Circle shears

A circle shear device for cutting holes and rings in sheet metal wherein a pair of spaced apart, coaxially aligned center shafts are each provided with a cutter wheel which is mounted on a radially extended arm. In operation a metal blank is inserted between the two spaced apart center shafts and the center shafts are brought together wherein the sheet metal blank is restrained from moving by the bearing mounted supporting platform members of each center shaft. Synchronous rotation of the center shafts is achieved by a jack shaft assembly which joins the two center shafts. In a preferred embodiment, a motor is provided to power the rotation of the shafts. In an alternate embodiment, the shafts may be rotated by the use of a hand crank. A pneumatic cylinder is also provided to one of the shafts to permit vertical reciprocation of the shafts for removal and insertion of metal blanks for cutting operation. In one embodiment, the circle shears may be implemented in an automatic feed system wherein sheet metal is directed onto a line from a spooling apparatus. The metal sheet is then cut into even sections via a blanking apparatus, after which each blank is passed through the circle shear station for hole cutting operation. The cut blanks may be removed from the line or advanced to another station for additional metal forming.

FIELD 
The present invention relates generally to an apparatus and method for 
cutting circles and rings in sheet metal. More particularly, the invention 
relates to a sheet metal circle shear apparatus and method whereby a pair 
of cutting wheels are rotatably mounted on a pair of coaxially aligned, 
spaced apart center shafts, and whereby at least one of the center shafts 
is reciprocable to permit the insertion of a sheet of metal therebetween 
for cutting circular holes therein. The center shafts are linked together 
by a common jack shaft and are powered to rotate about their longitudinal 
axes to permit the cutting wheels to rotate along a circular path and cut 
a hole in the metal sheet. 
BACKGROUND 
Sheet metal is the preferred material of construction for the fabrication 
of ducts and other fittings used in heating and ventilation systems. For 
many of the fittings, a hole or ring must first be cut in a flat metal 
sheet prior to the fixation of a tubular or conical piping member 
thereover. 
One method for cutting a hole in a sheet metal blank is by using a manually 
operated circle shear machine. An example of a typical manually operated 
circle shear machine is the model No. 298 offered by the Roper Whitney Co. 
of Rockford, Illinois. This machine includes two opposed cutter wheels 
which are clamped down on a top and bottom surface of the metal sheet. The 
cutter wheels are then power rotated to draw the metal sheet through the 
cutter wheels in a circular pattern to form a hole cut-out in a manner 
similar to a can opener spinning a can in which it is opening. 
A principal disadvantage with this type of circle shear machine is that it 
cannot be feasibly implemented in existing automatic feed systems. Current 
state of the art automatic feed systems for sheet metal fabrication 
typically comprise a plurality of different in-line sheet metal working 
stations (e.g., a blanking machine, a forming machine, etc.), and are 
linked together by a belt or chain drive transport mechanism. The sheet 
metal is held stationary at each metal working station and then advanced 
to the next station via a conveyor. Implementation of the aforementioned 
circle shear machine would result in major complications in the handling 
of the metal sheet, since now the metal sheet must be rotated in the 
middle of the automated line in order to generate a hole cut-out by the 
circle shear machine. The handling difficulties would only be increased 
when a wider diameter circle cut is desired since this requires that the 
entire sheet metal section be moved through a wider circular path by the 
cutter wheels. 
U.S. Pat. No. 4,397,207 (Isaao, 1983 ) teaches to provide a sheet metal 
cutting device which is mounted on a wheeled dolly. The device includes an 
adjustable trammel assembly which guides the dolly in an arc as a pair of 
powered cutting wheels work their way through the metal sheet. Isaac is 
directed towards cutting large radius curves and circles for forming 
conical upper portions of grain bins and like applications and is not well 
adapted for cutting smaller holes for use in heating and ventilation 
systems on a mass production scale. Also, it is not feasible to implement 
the cutting device of Isaao into existing automated sheet metal 
fabrication machines since the wheeled dolly must be permitted to move 
around the sheet metal to make a cut. 
Another method for cutting holes in sheet metal sections is by using a 
circular die to punch a hole in the metal sheet. This method is 
particularly well suited for use in an automated line wherein a large run 
of sheet metal blanks having the same size hole is desired. However, this 
method becomes cost prohibitive for smaller production runs of sheet metal 
blanks and for production runs having different sized diameter holes, 
since a separate die is required for each different size diameter hole. 
Replacing dies is a labor intensive process which slows down productivity. 
Also, the use of dies in general means increased tooling costs. It is not 
uncommon for sheet metal fabricators to invest $20,000 to $40,000 for an 
adequate supply of dies. Moreover, as the dies are used, additional 
expense is incurred for periodic resharpening and replacement 
Accordingly, there is a definite need in the art for an improved circle 
shear machine which is simple to operate and is easily implemented in 
current automatic feed sheet metal fabrication systems. There is also a 
need for such a circle shear machine which includes means for simple 
adjustment of the cutting hole diameter and is economical to operate in 
terms of tooling costs. 
The Invention 
OBJECTS 
It is a principal object of the invention to provide a circle shear machine 
having a cutting jaw formed by overlapping cutter wheels and whereby a 
first and second cutter wheel are separately mounted on a individual ones 
of a pair of coaxially aligned rotatable center shafts which, when 
operated under power, move the cutter wheels in a circular path to cut a 
hole or ring in a stationary metal sheet positioned within the cutting jaw 
formed by the cutter wheels; 
It is another object of the invention to provide the circle shear machine 
wherein the cutter wheels are mounted on laterally extending arms which 
are removable from the rotatable center shafts to permit easy replacement 
of the cutter wheels/arms and adjustment of the cutting hole diameter; 
It is another object of the invention to provide the circle shear machine 
having means for convenient and reliable adjustment of the hole cutting 
diameter without the need of removing the arms from the center shafts; 
It is another object of the invention to provide a circle shear machine 
that is easily implemented into existing automatic feed sheet metal 
fabrication systems; 
It is another object of the invention to provide a method for cutting a 
hole or ring in a metal sheet wherein a pair of cutting wheels are rotated 
in a circular motion about a stationary metal sheet positioned 
therebetween; and 
Still further objects will apparent from the following description, 
drawings and claims.

SUMMARY 
A circle shear machine for cutting holes and rings in sheet metal whereby 
the sheet metal is held stationary by a pair of coaxially aligned and 
opposed center shafts which are each provided with a thrust bearing 
mounted support platform to engage top and bottom surfaces of the metal 
sheet at the locus center of the hole to be cut. The center shafts are 
also provided with laterally extending arms having freely rotatable cutter 
wheels mounted thereon whereby the cutter wheels are disposed to engage 
the upper and lower surfaces of the metal sheet at a common point along 
the circumference of the circle to be cut. In an operating position, the 
cutter wheels are disposed to overlappingly engage one another to form a 
cutting jaw. 
To begin the cutting operation, the center shafts are simultaneously 
rotated about their longitudinal axes, thus driving the cutter wheels 
along the circumference of the circle to be cut until the circle cut is 
completed. Simultaneous rotation of the center shafts is accomplished by 
means of a linking assembly comprising a jack shaft and two gear and cog 
belt transfer assemblies, each associated with one of said upper and lower 
center shafts. In a preferred embodiment, the center shafts are rotatably 
mounted, preferably through the use of known journaled bearing assemblies, 
within upper and lower portions of a box-like frame work or housing. 
A pneumatic air cylinder is also provided to the upper center shaft to 
permit vertical reciprocating movement so that metal sheet may be inserted 
or removed from the cutting jaw formed by the overlapping cutter wheels. 
The invention is readily implemented in current state of the art automatic 
feed systems for sheet metal fabrication, since a hole is cut in a 
stationary sheet metal blanks without the need for rotating the blanks 
past the cutter wheels as is typically the case with prior art circle 
shear machines. The present invention also offers advantages over circle 
dies or punch-type hole machines of reduced tooling costs and ease of 
changing hole diameter cutting sizes. 
In a first alternate embodiment the arms include means for lateral 
extension to provide a measure of adjustability for changing the hole 
cutting diameter without the need for entirely replacing the arms or 
cutter wheels. Means for lateral arm extension is accomplished by 
adjustably sliding the horizontal shank portions of the arms through a 
receiving bore hole of its respective center shaft and securing the arm to 
that center shaft by means of a set screw or other like hardware securing 
means. 
In further alternate embodiments for adjusting the lateral extension of the 
arms, it is proposed to cut threads along the horizontal shank portion of 
the arm and provide a thumb wheel disposed transverse in the center shaft 
to laterally advance or retract the threaded arm portion in response to an 
actuation of the thumb screw. A dial indicator and an additional set screw 
may be provided to further assist in the precise positional setting of the 
arm with respect to the center shaft. Other alternate embodiments for 
providing arm extension means include stepper motors, a ball-type linear 
actuator, a solenoid motor or an air cylinder motor. 
Another alternate embodiment for the invention comprises an additional pair 
of arms having cutter wheels mounted thereon and whereby the second pair 
of arms are disposed to position the second pair of cutter wheels at a 
point outboard (greater circle diameter) of the first pair of cutter 
wheels so that a ring may be cut in the metal sheet during rotation of the 
center shafts. 
In another embodiment, the circle shear apparatus is implemented in an 
automatic feed sheet metal fabrication system wherein a continuous strip 
of metal sheet is first pulled off a spooling apparatus where it is then 
fed onto an automated line. The sheet metal is then passed through a 
blanking machine which measures and cuts the sheet metal into uniform 
sections. Each sheet metal blank or section is then advanced to the next 
station whereby the circle shear apparatus of the present invention cuts a 
hole in the blank section after which the perforated sheet metal blank is 
advanced to another station for stacking, sorting or further forming. 
DETAILED DESCRIPTION OF THE BEST MODE 
The following detailed description illustrates the invention by way of 
example, not by way of limitation of the principles of the invention. This 
description will clearly enable one skilled in the art to make and use the 
invention, and describes several embodiments, adaptations, variations, 
alternatives and uses of the invention, including what I presently believe 
is the best mode of carrying out the invention. 
A circle shear machine constructed in accordance with one embodiment of the 
present invention is indicated generally by the reference numeral 1 in 
FIG. 1. 
The circle shear machine 1 comprises a pair of center shafts, including an 
upper center shaft 20 and a lower center shaft 30, each having thrust 
bearing mounted sheet metal support members 25, and 35, respectively, 
which, when brought face together, engage on a top and bottom surface of a 
sheet metal blank 10 (shown in phantom), which is positioned therebetween. 
The upper center shaft 20 includes a top arm 23 which is secured at one 
end to the center shaft and includes a freely rotatable cutter wheel 24, 
mounted at its outer free end. Similarly, lower center shaft 30 includes a 
laterally extending arm 33 having one end fixed to the lower center shaft 
30 and also includes a freely rotatable cutter wheel 34 mounted at its 
other free end. 
The upper and lower center shafts 20, 30 are rotatably mounted within a 
frame work 5 by bearing assemblies 21 and 31, respectively. In the 
preferred embodiment, center shafts 20, 30 are power-driven by a motor 
(not shown) to rotate in the direction as shown by Arrow A while the 
support members 25 and 35 restrain the sheet metal blank 10 from moving. 
Synchronous movement of the upper and lower center shafts 20, 30 is 
achieved by use of a synchronizing drive assembly 11, well known in the 
prior art. In the present example, the drive assembly 11 comprises a jack 
shaft 15 which links together upper and lower toothed cog belts 14, 18 and 
gear assemblies 12, 13, 16, 17. The upper cog belt and gear assembly 
includes a first gear 12, disposed in fixed relationship with an outer 
sleeve portion 27 of upper shaft 20 and gear 13 connected to the upper end 
of jack shaft 15. Cog belt 14 transfers rotational motion between gears 12 
and 13. Similarly, the lower cog belt and gear assembly includes gear 17, 
disposed integral with lower center shaft 30 and gear 16 connected to a 
lower portion of jack shaft 15. Cog belt 18 transfers rotational motion 
between gears 16 and 17. 
The lower center shaft 30 is also mounted at its bottom end to a base 
support 32. An additional bearing member 36 may be used to rotatably 
anchor the lower center shaft 30 within the base support 32. The top end 
of the entire upper center shaft 20 also includes an air cylinder 22 which 
permits vertical reciprocating motion of the entire upper center shaft 20 
as indicated by Arrow B. 
In the preferred embodiment of the invention, it is desirable to provide a 
1/2" vertical displacement of the upper center shaft 20 so that 
conventionally sized 1/4" thick metal sheet may be inserted between the 
cutter wheels 24 and 34 for loading and unloading. In the preferred 
embodiment, the upstanding walls of the housing/framework 5 are spaced 
apart by a distance of at least 24 inches to accommodate standard width 
sheet metal blanks commonly handled in automatic feed systems. As is 
evident from FIG. 1, the accomodating frame width spacing is exemplary of 
a simple means for restraining the migration or rotation of a standard 
width sheet metal blank during cutting operation, thus obviating the need 
for manual intervention by a sheet metal worker in holding the work piece 
when the metal blank is fed into the circle shear apparatus. However, it 
is understood that the framework 5 may be modified to accommodate larger 
sheets, including, but not limited to commercially available 
4'.times.8'sheet metal blanks. 
While the preferred embodiment discloses the upper center shaft as having 
the air cylinder means for vertical reciprocation, it is understood that 
an air cylinder could just as easily be used in combination with the lower 
center shaft to provide further vertical reciprocation displacement 
capability to the cutter wheels. It is also understood that a hand crank 
may be used instead of a motor to drive the simultaneous rotation of the 
center shafts. 
FIGS. 2A and 2B illustrate in greater detail the vertically reciprocating 
movement of the upper center shaft 20 (indicated generally by reference 
Arrow B) with respect to the lower center shaft 30. FIG. 2A shows an 
"operating" position wherein upper support 25 of upper center shaft 20 
engages a top surface of a sheet metal blank (omitted for clarity), and 
lower support 35 of lower center shaft 30 engages a bottom surface of the 
sheet metal blank. In this position, the cutting edges of top cutter wheel 
24 and bottom cutter wheel 34 are brought together on both top and bottom 
sides of the sheet metal blank to begin cutting operation. As is best seen 
in FIG. 2B, the upper center shaft 20 has been reciprocated upward (albeit 
an exaggerated amount for purposes of illustration) to permit the removal 
or insertion of a sheet metal blank between upper support 25 and lower 
support 35. 
In the preferred best mode, the cutting edges of the cutter wheels 24 and 
25 overlap each other slightly to form a cutting jar. Also, each cutter 
wheel 24, 34 extends just beyond the blank bearing support surface of its 
corresponding support members 25 and 35. 
It should be noted that at all times during operation the sheet metal blank 
10 is held stationery while the cutting apparatus rotates about a circular 
path to cut a hole. This apparatus provides a simple approach for cutting 
holes in sheet metal and is easily implemented in current state of the art 
automatic feed systems which employ metal working stations that also 
require that the advancing sheet metal blanks be prevented from rotating 
during operation. 
FIG. 3 illustrates the implementation of the circle shear machine 1 in an 
automatic feed system 50. In this example, the automatic feed system 50 
comprises a spooling apparatus 40, a blanking apparatus 45, a circle shear 
machine 1 and a stacking apparatus 60. Spooling apparatus 40 includes a 
rotating mandrel 41 which directs sheet metal off a roll through rollers 
42 onto an assembly line where the metal sheet is first measured and then 
cut into sections or "blanks" by the blanking apparatus 45 and then each 
blank is advanced in turn to the next station. In the present example, the 
next station is the circle shear machine 1 of the present invention. As 
the blanks are advanced along the line, they are secured by upper and 
lower support members 25 and 35 of the center shafts 20 and 30, so that 
the cutter wheels 24 and 34 engage the upper and lower surface of the 
"engaged" blank at a common point. The motor for the sheet metal machine 1 
is then actuated, causing the center shafts to simultaneously rotate, so 
that cutter wheels 24 and 34 follow a circular path having a diameter 
which is determined by the lateral extension of arms 23 and 33. In this 
manner, a hole is formed in the metal sheet. 
Upon completion of this operation, the upper center shaft 20 is raised via 
air cylinder 22, and the metal blank is advanced to the next station for 
further metal forming operation. In the present example, a sorter or 
loader machine 60 drops conical sections over the cut holes in the metal 
blanks for subsequent fixation by welding, gluing or other known bonding 
techniques for metal fabrication. 
When a different sized diameter hole is needed, the arms 23 and 33 are 
simply removed from the center shaft 20 and 30 by loosening mounting 
hardware 23a and 33a, respectively. In this fashion, a different set of 
laterally extending arms 23 and 33 may be mounted onto center shafts 20 
and 30 with relative ease. It should be noted that the cutting wheels of 
this invention offer a significant advantage of greater savings in labor 
and tooling costs over conventional circle punch die machines The 
individual cutter wheels cost on the order of $50 a piece as compared to 
the price of $2500.00-$3500.00 for a single die, and retain their cutting 
edge for an equal amount of time as a dedicated circle diameter die 
FIG. 4 illustrates a first alternate embodiment of a circle shear machine 
having means for adjusting the lateral distance of the arms. In this 
embodiment, the circle shear machine la includes, as before, upper and 
lower center shafts 20a, 30a, having laterally adjustable arms 23a and 
33a. Arms 23a, 33a include measuring indicia along their horizontal shank 
portions 29a, 39a to permit the user/operator to keep a visual record of 
the lateral distance that the arms 23a, 33a have been extended. Upper 
center shaft 20a also includes a dial indicator 26a which assists the 
operator in accurately setting the desired circle hole cutting diameter. 
The arms 23a and 33a may be slidably secured in the circle shaft by any 
number of known means for doing so. In the present example, the shank 
portions 29a, 39a of arms 23a, 33a are received in transverse bore holes 
in vertical center shafts 20a, 30a and are held secure by allen bolts 28 
a, 38a. 
FIGS. 5-7 show further alternate embodiments for adjusting the lateral 
distance of the arms with respect to the center shafts. For purposes of 
brevity only the lateral arm adjustment means for the upper center shafts 
are discussed in detail. 
As best seen in FIG. 5, a set screw and thumb wheel is used to laterally 
adjust the arm 23b and cutter wheel 24b. The horizontal shank portion 29b 
of arm 23b is formed as a threaded shaft having a transverse slot 51 which 
cooperates with set screw 52 for holding the arm 23b fixed with respect to 
upper center shaft 20b. The upper center shaft 20b is also provided with a 
thumb wheel 53 using an arrow indicator 54 for accurately determining the 
distance that the arm 23b has been moved in the lateral direction (i.e., 
the direction of Arrow F of FIG. 5). 
FIG. 6 discloses the use of a stepper motor or a recirculating ball/linear 
actuator for laterally moving the arm 23c with respect to upper center 
shaft 20c. FIG. 7 shows the use of a solenoid 57 for laterally extending 
or retracting the arm 23d with respect to upper center shaft 20d. The 
solenoid 57 may be secured to the upper center shaft 20d by means of 
brackets 58 and may be linked to the existing motor or power supply of the 
automatic feed system via line 59. An air cylinder may also be used in 
place of the solenoid 57. 
FIG. 8 discloses yet another alternate embodiment for the present invention 
wherein a second set of cutter wheels 71, 81 are provided to permit the 
circle shear apparatus to cut rings in sheet metal blanks positioned 
between the two pairs of cutter wheels. For ease of description, the 
embodiments shown in FIGS. 4 and 8 are identical, except for the addition 
of second upper arm 70 and cutter wheel 71 and the extension member 80 and 
cutter wheel 81. It should be noted that additional lower arms may also be 
included and arranged similarly to, but in mirrored fashion of the upper 
arm members 23a and 70. For example, lower arm 82 (shown in phanton) may 
be provided to lower shaft 30a and function in the same way as upper arm 
70. 
It should be understood that various modifications within the scope of this 
invention can be made by one of ordinary skill in the art without 
departing from the spirit thereof. I therefore wish my invention to be 
defined by the scope of the appended claims in view of the specification 
as broadly as the prior art will permit.