Abrading – Abrading process – Utilizing shield
Reexamination Certificate
2002-04-05
2003-06-03
Wilson, Lee D. (Department: 3723)
Abrading
Abrading process
Utilizing shield
Reexamination Certificate
active
06572448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to sharpening equipment, and more particularly to apparatus that sharpens a wide variety of cutting blades.
2. Description of the Prior Art
Rotary power mowers of various types are well known and are in widespread use. They vary greatly in size, complexity, and operating characteristics. However, all rotary power mowers utilize the common component of a rotary cutting blade. The blades are relatively long, narrow, and thin. A cutting edge is sharpened into each end of the blade. As the blade rotates under power from the mowing machine, the cutting edges shear vegetation.
The cutting edges of some rotary blades lie along substantially straight lines for their full lengths. A typical example of such a blade is shown at reference numeral
3
in
FIGS. 1-3
. The blade
3
has a longitudinal centerline
4
and a flat bottom surface
6
, and opposed ends
34
. There are a pair of cutting edges
8
at the ends
34
, both of which lie along straight lines
10
that are substantially parallel to the longitudinal centerline
4
. The cutting edges
8
and the straight lines
10
coincide. The blade further has back edges
2
opposite the cutting edges
8
, and a top surface
80
opposite the bottom surface
Each cutting edge
8
is defined by the junction of the blade bottom surface
6
and a cutting surface
12
. The cutting surfaces
12
intersect the top surface
80
. The bottom surface
6
and cutting surface
12
subtend a cutting angle L. Each cutting edge
8
intersects an end
34
of the blade
3
at a tip
38
. The tips
38
are especially important, because they are the portions of the blade that first come into contact with the vegetation being cut by the blade. There are an infinite number of imaginary lines
14
along the blade bottom surface
6
between each cutting edge
8
and the corresponding back edge
2
. Flat blades such as the blade
3
are used to shear vegetation and expel it tangentially away from a mowing machine.
Other cutting blades have cutting edges that are not straight but instead lie along curved lines. The curved cutting edges are particularly useful for mulching the vegetation in addition to shearing it and expelling it.
FIGS. 4-7
show a typical mulching blade
16
having five sections: a relatively long center section
26
, a pair of angled sections
28
that slope downwardly and away from the ends of the center section
28
, and a pair of end sections
30
on the ends of the angled sections
28
. The end sections
30
lie in a plane that is substantially parallel to the plane of the center section
26
. The center section has a bottom surface
22
, the angled sections have respective bottom surfaces
48
, and the end sections
30
have respective bottom surfaces
49
. The center section has a top surface
84
, the angled sections have respective top surfaces
86
, and the end sections have respective top surfaces
88
. The mulching blade defines a longitudinal centerline
92
.
The mulching blade
16
further has curved cutting edges
18
. Each cutting edge
18
lies along a respective curved line
20
. The cutting edges
18
and lines
20
are generally parallel to the centerline
92
and are defined by the junctions of the bottom surfaces
22
,
48
,
49
of the blade sections with associated cutting surfaces
24
. The cutting surface
24
intersects the top surfaces
84
,
86
, and
88
. The cutting edges
18
also intersect the ends
40
of the mulching blade at tips
42
. There are an infinite number of imaginary lines
32
on the mulching blade bottom surfaces between the cutting edges
18
and the back edges
90
of the blade opposite the cutting edges.
A routine task associated with rotary power mowers is sharpening the blades. For that purpose, a variety of mechanized equipment has been developed. For example, a division of Wall Enterprises, Inc. of New Whiteland, Ind., markets rotary blade grinding machines. Magna-Matic Corporation of Waldo, Wis., is a manufacturer of blade grinding and balancing machines.
Prior blade sharpening machines have not been entirely satisfactory. For one reason, they generally have been limited to sharpening blades with straight cutting edges, i.e., flat blades such as blade
3
depicted in
FIGS. 1-3
. That is because the prior machines had flat work surfaces of substantial area and lying in a single plane. The blades were supported on the work surfaces and manually fed lengthwise, i.e., parallel to the longitudinal centerline
4
of the blade
3
, while in contact with a grinding wheel. The flat area of the work surface was satisfactory for straight edge blades, because no angular movements of the blade in space relative to the grinding wheel were required to grind the cutting edge.
On the other hand, the flat area work surfaces of prior blade sharpeners presented considerable difficulty with mulching blades, such as mulching blade
16
of
FIGS. 4-7
. That was because the mulching blade curved edges
18
required that the blades be fed crosswise in addition to lengthwise in order to properly grind the curved cutting edges. Simultaneous crosswise and lengthwise feeding of the blades was difficult to do, especially at the transitions between the various sections, such as the transitions between the center section
22
and the angled sections
28
, and the transitions between the angled sections and the end sections
30
. The prior sharpeners used relatively wide grinding wheels, such as one inch, which exacerbated the problem. Moreover, with a flat work surface of substantial area, the curved cutting edges of the different sections contacted the grinding wheel at different angular locations on the grinding wheel periphery. As a result, the cutting angles of the cutting edges at the different blade sections varied considerably. A uniform cutting angle was possible only by carefully imparting angular motions to the blade while lengthwise and crosswise feeding it.
An associated problem with the large flat work surface of a prior machine was that the work surface was cut out to make room for the grinding wheel. The work surface was therefore rather limber and prone to vibrate and create excessive noise during operation. A related problem with the cutout in the work surface was that the blade cutting edge was not supported directly in line with the transverse plane of the grinding wheel. It was very difficult to properly grind the tips of a blade using such a machine, because the cutting force of the grinding wheel required the operator to provide a resisting force. Even if the operator did not yield to the cutting force, the blade itself could bend because it was only cantilever supported by the work surface. Since the tips of the cutting edges are the most important part of the blade, any error in grinding the tips was quickly reflected in substandard mowing machine performance.
U.S. Pat. No. 5,329,731 shows an attachment for a grinding machine that facilitates sharpening mulching blades. The attachment has two flat work surfaces, each of substantial area, along which a blade is fed. However, the flat large area work surfaces limit the attachment's usefulness when sharpening mulching blades having certain contours. In fact, some style mulching blades can not be sharpened at all when using the attachment of the U.S. Pat. No. 5,329,731. For some other mulching blades, even using the attachment of the U.S. Pat. No. 5,329,731 produces varying cutting angles on the blade cutting edges along different sections of the blade.
Yet another deficiency of prior sharpening machines concerns the grinding wheels and their mountings. In prior machines, the grinding wheels were mounted directly to the armature shafts of electric motors. Accordingly, the grinding speed was limited to the motor speed. However, many grinding wheels are capable of cutting at higher speeds than conventional motor speeds. Hence, the full cutting capabilities of the grinding wheels were not used. A related problem concerns the composition of the grinding wheels used with pr
Cayen Donald
Magna-Matic Corporation
Wilson Lee D.
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