GB2431368A

GB2431368A - Spade drill bit

Info

Publication number: GB2431368A
Application number: GB0612804A
Authority: GB
Inventors: Laverne R Durfee
Original assignee: Irwin Industrial Tool Co
Current assignee: Irwin Industrial Tool Co
Priority date: 2005-10-20
Filing date: 2006-06-28
Publication date: 2007-04-25
Anticipated expiration: 2026-06-28
Also published as: GB2431368B; GB0612804D0

Abstract

The bit 1 includes a shaft 2, a blade 8 attached to the shaft, a cutting edge 18 & 20 formed on the blade and a smooth flute 50 & 52 formed in the blade adjacent to the cutting edge. The blade may have a pair of cutting shoulders 14 & 16 that extend inwardly from the outer sides of the blade toward a bit axis A. A tip 26 has converging sides 28 & 30 that create a point 32 that extends from the shoulders 14 & 16. The flute 50 & 52 may be provided on the leading portion of each blade face 10 & 12 adjacent the cutting edges 18 & 20. Each flute is a smooth curve that creates a substantially uninterrupted recess on each face of the blade to facilitate chip removal, increase the drill rate and lower the power required to drill a hole. The flute may have two curved surfaces with different radii of curvature. A non-stick coating may be applied to the blade to further facilitate chip removal.

Description

S 2431368

Description

SPADE BIT

BACKGROUND

[Para 1] This invention relates generally to boring tools and more particularly to so-called "spade bits," which are typically used with a drill for drilling holes In wood.

[Para 21 Spade bits are widely used for boring holes between approxImately 1/4" and 11/2" diameter In wood.and similar soft materials, because they are fast, true cutting, resharpenable, and relatively inexpensive. Their name derives from the shape of the spadeilke blade or cutter, in contrast to the spIral shape of augers and twist drills. The blade, which Is usually forged integrally from the shank, Is relatively thin and flat and may have a width several times the diameter of the shank.

(Para 31 One known spade bit is disclosed In United States Patent No. 4,682,917. A partial cross-section of this drill bit Is shown drilling a bore in FIg. 6. ThIs bit 11 includes a blade 3 shoulder flute 5 adjacent the cutting edge of each shoulder. The flute has a cross-sectional configuration having an inner surface portIon 7 and an outer surface portion 9 where the outer portion and inner portion consist of planar surfaces that meet at an angle. The shoulder flutes preferably do not extend all the way to the outer sides of the blade but rather stop inwardly of the sides of the blade.

(Para 4] The Inventor of the present drill bit determined that because the surface portions 7 and 9 comprIse substantially planar surfaces that meet at a relatively sharp angle, the approximate path of travel of chips generated by this bit Is as shown by the arrows In FIg. 8. Specifically the chips curl up face 9 until they strike face 7 at which point they are reflected at a relatively severe angle almost perpendicular to the direction of travel of the bit, represented by arrow C. The chips are trapped in the bore 13 where they are swirled around by the drill bit blade 3 as the drill bit rotates until the chips are eventually ejected from the bore.

(Para 5] It has been determined that moving the chips within the bore 13 byblade 3 slows the drilling rate and requires energy. Thus, not only is the drilling rate slower than optimal, the amount of energy used to drill the bore Is Increased. The use of excess energy to drill the bore can present a significant issue because many drills are battery powered such that the need for additional energy adversely affects the charge life of the battery resulting in the need for more frequent battery charges.

[Para 6] Thus, there is a need In the art for a bit that increases the 4,.

drilling rate and that requires less power.

SUMMARY OF PREFERRED EMBODIMENTS OF ThE INVENTION

[Para 7J The drill bit of the invention comprises a cutting blade formed at one end of a shank. The cutting blade has a pair of cutting shoulders that extend inwardly from the outer sides of the blade toward the bit axis. A tip having converging sides that meet at a point extends from the shoulders. The cutting edge of each shoulder is beveled with respect to the plane of the face of the blade. A flute is provided on the leading portion of each blade face adjacent the cutting edges. Each flute is a smooth curve that creates an uninterrupted recess on each face of the blade that facilitates chip removal, Increases the drill rate and lowers the power required to drill a hole. A non-stick coating may be applied to the blade to further facilitate chip removal.

BRIEF DESCRIPTION OF ThE DRAWINGS

[Para 8] Fig. 1 is a plan view of one embodiment of the drill bit of the Invention.

[Para 9] FIg. 2 Is a side view of the drill bit of Fig. 1.

[Para 101 Fig. 3 Is an enlarged side view of the drill bit of Fig. 2.

[Para 11] Fig. 4 Is an end view of the bit of Fig. 1.

[Para 12] FIg. 5 Is an enlarged partial section view of one embodiment of the drill bit of the Invention.

[Para 13] Ag. 6 Is a partial section view showing the drill bit of the invention drilling a bore, [Para 14] Fig. 7 Is a plan view of another embodiment of the drill bit of the Invention.

[Para 1 5] FIg. 8 Is a partial section view of a prior art bit drilling a bore.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[Para 16] ReferrIng more partIcularly to the drawings the drill bit of the invention Is shown generally at 1 and consists of a shaft 2 having a hex connection 4 formed at one end thereof for engaging a chuck of a drill such as an electric or battery operated hand tool. The hex connection 4 may be formed with a recess 6 to be engaged by the quick- coupling of the drill chuck as Is known In the art. The shaft 2 is connected to a cutting blade 8 having a first cutting face 10 and a second cutting face 12 where the blade Is connected to the shaft with a taper angle of approximately 2 . Specifically, each face of the blade 10, tapers from the axis of rotation of the blade A-A approximately 1 such that the angle between the faces Is approxImately 2 . The 20 taper provides a slightly thicker shaft thereby Increasing the strength of the drill bit over conventional configurations. A hole 25 may be provided to hang the drill bit for storage. While the 2 taper Is one preferred embodiment, the faces may be made parallel to one another such that the taper angle Is 0 .

(Para 17) The blade 8 has a pair of shoulders 14 and 16 that form cutting edges 1 8 and 20, respectively. The outer side edges 22 and 24 of blade 8 are spaced from one another approximately the diameter of the desired hole. The side edges are formed with a taper such that the blade 8 Is wider near the shoulders 14 and 16 than it is near the shaft 2 by approximately.01 Inches to provide clearance to allow the blade to pass through the material being drilled. The outer side edges 22 and 24 are also formed with a side bevel $ of approximately 7 - 9 to allow the blade to clear the hole being drilled as the blade rotates as best shown in Fig. 4.

[Para 18] ReferrIng to Fig. 4, the cutting edges 18 and 20 are on the leading edges of the blade 8 as the blade rotates in the direction of arrow A. The cutting edges 18 and 20 are formed, In part, by beveling the shoulders as best shown in Fig. 3 to create an acute angle p between the shoulders and the plane of the face of the blade. in one embodiment bevel angle p Is 12 to 22 with a preferred angle of 1 5 to 18 .

[Para 19] A tip 26, having converging sIdes 28 and 30, extends from between shoulders 14 and 16. The sides 28 and 30 of point 26 meet at point 32. in one embodiment a pyramid-type point is created where surfaces 42 and 44 are formed in the tip such that the point Is comprised of four surfaces meeting at a point.

lip 26 has cutting edges 29 and 31 formed at the leading edges thereof. Spurs 46 and 48 are formed at the ends of shoulders 14 and 16. Spurs 46 and 48 score and cut the periphery of the bore to create a clean cut Hne.

[Para 20) Adjacent to and forming part of each cutting edge 18 and 20 are flutes 50 and 52, respectively, that facilitate the removal of chips from the bore, increase the drilling rate and decrease the power required to drill the bore. The flutes 50 and 52 define a surface that has a smooth profile with no sharp corners or flat surfaces that impede chip flow out of the bore being drilled. in one embodiment the flutes extend approximately.45 inches from the cutting edge or at least one quarter of the length of the blade.

[Para 21) Flutes 50 and 52 may be made identical such that specific reference is made to flute 50 In FIg. 5 where flute 50 Is a curved surface formed of curves with two different radii. The first curved surface 54 is formed as a curved surface with a radius of curvature of r1 and extends from the cuttIng edge 18 to a point where the radius Is substantially perpendicular to the surface 10 of the blade 8. The first curved surface 54, where it intersects shoulder 14, defines cutting edge 1 8. The smaller the radius of curvature r1 of this surface, the sharper the cutting edge 18. In one embodiment the radius r1 Is between.292 and. 692 Inches with a preferred radius of.492 Inches. The second curved surface 56 is formed with a radius of curvature of r2 and extends from the end of the first curved surface to surface 10 of blade 8. Radius r2 is, in one embodiment, twice radius r1 and is between.784 and 1.184 Inches with a preferred radius of.984 Inches. Curved surfaces 54 and 56 are arranged such that surface 54 is tangential to surface 56 such that the flute 50 Is smooth with no pronounced surface Interruptions.

[Para 22] The flutes 50 and 52 are arranged such that they extend laterally from approximately the axIs A-A of the blade 8 to and through the outer surfaces 22 and 24, respectively. Because the flutes extend to the edges of the blade, manufacture of the blade Is simplified. Specifically, a basic blade form can be made such as by a stamping process where the width of the blade form exceeds the width of a range of finished blades. The blade form can then be trimmed to the desired width. This is to be compared to the situation where the flute terminates Internally of the edge of the blade such that each finished blade width must be based on a blade form that Is specifically manufactured to that width.

[Para 23] In one embodiment the flutes 50 and 52 extend Into the blade approximately half the thickness of the blade. While the flutes are shown as two curved surfaces having different radii of curvature, the flutes may be made of a curve having a constant radius of curvature. Moreover the flutes may be made of more than two surfaces having different radii of curvature. For example a third surface having a third smaller radius of curvature could be formed between surface 54 and cutting edge 18 to create a cutting edge having a sharper edge. In such an arrangement the third curved surface would be arranged tangential to surface 54. LikewIse an additional curve having a larger radius of curvature may be used that Is arranged tangential to surface 56.

[Para 24] The operation of the drill bit of the Invention will be described with reference to Fig. 6 where drill bit 1 is shown drilling bore 60. As cutting edges 18 and 20 engage the bottom of bore 60 chips are developed that flow in the direction of the arrows.

Specifically the chips contact surface 50 and are projected substantially parallel to the direction of movement of drill bit 1 (represented by arrow D) and propelled out of bore 60. Because flutes 50 and 52 are substantially smooth and are not formed with angles or other surface protrusions, the chips can flow substantially parallel to the axis of the drill and are quickly ejected from the bore. Because the chips are quickly ejected from bore 60, they are not swirled In the bore by blade 8. As a result, more of the power used to rotate the blade Is used for drilling, rather than being used to move the chips In the bore.

Thus, the drill of the invention drills at a faster rate and uses less power. Because the blade uses less power, it can Increase

L

the charge life of a typical battery powered drill.

[Para 25] Another embodiment of the drill bit of the invention is shown in FIg. 7 and Is similar to bIt 1 of Figs. 1 through 6, where like reference numerals are used to Identify like components in the embodiment Illustrated In FIg. 7. The blade is coated with a non-stick coatIng 62 to further enhance the ability of the blade to eject chips from the bore being drilled. in one embodiment the flutes 50 and 52 are covered with the non-stick coating.

The coating may be a powdered coat paint that Includes non- stick powder such as TEFLON. The coating may be sprayed on or dipped. The coating may be a thermoplastic that is applied In powder form and then heated to melt onto the blade.

Alternatively, the coating may be a thermal set powder that Is applied in powder form and heated where the heat creates a chemical reaction that bonds the coating to the metal blade.

While the non-stick coating Is shown applied to the flutes, the coating may be applied to other portions of the blade Including the entire blade 8.

Specific embodiments of an invention are disclosed herein. One of ordinary skill in the art will recognise that the invention has other applications in other environments. Many embodiments are possible. Without limitation, embodiments are envisaged which use any combination of optional features disclosed herein in any number (including, but not limited to, any combination of the features of the dependent claims, in any number).

Claims

1. A drill bit comprising: a shaft: a blade attached to the shaft; a cutting edge formed on the blade; and a smooth flute formed in the blade adjacent the cutting edge.

2. The drill bit of claim 1, wherein the smooth flute is curved.

3. The drill bit of claim 1 or claim 2 wherein the flute forms part of the cutting edge.

4. The drill bit of any preceding claim wherein the flute is formed of a first curved surface and a second curved surface.

5. The drill bit of claim 4 wherein the first curved surface and the second curved surface have different radii of curvature.

6. The drill bit of claim 4 or claim 5 wherein the first curved surface is tangential to said second curved surface.

7. The drill bit of claim 4 or claim 6 wherein the first curved surface has a first radius of curvature and the second curved surface has a second radius of curvature, the second radius of curvature being approximately twice the first radius of curvature.

8. The drill bit of any preceding claim wherein the flute is coated with a non-stick coating.

9. The drill bit of any preceding claim further including a second cutting edge formed on the shaft and a second smooth flute formed in the blade adjacent the second cutting edge.

10. The drill bit of any preceding claim further including a tip formed as a point located on the longitudinal axis of the blade.

11. The drill bit of claim 10 wherein the tip is a pyramid shaped tip.

12. The drill bit of any preceding claim wherein the blade includes a first outer edge and a second outer edge and spurs located at the first and second outer edges.

13. The drill bit of any preceding claim wherein the blade includes a first outer edge, said flute extending to said first outer edge.

14. The drill bit of claim 4 or any claim dependent directly or indirectly from claim 4 wherein the first curved surface has a radius of curvature between 0.292 and 0.692 inches (0.7 and 1.8 cm).

15. The drill bit of claim 4 or any claim dependent directly or indirectly from claim 4 wherein the second curved surface has a radius of curvature of between 0.784 and 1.184 inches (2 and 3 cm).

16. The drill bit of claim 4 or any claim dependent directly or indirectly from claim 4 wherein the centres of curvature of the first curved surface and the second curved surface are both located on a line substantially perpendicular to the blade.

17. A drill bit comprising: a shaft: a blade attached to the shaft: a cutting edge formed on the blade; a smooth flute formed in the blade adjacent the cutting edge: and a non-stick surface on the blade.

18. The drill bit of claim 17 wherein the non-stick surface is on the flute.

19. A drill bit comprising: a shaft: a blade attached to the shaft; a cutting edge formed on the blade; and a smooth flute formed in the blade adjacent the cutting edge, wherein the flute extends to the edge of the blade.

20. A drill bit substantially as described and illustrated with reference to Figures 1 to 6 of the accompanying drawings.

21. A drill bit substantially as described and illustrated with reference to Figure 7 of the accompanying drawings.