Cutter blade for a rotary cutter

The invention relates to a cutter blade for use on a rotary cutter of the tractor drawn type. Rotary cutters of this type usually have three or four cutter blades rotatably mounted on a blade carrier that can be rotated to induce cutter blade rotation and thereby permit cutting of grass. The cutter blade of the invention has a curved cutting edge with the section including the cutting edge being off-set with respect to the section whereby the blade is mounted on its blade carrier. The use of such cutter blades on a rotary cutter improves cutting efficiency, provides for an increased blade life and reduces the power requirements of the rotary cutter with which the blades are associated.

This invention relates to rotary cutters. More particularly, the invention 
relates to a cutter blade for a rotary cutter that is used for cutting 
grass, and like matter. 
The rotary cutter to which the present invention relates is a tractor drawn 
rotary cutter and includes an operatively horizontally disposed blade 
carrier that is mounted for rotation, about an axis of rotation that is 
operatively vertically disposed, on the body of the rotary cutter. The 
blade carrier can be mechanically linked by a power-take-off shaft to a 
power-take-off of a tractor, to be rotated thereby. The blade carrier 
carries a plurality, usually three or four, cutter blades that are mounted 
for free rotation on the blade carrier, being freely rotatable about axes 
of rotation that are parallel to the axis of rotation of the blade 
carrier. The blade carrier as above envisaged can be in the form of a 
disc, a beam, any other substantially planar member, or the like, the 
general configuration of such a blade carrier and its cutter blades in 
association with a rotary cutter, as described above, being well known and 
not being described in further detail herein. 
Each cutter blade of a rotary cutter of the above described type comprises 
an elongated flat bar of which one end is rotatably mounted on the blade 
carrier of the rotary cutter. The direction of rotation of the blade 
carrier will determine the direction of rotation of the cutter blade 
mounted thereon and, as such, one elongated side edge of each flat bar 
will form a leading edge, the said leading edge defining a linear 
sharpened region, whereby grass is cut. 
Accordingly, by the driven rotation of the blade carrier of the rotary 
cutter, centrifugal forces acting on the cutter blades will result in 
rotation thereof about their axes of rotation, the cutter blades thereby 
providing for cutting of grass. Because of the linear cutting edges of the 
cutter blades, the effective angle of attack of the cutting edges on grass 
being cut will continuously vary, as determined by the resistance of grass 
being cut, this variation in angle of attack providing for the blades to 
perform either a "chopping" action on grass being cut, or a slicing action 
which will decrease in efficiency as the angle between the longitudinal 
axis of each blade and a radial line extending through the centre of the 
blade carrier, increases. This can result in relatively inefficient 
cutting of grass and increased power and fuel requirements. Also, because 
of the linear configuration of the cutting edge of each cutter blade and 
the mode of cutting, as described, wear on each cutter blade is 
substantial, particularly at the end of each cutter blade remote from its 
axis of rotation. 
Accordingly, it is an object of this invention to provide a cutter blade 
for a rotary cutter which has improved wear characteristics. 
It is a further object of this invention to provide a cutter blade for a 
rotary cutter having an improved cutting efficiency, thereby to reduce the 
power requirements of the rotary cutter. 
According to the invention there is provided a cutter blade for a rotary 
cutter, which is formed of an elongated flat bar having substantially 
parallel longitudinal side edges and defining a longitudinal axis midway 
between and parallel to said side edges, the flat bar being formed to 
define a mounting section adjacent one end thereof that can be rotatably 
mounted on a blade carrier of a rotary cutter, a cutting section adjacent 
the other end thereof that defines a sharpened cutting edge along one end 
of its side edges, and an intermediate section that links the mounting 
section to the cutting section and that is cranked to off-set the plane of 
the cutting section with respect to the mounting section, the side edge 
portion of the flat bar is formed to define the cutting edge section being 
curved operatively rearwardly with respect to a straight line defined by 
the remainder of the side edge of the flat bar including the said side 
edge portion, the curvature of the side edge portion defining the cutting 
edge being such that the line defining the cutting edge defines an arc of 
a circle with the center of the circle being defined along a line dividing 
the cutting section and the intermediate section of the flat bar and which 
is perpendicular to the longitudinal axis of the straight section of the 
flat bar along the mounting section and intermediate section, the ratio of 
the radius of the circle and the length of the cutting section being 
between 2:1 and 1.5:1. 
The off-set of the cutting section of the flat bar with respect to the 
mounting section may be larger on the side edge portion side that defines 
the cutting edge than on the opposite side thereof, the cutting section 
being inclined with respect to the mounting section about an axis defined 
by the longitudinal axis of the elongated flat bar. The said angle of 
inclination of the cutting section of the flat bar with respect to the 
mounting section preferably is between 3.degree. and 10.degree. and, 
typically, is 6,5.degree.. 
The mounting section of the flat bar conveniently has a hole therein near 
the end of the bar, which permits mounting of the blade on a blade carrier 
of a rotary cutter by a bolt and nut arrangement. As such, the minimum 
off-set between the mounting section and the cutting section is larger 
than the maximum distance the said bolt and nut arrangement can project on 
the blade side of the cutter blade, when mounted on a blade carrier. 
Still further, the overall length of the flat bar forming the cutter blade 
may be determined by the dimensions of the blade carrier on which the 
blade can be mounted, the length of the blade being such that a plurality 
of blades mounted on the carrier are freely rotatable with respect to the 
carrier, without interference with one another. 
The ratio of the overall flat bar length to the length of the cutting 
section may be between 2:1 and 4:1, whereas the ratio of the overall flat 
bar length to the flat bar width may be approximately 5:1. Still further, 
the thickness of the flat bar may be between 5 mm and 15 mm. 
According to a preferred embodiment of the invention, the curvature of the 
cutting section of the flat bar may have been formed by a rolling process, 
whereas the cutting edge may have been formed by forging. 
The invention extends also to a rotary cutter for cutting grass, and like 
matter, which comprises a body that can be hitched to a tractor, a blade 
carrier mounted on the body for rotation about an operatively vertical 
axis, connector means for connecting the blade carrier to the power 
take-off of a tractor to be rotatable thereby, and a plurality of cutter 
blades mounted for free rotation on the blade carrier, each cutter blade 
being formed of an elongated flat bar having substantially parallel, 
longitudinal side edges and defining a longitudinal axis midway between 
and parallel to the side edges, the flat bar having a mounting section 
adjacent one end thereof where the flat bar is rotatably mounted on the 
blade carrier, a cutting section adjacent the other end thereof that 
defines a sharpened cutting edge along one of its side edges, and an 
intermediate section that links the mounting section to the cutting 
section and that is cranked to off-set the plane of the cutting section 
with respect to the plane of the mounting section, the side edge portion 
of the bar that is formed to define the cutting edge being curved 
operatively rearwardly with respect to a straight line defined by the 
remainder of the side edge of the flat bar including the said side edge 
portion. 
Each cutter blade of the rotary cutter particularly is a cutter blade 
having the features of the cutter blade, in accordance with the present 
invention, as are hereinabove defined.

Referring initially to FIGS. 1 and 2 of the drawings, a rotary cutter, in 
accordance with the invention, is designated generally by the reference 
numeral 10. The rotary cutter 10 includes a main body 12 that can be 
hitched to a tractor by suitable hitching formations 14. The body 12 
serves as a housing for surrounding a blade carrier, which in the 
configuration shown is in the form of a blade disc 16, and cutter blades 
18, the cutter blades 18 being rotatably mounted on the disc 16 in the 
configuration as is illustrated clearly in FIG. 2 of the drawings. The 
blade disc is rotatably mounted on the body 12, the disc being operatively 
connected to a drive shaft 20, which can be operatively connected to a 
tractor power-take-off by means of a power-take-off shaft 22 via a gear 
box 24. This arrangement provides for the rotation of the blade disc 16 
about an operatively vertical axis 26, thus providing for rotation of the 
disc 16 in a substantially horizontal plane, with the cutter blades 18 
being rotatable about axes substantially parallel to the said vertical 
axis 26. 
The above general configuration of the rotary cutter 10 is essentially 
conventional as for known rotary cutters and as this does not form a part 
of the present invention, this is not described in any further detail 
herein. 
Each cutter blade 18 of the rotary cutter 10 is formed of an elongated flat 
bar 28 having substantially parallel longitudinal side edges, 30 and 32 
respectively, the flat bar defining a longitudinal axis 34 midway between 
and parallel to the said side edges (see FIG. 4). 
Each cutter blade 18 is divided into a mounting section 36 adjacent one end 
38 of the flat bar 28, a cutting section 40 at the other end 42 of the 
flat bar 28 and an intermediate section 44 that links the mounting section 
to the cutting section and that is cranked to off-set the plane of the 
cutting section 40 with respect to the plane of the mounting section 36. 
The mounting section 36 of the flat bar 28 has a hole 46 defined therein 
near the end 38 of the flat bar whereby the cutter blade 28 is mounted on 
the blade disc 16 by means of a bolt and nut arrangement 48, as is 
illustrated clearly in FIG. 2 of the drawings. 
The cutting section 40 of the flat bar 28 on the side edge 32 side thereof 
defines a sharpened cutting edge 50, the cutting edge 50 being curved 
operatively rearwardly with respect to a straight line defined by the 
remainder of the side edge 32 of the flat bar 28, the curved configuration 
of the cutter blade 18 being illustrated clearly in FIGS. 3 and 4 of the 
drawings. 
The off-set of the cutting section 40 of the flat bar 28 with respect to 
the mounting section 36 as provided by the cranked intermediate section 
44, is larger on the side of the side edge 32 than on the side of the side 
edge 30 of the flat bar 28, the cutting section thus being inclined with 
respect to the mounting section about an axis defined by the longitudinal 
axis 34 of the flat bar 28. This angle of inclination of the cutting 
section 40 with respect to the mounting section 36 is illustrated clearly 
in FIG. 5 of the drawings and, typically, this angle of inclination A is 
equal to approximately 6,5.degree.. This will provide an effective 
flighting of the cutter blades 18, causing an upward movement of air 
within the housing 12 of the rotary cutter 10 during rotation of the blade 
disc 16 about its shaft 20 and of the blades 18 with respect to the blade 
disc 16, which has the benefit described hereafter. 
The line defined by the cutting edge 50 particularly defines an arc of a 
circle, with the centre of the circle being defined along a line 52, which 
divides the cutting section 40 from the intermediate section 44 of the 
flat bar 28 and which is perpendicular to the longitudinal axis 34 of the 
flat bar 28 along the straight section of the flat bar 28, being the 
mounting section 36 and the intermediate section 44. The radius of 
curvature of the line defining the cutting edge 50 is determined by the 
effective length of the cutting section 44 defining the cutting edge 50 
and, particularly, the ratio of this radius of curvature and the effective 
length of the cutting section of the flat bar is between 2:1 and 1,5:1. 
The overall length of the flat bar 28 forming the cutter blade 18 is 
determined by the dimensions of the blade disc 16 on which it is mounted, 
the length of the blade 18 particularly being such that a plurality of 
blades, when mounted on the disc 16, will be freely rotatable with respect 
to the disc 16 without interference with one another. 
Furthermore, the ratio of the overall flat bar length to the length of the 
cutting section is between 2:1 and 4:1, whereas the ratio of the overall 
flat bar length to the flat bar width is approximately 5:1. The thickness 
of the flat bar 28 typically is between 5 mm and 15 mm, as will be 
determined by the different applications of rotary cutters. 
As is envisaged above each cutter blade 18 of a rotary cutter, in 
accordance with the invention, will be formed in one piece of an elongated 
flat bar, with the curvature of the cutting section 40 and the cranking of 
the intermediate section 44 being provided by a rolling and pressing 
process, whereas the cutting edge will be formed by a forging process. 
Clearly, the cutter blade can be manufactured of any suitable material 
and, particularly, a material as is already commonly associated with 
cutter blades used on rotary cutters of the type envisaged herein. 
By providing a rotary cutter as herein envisaged with cutter blades 18 
having the features as described above, it is believed that the overall 
cutting efficiency of the rotary cutter will be greatly enhanced. This 
improved efficiency is due to the fact that the cutting edge 50, during 
operation of the rotary cutter 10, will perform a more effective slicing 
action on grass, or like matter being cut, the radius of curvature of the 
cutting edge 50 being such that the slicing action is facilitated for all 
relative positions of each cutter blade 18 with respect to the blade disc 
16. 
Blades having conventional straight line cutting edges either perform a 
chopping action on grass being cut, which is very inefficient, or perform 
a slicing action with the angle of attack on grass being cut varying 
constantly, which, once again, is inefficient. Furthermore, because of the 
curved configuration of the cutting edge 50, the effective length of the 
cutting edge is increased when compared to a conventional cutter blade 
having a straight line cutting edge and, thereby, cutting efficiency is 
further enhanced. 
Because of the improvement in cutting efficiency as provided by the cutter 
blades 18, the power requirements of the rotary cutter 10 are effectively 
reduced when compared to conventional rotary cutters having conventional 
blades and this will result in a saving in the fuel consumption of a 
tractor with which the rotary cutter 10 is used. 
The minimum off-set of the cutting section 40 with respect to the mounting 
section 36 of the flat bar 28, as provided by the intermediate section 44, 
will be larger than the maximum distance the bolt and nut arrangement 48 
can project on the blade side of the cutter blade when mounted on the 
blade disc 16, thus ensuring that the bolt and nut arrangement remains 
above the ordinary cutting level as provided for by the cutter blades 18. 
Thereby, wear on the bolt and nut arrangement is reduced, which could 
otherwise cause failure of the bolt and nut arrangement, which can be very 
dangerous. 
Also, because of the flighting of the cutting sections 40 of the blades 18 
as described above, the upward air movement created within the housing 12 
will cause effective lifting of grass being cut, once again improving the 
cutting efficiency of the rotary cutter 10. 
Still further, by providing each cutter blade 18 with the curved cutting 
edge 50 as defined, the wear characteristics of each cutter blade 18 is 
improved when compared with the wear characteristics of conventional 
cutter blades defining linear cutting edges, particularly near the end of 
the cutting edge 50 remote from the end where the cutter blade 18 is 
mounted on a blade disc. 
It is envisaged that the exact configuration of the cutting blade 18 can be 
varied in various different respects, while still incorporating the 
features of the cutter blade as are hereinabove described and defined and 
the invention extends also to such alternative configuration cutter blades 
for use on rotary cutters.