Drill With Balanced Inserts

The ordinary twist drill and the ordinary spade drill has two cutting edges disposed generally radial of one another and connected by a web. This wed is necessary in order to grind and sharpen the cutting edges of the drill.

The ordinary twist drill and the ordinary spade drill will drill a hole in a stack or layer of two or more plates, however, the web does cause resistance to drilling because at the web area no cutting can occur because there is due to its location on the drill axis cuts a minimal amount.

The newer metal cutting drills or hole mills which are designed to use each manufacturer's special design inserts will not drill a hole in a stack or layer of plates two or more because they do not cut through center on center. This design of drill develops a conical shaped where the drill exits the first part layer, this conical shaped disc then revolves with the drill making it impossible to cut this conical shaped disc into chips so that they may exit the cut. With the advancement of the drill feed and with rotation of the drill the only thing that can happen is for the drill to fail.

Applicant has discovered that by referencing the cutting edges of a drill to a central reference plane with the cutting edges of the drill in planes that are substantially on the reference plane (manufacturing tolerances will not permit the cutting edges to be exactly on the reference plane) and by curving the ends of the cutting edges adjacent the axial center of the drill, the drill will drill a hole through a stack, or layers of plates. Moreover, the overall efficiency of the drill is improved by applicant's arrangement of cutting edges.

Applicant is familiar with the following patents, none of which disclose a drill having cutting edges substantially on or offset a very small amount from a center of rotation of the drill and having inner ends curved about a very small radius adjacent the center of rotation in the manner that applicant arranges his cutting edges. By the arrangement of cutting surfaces herein, applicant is able to drill holes through layered parts or stacked plates and the efficiency of the drill is improved.

U.S. Pat. No. 4,565,471, and those referred to in that Patent, provide several embodiments of a drill wherein the main cutting edges terminate in spaced relation to the axis of rotation of the drill so that a cylindrical core is created at the center of the hole. This core is occasionally twisted off by the rotating drill bit. This twisted off piece presents a source of trouble when drilling hard material. Applicant provides two straight cutting edges that are disposed substantially in the axis of rotation of the drill and terminates adjacent the center in curved parts to get to the shaped part. These curved ends continually cut at the center of the hole and leave no material to be twisted off. Moreover, applicant provides chip breaker grooves in his cutting inserts which help reduce chip size and facilitate chip removal.

It is an object of the invention to provide an improved drill.

Another object of the invention is to provide a drill that has cutting edges that cut substantially at the axis of rotation of the drill.

Another object of the invention is to provide a drill having cutting edges that are straight and terminate adjacent the drill's axis of rotation in an arcuate part that is tangent to the reference plane and cuts metal substantially up to the axis of rotation.

Another object of the invention is to provide a drill that is simple in construction, economical to manufacture and simple and efficient to use.

With the above and other objects in view, the present invention consists of the combination and arrangement of parts hereinafter more fully described, illustrated in the accompanying drawing and more particularly pointed out in the appended claims, it being understood that changes may be made in the form, size, proportions and minor details of construction without departing from the spirit or sacrificing any of the advantages of the invention.

FIG. 1 is a side view of a drill according to the invention.

FIG. 2 is an end outline view of the bottom of the hole cut by the drill shown in FIG. 1 at a particular time.

FIG. 3 is an end view of the drill shown in FIG. 1.

FIG. 4 is an enlarged view of FIG. 3.

FIG. 5 is a cross sectional view taken on line 5--5 of FIG. 7.

FIG. 6 is a diagrammtic end view of the drill shown in FIG. 3, shown to an enlarged scale.

FIG. 7 is a side view of the screw of holding the inserts in place.

FIG. 8 is a side view of a part of FIG. 7.

Now with more particular reference to the drawings, I show a drill 10 having body 12. Body 12 has first end 14, second end 16 and tang 18 integrally attached to body 12. First planar surface 20 is formed on one side of body 12 and second planar surface 22 is formed on the other side of body 12, parallel to the plane of first planar surface 20. First planar surface 20 and second planar surface 22 support first insert 32 and second insert 34 having cutting edges disposed in planes that are disposed up to 0.015 inches apart on opposite sides of central axis of rotation 31 of drill 10. First planar surface 20 is formed on one side of drill 10 and second planar surface 22 is formed on the other side of drill 10 parallel to the plane of first planar surface 20. First planar surface 20 and second planar surface 22 form mounting surfaces for first insert 32 and second insert 34. First insert 32 and second insert 34 are generally parallelogram shaped of a type familiar to those skilled in the art.

Body 12, of drill 10, has a convex end surface made of first part 24 and second part 26. First insert 32 and second insert 34 are clamped rigidly to first planar surface 20 and second planar surface 22 by clamp screws 52 and clamp inserts 53, which are of a type familiar to those skilled in the art.

First insert 32 and second insert 34 each have first end 40, first side surface 38 and second side surface 36 which is parallel to first side surface 38, first end 40 and second end 42. First insert 32 has a first straight cutting edge 44 and first curved cutting edge 46. Second insert 34 has second straight cutting edge 45 and second curved cutting edge 47. First straight cutting edge 44 is tangent to first curved cutting edge 46. First straight cutting edge 44 and second straight cutting edge 45 have spaced notches 60 which act as chip breakers. Notches 60 in first insert 32 are staggered from notches 60 in second insert 34 to reduce chip size. The side edges of first insert 32 and second insert 34 will have a back taper A of about 15 degrees. First straight cutting edge 44 is inclined to a line 30 perpendicular to axis of rotation 31 at an angle of about 15 degrees of lead angle B.

Ideally, the radius of curvature of the arcuate first curved cutting edge 46 and second curved cutting edge 47 would be zero and first insert 32, and second insert 34 would come to a sharp point on axis of rotation 31 of drill 10. In practice, the points of first and second inserts would break off quickly and to remedy this matter first curved cutting edge 46 and second curved cutting edge 47 are provided which may have a radius of curvature of only about 0.015 inches. First curved cutting edge 46 and second curved cutting edge 47 cannot cut beyond axis of rotation 31 since this would be a reverse lead which would cause the tool to break. Consequently, first curved cutting edge 46 and second curved cutting edge 47 will cut a central core in the form of an inverted cone unless first straight cutting edge 44 and second straight cutting edge 45 are set on center radius of curvature of the curved side section. If first straight cutting edge 44 and second straight cutting edge 45 are set on their side of center, arcuate first straight cutting edge 44 and second straight cutting edge 45 cut constantly and no center post whatever is left or intermittently broken off during normal operation. When rotating drill 10 is properly set and lowered into engagement with a workpiece, a hole will be drilled having a substantially flat bottom which is formed by first straight cutting edge 44.

First insert 32 and second insert 34 are held to drill body 12 by headed screws 50. Screws 50 have frustoconical heads 52. Heads 52 fit into frustoconical holes 53 in frustoconical sleeves 54. First insert 32 and second insert 34 are clamped to first planar surface 20 and second planar surface 22 by screws 52. Fisrt insert 32 and second insert 34 are of a familiar type generally in the shape of a parallelogram with two flat parallel faces, two short parallel sides and two long parallel sides.

The foregoing specification sets forth the invention in its preferred, practical forms but the structure shown is capable of modification within a range of equivalents without departing from the invention which is to be understood is broadly novel as is commensurate with the appended claims.