A POCKET SHARPENER FOR KNIVES

Abstract: The pocket sharpener (10) is constructed from a pair of overlaid metal plates (12,14) each having a section with a substantially straight edge (18), the edges being mutually arranged to form a wedge-shaped gap (20) of approximately 40°. On each straight edge (18) is brazed a rectangular carbide tooth (26,28), longitudinally positioned on opposed seg­ ments of the straight edges such that the two juxtaposed teeth cross forming a similar but smaller wedge-shaped gap (30) with a narrow space between the crossed teeth. The teeth each have a compound-bevelled sharpening edge for re­ spectively engaging opposite sides of a knife blade that is lodged in the smaller gap (30) and drawn across the teeth in a uniform stroke for sharpening the knife.

Description: This invention relates to a device for sharpening blades having a tapered cutting edge. There are a variety of blade sharpening devices ranging from grinding wheels and sharpening stones to files and specialized edge stripping devices for blades having a tapered edge. While tapered edge sharpening can be accomplished with traditional sharpening devices such as grinding wheels and sharpening stones that consist of a composition abrasive material that is generally drawn across the edge of the blade, this requires skill to accurately orient the blade at a selected optimal angle on drawing the blade across the stone or stone across the blade. This action must be performed repeatedly on each side of the blade to properly sharpen the blade. A skillfully honed knife sharpened with a whetstone undoubtedly provides the sharpest cutting edge. However, if ineptly performed, a stone sharpened knife can result in a blade that is duller than before the attempted sharpening. Other devices such as a butcher's steel sharpen a blade by a combination cross draw, longitudinal sliding motion on each side of the blade by a cylindrical, finely fluted metal file. A butcher's steel is relatively large in size and is ideally suited for imparting a finished edge to large knives and cleavers. Strip sharpeners of the type related to this invention operate longitudinally along the edge to simultaneously shave both sides of a tapered blare edge. Strip sharpeners have the advantage of automatically providing a proper angle of taper to the blades' edge. Sharpening by edge stripping allows for compact design of the sharpener. The strip sharpener of this invention, which is defined in the claims, can be particularly compact in size and inexpensive to manufacture and comprises an improvement in design and construction over prior sharpeners. One such sharpener, described and illustrated in GB-A-2133724, comprises a pair of moulded-plastic shell-like mirror-image components that are welded to each other to form a rigid casing in which are mounted two pairs of sharpening cylinders of ceramic abrasive. The casing is of increased thickness in the region of the cylinders and each moulding is formed with integral means for supporting the cylinders within the casing. Such a construction is quite bulky and whilst it can quite readily be hand-held it is not of a size or shape such as to be carried and kept in a pocket. Because it can be of such compact size, the sharpener of this invention is ideally suited for sharpening pocket knives and for pocket portage. One embodiment configuration is circular, sized approximately to a US silver dollar and is designed to be carried in the manner one carries change, for example in one's change purse or pocket. Another embodiment configuration is oblong for improved holding during operation. The flat compact design of both embodiments allows the sharpener to be adapted for use as a support for advertising, a memento, a key chain tag and/or a money clip. As set forth in claim 1, the pocket sharpener of this invention comprises a pair of plates shaped and fixed to each other in an overlapping configuration, such that each plate defines part of an open gap. In this gap are fitted a pair of intersecting teeth of hard material. The teeth are secured each to a respective one of said plates in substantially edge to edge relationship therewith to form between them an open wedge-shaped gap of approximately 40° at least in the region of their intersection. In this region at least, the teeth have bevelled edges shaped to strip a tapered cutting edge of a blade when the latter is drawn across the teeth at right-angles thereto while angularly centered in the wedge-shaped gap. Preferably, the hard material is tungsten carbide and the plates are made of steel with the teeth being secured to the plates by brazing. A composition ceramic or diamond impregnated material may also be used for the teeth and secured by a means compatible with the material utilized for the plates. Preferably also, the intersecting teeth are positioned on opposed straight segments of the plates and their bevelled edges are rectilinear. The two teeth preferably each have a compound bevelled edge which respectively engage the opposite sides of the tapered edge of the knife blade. An angle of approximately 40° for the gap between the juxtaposed teeth ensures that a proper edge will be imparted to the blade. One or two strokes is generally sufficient to sharpen a blade. The strip sharpener of this invention is particularly useful for difficult to sharpen stainless steel blades. These and other features will be described more fully in the following detailed description of two preferred embodiments of the pocket sharpener provided by the invention. In the accompanying diagrammatic drawings, given by way of example: Figure 1 is a plan view of the first preferred embodiment Figure 2 is an enlarged end view in a section along lines 2 - 2 of Figure 1; Figure 3 is an enlarged fractional end view of a detail of Figure 2; and Figure 4 is a plan view of the second preferred embodiment. The strip sharpener 10 shown in Figures 1 and 2 is constructed from a pair of substantially semi-circular metal plates 12 and 14 made of steel which are overlapped as shown and secured together by a spot weld 16. Each of the two plates 12 and 14 has a generally straight edge 18. The edges 18 are mutually arranged to form an open wedge-shaped gap 20 with exposed edge segments 22 and 24 forming an angle of approximately 40°. On the exposed edge segments 22 and 24 are respectively fitted elongated rectangular stripping teeth 26 and 28 having a straight edge and made of a hard material, preferably tungsten carbide. The teeth cross providing a wedge-shaped gap 30 of the same angle as the edge segments 22 and 24. An angle of 40° is considered optimal for most knives of the type intended to be sharpened by the pocket sharpener. A reduced angle will provide a keener but more easily damaged edge and an increased angle will provide a blunter more durable edge. For a pocket knife, which is a general purpose instrument, the selected angle is appropriate. The elongated teeth 26 and 28 are longitudinally mounted on the segments 22 and 24 with the aid of a locating shoulder 29 provided along the latter. The teeth have a thickness less than the thickness of the plates and are positioned and mounted in spaced apart relationship as shown in the side view of Figure 2, such as to provide a narrow space between the teeth where they overlap. The teeth are secured by brazing which for the preferred tungsten carbide material of each tooth is a compatible bonding means with the preferred steel material of plates 12 and 14. The straight edges of the teeth each has a compound bevelled edge with a 15° bevel for the top face and a 5° degree bevel for the side face, as shown in Figure 3. The narrow space between the teeth where they overlap eliminates the potential for entrapment of minute shavings or chips at the intersection of the teeth. The illustrated arrangement of plates 12, 14 and teeth 26, 28 assures accurate sharpening. To sharpen a knife blade 31, shown in phantom, the knife is held in the user's dominant hand and the sharpener is held substantially horizontally between thumb and curled fore-finger of the other hand, with the wedge-shaped gap 20 positioned forward of the thumb and oriented towards the dominant hand and with the top bevel faces turned upwards. The knife blade 31 is held substantially vertically at right angles to the general plane of the coupled plates 12 and 14 with the blade tip uppermost and leaned slightly towards the sharpener. The cutting edge of the blade 31 is engaged with the crossed teeth proximate the knife hilt and angularly centered in the wedge-shaped gap 30. The knife is carefully drawn downwardly, continuing the engagement of the sharpening teeth with the tapered blade edge until the tip passes the teeth. A moderate to light pressure is all that is required with only a small number of passes needed to fully sharpen a blade. During each pass the sharpener strips metal from each side of the blade cutting edge to produce a sharpened blade. Alternatively, the sharpener can be pressed against the edge of a table top or other ledge structure with a portion of the sharpener, having the gap, cantilevered over the edge. A gain holding the knife in the dominant hand and engaging the teeth of the sharpener with the tapered blade proximate the knife hilt, with upwardly oriented and slightly tilted tip, the knife is drawn downward with moderate to light pressure against the sharpener to sharpen the blade. The strip sharpener 32 shown in Figure 4 is constructed with an oblong plate 34 with an oblique end 35 coupled to a roughly semicircular plate 36 in overlapped arrangement as in the previously described embodiment. The oblong plate provides the user with an enlarged gripping surface for hand holding the sharpener during use. The sharpener 32 includes a similar arrangement of crossed teeth 38 which engage the tapered edge of a blade for strip sharpening as described.

Claims: A pocket sharpener for sharpening a tapered cutting edge of a blade, comprising a pair of plates (12,14;34,36) shaped and fixed to each in an overlapping configuration,such that each plate defines part of an open gap (20), and, in said gap, a pair of intersecting teeth (26,28;38) of hard material each secured to a respective one of said plates in substantially edge to edge relationship therewith to form between them an open wedge-shaped gap (30) of approximately 40° at least in the region of their intersection, said teeth having, in said region at least, bevelled edges shaped to strip said tapered cutting edge of a blade (31) when the latter is drawn across the teeth at right-angles thereto while angularly centered in the wedge-shaped gap (30). A pocket sharpener as in claim 1, wherein the teeth are mounted on the plates such that there is a narrow space between the teeth where they overlap. A pocket sharpener as in any preceding claim, wherein the plates (12, 14) are approximately semicircular in configuration. A pocket sharpener as in any preceding claim, wherein one plate (36) is approximately semicircular and the other plate (34) is oblong with an oblique end (35). A pocket sharpener as in any preceding claim, wherein the bevelled edges of the teeth each have a compound bevel with a top face angle of about 15° and a side face angle of about 5°. A pocket sharpener as in any preceding claim, wherein the plates (12,14;34,36) are made of steel and the teeth (26,28; 38) are made of tungsten carbide, said teeth being brazed to the plates. A pocket sharpener as in any preceding claim, wherein the open gap defined by the plates is wedge-shaped and forms an angle of approximately 40°. A pocket sharpener as in any preceding claim, wherein the plates (12 14;34,36) each have in the region of the gap they form an exposed substantially straight edge segment (22,24) with said teeth (26,28; 38) arranged on said edge segments. A pocket sharpener as in claim 8, wherein the straight edge segments each have a locating notch for positioning the teeth on the straight edge segments.

Inventors: FOREST, CHARLES WILLIAM
Applicants: FOREST, CHARLES WILLIAM
Application year: 1986
Main classification: B24D15
IPC codes: B24D15