Rotary shear

An improved rotary power shear that includes an electric motor which drives, through a reduction gear assembly, a rotary shear assembly comprised of a driving shear wheel which rotates against a cooperating driven shear wheel. The design of the tool is characterized by a handle that extends above the motor housing and gear casing, and which supports the tool at one end from the gear casing and at the other end from the rear of the motor housing. In this manner the tool is balanced when held by the handle as the weight of the gear casing and cutting assembly at the forward end of the tool offsets the weight of the motor at the rearward end of the tool. In addition, the design of the tool is facilitated by the provision of a single bracket member that serves the multiple functions of supporting and biasing together the rotary shear wheels, providing a cover for the gear casing, and also providing a support for the stub shafts on which the gears are journalled. An overload release clutch is also incorporated into the reduction gear assembly to protect the tool from being damaged by excessive workpiece resistance. The preferred embodiment of the tool further includes a forward-and-reverse switching capability.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to rotary power shears and in particular to 
an improved rotary shear design that is safe, easy to operate and 
inexpensive to manufacture. 
Rotary power shears of the type to which the present invention pertains are 
known in the art and typically comprise a motor driven worm gear which 
extends axially from the end of the motor shaft and which in turn drives a 
shear wheel that rotates against a cooperating driven shear wheel. 
Material to be cut is fed between the shear wheels where it is cut and 
then passed below the motor housing which typically serves also as the 
handle for the tool. 
The present invention seeks to provide an improved rotary shear design that 
provides better balance for better control of the cutting head. With 
conventional rotary shears, the motor housing either comprises the handle 
for the tool as noted or serves as a support for a handle which is 
typically fastened to the end of the motor housing opposite the cutting 
head. This arrangement creates an imbalance in the tool due to the 
extension of the gear box and cutting head assembly beyond the front end 
of the motor. In other words, the tool tends to feel "front-heavy" when 
operated. This in turn compromises the ease with which the tool can be 
controlled, particularly when used to make irregular-shaped or lengthy 
cuts. The present invention eliminates this disadvantage by providing a 
rotary shear design having a handle that extends above the motor housing 
and gear box and which supports the tool from the gear box at one end and 
the rear of the motor housing at the other. In this manner, the tool is 
almost perfectly balanced when held by the handle. In addition, the 
position of the handle serves to remove the operator's hand from the 
vicinity of the cutting head. This improves the safety of the tool and 
also insures that the user's hand will not interfere with cut material as 
it passes beneath the underside of the motor housing. 
Additionally, the present rotary shear design eliminates the more expensive 
worm gearing used in prior art designs and instead utilizes less costly 
spur gearing to provide the necessary gear reduction to drive the shear 
wheels. Moreover, the entire gear mechanism is enclosed in a compact gear 
casing located forward of the motor in the lower front portion of the tool 
to balance the weight of the motor as described above. As will be more 
fully discussed in the description of the preferred embodiment, the 
compactness of the gear casing and cutting head assembly is in part due to 
the utilization of a single bracket member to support and bias together 
the shear wheels, provide a cover for the gear casing, and to also provide 
a bearing support for the stub shafts or pins on which the gears are 
journalled. 
Further improvements in the design of the present rotary shear include an 
overload release clutch which is provided in the gearing mechanism to 
protect the tool against excessive torque loads, and a reverse capability 
which facilitates the removal of a jammed workpiece with minimum damage to 
the workpiece and also allows easy withdrawal of the tool from a workpiece 
when making a "blind" cut. 
Additional objects and advantages of the present invention will become 
apparent from a reading of the detailed description of the preferred 
embodiment which makes reference to the following set of drawings in which 
:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a rotary shear 10 according to the present invention 
is shown. The present rotary shear 10 is adapted to cut a wide variety of 
materials commonly found in the home or shop such as carpeting, cloth, 
sheet metal, wire mesh, chicken wire, aluminum siding, cardboard, vinyl 
tiles and linoleum. Basically, the rotary shear 10 comprises an electric 
motor 12 which drives through a reduction gear assembly 16, a cutting 
assembly 18 comprised of a driving and a driven pair of rotary shears, 20 
and 22 respectively. The driven rotary shear 22 is offset relative to, and 
supported directly below, the driving rotary shear 20 by a bracket 30 so 
that a small portion of the planar surface of the driven rotary shear 22 
overlaps the planar surface of the driving rotary shear 20. In addition, 
as best illustrated in FIG. 3, the driven rotary shear 22 is canted 
slightly and biased toward the driving rotary shear 20 by the bracket 30 
so that the cutting edges of the two rotary shears are biased together at 
their point of contact to provide a positive shearing action. The biasing 
function provided by the bracket 30 permits the present rotary shear to be 
utilized to cut thin, highly flexible material such as cloth. 
Material to be cut by the tool 10 is fed between the two shear wheels 20 
and 22 where it is severed and then passed below the motor housing 14. It 
will be noted that the cover 24 which is secured to the bracket 30 to 
protect the bearings of the driven shear wheel 22, also serves to direct 
cut material over bracket 30 so that it does not "hang up" on the leading 
edge 31 of the bracket 30. In addition, another bearing shield 25 disposed 
over the bearing of the driving shear wheel 20 is provided with a 
depending portion which serves to direct the remaining portion of cut 
material below the leading edge 31 of the bracket 30. 
The motor 12 is encased in a housing 14 and receives electrical power via a 
line cord 15 which is connected at its other end to a power source. 
Operation of the motor 12 is controlled by a switch 26 which in the 
preferred embodiment is of the variable speed type well known to those 
skilled in the art. A forward and reverse switch 28 is also preferably 
provided so that the direction of rotation of the cutting assembly 18 can 
be reversed. This is a desirable feature that is particularly useful when 
removing material jammed between the cutting shears 20 and 22, or when 
withdrawing the tool 10 after making a blind cut. 
The overall configuration of the tool 10 is characterized by a handle 32 
spaced above the motor housing 14, which is supported by a front portion 
34 extending upwardly from, and encompassing at its lower end, the gear 
assembly 16, and a rear portion 36 extending upwardly from the rear of the 
motor housing 14. Importantly, it will be appreciated that the 
configuration and location of the handle 32 is such that when the tool 10 
is held by the handle 32, the weight of the motor 12 at one end is almost 
perfectly balanced by the combined weight of the gear assembly 16 and 
cutting assembly 18 at the other end. Thus, control over the movement of 
the tool 10 is greatly improved. In addition, it will further be 
appreciated that by placing the handle above the motor housing 14 away 
from the vicinity of the cutting assembly 18, the safety of the tool is 
improved. 
Turning now to FIG. 2, a partially cutaway side elevation view of the 
rotary shear 10 according to the present invention is shown. As can be 
seen in the drawing, the motor compartment defined by housing 14 is 
separated from the gear assembly 16 by a transverse wall 35. The shaft 40 
of the motor 12 which drives a cooling fan 37, is journalled in a bushing 
41 mounted in an opening in the wall 35. The end of the motor shaft 40 
extending through the wall 35 defines a pinion gear 42. As best 
illustrated in FIG. 5, the pinion gear 42 drivingly engages a face gear 44 
which comprises the driving member or input element of a torque-responsive 
overload clutch assembly 60. The clutch assembly 60 further includes a 
driven member or output element 62 which in turn drives a spur gear 46. 
Torque is transferred from the driving member 44 of clutch assembly 60 to 
the driven member 62 through a torque limiting arrangement comprised of a 
plurality of balls 64 seated in a corresponding plurality of pockets 63 
formed in the face of driven member 62. The balls 64 are biased into the 
pockets 63 of driven member 62 by compression springs 66 disposed in 
axially extending recesses 68 formed in the opposed face of driving member 
44. 
Under normal operation the balls 64 are retained in the pockets 63 in 
driven member 62 by the bias force exerted by springs 66. However, in an 
overload condition when the workpiece resistance exceeds the level that 
can properly be handled by the rotary shear 10, the walls of the pockets 
63 act upon the balls 64 causing them to compress springs 66 and retract 
into the recesses 68 in driving member 44, thereby permitting driving 
member 44 to rotate while driven element 62 remains stationary. Upon 
removal of the overload condition, the balls 64 will automatically re-seat 
into the pockets 63 in the driven member 62 under the bias force of the 
springs 66. The torque threshold release level of the clutch assembly 60 
may of course be preset to any desired level by varying the spring tension 
or in any other known manner. 
The primary function of the overload release clutch is to protect the 
bracket 30 from excessive material resistance. In particular, the biasing 
function performed by the bracket 30 in supporting the driven shear wheel 
22 in the manner described is important to the shearing operation of the 
tool 10 because it insures that proper forced contact is maintained 
between the cutting edges of the two shear wheels. If an excessively shear 
resistant piece of material is fed between the shear wheels, however, the 
large amount of torque present at the cutting head may nonetheless cause 
the material to be drawn between the shear wheels 20 and 22. This in turn 
will result in the shear wheels 20 and 22 being forced apart thereby 
causing a deformation of the portion of bracket 30 supporting the driven 
wheel 22. If this deformation is excessive enough, it can result in 
permanent deformity of the bracket 30 causing a loss of contact between 
the two shear wheels 20 and 22. While this condition may not affect the 
tool's ability to cut rigid material such as sheet metal, it can render 
the tool completely ineffective for cutting flexible material such as 
cloth. Accordingly, in the preferred embodiment, the torque limit of the 
overload release clutch 60 is set so that the resulting maximum torque 
load attainable at the cutting head is not substantial enough to cause 
permanent deformation of the support bracket 30. 
Significantly, it will also be noted that the overload release clutch 60 is 
located at the output of the motor drive shaft 40 and not at the output of 
the gear reduction assembly 16 where the rotational speeds are 
significantly reduced. This is due to the torque loads present at the 
output of the reduction gear assembly 16 which were determined to be too 
great to be reliably accommodated by an overload release clutch having the 
physical dimensions required to fit within the gear casing 38. However, 
the placing of the clutch at the input of the gear assembly 16 imposed 
further constraints on the size of the clutch, which in turn presented an 
assembly problem due to the resulting small size of the clutch components. 
Consequently, to facilitate assembly of the tool 10, the present overload 
release clutch 60 is designed to be pre-assembled as a separate 
sub-assembly so that the small components of the clutch 60 cannot 
accidentally be dislodged in the gear casing 38 during assembly. This is 
accomplished by providing the driving member 44 of the clutch 60 with an 
extended neck portion 45 which is adapted to fit within the enlarged bore 
65 of the driven member 62. In this manner, when the clutch 60 is 
assembled by joining the driving 44 and driven 62 member together, the 
neck portion 45 will extend slightly beyond the shoulder 67 at the end of 
the bore 65, thus permitting the neck portion 45 to be cold-staked as 
shown at 69 and secured to the shoulder 67. Accordingly, it will be 
appreciated that the present overload release clutch 60 can be easily 
installed as a complete sub-assembly. 
Continuing with the description of the gear assembly 16, spur gear 46, 
which is driven by the output element 62 of clutch assembly 60, drivingly 
engages gear 48. The spur gear 50 associated with gear 48 then drives gear 
52 whose associated spur gear 54 in turn drives gear 56 which is affixed 
to the drive shaft 70 of the driving rotary shear 20. In the preferred 
embodiment of the invention the total gear reduction provided by the gear 
assembly 16 is 288-to-1. 
The gear assembly 16 is housed within a casing 38 that is completely 
enclosed on the side exposed in FIG. 2 by the bracket member 30, which is 
the same bracket that extends below the forward end of the tool 10 and 
supports the driven rotary shear 22 as described above. Bracket member 30 
is secured to gear casing 38 by a plurality of bolts 78. Thus, as can best 
be seen in FIGS. 3 and 4, the gear assembly 16 is completely confined by 
the enclosure defined by the gear casing 38, the transverse wall 35 and 
the cover bracket 30. In addition, it will be noted that the bracket 
member 30 also serves to support the stub shafts 70-76 on which are 
journalled the entire gear assembly 16. In particular, as best shown in 
FIG. 3, the stub shafts 70-76 are supported at one end by the gear casing 
38 and at the other end by the bracket member 30. Accordingly, it can be 
seen that the bracket member 30 serves four functions: (1) it supports 
both the driving and driven rotary shears, 20 and 22 respectively, (2) it 
biases the driven rotary shear 22 against the driving rotary shear 20, (3) 
it seals the gear casing 38, and (4) it supports the stub shafts 70-76 of 
the gear assembly 16. 
Thus, it will be appreciated that there is disclosed by the present 
invention an improved portable rotary power shear that includes an 
overload release clutch incorporated into a reduction gear assembly 
comprised of relatively inexpensive spur gearing that is completely 
enclosed in a compact gear casing which is sealed by a multi-purpose 
bracket which serves also to support both the journal pins for the gearing 
and the two rotary shear wheels, as well as providing a bias force between 
the two shear wheels. In addition, the present design is characterized by 
an integral overhead handle which supports the gear casing and cutting 
assembly at the forward end of the tool and the motor housing at the 
rearward end of the tool, so that the tool is well balanced for good 
control and easy maneuverability. 
While the above description constitutes the preferred embodiment of the 
present invention, it will be appreciated that the invention is 
susceptible to modification, variation and change without departing from 
the proper scope or fair meaning of the accompanying claims.