Cutting by use of rotating axially moving tool – Tool or tool with support – Having peripherally spaced cutting edges
Patent
1990-09-14
1992-01-07
Bishop, Steven C.
Cutting by use of rotating axially moving tool
Tool or tool with support
Having peripherally spaced cutting edges
408227, B23B 5102
Patent
active
050785540
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a drill capable of efficient and accurate drilling, and more particularly, to a drill having a variety of cutting edges which are respectively formed into appropriate shapes for efficient and accurate drilling.
BACKGROUND ART
Improved sharpness of a drill, prevention of occurrences of burrs at the exit side of a machined bore (at that portion at which the machined bore opens to a drilled face), suppression of an enlarged amount of the bore size attributable to drilling (prevention of an excessive increase of the machined bore), assurance of strength of the drill, etc. are important in drilling.
Conventionally, to improve the sharpness of a chisel edge provided at the distal end of a drill, i.e., the sharpness of the drill, a primary or secondary face having a positive rake angle is formed in a chisel-edge-forming portion of the drill (see, U.S. Pat. No. 4,688,972). In this case, however, the thickness of the drill becomes small at the chisel-edge/rake-face-forming portion of the distal end of the drill. Thus, there occurs a drawback such that the strength and rigidity of that drill portion become insufficient.
It is considered that burrs are caused by the flow of machined material (chip) flowing in the radial direction from the inward of the machined bore to the outward thereof. Thus, it appears desirable to provide a cutting edge at a peripheral portion of the distal end of the drill, so as to cause the flow of machined material to be directed toward the inward direction. However, during the course of drill production, it is impractical to machine a drill to be produced in such a manner that the drill is simultaneously formed at its distal end with both of a chisel edge face and an outer peripheral cutting edge, because interference can occur between a tool for forming the rake face and a tool for forming the cutting edge.
To suppress the excessive enlargement of the bore size resulting from the drilling, conventionally employed is a drill having a pair of cutting edges which have the same shape and are well-balanced with each other, or a drill having a single cutting edge and a guide shoe.
Conventionally, various countermeasures have been taken for the sake of improvement of the drill sharpness, prevention of burrs, and suppression of excessive enlargement of the bore size, as mentioned above. However, in the industrial production of drills, difficulties have been encountered in adopting all the countermeasures simultaneously. Particularly, it is difficult to provide the resultant drills with an adequate strength.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a drill which is excellent in sharpness and strength.
Another object of the present invention is to provide a drill capable of preventing occurrences of burrs at an exit side of a machined bore.
A still another object of the present invention is to provide a drill capable of suppressing an excessive enlargement of a bore size attributable to machining.
A further object of the present invention is to provide a drill which is low-priced in production costs and is easy to effect re-grinding, to thereby make it possible to always maintain the drill in appropriate conditions.
In order to achieve the above-mentioned objects, a drill of the present invention comprises first and second main cutting edges which are respectively formed in a distal end of the drill. These cutting edges are the same with each other in a half point angle and in an offset amount relative to the center of the drill. The drill further comprises a single chisel edge formed in the distal end of the drill and extending only between the center of the distal end of the drill and one of the first and second main cutting edges, and a rake face formed in the distal end of the drill in association with the chisel edge.
Preferably, a non-chisel-edge-forming portion is provided between the center of the distal end of the drill and the other main cutting edge. A peripheral portion of the distal end of the dr
REFERENCES:
patent: 546041 (1895-09-01), Tyberg
patent: 4222690 (1980-09-01), Hosol
patent: 4688972 (1987-08-01), Kubota
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