Tool driving or impacting – Impacting devices – Hammer head driven by relatively moving motion transmitting...
Patent
1994-06-16
1995-06-27
Smith, Scott A.
Tool driving or impacting
Impacting devices
Hammer head driven by relatively moving motion transmitting...
74 55, B25D 1110
Patent
active
054271886
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is concerned with power tools, particularly but not exclusively, with power tools which are relatively lightweight and suitable for use by the general public.
In my British Patent No. 2219958 there is described a portable power tool which comprises a housing and a drive means for operating a range of interchangeable tool bits such as scrapers and chisels or even tool bits which perform the function of a small spade in breaking up soil. All these power tools provide the user with the advantages of a linear path for the powered stroke of the bit, without a component of rotary motion. This is achieved by provided a cylinder cam mounted for rotation with an output shaft and provided with a circumferential sinusoidal cam track in which run cam followers associated with the drive shaft, which is captive against rotation. Tools made in accordance with the invention described in that specification are remarkably efficient in use as small hand-held tools, but if the intended purpose of the tool requires a greater cam throw range and/or a larger cam cylinder for smoothing action, the shaft portion carrying the cam followers is also enlarged making the components too cumbersome for ease of use and incorporation into a reasonably sized housing.
SUMMARY OF THE INVENTION
The present invention seeks to provide an arrangement which will increase the versatility and capability of a portable tool such as referred to above while tending to avoid the penalty of increased size of component parts.
The invention provides a portable power tool means comprising a housing, a drive means and a mounting arrangement for a selected tool bit, said drive means being adapted to drive an output shaft means in a reciprocatory axial motion with respect to a longitudinal axis thereof to drive said tool bit, wherein there is provided a rotatable cam member to convert rotary motion from the drive means into said reciprocatory motion, said cam member being provided with an axially arranged bore into which is received a portion of the output shaft means, inner walls of said bore being formed to provide a continuous sinusoidal cam track, said output shaft means portion being provided with cam follower means projecting outwardly therefrom to engage with the cam track, and means being provided to restrain said output shaft means against rotation when said output shaft means is partaking of said reciprocatory motion.
Conveniently said output shaft means may pass through the bore of the cam member and be received in bearing devices adapted to permit longitudinal motion. Alternatively, the bore may be provided with an end wall so as to form a blind bore, an end portion only of the shaft means being received therein.
It will be understood that the power tool means of the present invention may be used as a conversion unit for a conventional power tool or may form part of a combination power tool assembly.
In one example of a device according to the invention, the means to restrain the output shaft means against rotation during the reciprocal motion thereof may comprise a bearing arrangement in which a non-circular or splined portion of the shaft means is slidingly received in a corresponding-shaped passage.
In a further example of another device according to the invention, said means to restrain the output shaft means against rotation may be adapted to be releasable at the operator's option. Selection means may therefore be provided which are capable of controlling the adoption of a first mode in which said output shaft means is in a drive sequence for reciprocal motion and a second mode in which said output shaft means is in a drive sequence for rotary motion. Conveniently said selection means may comprise a slidable key arrangement.
There will now be described three examples of tools according to the invention. It will be understood that the description which is intended to be read with reference to the drawings is given by way of example only and not by way of limitation.
BRIEF DESCRIPTION OF THE DRAWING
REFERENCES:
patent: 1777875 (1930-10-01), Champayne
patent: 2051053 (1936-08-01), Morris
patent: 2970483 (1961-02-01), Schrum, Sr.
patent: 3322208 (1967-05-01), Skoog
patent: 3430709 (1969-03-01), Miller
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