Portable Blade Sharpener

Abstract

A portable blade sharpener which is useful for sharpening lawnmower blades without having to remove the blade from the mower and which sharpens the blade accurately to an acute angle formed by a grinding wheel and a die plate.

Description

BACKGROUND OF THE INVENTION

With continuing development and expansion of urban and semi-urban areas, particularly in the suburbs surrounding major metropolitan areas, increasingly large expanses of grass must be cut. One of the common ways of cutting this grass is through the use of rotary bladed lawnmowers. Unfortunately, the blades in such mowers tend to wear quite rapidly and should be sharpened rather often. Consequently, it is quite desirable to be able to sharpen these blades without having to remove the blade from the lawnmower or to take the lawnmower blade to a repair shop.

Another problem in sharpening the blades is that if a portable sharpener is used on the blade while the blade is mounted in the lawnmower it is extremely difficult to sharpen to give an accurate angle. Thus, if the blade is sharpened in the mower it is likely that the blade edge will be curved or sharpened unevenly or that the blade will be thrown out of balance. This is complicated by the need for repeated sharpenings, which compounds and magnifies the possible errors. U.S. Pat. No. 2,993,312 describes a sharpening device with a rotatable straight-line contact intended to sharpen blades while still mounted in a rotary mower. However, such a device may easily create "waves" in the sharpening of the blade. Moreover, the device is difficult to use because the user must pull back on the tool so that the grinding wheel contacts the blade and at the same time must push downwardly at an acute angle so that the contact member stays flush against the blade. Furthermore, such a device could prove to be quite dangerous, since the grinding wheel is unshielded.

SUMMARY OF THE INVENTION

It is a principal object of the present invention, therefore, to provide a new and improved blade sharpener, for sharpening a rotary mower blade while still mounted in the mower, which defines an extremely accurate angle to which the blade may be sharpened.

Another object of the invention is to provide a new and improved portable blade sharpener which is easily used by the home consumer as well as a professional lawnmower serviceman.

A still further object is to provide a portable blade sharpener tool which is precise enough to balance a blade while sharpening the blade in place in a mower.

Accordingly, the invention relates to a portable blade sharpener comprising a motor, a motor housing with a flat guide plate affixed to the motor housing, a grinding wheel mounted within a sharpener housing which is affixed to the motor housing so that the grinding wheel forms an acute angle with the surface of the guide plate, and a means for connecting the motor to the grinding wheel. Thus, the portable blade sharpener can be simply pressed flush against the lawnmower blade and an accurate angle can be ground on the blade.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

FIG. 1 is a view showing the use of the portable sharpener of the invention upon a lawnmower blade still mounted on the lawnmower; and

FIG. 2 is a side sectional view of the portable blade sharpener.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates how a blade sharpener 10 constructed in accordance with the present invention is used to sharpen a lawnmower blade 12. Blade 12 protrudes from the underside of the lawnmower, and is centered within the protective covering or skirt of the mower. In this particular view blade 12 turns counterclockwise; consequently, one leading edge 12A of the blade which will impact and cut the grass is being sharpened. To use blade sharpener 10, one simply grasps the device by its motor housing 14, or by the motor housing and the sharpener housing 19 and passes the sharpener back and forth across the blade, as shown by the double arrow A, until an edge of the desired sharpness is obtained.

In FIG. 2, which is a side sectional view through the center of the sharpener, it is seen that sharpener 10 is guided along blade 12 such that the blade will be sharpened to an accurate angle. This angle is defined by a flat guide plate 11 which is pressed firmly against outer surface 12C of the blade. Guide plate 11 is treated or coated to afford an outer guide surface 36 having a low coefficient of friction for ease of movement along blade surface 12C. A smooth metal surface, with some lubrication, can be used. Alternatively, a coating of resilient, low friction plastic (e.g., nylon), can be utilized.

Guide plate 11 is attached to motor housing 14, which houses a motor 21. HOusing 14 also encloses a means 22 for supplying power to the motor 21, which means may comprise a battery pack, an electric power line connection, or any other suitable means to drive the motor. Motor 21 can be turned on and off as desired by a switch 23. Motor 21 drives a main shaft 25 which is mounted in motor housing 14 by a bearing 26. On the outer end of the main shaft 25 there is a pinion 27 which drives a spur gear 28. The driven gear 28 is mounted in the sharpener housing 19, which is an angled extension of motor housing 14, by another bearing 24. Firmly affixed to the driven gear 28 is a grinding wheel 30. Grinding wheel 30 is mounted within the sharpener housing 19 such that an acute angle C is formed between the outer face 35 of the grinding wheel and the outer surface 36 of guide plate 11. The gear teeth on each of the gears 27 and 28 are aligned at acute angles to the gear axes to provide the desired angle C.

Any effective means of driving the grinding wheel 30 from the motor 21 would be acceptable. The preferred embodiment uses the offset gears 27 and 28 to accomplish this purpose; however, a system of pulleys or other systems of gears or the use of universal type joints would be encompassed within the scope of the present invention. Moreover, in keeping with the invention, the guideplate 11, which is preferably flat for a lawnmower blade, could be curved if it was desired to sharpen a curved blade. The axis of motor 21 is preferably parallel to the guide surface 36 of plate 11, affording a compact handle structure and facilitating maintenance of the desired surface engagement between the mower blade and guide plate.

Sharpener 10 may also include a slidable stop 40 mounted in a channel 43 in housing 14 and connected to a pointer 42 which extends through the motor housing. The outer end of pointer 42 is aligned with a scale 41 affixed to housing 14. Stop 40 is moved, as indicated by arrow B, until it is engaged snugly against the side of blade 12 opposite the edge 12A being sharpened. Thus, the width of the blade can be accurately measured, allowing the blade to be sharpened until it is accurately balanced by sharpening both edges 12A and 12B to give equal widths.

A bias spring (not shown) can be used for stop 40, biasing the stop against the rear of the blade. Alternatively, a clamp can be provided so that the stop may be manually set against the blade to give an accurate read-out of how wide the blade is. Thus, when the user changes from one blade edge to another, he can sharpen them down to the same width and be assured of having an accurately balanced blade. Stop 40 may also be extended outwardly axially of the motor housing so that extremely wide blades may be sharpened.

Thus, it is apparent that there has been provided in accordance with the invention, a blade sharpener that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.

Claims

I claim:

1. A portable sharpener for sharpening a mower blade while the blade remains mounted within a mower guard, comprising:

a main motor housing;

an electric motor mounted within said housing;

a guide plate affixed to one side of said housing and affording an outwardly facing flat guide surface;

a housing extension, projecting from said one side of said main housing;

a grinding wheel rotatably mounted in said housing extension, said grinding wheel having a grinding surface forming an acute angle with said guide surface, whereby said sharpener may be placed over a mower blade cutting edge and the cutting edge sharpened by said grinding wheel while maintaining the outer surface of the blade flush against said guide surface;

and angle drive means, mounted in said housing and said housing extension, affording a drive connection from said motor to rotate said grinding wheel.

2. A portable blade sharpener according to claim 1, in which said angle drive means comprises a pinion gear mounted on the shaft of said motor in meshing engagement with a spur gear affixed to said grinding wheel, at least one of said gears having gear teeth aligned at an acute angle to the axis of said gear.

3. A portable blade sharpener according to claim 2, in which the axis of said motor is approximately parallel to the plane of said guide surface.

4. A portable blade sharpener according to claim 1, in which said guide surface is formed of a material having a low coefficient of friction.

5. A portable blade sharpener according to claim 1, and further comprising gauge means for measuring the width of the sharpened blade.

6. A portable blade sharpener according to claim 1, in which said housing is of elongated handle-like configuration, affording a means for manually maintaining both said guide surface and said grinding surface in consistent surface-to-surface contact with said blade.