Protective guard for a utility knife

A utility knife can be equipped with a removable blade protective guard structure to prevent the person from being cut when the knife is not in use. The guard structure includes a mounting element having a pivotable connection with an elongated guard element near the leading end of the knife handle. A torsion spring is coiled around the pivot shaft to normally urge the guard element to a position extending along the cutting edge of the blade. However, the guard element can be swung through an arc of about one hundred eighty degrees (180) to assume a position lying alongside a side edge of the knife handle, away from the cutter blade.

BACKGROUND OF THE PRESENT INVENTION 
1. Field of the Invention 
This invention relates to utility knives usable for cutting cardboard, 
twine, plastic materials, thin wood, shrubbery, etc. More particularly, 
the invention relates to a protective guard structure for preventing 
injury to a person while holding a utility knife in his hand or storing 
such a knife in his pocket. 
2. Prior Developments 
Various types of guard structures for utility knives have been proposed. 
However such guard structures differ in material respects from the guard 
structure herein proposed. The herein-proposed guard structure is designed 
for use with a conventional utility knife, such that the guard structure 
can be supplied as an attachment to utility knife structures already in 
use; users of existing knife structures are enabled to purchase the guard 
structure without having to purchase a new knife. 
A further feature of the herein-proposed guard structure is that it is 
automatically biased to the blade protective position when the person 
releases his grip on the knife handle. The person does not have to 
consciously think about moving the guard structure to its protective 
position, as movement to the protective position is automatic. 
An additional advantage of the herein-proposed guard structure is that it 
is usable with knives having fixed cutter blades, i.e. knives wherein the 
cutter blade is rigidly mounted in the handle so as to be free from wobble 
or play when the knife is in use. 
U.S. Pat. No. 4,086,698 to W. Sparks, shows one prior art knife 
construction having a guard that includes a shoe carried on a 
spring-biased plunger. The spring continually urges the shoe and plunger 
to the protective position. However the person can manipulate the knife so 
that the shoe presses against the work surface whereby the guard is 
retracted relative to the knife element, so that the knife element can 
penetrate the work. The guard operates in a different manner than the 
guard of the present invention. 
J. Peyrot, U.S. Pat. No. 4,757,612, shows a utility knife having a fixed 
blade and a longitudinally slidable cover movable between a retracted 
position (FIG. 2), and an extended position overlying the fixed blade 
(FIG. 1). A manually-operated trigger is pivotably connected to the rear 
end of the handle to move the cover to its retracted position (by cam 
action). A major drawback of the Peyrot arrangement is its complexity and 
use of multiple moving parts. The manufacturing cost would also be 
relatively high. 
U.S. Pat. No. 4,713,885, issued to R. Keklak, M. Couture and J. Whitehouse, 
shows a utility knife having a retractible cutter element (blade). The 
guard function is achieved by sliding the blade into the holder (handle) 
during non-use periods. The patented arrangement has a certain degree of 
complexity as regards the mechanism used to move the cutter blade out of 
the holder. As shown in FIG. 2 of the patent drawings, the mechanism 
includes a slide, pivotable links, a slideway for the link connector, and 
a squeezable lever. The mechanism is relatively complex. 
J. Wood, U.S. Pat. No. 3,999,290, shows a utility knife wherein the cutter 
blade is slidable into and out of the handle (holder). In this respect the 
Wood patented device is similar to the devices shown in Peyrot U.S. Pat. 
No. 4,757,612 and Keklak et al U.S. Pat. No. 4,713,885, discussed above. 
In the Wood patented arrangement, the blade carrier is equipped with a 
wire spring arm having a hooked end, whereby the hooked end can catch on 
the cardboard work surface to draw the cutter blade out of the handle. The 
arrangement proposed by Wood is considerably different than what is 
proposed in the present invention. 
U.S. Pat. No. 3,781,988, to R. Jones, discloses a utility knife having a 
guard swingable around a pivot between a retracted position (FIG. 2) and a 
use position (FIG. 1). An overcenter tension spring holds the guard in its 
two positions (retracted or extended). The guard is moved to its the 
retracted position when it is desired to change the cutter element. During 
normal operation the guard has its nose riding on the work surface to 
permit the blade to penetrate the work. The principal disadvantage of the 
patented arrangement would appear to be the cost of manufacture of the 
guard. The exposed location of spring S would also appear to be a 
disadvantage, in that the person's fingers could conceivably be pinched 
between the spring coils, under some circumstances. 
Houghton et al, U.S. Pat. No. 4,028,802, shows a specialized yarn (loop) 
cutting tool having a swingable guard for the blade. The overall 
arrangement significantly differs from the arrangement of the present 
invention. 
Vito, U.S. Pat. No. 4,531,286, shows a utility knife having a guard 
attached to the handle by a thin flexible wall. As best shown in FIG. 4, 
the flexible wall can flex to enable the blade to cut into the work 
surface. The patented arrangement differs considerably from the 
arrangement contemplated in the present invention. 
Davis et al, U.S. Pat. No. 4,949,458, shows a utility knife having an 
extendable blade. The patentee states that if the handle is moved 
violently downwardly a latch member will be actuated to enable a guard 
(FIG. 4) to be projected out of the holder. 
Chomiak, U.S. Pat. No. 5,241,750, shows a guard construction that includes 
a hood swingable between a protective position (FIG. 1) and a retracted 
position (FIG. 2). Springs normally hold the hood in its FIG. 1 position. 
A manual latch normally prevents dislocation of the hood from its FIG. 1 
protective position. 
The patents discussed above show various types of blade guards for use on 
utility knives. However, these patents do not show the specific guard 
structure proposed in the present invention. 
SUMMARY OF THE PRESENT INVENTION 
The present invention relates to a utility knife, and more particularly, to 
a utility knife having a spring-loaded guard for protecting the user from 
cuts when the knife is not in use. The knife element (razor blade) is 
rigidly mounted in the handle (holder) so as to project from one end of 
the handle; the spring-loaded guard is pivotably mounted at one edge of 
the holder for swinging movement between a retracted position lying 
against the holder (handle), to an operative (protecting) position 
extending along the cutting edge of the knife element. The guard has a 
motion arc of about one hundred eighty degrees. 
The loading spring for the guard structure is designed to bias the guard 
element to its blade protecting position automatically when the person 
releases his grip on the knife handle. The person does not have to think 
about moving the guard to its protecting position; movement of the guard 
to its protecting position is automatic. 
Further features and advantages of the invention will be apparent from the 
attached drawings and description of an illustrative embodiment of the 
invention. 
In summary, and in accordance with the above discussion, the foregoing 
objectives are achieved in the following embodiments. 
1. A guard structure for a utility knife, wherein the knife comprises an 
elongated hollow handle having a leading end, and a planar cutter blade 
extending from the leading end of said handle; said cutter blade having a 
cutting edge terminating in a sharpened tip; said guard structure 
comprising: 
an elongated guard element, pivot means for swingably mounting said guard 
element on the handle around a pivot axis normal to the plane of the 
cutter blade; and 
said pivot means being located proximate to the leading end of the handle, 
such that said guard element is pivotably movable between a protective 
position extending along the blade cutting edge, and a retracted position 
extending along the handle. 
2. The guard structure, as described in paragraph 1, wherein said guard 
element has an arcuate motion of approximately one hundred eighty (180) 
degrees when moving between the protective position and the retracted 
position. 
3. The guard structure, as described in paragraph 1, and further comprising 
spring means biasing said guard element to its protective position, 
whereby a manual force is required to move the guard element from its 
protective position to its retracted position. 
4. The guard structure, as described in paragraph 1, and further comprising 
mounting means for said pivot means, said mounting means having a 
detachable connection with said knife handle, whereby the guard structure 
is removable from the knife without affecting knife operability. 
5. The guard structure, as described in paragraph 1, and further comprising 
spring means biasing said guard element to its protective position, 
whereby manual force is required to move the guard element from its 
protective position to its retracted position; 
said pivot means comprising two ears spaced apart in a direction normal to 
the plane of the cutter blade, a pivot shaft extending between said ears, 
and two spaced arms extending from said guard element into the space 
between said ears; and 
said arms being rotatable on said pivot to support the guard element for 
swinging motion around the shaft axis. 
6. The guard structure, as described in paragraph 5, wherein said spring 
means comprises a torsion wire spring coiled around said shaft in the 
space between said arms. 
7. A guard structure for a utility knife, wherein the knife comprises an 
elongated hollow handle having a leading end, two essentially flat side 
surfaces, and an elongated side edge connecting said side surfaces; said 
knife further comprising: 
a planar cutter blade extending from the leading end of said handle; said 
cutter blade having a straight cutting edge terminating in a sharpened 
cutting tip; said guard structure comprising: 
a mounting element detachably secured to the knife element, and a guard 
element swingably connected to said mounting element; 
said mounting element comprising a central wall positionable against the 
side edge of the knife handle and two spaced ears extending from said wall 
away from the knife handle; 
said guard element comprising an elongated guard member having two spaced 
arms extending into the space between said ears; and 
a pivot shaft extending through said arms into said ears, whereby said 
guard member is swingable between a blade protective position along the 
blade cutting edge, and a retracted position extending along the side edge 
of the knife handle. 
8. The guard structure, as described in paragraph 7, and further comprising 
spring means biasing said guard member to its protective position, whereby 
a manual force is required to move the guard member to its retracted 
position; and 
said spring means comprises a torsion spring coiled around said pivot shaft 
in the space between said arms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION 
FIG. 1, is a side view, of a utility knife for which the guard structure of 
the present invention is especially useful. The utility knife is shown in 
an open condition, suitable for replacing a worn blade with a sharpened 
blade. 
Referring to FIG. 1, there is shown in simplified form a conventional 
utility knife 10, that includes an elongated hollow handle 12 and a planar 
cutter blade 14 extending from the leading end 16 of the handle 12. The 
handle 12 comprises two half sections, 17 and 19, joined together by a 
screw 20. The screw 20 extends through a hole in handle half section 17 
into a threaded opening in the other handle half section 19. 
When the screw 20 is tightened the two handle half sections can be rigidly 
clamped together to form a unitary handle structure, as shown in FIGS. 2, 
4 and 5. When screw 20 is loosened, the handle half sections 17 and 19 can 
be swung around the screw axis to expose the hollow space within the 
handle. As shown in FIG. 1, the handle interior space can be used to store 
a second planar cutter blade 15. When blade 14 becomes worn it can be 
replaced with the sharpened reserve cutter blade 15. 
FIG. 2, shows the FIG. 1 utility knife in its closed (operating) position. 
A guard structure of the present invention is mounted on the knife handle 
to protect against injury from the sharpened cutter blade. 
FIG. 2, shows the FIG. 1 utility knife equipped with a guard structure 22 
of the present invention. The knife 10, does not have to be modified, or 
changed, in order to accommodate guard structure 22. However, it is 
necessary to use a longer screw (in place of screw 20), since the guard 
structure 22 is removably secured to the knife handle 12 by means of a 
screw extending through the handle 12 and a guard structure mounting 
element 24. 
Mounting element 24 comprises a channel structure that includes a central 
wall 26 and two flanges 27 extending from central wall 26 along the flat 
side surfaces of handle 12. A screw 20a extends through the existing hole 
structure in the handle 12 and two aligned holes in walls 26, to clamp the 
mounting element 24 of the guard structure 22 to the knife handle 12. One 
of the aligned holes will be threaded to mesh with the threaded area of 
the screw 20a. The other hole will be countersunk to accommodate the head 
of the screw. 
Mounting element 24 includes two spaced ears 29 projecting from central 
wall 26 away from the knife handle 12. A pivot shaft 30 extends between 
ears 29 in a direction normal to the plane of cutter blade 14, such that 
shaft 30 is enabled to serve as a pivot means for a guard element 32. 
Guard element 32 comprises an elongated guard member 34 having two spaced 
arms 36 extending into the space between ears 29. Arms 36 have aligned 
holes therein, slidably encircling pivot shaft 30, whereby the guard 
element 32 is swingable on shaft 30 between a blade protective position 
extending along the blade cutting edge 18 (FIG. 2), and a retracted 
position extending along edge 21 of knife handle 12 (FIG. 4). 
Elongated guard member 34 has sufficient length to extend beyond sharpened 
tip 23 of blade 14 when the guard 34 is in its FIG. 2 protective position. 
Also, surface 37 of guard member 34 has a concave surface area 39 designed 
to fit comfortably on the person's first finger when the guard element is 
in its retracted position (FIG. 4). 
FIG. 4, is a view, taken in the same direction as FIG. 2, but showing the 
knife structure in an operative cutting position. The guard structure is 
swung to a retracted position extending along the edge of the knife 
handle, whereby the person is enabled to exert a gripping force on the 
guard structure. 
FIG. 4, shows in phantom a representative outline of the person's hand 
gripping the knife handle 12 and the guard element 32 during use of the 
knife for cutting purposes. The presence of the guard element 32 tends to 
enhance the handgrip, whereby the knife has a lessened tendency to slip 
out of the person's hand during usage of the knife for cutting purposes. 
A spring mechanism is provided for biasing guard element 32 to its blade 
protective position (FIG. 2). As shown in the drawing, the spring 
mechanism comprises a torsion wire spring 40 having a multiple number of 
turns encircling pivot shaft 30. Opposite ends of the wire spring 40 abut 
against wall 26 of the mounting element 24 and an interior surface on 
guard element 32 to anchor the spring; the spring 40 is pre-loaded to 
exert a clockwise biasing force on guard element 32 (as viewed in FIG. 2). 
When the person releases his grip on guard element 32, spring 40 
automatically swings the guard element 32 to the FIG. 2 protective 
position; the left end edge of wall 26 acts as a stop to limit the 
swinging movement of guard element 32. Guard element 32 may be swung to 
its FIG. 4 position by exerting finger pressure on the protruding tip of 
member 34. During use of the knife for cutting purposes the guard element 
32 is in its FIG. 4 position. 
The guard structure can be removed from the utility knife by removing screw 
20a, and replacing it with the original screw 20. The guard structure can 
be supplied as an entity separate from the knife, such that the guard 
structure can be used on pre-existing knives. 
FIG. 5, is a side elevational view, of a utility knife equipped with 
another guard structure embodying the present invention. 
FIG. 5, shows an alternative guard construction that can be used in 
practice of the invention. In this case the mounting element 24a comprises 
a central wall 26 engaging the edge 21 of knife handle 12, and a band 
mechanism 46 extending from wall 26 around the knife handle 12. The band 
mechanism 46 is split to form two flanges 47 that are spaced apart 
slightly when the band mechanism 46 is on the knife handle. A nut-screw 
assembly 49 is used to draw the flanges 47 toward each other, whereby the 
mounting element 24a is clamped to the knife handle. 
The relationship between mounting element 24a and the guard element 32 is 
similar to the relationship between elements 24 and 32 in the FIG. 2 
embodiment. Thus, the FIG. 5 embodiment differs from the FIG. 2 embodiment 
only as respects the mechanism used to mount the guard structure on the 
knife handle 12. 
The present invention, described above, relates to a Protective Guard for a 
Utility Knife. Features of the present invention are recited in the 
appended claims. The drawings contained herein necessarily depict 
structural features and embodiments of the Protective Guard for a Utility 
Knife, useful in the practice of the present invention. 
However, it will be appreciated by those skilled in the arts pertaining 
thereto, that the present invention can be practiced in various alternate 
forms and configurations. Further, the previous detailed descriptions of 
the preferred embodiments of the present invention are presented for 
purposes of clarity of understanding only, and no unnecessary limitations 
should be implied therefrom. Finally, all appropriate mechanical and 
functional equivalents to the above, which may be obvious to those skilled 
in the arts pertaining thereto, are considered to be encompassed within 
the claims of the present invention.