Woodworking – Cutter hood or dust conveyor
Reexamination Certificate
1999-06-22
2001-05-29
Bray, W. Donald (Department: 3725)
Woodworking
Cutter hood or dust conveyor
C144S136950, C144S154500, C015S336000, C409S137000, C409S182000, C451S453000, C451S456000
Reexamination Certificate
active
06237657
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device, particularly a router, for cutting a workpiece by means of a tool bit rotatingly driven in working rotation direction, with a suction hood surrounding the tool bit in annular manner and having a workpiece engagement surface, which has a through-opening for the tool bit to pass through, whose clear width is a multiple of the diameter of the tool bit and which forms a suction duct open to the tool bit, which is limited by an outside wall, in which at least a part-zone of the outer wall is curved at least over a part of the circumference of the through-opening in a plane which runs parallel to the rotation axis of the tool bit and intersects the outer wall at two points spaced from each other.
With a known device of this type (U.S. Pat. No. 4,946,322) a cup-shaped suction hood open at the top and bottom is arranged about the rotatingly driven tool bit, said suction hood has a curved, upwardly widening outer wall, between which and a correspondingly shaped inner wall compressed air is fed, while there is a suction connection at the upper end of the suction hood. With this suction hood, the chips which are generated during the machining of the workpiece and the dust from the machining area are moved upwards and sucked away out of the inside zone of the suction hood. This requires an essentially closed top of the inner space of the suction hood, with the result that the operator's view of the machining area of the workpiece is blocked. The known suction hood is also extremely bulky and in addition operates with compressed air to effect the removal of the dust by suction.
With another known device (U.S. Pat. No. 5,031,678) the rotatingly driven tool bit is surrounded by a suction hood whose outer wall is rectilinearly inclined, at least in a part-zone, from the bottom upwards and in the direction of the rotation axis of the tool bit. A tubular suction duct joins on to this suction hood. When, with this known suction hood, chips are thrown against the inclined outer wall by the rotating tool bit, they can be reflected in the direction of the tool bit and in particular in the direction of the machining point of the workpiece. This can lead to chips and dust not being sucked out efficiently, but escaping through the groove in the workpiece created by the tool bit. In order to avoid this, a brush is therefore provided which extends into the manufactured groove and forms a barrier to the escape of chips and dust.
With another device (German Patent Application P 23 35 177) in the form of a hand-held sanding machine with rotatingly driven sanding plate, the outer wall of the dust-suction hood which surrounds the sanding area laterally is curved, with the result that sections of the outer wall which are situated above the sanding plate lie radially further inward than sections situated in the peripheral zone of the sanding plate. The suction hood is essentially completely closed at the top, with the result that the dust which has formed is retained inside the suction hood and is removed only through connected suction hoses. The curvature of the outer wall clearly serves merely to stabilise the total structure.
SUMMARY OF THE INVENTION
The object of the invention is to develop the suction hood of a device for cutting a workpiece so that as unimpeded as possible a view of the machined area of the workpiece is provided with a simple structure, without the risk of chips detached from the workpiece by the rotating tool bit being thrown out upwards through the through-opening of the suction hood.
To achieve this object, a device of the type mentioned initially is designed in such a way according to the invention that the part-zone of the outer wall of the suction hood has a parabolic curve and the focal point of the parabola is located between outer wall sections lying opposite each other and at a lesser distance from the plane of the workpiece engagement surface than from the plane of the surface of the suction hood lying opposite this.
The effect of the shape of the outer wall of the suction hood is that chips which are generated in the focal point of the parabola and in its vicinity are reflected essentially horizontally, i.e. parallel to the workpiece engagement surface, upon striking the parabolic outer surface, and thereby remain inside the zone of the suction hood and neither escape upwards through the through-opening of the suction hood nor enter the engagement area of the tool bit with the workpiece. In this way, the operator is protected against injury and the work environment is polluted with less dust and fewer chips.
The parabolic curve defines a plurality of parabolas in the circumferential direction. Each parabola defines a parabola plane extending tangentially to a circle lying concentrically about the rotation axis of the tool bit. The tangent contact point between each parabola plane and the circle is adjacent to the portion of the tool bit that in operation moves in the direction of the outer wall having the associated parabola. The focal point of each parabola lies on the contact point of its associated parabola plane and circle.
The effect of such a structure of the outer surface running in circumferential direction about the tool bit is that the chips of the workpiece produced by the tool bit during operation move essentially in the parabola plane in the direction of the outer wall, to which end the circle is preferably equal to the cutting circle of the tool bit, but which for the sake of simplicity and with sufficient accuracy for practical purposes is generally assumed to have a diameter of 10 mm.
The focal point of the parabola is preferably situated outside the area limited by said planes, i.e. beneath the workpiece bearing surface and preferably at a distance equal to the projection of the tool bit beneath the workpiece engagement surface. In this position, the focal point lies in the engagement area of the tool bit with the workpiece and thus in the area in which the chips form. In practice a position of 20 mm below the workpiece engagement surface appears appropriate in view of the different amounts by which workpieces project in practice.
In a preferred version, the device according to the invention has a conventional suction channel joining on to the suction duct and connectable to an underpressure source, in order to remove the chips and the dust from the machining zone. With such a structure, at least a part of the circumference of the outer wall of the suction hood increases its distance in the form of a spiral from the rotation axis of the tool bit in work rotation direction of the tool bit in a particularly preferred manner. As a result, on the one hand the course of the suction duct from the zone of the outer wall running essentially concentrically relative to the rotation axis of the tool bit to the suction channel is adapted to the flow around the tool bit resulting from the rotation of the tool bit, and thus to the corresponding direction of flight of the chips, while on the other hand the effect of the spiral-shaped structure is that chips which would be reflected against the tool bit if the structure were in the form of a circle can now pass by it.
The transition from outer wall increasing its distance in the form of a spiral from the rotation axis of the tool bit to the wall of the suction channel preferably takes place tangentially.
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Black & Decker Inc.
Bray W. Donald
Harness & Dickey & Pierce P.L.C.
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