particularly preferred embodiment of the invention the locking means is a screw movable axially of the drive shaft in a manner similar to the arrangement of the prior art shown in G.B.-A-1173172. In this case, the release device preferably comprises a screw rotating member extending axially through the drive shaft, the screw rotating member being permanently engaged with the screw in a manner which permits relative sliding movement between the screw and the screw rotating member, but prevents relative rotation between the screw and the screw rotating member. In this case, a manually graspable release member is connected to the screw rotating member for rotating the screw rotating member, and with it the screw. Preferably, a torque limiting device is interposed between the manually graspable release member and the screw rotating member to limit the torque which can be applied to the screw in the direction which moves the screw towards the blade. In this manner, damage caused by over-tightening of the screw is avoided. Preferably, the torque limiting device or torque limiter does not limit the torque which can be applied by the manually graspable release member in the direction tending to move the screw away from the blade.
In an alternative embodiment of the invention the locking means comprises a spring which biases the blade outwardly of the drive shaft to main
REFERENCES:
patent: 4528753 (1985-07-01), Kuhlmann et al.
Robert & Bosch GmbH
Striker Michael J.
Watts Douglas D.
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