Parallel action die cutting hand tool

An improved parallel action die cutting hand tool having a pair of scissors-action handle levers pivoted on a transverse pivot axis, so that the handle levers operate in a plane. The hand tool includes first and second die cutting jaws connected to the handle levers for parallel movement toward and away from each other. The hand tool has a pair of guide pins extending between the die cutting jaws and slidable with respect to at least one of the jaws. Each pin lies outside of and parallel to the plane of the handle levers. A die plate, held on one of the jaws by a pair of ribs, has curved corners that meet the ribs at a tangent angle of substantially zero degrees. In an alternate embodiment of the invention, the guide pins are spaced apart, lying in the plane of the handle levers, and located on opposite sides of the cutting edges. In another alternate embodiment, there is a single guide pin only, lying in the plane of the handle levers and located approximately midway between the forward pivot pins and the transverse pivot axis.

TECHNICAL FIELD 
This invention relates in general to parallel action die cutting hand 
tools. In particular, the invention relates to hand-operated cutting tools 
adapted to trim sheet materials, such as venetian blind slats. 
BACKGROUND AND SUMMARY OF THE INVENTION 
Venetian blind trimmers are used to adapt a premanufactured blind to the 
specific requirements of an opening by trimming one end of each slat. For 
this purpose, cutting dies are attached to the jaws of a scissors-action 
hand tool similar to a tin snip. A depth gauge is connected to one of the 
dies to provide a uniform measurement for evenly modifying the length of 
each slat. The typical scissors-action venetian blind trimmer brings the 
dies together with a variable shear so that a slat is trimmed 
progressively from one edge to the other as the pivoted handles of the 
trimmer are closed. An ordinary shear cannot be used for this trimming 
operation because venetian blind slats have curved corners. These curved 
corners must be preserved for cosmetic uniformity among slats of a single 
blind. 
The task of trimming venetian blind slats with acceptable uniformity 
presents several problems. First, the slats are slightly bowed from front 
to rear and tend to flatten under the pressure of a cutting tool, 
presenting an alignment problem between the slats and the cutting dies. 
Second, the slats are constructed from thin sheet material, such as 
aluminum, so the edges are subject to burring if the clearance between the 
dies is excessive. Burring is a recurrent problem with scissors-action 
trimmers, since alignment between the dies is controlled only at the 
single pivot point between the shear handles. If either burring or an 
uneven corner results from a trimming operation, it is necessary to retrim 
or to replace the slat. Retrimming one slat may produce an unevenness 
among the slats. Therefore, it is highly desirable for a trimmer to be 
accurate and consistent in its operation. 
U.S. Pat. No. 4,272,888 to Hartmeister discloses a parallel action die 
cutting hand tool having a pair of scissors-action handle levers pivotally 
connected together on a transverse pivot axis. Each of the handle levers 
has a forward pivot pin and a rear pivot pin extending parallel to the 
transverse pivot axis. The transverse pivot axis and the forward and rear 
pivot pins are normal to the plane of the handle levers. The tool has 
first and second opposed die cutting jaws connected to the handle levers 
by engagement of the forward and rear pivot pins for movement toward and 
away from each other. Each jaw is connected to the forward pivot pin of 
one handle lever and to the rear pivot pin of the opposite handle lever in 
corresponding pivot pin receiving openings in each jaw. At least one of 
the pivot pin receiving openings in each jaw is longitudinally elongated. 
The Hartmeister tool also has a pair of guide pins extending between the 
die cutting jaws and slidable with respect to at least one of the jaws. 
The pins are spaced apart, each near a forward or rear pivot pin and lying 
in the plane of the handle levers. The guide pins are approximately in 
longitudinal alignment with the cutting edges of the jaws. 
The guide pins provide for accurate and consistent operation of the jaws as 
cutting dies. However, when the guide pins need to be replaced for any 
reason, the tool must be disassembled and the pins forcibly removed from 
the jaw in which they are rigidly mounted. Further, the use of two guide 
pins in the plane of the handles requires considerable precision and 
accuracy in attaching one of the jaw handles to the other. 
The Hartmeister tool also has a spring between the die cutting jaws for 
biasing the jaws apart. The spring is located between the guide pins. 
The present invention is a parallel action die cutting hand tool generally 
of the type described in U.S. Pat. No. 4,272,888 to Hartmeister. In one 
embodiment of the invention, the guide pins lie outside of and parallel to 
the plane of the handle levers. The guide pins may be located on the same 
side of the plane of the handle levers, or on opposite sides of the plane. 
In each of the first two embodiments, the pins are mounted in guide 
members removably attached to the cutting jaws. 
A third embodiment of the invention has guide pins lying in the plane of 
the handle levers, and located on opposite sides of the cutting edges. A 
fourth embodiment of the invention has a single guide pin only. The single 
guide pin lies in the plane of the handle levers and is located 
approximately midway between the forward pivot pins and the transverse 
pivot axis.

DETAILED DESCRIPTION OF THE DRAWINGS 
A first embodiment of the invention is shown in FIGS. 1-4. The invention 
involves a hand-operated parallel action die cutting tool 10 having a 
first handle lever 12 and a second handle lever 14 pivotally connected 
together. The handle levers 12 and 14 pivot about a transverse pivot axis 
16 through a main pivot pin 17, so that the handle levers 12 and 14 
operate in a plane 15 (see FIG. 2). The rearward portions of the handle 
levers 12 and 14 have hand grips 18 and 19. 
Each handle lever 12 and 14 has a forward pivot pin 20 and a rear pivot pin 
22. The two forward pivot pins 20 are positioned at a distance forward of 
the transverse pivot axis 16 and the rear pivot pins 22 are positioned at 
a distance to the rear of the transverse pivot axis 16. The longitudinal 
axes 21 and 23 of the forward and rear pivot pins 20 and 22 are parallel 
to the transverse pivot axis 16 and normal to the plane 15 of the handle 
levers 12 and 14. The distance from the transverse pivot axis 16 to the 
forward pivot pins 20 is approximately equal to the distance from the 
transverse pivot axis 16 to the rear pivot pins 22. 
A first or upper die cutting jaw 24 is connected to the first handle lever 
12 by forward pivot pin 20 and to the second handle lever 14 by rear pivot 
pin 22. A second or lower die cutting jaw 26 is connected to the first 
handle lever 12 by a rear pivot pin 22 and to the second handle lever 14 
by a forward pivot pin 20. The rear pivot pins 22 engage the upper and 
lower jaws 24 and 26 at corresponding pivot pin receiving openings 28. The 
pin receiving openings 28 are elongated to allow the rear pivot pins 22 to 
slide with respect to the upper and lower jaws 24 and 26. 
When the hand grips 18 and 19 are squeezed, the handle levers 12 and 14 
rotate about the transverse pivot axis 16. The forward and rear pivot pins 
20 and 22 move in small arcs about the transverse pivot axis 16. As the 
rear pivot pins 22 slide in the elongated pin receiving openings 28, the 
upper and lower jaws 24 and 26 move toward one another in parallel 
straight lines. A pair of resilient compression springs 29 are mounted 
between the upper and lower jaws 24 and 26. The springs 29 bias the upper 
and lower jaws 24 and 26 apart. 
The lower jaw 26 includes a die base 30, a flat angle support 32, and a die 
plate 34. The angle support 32 is attached to the die base 30 by means of 
capscrews 36 threaded through the lower flange 38 of the angle support 32 
and into the base 30. The upper flange 40 of the angle support 32 extends 
laterally and is bounded on its upper edges by ribs 42. 
The die plate 34 is attached to the upper flange 40 of the angle support 32 
by means of removable fasteners 44. A dowel 45 passes through aligned 
holes in the upper flange 40 and the die plate 34 to accurately locate the 
die plate 34 and to add sturdiness to the tool 10. 
As shown best in FIG. 3, the right hand edge 46 of the die plate 34 extends 
between the ribs 42 over the top of the base 30. The die plate 34 has 
curved corners 48 at the transitions between the edge 46 and the ribs 42. 
The curved corners 48 continue until the corners 48 meet the ribs 42 at a 
tangent angle of substantially zero degrees. 
An L-shaped guide rod 50 having an upright portion 52 and a lower portion 
54 is mounted on the tool 10 in order to gauge the amount of the venetian 
blind slat that is to be trimmed. The lower portion 54 of the guide rod 50 
extends through a hole in the lower flange 38 of the angle support 32 and 
is secured with a fastener 56. The upright portion 52 extends upward 
beyond the edge 46 of the die plate 34. The position of the guide rod 50 
can be adjusted if the fastener 56 is loosened. 
The upper jaw 24 has a cooperating die surface 58 that is substantially 
identical in contour to the lower die edge 46. The upper die surface 58 
has a straight portion corresponding to the edge 46 and curved sections 
corresponding to the corners 48 of the die plate 34. 
A guide member 60 is attached to each jaw 24 and 26. The guide member 60 on 
the lower jaw 26 is attached with a pair of capscrews 62. A dowel 65 
extends through the guide member 60 into a hole in the lower jaw 26 to 
provide additional sturdiness. 
A pair of flat head screws 63 are used to attach the other guide member 60 
to the upper jaw 24. The flat head screws 63 are used to positively locate 
the guide member 60, because the upper jaw 24 is heat treated and cannot 
be drilled for a dowel. 
Each guide member 60 has a pair of parallel holes 64 that are aligned with 
corresponding holes 64 in the other guide member 60. An elongated guide 
pin 66 is located in each pair of aligned holes 64. The guide pin 66 may 
be securely attached to one or the other of the guide members 60, but the 
guide pin 66 is slidable with respect to at least one of the guide members 
60. The guide pins 66 are parallel to each other and lie outside of and 
parallel to the plane of the handle levers 12 and 14. In the embodiment 
shown in FIGS. 1-4, both guide pins 66 lie on the same side of the handle 
levers 12 and 14. 
In operation, the springs 29 bias the tool 10 in the open position, shown 
in FIG. 1. A venetian blind slat to be trimmed is placed in the angle 
support 32 between the ribs 42. The slat is then pushed forward until the 
end of the slat contacts the upright portion 52 of the guide rod 50. As 
the handle levers 12 and 14 are squeezed together, the upper and lower 
jaws 24 and 26 move toward one another. The upper die surface 58 and the 
die plate 34 cooperate to trim the slat at the edge 46 of the die plate 
34. The substantially zero tangent angles of the corners 48 of the die 
plate 34 form rounded corners on the end of the venetian blind slat. When 
the handle levers 12 and 14 are released, the springs 29 open the upper 
and lower jaws 24 and 26. The slat is then removed and replaced with a 
second slat to be trimmed. 
The guide members 60 and the guide pins 66 can be easily replaced, without 
disassembling the entire tool 10. The fasteners 62 are simply removed from 
the jaws 24 and 26. New guide members 60 and guide pins 66 are then 
mounted and secured with the fasteners 62. 
FIGS. 5-7 show a first alternate embodiment of the tool 10 of the 
invention. The first alternate embodiment differs from the preferred 
embodiment in the location of the guide pins 66. In the first alternate 
embodiment, the elongated guide pins 67 are located on opposite sides of 
the plane 15 of the handle levers 12 and 14. The guide pins 67 pass 
through aligned holes 68 in the guide members 69. The guide pins 67 still 
lie outside of and parallel to the plane 15 of the handle levers 12 and 
14. 
As in the embodiment shown in FIGS. 1-4, the guide members 69 and guide 
pins 67 of the first alternate embodiment can be replaced easily. The 
capscrews 62 and flat head screws 63 are removed from the jaws 24 and 26 
to release the old guide members 69 and guide pins 67. New guide members 
69 and guide pins 67 are then mounted and secured with the capscrews 62 
and flat head screws 63. 
FIGS. 8-10 show a second alternate embodiment of the invention. The second 
alternate embodiment does not have guide members corresponding to the 
guide members 60 of the first embodiment. The guide holes 70 pass directly 
through the upper and lower jaws 72 and 74. Therefore, the elongated guide 
pins 76 lie within and parallel to the plane 15 of the handle levers 12 
and 14. The two guide pins 76 lie on opposite sides of the cutting edges 
46 and 58 of the upper and lower jaws 74 and 76. 
FIGS. 11-13 show a third alternate embodiment of the invention. In the 
third alternate embodiment there is a single elongated guide pin 78 only. 
The single guide pin 78 has flat sides 79 and passes through a guide hole 
80 that passes through the upper and lower jaws 82 and 84. The guide pin 
78 thus lies in the plane 15 of the handle levers 12 and 14. The guide pin 
78 is located approximately midway between the forward pivot pins 20 and 
the transverse pivot axis 16. The flat sides 79 on the guide pin 78 help 
prevent the jaws 82 and 84 from rotating with respect to one another 
during use. 
Only the preferred embodiments of the invention have been shown. It should 
be understood that the invention is not limited to the embodiments 
disclosed, but is capable of numerous rearrangements, modifications, and 
substitutions of parts and elements without departing from the spirit of 
the invention.