EP1606073B1

EP1606073B1 - Spade drill bit

Info

Publication number: EP1606073B1
Application number: EP03816276A
Authority: EP
Inventors: Juergen Wiker; Gregory A. Phillips
Original assignee: Credo Technology Corp
Current assignee: Credo Technology Corp
Priority date: 2003-03-11
Filing date: 2003-03-11
Publication date: 2012-11-21
Anticipated expiration: 2023-03-11
Also published as: WO2004080632A1; EP1606073A4; AU2003225722A1; CN1758977A; EP1606073A1; CN1758977B

Description

The present invention relates to a spade drill bit according to the preamble of claim 1 which is known from US 5 291 806 A .
US 5 291 806 A relates to a spade-type drill bit having a shank portion and a spade bit portion extending from the shank portion. The spade bit portion includes a spade portion with a planar region, and a center tip concentric with a longitudinal axis and extending from the spade portion.
WO 98/05459 A1 relates to a spade drill bit design in which the chip flow direction along the cutting edge is always in the same direction. As the chip flow direction is governed by the chip velocity vector, the cutting edge is designed so that the chip velocity is always generally perpendicular to a line drawn on the main cutting edge to the center axis of the cutting bit.
DE 100 07 736 A1 relates to a drill bit for drilling a hole of a selected diameter in a wood workpiece includes a conically shaped tip having a main cutting portion and a thread series operable to threadingly draw the drill bit into the wood workpiece. The described thread series has a diameter which progressively increases in a direction opposite to the drilling penetration direction of movement of the drill bit to a maximum diameter which is the same as the selected diameter of the hole to be drilled. The drill bit also includes a cylindrical portion extending from the conically shaped tip, a spiral screw shaped splinter groove for conducting splinters in the drilled hole away from the drill bit penetration area and a centering drill portion with a self cutting thread series.
One conventional spade-type drill bit is depicted in Figs. 1A-C. The bit 2 has a cutting head 6 situated at the end of an elongated shaft 4. The opposite end of the shaft 4 is preferably provided with hexagonal flats 5 for engagement within a conventional drill chuck. As best in FIG. 1B, the head 6 is substantially flat and is provided with cutting edges 22 and 24. A central point 16 is provided along the longitudinal axis of the bit 2. The outer periphery of the bit is provided with cutting spurs 26, 28.
In use, the point 16 of the rotating bit 2 penetrates the workpiece first and serves as a centering guide for the bit. As the bit is advances further into the workpiece, the spurs begin cutting into the material. Finally, as the bit is advanced further, the cutting edges 22, 24 begin to shave thin layers of the workpiece. The bit 2 continues to penetrate the workpiece until it is in the position shown in FIG. 2, at which point the spurs 26, 28 cut through the workpiece material. As the user of the drill bit prepares to exit the hole, the spurs 26 and 28 of conventional spade bits tend to grab the workpiece 30.
Once the outer most parts of the spurs have exited the material 30, the spurs cause the drill bit to pull itself aggressively back into the material. This is generally due to the hook angle 6 on the spurs of the spade bit, which can be about 15" in a typical bit. When the drill bit starts getting pulled into the material by the spurs, the user will frequently experience a jerk, typically referred to as grabbing. Grabbing may result in a wood blowout and splintering on the backside because the last portion of the uncut material 31 is pushed out rather than cut.
Another problem associated with this type of prior spade drill bit is that the spurs 26, 28 frequently experience high localized temperatures and high wear rates. In order to address these and other problems, a new drill bit 106 was developed as depicted in FIGS. 3A-C. This bit 106 includes a shaft 104 having hex drive features 105 at one end and terminating in a drill head 106 at the opposite end. The head 106 includes a central point 116 and two cutting edges 122, 124.
In contrast to the prior bit of FIGS. 1A-C, the cutting edges 122, 124 of the bit 102 in FIGS. 3A-C are rounded so that the edges exit the workpiece material at essentially the same time, as shown in FIG. 4. This configuration reduces the risk of blowout and splintering of a wood workpiece, and reduces the wear and temperature problems associated with the bit 2.
The head of the bit in FIGS. 3A-C can be modified as shown in FIG. 5. More specifically, center point 116' of the head 106' is threaded so that the lateral edges of the point 116' define a series of grooves 137. The threaded point 116' allows the bit to be self-feeding. In other words, as the bit of FIG. 5 is rotated, the threaded point engages the workpiece and draws the bit into the material. This feature greatly reduces the thrust force that must be applied by the user to penetrate the workpiece.
The threads on the point 116' of the bit shown in FIG. 5 can be provided in different pitches, or threads per inch. In a typical configuration, the threads will vary in the range of 16-26 TPI. A lower number of threads will cause the bit to penetrate more aggressively into the workpiece, and conversely for a greater number of threads. In one modification, the grooves 137 of the threaded point 116' can vary in depth along the length of the point. More particularly, the threads can have a greater depth at the base of the point 116' than at the tip. This feature makes the threaded tip 116' better able to withstand the impact of hitting a nail or other fastener embedded within the workpiece.

Summary of the invention

It is therefore an objective of the present invention to provide an energy efficient drill bit.
The present invention provides a spade drill bit according to claim 1, comprising: a shaft having one end configured to be engaged to a driving tool; a cutting head attached at an opposite end of said shaft, said head including; a center point portion having a tip and a base; a pair of cutting edges extending generally radially outwardly from said base of said center point; and threads defined on said center point portion, said threads including continuous threads adjacent said tip and discontinuous threads thereafter toward said base, characterized in that: said cutting head includes a spur defined at an outboard end of each of said cutting edges and extending upwardly from the cutting edge; and said discontinuous threads terminate at a line extending between an uppermost part of the spur of each of said cutting edges.

Brief Description of the Drawings

The accompanying drawings illustrate various embodiments of the present invention and together with a description serve to explain the principles of the invention. In the drawings:

FIGS. 1A, 1B and 1C are respectively a top view and a side and edge projection view of a conventional spade drill bit.
FIG. 2 illustrates the conventional spade bit of FIGS. 1A-C exiting a wooden workpiece.
FIGS. 3A, 3B and 3C are respectively a top view and a side and edge-wise view of an improved spade drill bit design.
FIG. 4 illustrates the improved spade bit of FIGS. 3A-C exiting a wooden workpiece.
FIG. 5 is a depiction of the improved spade bit of FIGS. 3A-C with a threaded center point.
FIG. 6 is a top view of a spade drill bit in accordance with one embodiment of the present invention.
FIG. 7 is an enlarged view of the threaded point of the spade drill bit designated as area 7 in FIG. 6.
FIG. 8 is an enlarged side view of the threaded point depicted in FIG. 7.
FIG. 9 is a perspective view of a spade drill bit in accordance with an alternative embodiment of the invention.
FIG. 10 is a representation of the drill it shown in FIG. 9 with the side edges substantially parallel.
FIG. 11 is a representation of the drill it shown in FIG. 9 with the side edges converging toward the shaft of the bit.
FIG. 12 is a representation of the drill it shown in FIG. 9 with the side edges diverging toward the shaft of the bit.

Detail Description of the Invention

Reference will now be made in detail to various presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the various FIGS. some of the structures are referenced with similar reference numerals.
Referring to FIG. 6, one embodiment of the invention is depicted in which a spade-type drill bit 202 includes a shaft 204 terminating in a driving end 205. A cutting head 206 is formed at the opposite end of the shaft. These components of the drill bit 202 can be similar to the like components of the bits 2 and 102 in FIGS. 1A-c and 3A-C, respectively. In other words, the driving end 204 can have a hex configuration to mate with a drill chick and the head 206 can have a flat, spade profile. The head 206 includes a center point 216 and cutting edges 222 and 224, like both prior drill bits described above. Moreover, the head 206 of the present embodiment includes spurs 226 and 228, similar to the spurs 26 and 28 of the bit shown in FIGS. 1A-C.
The cutting head 206 includes angled surfaces 223 and 225 corresponding to the cutting edges 222 and 224, as shown in FIG. 9. These surfaces are angled in the direction of rotation of the drill bit. The side edges 220 can include a rake angle at the upper end of the edges adjacent the angled surfaces 223, 225. These features of the drill bit 202 of the present embodiment are similar to the like features shown and described in U.S. Patent No. 5,433, 561 .
However, the head 206 is not identical to the prior drill bits of FIGS. 1-5. For instance, in one feature of the present invention, the center point 216 is threaded, as shown in the enlarged detail views of FIGS. 7 and 8. In particular, the center point 216 includes a series of threads 240 extending substantially along the length (or height) of the point 216. The threads 240 terminate before reaching the outer diameter of the head 206. In other words, the threads terminate at a height above the cutting edges 222, 224 that is equal to the height of the spurs 226, 228 above the edges.
In one aspect of this embodiment, the center point 216 includes opposite flat surfaces 230 that coincide with the flat surfaces 218 of the head 206 (FIG. 6). The threads 240 then form edge-wise threads 242 along the tapered side edges of the center point, as shown in FIG. 7. These threads continue to the tip 218 of the center point. In this top projection (i.e., with the flat surfaces 218 and 230 in plan view), the threads 240 include a root 244 and crest 245 which define a thread depth d. In the preferred embodiment, this depth is constant with respect to this plan view projection of the drill bit 206. This constant depth d makes the drill bit 206 a fast starting bit that requires only minimal pressure to start in most types of wood. In a specific embodiment, this thread depth d is about 0.05 inches (1,27 mm).
The side view of the threaded center point 216 presents a different impression. In particular, while the majority of the point 216 includes the opposite flat surfaces 230, the portion of the point near its tip 218 is tapered. In other words, the threads 240 include a tapered root 246 near the tip 218 of the center point, as shown in FIG. 8. The root is tapered at an angle A, which in a preferred embodiment is essentially the same as the angle of taper of the center point in its plan view projection shown in FIG. 7. In a specific embodiment, this angle A is an included angle of about 28-45 degrees depending upon the size of the drill bit 206. For a 1 ½ inch (38 mm) bit, the angle A can be about 33 degrees.
The crest 247 of the threads 240 in this portion of the center point preferably fall at the same crest diameter as the crest 245 for the lower portion of the threads 240. Thus, in the side presentation of the threaded center point 216, the threads 240 exhibit an increasing depth toward the tip 218 of the center point. The threads 240 commence at a leading edge 248 which facilitates initial penetration of the threaded center point 216 into the workpiece.
The threads 240 of the center point 216 combine a self-starting feature with a self-driving feature. In other words, with the exposed leading edge 248 of the threads, the bit can easily penetrate the workpiece. The continuation of the threads along the center point 216 draws the bit toward the workpiece with only minimal thrust pressure being exerted by the user on the drill. These features of the threads 240 combine to reduce the wear experienced by the center point. Moreover, the resulting spade drill bit provides a smoother drilling action at a quicker rate than conventional prior drill bits. The smoother drilling action and feed rate generates a better quality drilled hole in the workpiece, particularly is the workpiece material is wood.
The threads 240 can be provided in different pitches depending upon the particular application for the bit. In general, lower pitch bits drill faster into the workpiece, while higher pitches result in slower drilling rates. In a specific embodiment, the threads 240 can have a pitch of 16 TPI, which is particularly well-suited for softer wood materials. On the other end of the spectrum, a pitch of 26 TPI is ideal for hard woods. It has been found that a pitch of 20 TPI is optimum for most woods used in building and construction. This thread pitch works well in both soft and hard woods, with an acknowledged decrease in drilling speed when used in hard woods.
In prior drill bits, such as the drill bit disclosed in published PCT application WO 98/05459 , the center point is threaded only on the side edges of the point. This threading represents an improvement over earlier drill bits because it provided a self-feeding characteristic to the bit. The present invention represents an improvement over this feature by the inclusion of substantially continuous threads 247 at the tip 218 of the center point 216. These threads continuously penetrate the workpiece as the bit drives deeper into the material, which reduces the thrust force that must be maintained on the drill over the prior drill bits. In addition, as mentioned above, the exposed leading edge 248 of the threads 240 allows the center point 216 to initially penetrate the workpiece than the prior bit designs.
The center point 216 of the illustrated embodiment includes a further feature in the form of a flute 250 defined on the opposite flat surfaces 230 of the center point. These flutes 250 improve removal of chips generated by the center point 216 as it drills into the workpiece. As shown best in FIG. 7, this flute 250 begins just below the lower end of the continuous threads 247 and continues into the flat surface 218 of the head 206, just below the cutting edges 222, 224. When the center point is initially engaged with the workpiece, the continuous threads pump the chip material upward through the brief extent of the continuous threads 247. As the center point penetrates further into the workpiece, the chip volume increases. Absent the flute 250, the increasing chip volume would tend to clog the initial bored hole formed by the center point, thereby increasing the required thrust force, increasing the heat build-up in the bore, and decreasing the life of the threaded center portion 216. Thus, the flute 250 relieves the drilled hole of the chip material as quickly as possible, while still preserving the beneficial features of the continuous threads 247.
In the embodiment of FIG. 6, the drill bit 202 includes smooth sides 220. In an alternative embodiment of the invention shown in FIG. 9, a drill bit 202' includes threads 260 defined in the comparable sides 220'. As shown in FIG. 9, the drill bit 202' can include similar features to the bit 202 shown in FIG. 6. However, as can be seen in FIG. 9, the sides include a series of grooves 260 substantially along the entire extent of the sides 220'. These grooves 260 can be formed in lathe machine configured to turn threads. Thus, the grooves 260 on the opposite sides 220' of the head 206' essentially constitute segments of a helical thread running the length of the head 206'.
These outer threads 260 pick up where the threads 240 of the center point 216 leave off. In other words, once the spurs 224, 226 contact the workpiece, the threads 260 of the head 206' engage the workpiece material and help drive the bit into the workpiece. The threads 260 continue to draw the bit into the workpiece as the cutting edges 222, 224 begin shaving workpiece material.
One benefit provided by the outer threads 260 is realized when the spurs 226, 228 reach the end of the workpiece bore. As explained in the PCT publication WO 98/05459 discussed above, one problem with spurs on spade drill bits is that the spurs tend to cause grabbing near the end of the cut. It has been found that the addition of the threads 260 to the sides 220' of the bit head 206' helps maintain a smooth advance of the drill bit through the material, even as the bit breaks through the opposite side of the workpiece.
Preferably, the threads 260 follow the same thread pitch as the threads 240 of the center point 216. On the other hand, the threads 260 preferably have a shallower thread depth than the threads of the center point. In a preferred embodiment, the threads 260 have a depth about half the depth d of the center point threads 240. In a specific embodiment, the threads 260 have a depth of about 0.20-0.25 inches (5,08-6,35 mm). This shallower thread depth is preferable because the threads 260 are sweeping through a larger circumferential path than the threads of the tapered center point 216.
The extent of the continuous threads can be varied depending upon the particular drill application. In the most preferred embodiment, the continuous threads 240 extend for about two revolutions for a standard thickness drill bit (i.e., about 0.080 inches, i.e. 2 mm, thick). The extent of the continuous threads 247 can also depend upon the length (or height) of the center point. In the typical spade bit, the center point 216 projects about 0.50 inches (12,7 mm) above the cutting edges 222, 224 of the head 206. In this typical case, the continuous threads 247 extend about 0.10 inches (2,54 mm) from the tip 218.
In the preferred embodiment, the sides 220' of the drill bit 202' are substantially parallel, as shown in FIG. 10. However, it is contemplated that the sides bearing the threads 260 can be arranged at alternative orientations, as shown in FIGS. 11 and 12. Specifically, as depicted in FIG. 11, the sides 220" can converge toward the bit shaft 204 at an angle M^-. This convergence can commence at the spurs or can begin downstream of the cutting edges 222, 224.
Alternatively, the sides 220"' can diverge toward the bit shaft 204, as shown in FIG. 12. Thus, the sides 220"' can diverge at an angle M⁺. (It is understood that the threads 260 are also present on the sides 220" and 220"'). Preferably both the converging and diverging angles are on the order of about 1 degree. The diverging sides 220"' can help stabilize the drill bit as it drives deeper into the workpiece. On the other hand, the converging sides 220" can reduce the force required for the rotating drill bit to penetrate into the workpiece. The threaded diverging sides 220"' can also produce a smoother or "cleaner" bore through the workpiece as the increasing diameter of the diverging threads gradually widen the bore. The selection of the parallel 220', converging 220", or diverging 220"' sides can depend upon the nature of the workpiece material and on the driving torque of the drill to which the drill bit is engaged. For instance, where the drill is a portable electric drill, it may be desirable to minimize the driving force and drilling time, so the converging drill of FIG. 11 bit may be preferable. On the other hand, where a more powerful drill is available, the diverging drill bit of FIG. 12 may be desirable.
The drill bits of the illustrated embodiments can be formed according to known processes, such as the process described in U.S. Patent No. 5,433,561 . The outer threads 260 on the sides 220 of the drill head 206 are preferably formed using a lathe configured for producing helical threads. The threads 240 on the center point are preferably formed using a tapered thread cutting die. It is understood that the tapered die will not cut threads in the flat surfaces 230 of the center point, since these surfaces reside below the tapered diameter of the center point. On the other hand, the portion of the center point adjacent the tip 218 will maintain its circular tapered configuration since the tapered diameter at this portion is less than the thickness of the bit head 206.
The embodiments illustrated were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
For instance, the outer threads 260 may be used alone, in combination with the threads 240 of the center point, or not at all, depending upon the requirements of the drill bit. In smaller bits, it is preferable to use only the threaded center point, without the threads on the sides of the bit head. However, in accordance with the present invention, one constant among the contemplated embodiments is the provision of the continuous threads at the tip 218 of the center point that merge into the discontinuous threads at the flat surface portion of the center point.
The illustrated embodiments are best suited for drilling through wood materials. The wood materials can range from soft to hard woods, with appropriate changes to the various dimensions, as mentioned above. It is contemplated that these bits can have application for boring through other materials having similar properties to wood materials.

Claims

A spade drill bit, comprising: a shaft (204) having one end configured to be engaged to a driving tool;
a cutting head (206) attached at an opposite end of said shaft (204), said head (206) including;
a center point (216) having a tip (218) and a base (217);
a pair of cutting edges (222, 224) extending generally radially outwardly from said base (217) of said center point; and
threads defmed on said center point (216), said threads including continuous threads (247) adjacent said tip (218) and discontinuous threads (242) thereafter toward said base (217), characterized in that:
said cutting head includes a spur (226, 228) defined at an outboard end of each of said cutting edges (222, 224) and extending upwardly from the cutting edge; and

said discontinuous threads (242) terminate at a line extending between an uppermost part of the spur (226, 228) of each of said cutting edges (222, 224).
The spade drill bit of claim 1, wherein said continuous threads (247) includes a tapered root (246).
The spade drill bit of claim 1, wherein said center point (216) includes opposite flat surfaces (230) continuous with said discontinuous threads (242).
The spade drill bit of claim 3, wherein said central point (216) includes opposite side edges interposed between said opposite flat surfaces (230), and said discontinuous threads (242) are defined on said opposite side edges.
The spade drill bit of claim 4, wherein said discontinuous threads have a constant thread depth.
The spade drill bit of claim 5, wherein said constant thread depth extends into said continuous threads.
The spade drill bit of claim 1 wherein said cutting head includes opposite flat surfaces (230) and opposite sides (220) interposed between said flat surfaces.
The spade drill bit of claim 7, wherein said cutting head includes exterior threads (260) defined in said opposite sides.
The spade drill bit of claim 8, wherein said threads of said center point and said exterior threads of said cutting head have substantially the same thread pitch.
The spade drill bit of claim 8, wherein said exterior threads have a thread depth less than a thread depth of said threads of said center point.
The spade drill bit of claim 9, wherein said opposite sides (220) are configured to diverge away from said shaft.
The spade drill bit of claim 9, wherein said opposite side (220) are configured to converge toward said shaft.
The spade drill bit of claim 1, wherein said continuous threads (247) extend about two revolutions from said tip (218) .
The spade drill bit of claim 1, wherein said discontinuous threads (242) of said central point portion terminate above said base of said center point (216).
The spade drill bit of claim 1, wherein said center point (216) includes at least one flute (250) defined therein.
The spade drill bit of claim 1, wherein said center point (216) includes at least one flute (250) defined in each of said opposite flat surfaces (230).
The spade drill bit of claim 3, wherein said at least one flute (250) commences between said continuous threads (247) and said base of said center point (216).