Lawn mower sharpener

An improved rotary, power lawn mower sharpener is disclosed which includes a base member having a lever pivotally mounted thereon for horizontal motion and having a handle for actuating the lever. The sharpener further includes a wedge having a horizontal, planar, bottom surface for sliding engagement with the upper surface of the base, and having an inclined, planar, upper surface, the wedge connected by means of a link element to the lever, the lever acting to displace the wedge in a horizontal direction. A tray member is pivotally mounted by means of a horizontal pivot, the tray having a planar, bottom surface adapted for sliding engagement with the inclined, upper surface of the wedge when the wedge is moved horizontally by the lever. A grinding stone is mounted in the tray, having an upper, planar grinding surface which is raised when the wedge moves inwardly beneath the tray and which is lowered when the wedge is moved outwardly from beneath the tray. In operation, the base member is positioned beneath a rotary power lawn mower by rolling the wheels of the mower over the base and moving the handle so that the lever pulls the wedge outwardly from beneath the tray member, lowering the grinding stone so that the upper surface thereof clears the bottom edge of the mower. In further operation, the blade is sharpened by moving the handle so that the lever pushes the wedge inwardly beneath the tray member, raising the grinding stone to operatively contact the moving blade.

FIELD OF THE INVENTION 
The invention disclosed broadly relates to blade sharpening devices and 
more particularly relates to improvements in lawn mower sharpeners. 
BACKGROUND OF THE INVENTION 
The primary technique for sharpening the blade of a power lawn mower is to 
remove the blade from the machine and then to apply a file or grinding 
stone to sharpen the blade edge. This is a time consuming task and can 
result in the unbalancing of the blade by removing too much of the blade's 
material on one if its sides. 
One approach in the prior art to reducing the labor involved in sharpening 
the blades on rotary power lawn mowers has been to mount the sharpening 
device on the body of the mower. U.S. Pat. No. 3,225,527 is an example. 
Although this mode is convenient to the operator, it results in excessive 
wear on the blade because of the inherent imprecision of this type of 
device. Stationary sharpening devices have also been tried in the prior 
art, requiring the mower to be brought to the sharpening station. U.S. 
Pat. No. 3,596,412 is an example. With the power of the mower's motor 
applied to the rotating blade, the blade is brought into contact with the 
grinding stone at the station. Although this form of device provides a 
more controlled application of the grinding stone to the blade and 
therefor a better quality sharpening operation, the operator is confronted 
with the inconvenience of taking the mower to the sharpener, instead of 
taking the sharpener to the mower. Furthermore, this fixed-base type of 
prior art sharpener typically has many moving parts requiring excessive 
maintenance. Portable sharpeners are also available in the prior art, 
which do not mount onto the mower. U.S. Pat. No. 4,285,169 is an example. 
However, this type device relies on the vacuum developed by the rotary 
mower's blade and is inherently imprecise in its operation. 
OBJECTS OF THE INVENTION 
It is therefor an object of the invention to provide an improved sharpener 
for a rotary power lawn mower. 
It is another an object of the invention to provide an improved sharpener 
for a rotary power lawn mower which is both portable and precise in its 
operation. 
It is a further object of the invention to provide an improved sharpener 
for a rotary power lawn mower which has the precision of a fixed-station 
sharpening device but which is both portable and which has fewer moving 
parts than the prior art. 
SUMMARY OF THE INVENTION 
These and other objects, features and advantages are accomplished by the 
invention disclosed herein. An improved rotary, power lawn mower sharpener 
is disclosed which includes a base member having a lever pivotally mounted 
thereon for horizontal motion and having a handle for actuating the lever. 
The sharpener further includes a wedge having a horizontal, planar, bottom 
surface for sliding engagement with the upper surface of the base, and 
having an inclined, planar, upper surface, the wedge connected by means of 
a link element to the lever, the lever acting to displace the wedge in a 
horizontal direction. The sharpener further includes a tray member 
pivotally mounted by means of a horizontal pivot, the tray having a 
planar, bottom surface adapted for sliding engagement with the inclined, 
upper surface of the wedge when the wedge is moved horizontally by the 
lever. The sharpener further includes a grinding stone mounted in the 
tray, having an upper, planar grinding surface which is raised when the 
wedge moves inwardly beneath the tray and which is lowered when the wedge 
is moved outwardly from beneath the tray. In operation, the base member is 
positioned beneath a rotary power lawn mower by rolling the wheels of the 
mower over the base and moving the handle so that the lever pulls the 
wedge outwardly from beneath the tray member, lowering the grinding stone 
so that the upper surface thereof clears the bottom edge of the mower. In 
further operation, the mower having a rotary blade with a leading edge 
which is to be sharpened, the blade is driven into horizontal motion by 
means of its motor, the blade is sharpened by moving the handle so that 
the lever pushes the wedge inwardly beneath the tray member, raising the 
grinding stone so that the upper surface thereof operatively contacts the 
lower surface of the leading edge of the blade at an inclined angle. In 
this manner, the blade is conveniently and safely sharpened. The invention 
combines the feature of portability with a precision operating 
characteristic and it has a minimum number of moving parts.

DISCUSSION OF THE PREFERRED EMBODIMENT 
The invention is shown in FIGS. 1, 2 and 3. FIG. 1 is a rear, break-away 
view of the invention, showing the grinding stone 34 in its raised 
position for sharpening the blade of a rotary power lawn mower. FIG. 2 is 
similar to FIG. 1, but shows the grinding stone 34 in its lowered position 
to enable the mower to move away from the sharpener. FIG. 3 is a top view 
of the invention. 
The improved rotary, power lawn mower sharpener includes a base member 10 
having a vertical pivot pin 12 mounted on an upper, horizontal surface 15 
thereof. 
A lever 14 is pivotally mounted on the pivot pin 12 for horizontal motion 
about the pivot pin 12, having a handle 24 connected thereto for actuating 
the lever 14. 
A wedge 18 has a horizontal, planar, bottom surface 20 for sliding 
engagement with the upper surface 15 of the base 10, and has an inclined, 
planar, upper surface 22, the wedge 18 connected by means of a link 
element 16 to the lever 14, the lever 14 acting to displace the wedge 18 
in a horizontal direction. 
A pair of guide rails 26 are mounted on the upper surface 15 of the base 
10, the rails 26 being parallel and spaced apart forming a trough in which 
the wedge 18 can slide horizontally between the rails 26. 
A tray member 30 is pivotally mounted between the pair of rails 26 by means 
of a horizontal pivot 28, the tray 30 having a planar, bottom surface 32 
adapted for sliding engagement with the inclined, upper surface 22 of the 
wedge 18 when the wedge 18 is moved horizontally by the lever 14. 
A grinding stone 34 is mounted in the tray 30, having an upper, planar 
grinding surface 36 which is raised when the wedge 18 moves inwardly 
beneath the tray 30 and which is lowered when the wedge 18 is moved 
outwardly from beneath the tray 30. 
The base member 10 is positioned beneath a rotary power lawn mower 40 by 
rolling the wheels 44 of the mower 40 over the base 10 and moving the 
handle 24 so that the lever 14 pulls the wedge 18 outwardly from beneath 
the tray member 30, lowering the grinding stone 34, as shown in FIG. 2, so 
that the upper surface 36 thereof clears the bottom edge 54 of the mower 
40. 
The mower 40 has a rotary blade 48 with a leading edge 50 which is to be 
sharpened, the blade being driven into horizontal motion 52 by means of 
its motor 46. The blade 48 is sharpened by moving the handle 24 so that 
the lever 14 pushes the wedge 18 inwardly beneath the tray member 30, 
raising the grinding stone 34, as shown in FIG. 1, so that the upper 
surface 36 thereof operatively contacts the lower surface of the leading 
edge 50 of the blade 48 at an inclined angle. 
In this manner, the blade 48 is conveniently and safely sharpened. 
A spring means 38 connected between the lever 14 and the base member 10, 
provides for spring biasing the wedge 18 outwardly from beneath the tray 
30. 
In a first embodiment, at least one stop element 56 is mounted on the base 
10 in spaced relation to the rails 26, for contacting the side 42 of the 
mower 40, to horizontally position the mower 40 and its blade 48 with 
respect to the horizontal position of the grinding stone 34. 
In a second embodiment, a pair of adjustable stop elements 58 are mounted 
on the base 10 in spaced relation to the rails 26, for contacting the side 
42 of the mower 40, to horizontally position the mower 40 and its blade 48 
with respect to the horizontal position of the grinding stone 34. 
The pair of stop elements 58 are variably positionable on the base member 
10 to accomodate a variety of shapes for the side 42 of the mower 40. 
A base handle 60 can be mounted to the base member 10, for enabling the 
operator to hold the base member 10 stationary with one hand while the 
lever 14 is actuated with the other hand. In this manner, the portability 
of the sharpener invention is also enhanced. 
The resultant invention provides an improved sharpener for a rotary power 
lawn mower which is both portable and precise in its operation. The 
improved sharpener has the precision of a fixed-station sharpening device 
but is both portable and has fewer moving parts than the prior art. 
Although a specific embodiment of the invention has been disclosed, it will 
become clear to those workers having skill in the art that other 
alternatives can be used for carrying out the teachings herein without 
departing from the spirit and the scope of the invention.