Field of the Inven inn

This invention generally relates to a blade sharpener and more specifically to an apparatus for sharpening the end point of the cutting edge on a tri¬ angularly shaped blade.

Background of the Inven ion

Devices for sharpening are well known in the art. For example U.S. Patent,* 3,769,759 describes a drill bit sharpener, U.S. Patent '2,365,759 a toolbit grinder, U.S. Patent "2,565,309 a needle sharpener and U.S. Patent -1,601,339 a razor sharpener. A common flat blade employed in drafting offices is a triangular blade, known as an EXACTO blade, ³ which has a cutting edge that normally terminates at a sharp point. This point tends to dull from time to time and a need exists to resharpen the point for further use of the blade.

Summary of the Invention

With a blade point sharpener in accordance with the invention the point of a triangular planer blade can be conveniently sharpened. This is done by applying the blade point against a surface of a grinding wheel in a manner whereby a blade portion is ground off extending from a rear edge to the cutting edge. The blade is pre¬ ferably oriented so that its flat surfaces are transverse to the grinding surface.

As described herein for one blade point sharp¬ ener in accordance with the invention, a housing is provided to enclose a grinding wheel and a motor to rotate it. A blade guide is located in the housing to

receive and then guide a blade along an insertion axis for sharpening in a grinding zone inside the housing. The grinding wheel has a flat end surface which is located in the grinding zone. The orientation of the blade guide is so selected that the cutting edge of the blade forms an acute angle with the normal to the grind¬ ing surface at the area of the grinding contact when the blade point is applied against the grinding wheel end sur¬ face.

Contact between the blade and the wheel is so selected that the grinding wheel can sharpen the blade point by grinding away a portion of the blade that is behind the cutting edge and at its end.

With a blade sharpener in accordance with the invention a blade with a triangular working end such as the EXACTO blade can have its end resharpened in an effective and convenient manner.

It is, therefore, an object of the invention to provide a blade sharpener with which an end point on the blade can be conveniently and effectively resharpened. These and other advantages of the invention can be understood from the following detailed description of a blade point sharpener described in conjunction with the drawings.

Brief Description of the Drawings

Fig. 1 is a partial sectional view in elevation of a blade point sharpener in accordance with the invention;

Fig. 2 is a full sectional view in elevation of the blade point sharpener as shown in Fig. 1;

Fig. 3 is a top plan partially broken away view of the blade point sharpener as shown in Fig. 2;

Fig. 4 is a section view of the blade point sharpener as shown in Fig. 1 and taken along the line 4-4 therein;

Fig. 5 is a partial plan view of a blade sharpened with an apparatus in accordance with the invention.

Detailed Description of the Drawings

With reference to Figs. 1-3 a blade sharpener 10 in accordance with the invention is shown formed with a housing 12. Housing 12 has a first segment 14 which includes a grinding wheel 16 that is driven into rotation about an axis 18 by a motor 20. The grinding wheel has a flat end surface 22 located in a grinding zone 24.

Housing 12 has a second segment 26 which is inclined at an angle A as shown relative to the horizontal first segment 14. The second segment 26 includes a cylindrical guide 28 through which a planer blade 30 that is attached to a holder 32 can be inserted and placed with its end point 34 in grinding zone 24.

The guide 28 -is aligned along an -insertion axis 36 whose orientation is selected to provide a desired incidence angle B (see Fig. 2) with the flat end surface 22 of the grinding wheel 16. The angle B is selected so that the cutting edge 38 of blade 30 forms an acute angle C with the normal 40 to the contact area with grinding surface 22. The guide 28 has a cylindrical bore 42 sized to slidingly receive the blade 30 and its handle 32. The acute angle C is selected so that the point 34 of blade 30 can be resharpened. The sharpening is done by grinding the blade 30 starting from behind the cutting edge 38 whose end point 34 is ground away to be replaced with a sharpened point at 42. Hence, when a blade 30 is to be sharpened its rear edge 43 is applied to the grinding zone 24 with the flat surfaces or plane of the blade 30 essentially perpendicular to the contact area of grinding surface 22 as illustrated in the view of Fig. 4. In the embodiment this places the entire surface 22 of grinding wheel transverse to the plane of flat blade 30.

The angle B between the insertion axis 36 and normal 40 to the grinding contact area preferably is so selected that the angle C is acute. Generally an angle C _r that is the angle between cutting edge 38 and normal 40, is less than about 75°, though an angle of about thirty degrees is preferred.

Blade point sharpener 10 is made portable by use of batteries such as 50 to power motor 20 as illustrated in Fig. 2. The motor 20 is connected to the batteries 50 in response to the insertion of blade 30 through guide 28. This is done with a spring biased lever 52 that is pivotally urged in front of the discharge end of bore 42 as illustrated in Fig. 2. When a blade 30 is inserted through guide 28 the lever 52 is pivoted out of the way and against a first spring contact 54 connected to one of the terminals of batteries 50. As the blade is further inserted spring contact 54 is pushed against a second spring contact 56 connected to the other terminal of the batteries 50 to complete the circuit and activate motor 20.

Having thus described a blade point sharpener in accordance with the invention its advantages can be appreciated. Variations can be implemented without departing from the invention. For example, the grinding wheel 16 may be repositioned so that its peripheral cylindrical grinding surface 60 is used, see Fig. 4, to sharpen the end point of cutting edge 38 of blade 30.