US20060040598A1

US20060040598A1 - Precision sharpener tool

Info

Publication number: US20060040598A1
Application number: US10/923,618
Authority: US
Inventors: Rudolf Koppe
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-08-20
Filing date: 2004-08-20
Publication date: 2006-02-23
Also published as: CN1796052A; US20060040600A1

Abstract

A precision sharpening tool is disclosed, having an opposing sharpening elements arranged to form a generally “V” shaped sharpening slot and first and second elongate guide members arranged on opposite sides of the sharpening slot which comprise mating toothed spur gears arranged so that turning the guide pin element of the first guide member simultaneously turns the guide pin element of said second guide member in aligned mirrored movement.

Description

This invention relates to a novel system and tool for sharpening the cutting edge of knives and the like, being particularly suitable for maintaining precision sharpening angles to enable consistent, quality edge sharpening.

BACKGROUND OF THE INVENTION

Sharpening tools are well known in the prior art, for use in sharpening cutting edges such as the blades of knives and the like cutting instruments.
Knife sharpening tools, particularly hand tools and simple automated tools that are easy to use and provide precision sharpened edges of consistent quality continue to be desired by the consuming public. Sharpening tools generally used by the consuming retail public are generally referred to as pocket and hand knife sharpeners. Pocket knife sharpeners generally comprise a sharpening element such as an abrading composite stone or the like material, that is generally packaged in a pouch or the like for pocket carrying. The size of the stone is generally small for convenient pocket carrying, which makes the hands on manipulation of the small stone during the sharpening process generally unsafe for the user and generally requires significant hand manipulation skills to conveniently and accurately sharpen a cutting edge.
A very popular knife sharpener generally comprises opposing disks, blades or composite stone manufactured from carbide, abrasive or the like materials which are generally arranged so that the knife blade can be moved through a “V”, shaped slot or the like, with opposite sides of the edge thereof engaging static or revolving disks or the like to shave sides along a bevel of the edge of the knife to sharpen the edge. Such tools are useful, but are limited in the quality of sharpened edge that can be attained and thus the durability and usefulness of the knife so sharpened.
For general purpose cutting, an efficient knife blade cutting edge is generally considered to be one in which the edge is formed at the apex of opposite sides of a knife blade beveled to about a 20 degree angle to the center line of the plane of the blade. Blades so sharpened generally retain their edge longer, have reduced binding of blade sides particularly with thick substances being cut during the cutting process, and experience reduced wear at the cutting edge. “V” notch sharpening arrangements are generally designed to fix opposing sharpening disks and/or straight edged sharpening blades in an arrangement forming an about 40 degree sharpening notch, which if the blade of the knife is held in perfect position bisecting the notch during the sharpening process, will simultaneously abrade or shave both sides of the blade during the sharpening process to about a 20 degree bevel and the edge will be a precisely formed to its most efficient cutting edge.
Unfortunately, holding a knife blade to perfectly bisect a “V” slot during the sharpening process requires skilled manipulation of the tool, and frequently the person manipulating the tool ends up producing a sharpened knife having different beveled angles on opposite sides of the knife and/or variations in beveled angle along the length of the blade on the same and/or different sides of the blade. The result is an improperly sharpened knife which though it may have a sharp edge, is easily dulled and since the sharpened edge is not centered along the thickness of the blade, a blade which tends to tear or bind during cutting through the thickness of materials.
U.S. Pat. No. 6,626,066 discloses a foldable sharpening tool having an elongate sharpening guide which is compactly foldable or removable for storage within the tool. Two sharpening guides are arranged on either side of a “V” shaped sharpening slot and a guide comprises an eccentric mounted guide cap which can be turned to adjust the eccentric cap toward or away from each other to adjust distance between guides. Though the use of such guides can theoretically enable the positioning of a knife blade in an ideal position for sharpening, each guide must be independently adjusted and the attaining of such ideal position is dependent upon the skill of the user, particularly his/her ability to visually align the guides within a narrow range of ideal proximity.
It is an object of the present invention to provide a sharpening device and system which will enable the production of consistent precision sharpened edges.
It is a further object of the invention to provide a means for safely and accurately guiding a cutting edge along a sharpening surface during a sharpening process.
These and other objects of the invention will become apparent in the following recitation of the invention.

SUMMARY OF THE INVENTION

The present invention is an improved sharpening tool and system, generally comprising unique, self-centering, micro-adjustable sharpening guides arranged to assure consistent, precision retaining of knife blades of varying thickness within precision angular tolerances against opposing element blade sharpening means. By opposing element sharpening means is meant an arrangement wherein a blade is sharpened by means which simultaneously engage and abrade opposite sides of a blade or the like during the sharpening process.
The micro-adjustable sharpening guides of the invention comprise generally parallel, opposing members mounted to a sharpening tool adjacent a “V” shaped sharpening slot formed by opposing sharpening elements. The guide members are generally arranged to extend from the body of the sharpening tool and comprise opposing surfaces which support the blade to be sharpened in a preferred orientation in the “V” shaped slot during sharpening.
A guide member of the invention comprises a base spur gear element and an eccentric guide pin element. The base spur gear element comprises a shaft having a toothed gear at a first end and an eccentric guide pin element extending from the opposite end. In a preferred embodiment, the centerline of the guide pin element is arranged offset from and generally parallel to the centerline of the shaft of the spur gear element.
Guide members are arranged in generally parallel alignment, at opposite sides of an ideal sharpening plane for engaging the knife blade with opposing sharpening means. The toothed gear of a first guide member is arranged to matingly engage the toothed gear of a second guide member, such that rotatably turning the shaft of the spur gear of a first guide member institutes synchronized rotation of the corresponding shaft of a second guide member. The gears are in mating alignment so that during rotation of the guide members, the shafts of the spur gears rotate in position and the eccentric pin elements of the guide members move toward and away from each other in aligned mirrored movement.
In a preferred arrangement of the invention, the shafts of two or more base spur gear elements are rotatably mounted in bearing holes arranged on opposite sides of the plane of the bisect of a generally “V” shaped sharpening slot formed by opposing blade or disk sharpening elements. The base spur gear elements are arranged about equidistant from the centerline of the “V” shaped slot with their toothed gears in mating alignment generally below the sharpening level of the blades or disks, with their respective eccentric guide pin elements extending upwardly on opposite sides and about equidistant from the plane of the bisect of the “V” shaped slot, generally above the sharpening level. When a knife blade is to be sharpened, an eccentric guide pin element of a guide member can be rotated to adjust the spacing between eccentric guide pin elements as may be suitable for the thickness of the knife blade. A guide member is generally rotated sufficiently so that opposing eccentric guide pin elements closely engage opposite sides of the knife blade arranged in the “V” shaped slot between the eccentric guide pin elements. Since the guide members are arranged about equidistant from the plane of the bisect, mirrored adjustment of guide pin elements toward and away from each other synchronically maintains the center of the space between the guide pin elements and thus the knife blade at about the center of the “V” shape and at or about the ideal sharpening plane.
Disks or blades in a “V” slot sharpening arrangement are typically overlapped in opposing staggered orientation to provide a sharpening slot of about 35-45°, preferably about 40°, with sharpening means engaging opposite sides of a blade bisecting the slot, at an angle of about 20° to each side of the blade to be sharpened. Once set to the thickness of a blade, the guide members of the present invention retains the blade in a precision manner along about the center bisect of the “V” slot as the blade is being drawn through the slot, overcoming inadequate manipulation skills of the user and thus sharpens the blade to its most efficient edge for cutting a variety of materials.
In one embodiment of the invention an elongate guide pin element is formed integral to the shaft of the base spur gear element. In another embodiment the guide pin element is a separate unit securely mounted to the shaft of the base spur gear element. In a preferred embodiment, the shaft of the spur gear comprises a hollow and an attachment shaft of the guide pin element is securely pressed therein for attachment to the shaft of the base spur gear element. In a still further embodiment the guide pin element comprises a shaft fixed to the shaft of the spur gear element and a rotatable cap which rotates independently from the fixed shaft. Generally, the end of the shaft of the pin element is slotted or otherwise configured to accept a tool to enable convenient turning of a guide member which simultaneously turns an opposing guide member for adjusting distance for variable blade thickness.
In a preferred embodiment, the guide member is mounted in a bearing hole sized to rotatably secure the shaft of the spur gear element in centered alignment. The eccentric pin element is generally arranged at the end of the shaft to rotate within a circumscribed diameter greater than the diameter of the shaft. Thus, the eccentric pin element generally extends from the remote end of the bearing hole of the spur gear shaft which may be sized greater than that supporting the spur gear shaft. It should be understood however, the invention further contemplates an eccentric pin element having a diameter sized to enable offset rotation thereof within a circumferential diameter the same or smaller than the diameter of the shaft of the spur gear.
Opposing element sharpening means generally includes a wide variety of two or more opposing mounted sharpener elements between which a knife blade or the like can be drawn for sharpening. The elements may be plates, disks or the like formed to comprise any suitable knife blade abrading material. Opposing disks may be mounted in a generally static arrangement, loosely mounted for self adjusting movement or rotatably or the like driven to assist in abrading. Sharpener elements are generally arranged so that orientation of the generally “V” shaped drawing slot enables drawing of the blade in a direction generally transverse to the plane of the sharpening elements of the device. Such arrangement of sharpening elements is well known in the art.
In one embodiment of the invention two or more opposing elements are mounted in generally parallel planes in a partially overlapping arrangement forming a generally “V” shaped slot at the overlapping boundaries. In one arrangement the elements are disks comprising a composite abrading material along their periphery, the abrading peripheries of the disks forming a curved “V” shaped slot which abrades a curved or hollow ground surface on opposite sides of a blade drawn therethrough. In another arrangement the elements are polygonal comprising an abrading material along opposing generally straight peripheral surfaces forming a generally angular “V” shaped slot which abrades a generally straight surface on opposite sides of a blade drawn therethrough.
Particularly in an embodiment wherein a plurality of opposing sharpening disks are used, they are generally mounted in two interleaved parallel stacks, forming a generally “V” shaped slot comprises a plurality of opposing disks, through which a blade of a knife can be slidably drawn for abrading the sides of the knife blade. Disks can be axle mounted for free rotation and/or can be enabled for driven rotation by crank, motorized means or the like.
In another embodiment of the invention, opposing polygonal sharpening blade elements comprising two or more generally straight carbide sharpening edges are mounted in overlapping retaining slots such that a sharpening edge of each opposing element defines a leg of a generally “V” shaped slot.
In a preferred embodiment, rectilinear sharpener elements are mounted within open ended rectilinear retaining slots arranged in the body of the tool so that exposed sharpening surfaces of the elements define legs of the “V” shaped slot, and elements are slidably movable along the length of the slot. As the sharpening surface of the element wears, the element can be moved along the length of the slot and its position fixed to provide a fresh sharpening surface to engage the knife blade. In various embodiments, a sharpening surface of a rectilinear element is arranged to engage the knife blade along a beveled edge or an edge is arranged to engage a side of a blade at an angle.
In a one preferred embodiment, the quadrilateral rectilinear sharpening elements have generally parallel, elongate sharpening edges and angled ends. Element retaining slots are arranged at about a 40° angle to each other to define the “V” shaped slot and the elements are slidable mounted in the slots. The ends of the sharpening elements are angled so that when mounted, the ends lay at about a 90° angle to the centerline bisecting the “V” shaped slot, enabling convenient variable adjustment of the positioning of the elements in their respective retaining slots by various support means engaging the ends, without change to the geometry or relative position of the “V” shaped slot.
In one particularly preferred embodiment an adjusting screw having a generally flat end, is arranged along about the plane of the bisect below the “V” shaped slot so the flat end simultaneously engages the angled ends of both opposing elements and simultaneously slidably adjust the position of the elements upward and downward along their respective retaining slots to vary the crossing points along the abrading edge of both elements forming the apex of the angle of the “V” shaped slot.
In a further particularly preferred embodiment, cam means is arranged about perpendicular to the centerline of the bisect, below the apex of “V” shaped slot, to simultaneously support the elements and adjust the position thereof. In a still further preferred embodiment, a levered plate, stud, rod or the like engages the ends of the rectilinear sharpening plates to adjust the position of the elements along their respective retaining slots.
For a fuller understanding of the device of the present invention, reference should be made to the following detailed description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front sectional view of a sharpening arrangement of the invention.
FIG. 2 is a top plan view of the sharpening arrangement of FIG. 1.
FIG. 3 is a side sectional view of the arrangement of FIG. 1 taken along about line A-A′ of FIG. 2.
FIG. 4 is a bottom plan view of the mounting block of FIG. 1.
FIG. 5 is a top plan view of an angular sharpening element of the invention.
FIG. 6 is a cross-sectional view of the sharpening element of FIG. 5, taken along about line B-B′ of FIG. 5.
FIG. 7 is a cross-sectional view of a further sharpening element in accord with the invention.
FIG. 8 is a front partial sectional plan view of a sharpener element screw adjustment arrangement of the invention.
FIG. 9 is a front sectional plan view of a sharpener element lever adjustment arrangement of the invention.
FIG. 10 is a perspective view of the lever adjustment means of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1-4, wherein is illustrated an embodiment of the sharpening arrangement of the invention.
Therein a sharpening tool embodiment of the sharpening arrangement of the invention is illustrated as comprising a housing 10, with sharpening arrangement mounting block 15, contained between opposite sides 11 and 12 thereof. Mounting block 15 is illustrated as comprising spur gear hollow 13, spaced pinion shaft bearing holes 14 b and 14 c (not shown), blade clearance slot 16, and opposing sharpening element mounting slots 17 and 18. Spaced restraining pins 19 and 20 are arranged to extend into mounting slots 17 and 18, to restrict sliding movement of sharpening elements mounted in the mounting slots.
Opposing quadrilateral sharpening elements 25 and 26, containing restraining pin slots 25 a and 26 b respectively, are mounted in slots 17 and 18, and arranged to overlap so as to form a generally “V” shaped sharpening slot between their respective carbide sharpening edges 25 b and 26 b. In the illustrated embodiment, the dimensions from cutting edge to opposing cutting edge of the sharpening elements closely mate with the width of slots 17 and 18 to resist pivoting of the sharpening elements in the slot during sharpening and thus resist change in the vertex angle 30 of the “V” shaped sharpening slot formed by the sharpening edges. When the comparative dimensioning of the width of the slots in respect to the mating dimensioning of the width of the sharpening elements is significantly different, the vertex angle of the “V” shaped sharpening slot can change and thus vary the sharpening angle from the cutting edge to the side of the blade. The greater the difference in dimensioning, the greater the vertex change and the greater the variation in sharpening angle. It is generally considered desirable for cutting efficiency, that the sharpening angle from the cutting edge to the side of a blade be from about 15 degrees to about 25 degrees and most preferably about 20 degrees. Thus, the vertex angle of the “V” shaped sharpening slot is preferably from about 35 degrees to about 45 degrees and most preferably about 40 degrees.
Sides 11 and 12 of housing 10 are illustrated as comprising slots at 11 a and 12 a respectively, adjacent the ends of blade clearance slot 16 in general alignment with the generally “V” shaped slot formed by opposing sharpening edges 25 b and 26 b, to avoid undesirable engaging of a blade being sharpened with the sides of the housing.
Guide members are illustrated as comprising base spur gear elements 32 (not shown) and 33 respectively, with mating eccentric guide pin elements 35 and 36 respectively mounted thereon. Base spur gear elements 32 and 33 comprise toothed spur gears 32 a and 33 a respectively and pinion shafts 32 b (not shown) and 33 b respectively. Spur gears 32 a and 33 a are arranged to matingly engage in spur gear hollow 13 of mounting block 15 with pinion shafts 32 b and 33 b extending into spaced pinion shaft bearing holes 14 b and 14 c respectively. Guide pin elements 35 and 36 are illustrated as eccentrically mounted to the ends of pinion shafts 32 b and 33 b respectively. Slots 35 a and 36 a are provided at the ends of guide pin elements 35 and 36 respectively for mating engagement with a screwdriver or the like to enable convenient rotation thereof so as to micro-adjust spacing between the pin elements toward and away from the blade being guided, by rotation of a single guide member.
Referring now to FIGS. 5-6 wherein is illustrated a top plan view and cross-sectional view respectively of elongate rectilinear sharpening element 37 comprising opposing generally parallel cutting edges 37 a and 37 b, generally parallel opposing ends 37 c and 37 d, and restraining pin slot 38 which is arranged generally parallel to the cutting edges. In this embodiment an opposing end is angled to an included angle of about 70° to a cutting edge of the element so that when two crossing opposing elements are arranged in retaining slots in a mounting block to form a generally “V” shaped arrangement, the ends of the two elements below the vertex of the generally “V” shaped arrangement can be aligned in a common plane. Such angular arrangement of the generally parallel opposing ends enables convenient simultaneous adjustment of the position of opposing sharpening elements along their respective mounting slots.
The sharpening element itself is illustrated as a four cornered plate formed from a carbide material with cutting edges 37 a and 37 b illustrated as beveled from perpendicular to the plane of the plate. It should be understood that the element can be formed from any suitable material with the edges comprising any suitable abrading material.
FIG. 7 illustrates a sectional view of a rectilinear sharpening element wherein the cutting edges 39 are generally perpendicular to the surface of the plate forming the element.
Referring to FIG. 8, therein is illustrated a sharpening blade adjustment embodiment of the invention wherein opposing sharpening elements 41 and 42, comprising ends 41 a and 42 a respectively and restraining pin slots 41 b and 42 b respectively, are slidably mounted in sharpening element slots 45 and 46 respectively of mounting block 40. Ends 41 a and 42 a of the sharpening elements are angled from the cutting edges as illustrated in FIG. 5, and threaded adjusting screw 43 is arranged to twist through mating threaded hole 44 in mounting block 40, aligned along about the centerline of the “V” shaped slot formed by the sharpening elements to simultaneously engage ends 41 a and 42 a. The sharpening elements are restricted by restraining pins 47 to slidable movement within sharpening element slots 45 and 46 to the length of restraining pin slots 41 b and 42 b respectively. Twisting adjusting screw 43 into threaded hole 44 engages ends 41 a and 42 a of sharpening elements 41 and 42 and forces the sharpening elements to simultaneously slide upwardly along sharpening element slots 45 and 46, changing the point along their respective cutting edges which engage a knife blade to be sharpened, but maintaining the spacial position and the angle of the vertex of the “V” shaped slot formed by the sharpening elements.
Referring to FIGS. 9-10, wherein is illustrated a further sharpening blade adjustment embodiment of the invention wherein opposing sharpening elements 51 and 52, comprising ends 51 a and 52 a respectively and restraining pin slots 51 b and 52 b respectively, are slidably mounted in sharpening element slots 55 and 56 respectively of mounting block 50. Ends 51 a and 52 a of the sharpening elements are angled from the cutting edges with levered sharpening element adjustment means arranged to engage ends 51 a and 52 a for simultaneous movement of the sharpening elements through the length of restraining pin slots 51 b and 52 b respectively.
The levered sharpening element adjustment means is illustrated as comprising an arm hook, wherein a first end of arm 57 comprises lever extension 57 a and mounting opening 57 b, and an opposite end comprises hook rod 57 c extending angularly therefrom, arranged to engage the ends of the opposing sharpening elements. The arm hook is illustrated as mounted to the sharpening device by screw 58. With screw 58 loosened in place, lever extension can be depressed to rotate arm 57 so that hook rod 57 c engages the ends of the opposing sharpening elements forcing them to slide upwardly in slots 55 and 56 to adjust the point of engagement of the knife blade along the cutting edges of the sharpening elements and to be locked into place through tightening of the screw.

Claims

1. A sharpening tool comprising:

opposing sharpening elements arranged to form a generally “V” shaped sharpening slot;

first and second elongate guide members extending from opposite sides of said sharpening slot, each comprising a base spur gear element and an elongate eccentric guide pin element;

wherein a base spur gear element comprises a mounting shaft having a toothed gear at a first end and an elongate eccentric guide pin element at the opposite end, the toothed gear of said first guide member arranged in mating engagement with the toothed gear of said second guide member.

2. The sharpening tool of claim 1 wherein a centerline of a guide pin element is arranged offset from a centerline of a mounting shaft of a spur gear element of an elongate guide member.

3. The sharpening tool of claim 1 wherein said guide pin elements are arranged about equidistant from and generally parallel to a bisecting plane of said generally “V” shaped sharpening slot.

4. The sharpening tool of claim 3 arranged so that turning the guide pin element of said first guide member simultaneously turns the guide pin element of said second guide member in aligned mirrored movement.

5. The sharpening tool of claim 1 wherein said sharpening elements are arranged in off-set overlapping opposition.

6. The sharpening tool of claim 5 wherein said opposing sharpening elements comprise polygonal plates, arranged so that sharpening edges thereof forms the generally “V” shaped sharpening slot.

7. The sharpening tool of claim 6 wherein said opposing sharpening elements comprise two overlapping quadrilateral plates having abrading edges.

8. The sharpening tool of claim 5 wherein said opposing sharpening elements comprise disks.

9. The sharpening tool of claim 8 wherein a plurality of opposing sharpening disks are generally mounted in interleaved about parallel stacks, forming the generally “V” shaped sharpening slot.

10. The sharpening tool of claim 8 wherein said disks are rotationally driven.

11. The sharpening tool of claim 8 wherein said disks comprise a cylindrical abrading surface.

12. The sharpening tool of claim 5 wherein said disks comprise an abrading edge.

13. The sharpening tool of claim 1 wherein said the angle of the vertex of said generally “V” shaped sharpening slot, is from about 35 degrees to about 45 degrees.

14. The sharpening tool of claim 12 wherein said the angle of the vertex of said generally “V” shaped sharpening slot, is about 40 degrees.

15. The sharpening tool of claim 1 wherein said first and second guide members support a knife blade along about the bisect plane of said generally “V” shaped sharpening slot.

16. The sharpening tool of claim 1 wherein a guide pin element is configured to engage a tool for turning.

17. The sharpening tool of claim 1 wherein an eccentric guide pin element is arranged to circumscribe a diameter greater than the diameter of the shaft of the spur gear element.

18. The sharpening tool of claim 1 wherein the shaft of the spur gear element comprises a hollow and a shaft of the guide pin element is securely pressed therein for attachment thereto.

19. The sharpening tool of claim 1 wherein a guide pin element comprises a rotatable cylindrical surface.

20. The sharpening tool of claim 7 wherein a sharpening element comprises a quadrilateral plate having generally parallel sharpening edges and generally parallel angled ends, said ends being angled so that when sharpening edges of the plates are arranged to form the generally “V” shaped sharpening slot, the ends thereof lay at about a 90° angle to a centerline bisecting the “V” shaped sharpening slot.

21. The sharpening tool of claim 20 comprising screw means arranged to adjustably engage adjacent angled ends of sharpening elements retained in a generally “V” shaped orientation.

22. The sharpening tool of claim 20, comprising a levered means arranged to adjustably engage adjacent angled ends of sharpening elements retained in a generally “V” shaped orientation.

23. A sharpening tool comprising:

a mounting block, comprising slots arranged for mounting opposing sharpening elements comprising overlapping rectilinear plates having sharpening edges arranged in a generally “V” shaped sharpening slot arrangement;

first and second elongate guide members extending from said mounting block on opposite sides of said sharpening slot, each guide member comprising a base spur gear element and an elongate eccentric guide pin element;

said base spur gear elements comprising a mounting shaft having a toothed gear at a first end and an elongate eccentric guide pin element at the opposite end;

wherein the toothed gears of said first guide member is arranged in mating engagement with the toothed gear of said second guide member in a hollow of said mounting block.

24. The sharpening tool of claim 23 wherein said sharpening elements have generally parallel sharpening edges and generally parallel angled ends, said ends being angled so that when sharpening edges of the plates are arranged to form the generally “V” shaped sharpening slot, the ends thereof lay at about a 90° angle to a centerline bisecting the “V” shaped sharpening slot.

25. The sharpening tool of claim 24 comprising screw means arranged to adjustably engage adjacent angled ends of sharpening elements retained in a generally “V” shaped orientation.

26. The sharpening tool of claim 24, comprising a levered means arranged to adjustably engage adjacent angled ends of sharpening elements retained in a generally “V” shaped orientation.

27. A quadrilateral plate sharpening element comprising opposing generally parallel sharpening edges and opposing generally parallel angled ends, said ends being angled to said edges so that when sharpening edges of opposing plate sharpening elements are arranged to form a generally “V” shaped sharpening slot, ends of the opposing plates lay at about a 90° angle to a centerline bisecting the “V” shaped sharpening slot.

28. A sharpening element of claim 27 wherein an included angle of an angled end to a sharpening edge is about 70 degrees.