Cutlery – Cutting tools – With blade moving means
Reexamination Certificate
2000-03-10
2001-11-13
Payer, Hwei-Siu (Department: 3724)
Cutlery
Cutting tools
With blade moving means
C030S275400, C056S012700, C384S295000, C384S296000
Reexamination Certificate
active
06314649
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a work apparatus having a drive motor and the work apparatus is especially a vegetation cutter. The invention also relates to a method for the axial assembly of a shaft bearing.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,414,934 discloses a vegetation cutter apparatus which includes a bearing axially inserted into the end section of the guide tube of the apparatus. The bearing holds the cutterhead on the guide tube and is axially secured by providing a stop projecting radially into the end section.
The bearing must be configured so that it is adapted with respect to its outer diameter to the inner diameter of the end section in order to ensure a play-free seating of the bearing in the end section. However, this leads to problems during assembly. If the bearing is configured to have an oversize, then considerable force must be applied when axially inserting the bearing into the end section. At the same time, material is abraded during insertion so that chips are formed. If the bearing has an undersize, then the bearing lies in the end section with play which can lead to impact movements and shaking movements during operation.
SUMMARY OF THE INVENTION
It is an object of the invention to improve a work apparatus of the kind referred to above so that a play-free seating of the bearing which lies in the end section is ensured while, at the same time, ensuring an easy assembly.
The work apparatus of the invention includes: a drive motor; a guide tube having an end connected to the drive motor and having an end section facing away from the drive motor; a rotatably driven work tool mounted on the end section; a drive shaft rotatably journalled in the guide tube and connecting the drive motor to the work tool so as to permit the drive motor to rotatably drive the work tool; the end section defining a longitudinal axis and having an interior space; the end section further having an inner diameter (D
I
) before being formed; a bearing axially inserted into the interior space for mounting the work tool on the end section; the bearing having an outer surface and a plurality of axial ribs formed on the outer surface; the axial ribs having respective rib roofs conjointly defining an imaginary cylinder having an outer diameter greater than the inner diameter (D
I
) of the end section; the bearing having an outer shape when viewed in cross section characterized by the outer surface with the axial ribs; and, the end section of the guide tube being elastically formed to assume a shape corresponding to the outer shape of the bearing for surroundingly force tightly holding the bearing.
The method of the invention is for axially assembling a bearing in an end section of a guide tube which approximately concentrically surrounds a drive shaft. The end section has a longitudinal center axis and has an inner diameter (D
I
) before being formed. The bearing has an outer surface and a plurality of axial ribs formed on the outer surface. The axial ribs have respective rib roofs conjointly defining an imaginary cylinder having an outer diameter greater than the inner diameter (D
I
) of the end section. The method includes the steps of: essentially elastically deforming the end section by clamping the end section between clamping jaws so that a cornered cross-sectional shape is imparted to the end section with the clamping jaws being applied until the cornered cross-sectional shape has a diameter (D
V
) measured from a corner which is slightly greater than a distance measured between a rib roof of one of the axial ribs and a diametrically opposite lying outer wall surface of the bearing through the longitudinal center axis; after reaching the diameter (D
V
), pushing the bearing into the end section in such a rotational position substantially without force so that the axial ribs come to rest in corresponding ones of the corners of the deformed end section; and, allowing the elasticity forces of the material of the end section to return deform the end section by loosening the clamping jaws so that the end section comes into force-tight contact engagement with the axial ribs.
The bearing lies only over portions of its periphery against the inner wall of the end section because of the outer configuration of the bearing. The outer diameter of the imaginary cylinder wall is greater than the inner diameter of the undeformed end section. The outer diameter of the imaginary cylinder wall is defined by the rib roofs of the axial ribs.
An axial insertion of the shaft bearing into the end section of the guide tube with little force is achieved by deforming or forming the end section to have corners by clamping the end section between clamping jaws. The number of corners corresponds to the number of axial ribs formed on the bearing. The deformation of the cross section of the end section into an approximately triangularly-shaped configuration when there are three axial ribs (similar to an equilateral triangle) provides a spacing between a corner and the inner wall of the deformed cross section which lies diametrically opposite the corner. Because of the deformation, the cross section is greater than the extension measured along the longitudinal center axis between a rib roof and the opposite-lying wall section. The bearing is now so aligned in its rotational position that each corner is assigned an axial rib. The spacing between a rib roof and the diametrically opposite-lying wall section of the bearing is less than the spacing of the corner to the diametrically opposite-lying wall of the deformed section. For this reason, the bearing can be axially inserted into the end section without force because of the radial play. The deformation of the end section to the configuration, which is required for the forceless insertion of the bearing, takes place in the elastic range of the material of the guide tube, which is preferably aluminum. Accordingly, when stress is taken off of the clamping jaws (that is, when the clamping device is withdrawn), the end section tends to return to its original cylindrical shape. The wall of the end section therefore lies force tight against the rib roofs whereby the bearing is held force tight in the end section so that it cannot separate in the axial direction and is held tightly in the peripheral direction so it cannot rotate.
The bearing, which is held force tight in the end section, can be additionally secured by a pin which projects radially into the end section and is preferably a holding screw.
REFERENCES:
patent: 4172322 (1979-10-01), Ballas
patent: 4226021 (1980-10-01), Hoff
patent: 4463498 (1984-08-01), Everts
patent: 4505040 (1985-03-01), Everts
patent: 5170561 (1992-12-01), Sepke
patent: 5414934 (1995-05-01), Schlessmann
Andreas Stihl AG & Co.
Ottesen Walter
Payer Hwei-Siu
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