Title:
STEPPED DRILL BIT ASSEMBLY
Kind Code:
A1


Abstract:
A wet drill bit assembly and a dry drill bit assembly for cutting a borehole in the earth strata of a mine wherein the borehole has a reduced dimension interior region and an enlarged dimension exterior region. The wet drill bit assembly includes an axial forward spade-style cutting member, which has a spade hard cutting member with a first transverse cutting dimension, and an axially spaced apart axial rearward reamer cutting member, which has a hard insert with a second transverse cutting dimension, which is greater than the first transverse cutting dimension. The dry drill bit assembly includes an axial forward cutting member, which has an axial forward hard cutting insert with a first transverse cutting dimension, and an axially spaced apart axial rearward hard cutting insert that has a second transverse cutting dimension which is greater than the first transverse cutting dimension. An elongate sleeve is adapted to receive cutting debris from the operation of the axial forward hard cutting insert.



Inventors:
Bise, Douglas E. (Chilhowie, PA, US)
Application Number:
13/748685
Publication Date:
08/22/2013
Filing Date:
01/24/2013
Assignee:
Kennametal Inc. (Latrobe, PA, US)
Primary Class:
Other Classes:
175/385
International Classes:
E21B10/26
View Patent Images:
Related US Applications:
20150361741High Pressure Downhole Pump AssemblyDecember, 2015Nackerud
20100193255EARTH-BORING METAL MATRIX ROTARY DRILL BITAugust, 2010Stevens et al.
20010037902Force-balanced roller-cone bits, systems, drilling methods, and design methodsNovember, 2001Chen
20140231146METHOD OF ENHANCING DRILLING FLUID PERFORMANCEAugust, 2014Nguyen
20110174549SUPERHARD INSERT AND AN EARTH BORING TOOL COMPRISING SAMEJuly, 2011Dolan et al.
20070221414Releasable millSeptember, 2007Degeare et al.
20140367178CUTTING STRUCTURES FOR FIXED CUTTER DRILL BIT AND OTHER DOWNHOLE CUTTING TOOLSDecember, 2014Azar et al.
20090050375STEERABLE DRILL BIT ARRANGEMENTFebruary, 2009Stroud et al.
20110290559SURFACE REAL-TIME PROCESSING OF DOWNHOLE DATADecember, 2011Rodney et al.
20170058649HIGH SHOT DENSITY PERFORATING GUNMarch, 2017Geerts et al.
20090025980Modular coiled tubing and sectional pipe drilling rigJanuary, 2009Callander et al.



Primary Examiner:
SCHIMPF, TARA E
Attorney, Agent or Firm:
KENNAMETAL INC. (LATROBE, PA, US)
Claims:
What is claimed is:

1. A wet drill bit assembly for cutting a borehole in the earth strata of a mine wherein the borehole has an interior region with a reduced transverse dimension and an exterior region with an enlarged transverse dimension, the drill bit assembly comprising: an axial forward spade-style cutting member having a spade hard cutting member with a first transverse cutting dimension; an axial rearward reamer cutting member having a hard insert with a second transverse cutting dimension; the axial forward spade-style cutting member being axial spaced apart from the axial rearward reamer cutting member; and the first transverse cutting dimension being less than the second transverse cutting dimension.

2. The wet drill bit assembly according to claim 1 further comprising an upper section of tubing having an axial forward end and an axial rearward end, and the axial rearward reamer cutting member having a central axial bore with an reduced diameter section, and a section of the tubing adjacent the axial rearward end being received within the reduced diameter section of the central axial bore.

3. The wet drill bit assembly according to claim 2 wherein an upper mechanical fastener engages the upper section of tubing to retain the upper section of tubing within the reduced diameter section of the central axial bore.

4. The wet drill bit assembly according to claim 2 further including a lower section of tubing having an axial forward end, and the lower section of tubing being received within an enlarged diameter section of the axial rearward reamer cutting member.

5. The wet drill bit assembly according to claim 4 wherein a lower mechanical fastener engages the lower section of tubing to retain the lower section of tubing within the enlarged diameter section of the central axial bore.

6. The wet drill bit assembly according to claim 1 wherein the axial rearward reamer cutting member including a plurality of the hard inserts being spaced-apart.

7. The wet drill bit assembly according to claim I wherein the axial forward spade-style cutting member having a single one of the spade hard cutting member.

8. The wet drill bit assembly according to claim 1 wherein the axial forward spade-style cutting member containing an outlet opening for the exit of drilling fluid.

9. A dry drill bit assembly for cutting a borehole in the earth strata of a mine wherein the borehole has an interior region with a reduced transverse dimension and an exterior region with an enlarged transverse dimension, the drill bit assembly comprising: an axial forward cutting member having an axial forward hard cutting insert with a first transverse cutting dimension; an axial rearward hard cutting insert with a second transverse cutting dimension; the axial forward hard cutting insert being axial spaced apart from the axial rearward hard cutting insert; the first transverse cutting dimension being less than the second transverse cutting dimension; and an elongate sleeve adapted to receive cutting debris from the operation of the axial forward hard cutting insert.

10. The dry drill bit assembly according to claim 9 wherein the axial forward cutting member further including a mediate helical region defining helical flights with hard edging inserts, and the mediate helical region having a third transverse cutting dimension.

11. The dry drill bit assembly according to claim 10 wherein the third transverse cutting dimension being equal to or less than the first transverse cutting dimension.

12. The dry drill bit assembly according to claim 9 wherein the axial forward cutting member further including a base region containing a dust port through which debris can travel under a vacuum.

13. The dry drill bit assembly according to claim 12 further including a vacuum chuck operatively attached to the base region.

14. The dry drill bit assembly according to claim 13 further including a tube operatively attached to the vacuum chuck, and an adjustable clip adjustably attached to the tube to provide an abutment for the elongate sleeve.

15. The dry drill bit assembly according to claim 9 wherein the elongate sleeve being movable between a forward position in which the elongate sleeve fully encompasses the axial forward cutting member and a rearward position in which the elongate sleeve fails to encompass any of the axial forward cutting member.

16. The dry drill bit assembly according to claim 9 wherein the elongate sleeve having a reduced axial rearward section with an inside transverse rearward dimension and an enlarged axial forward section with an inside transverse forward dimension, and where the inside transverse forward dimension is greater than the inside transverse rearward dimension.

17. The dry drill bit assembly according to claim 16 wherein the inside transverse forward dimension is greater than the second transverse cutting dimension.

18. The dry drill bit assembly according to claim 16 wherein the inside transverse rearward dimension is less than the second transverse cutting dimension.

Description:

CROSS-REFERENCE TO EARLIER PATENT APPLICATION

This patent application is a continuation of co-pending U.S. Provisional Patent Application Ser. No. 61/601,709 filed Feb. 22, 2012 for STEPPED DRILL BIT ASSEMBLY by Douglas Edward Bise, which is hereby incorporated by reference herein in its entirety, and under the United States Patent Statute including 35 USC §120 applicant hereby claims priority on said provisional patent application (i.e., U.S. Provisional Patent Application Ser. No. 61/601,709 filed Feb. 22, 2012 for STEPPED DRILL BIT ASSEMBLY by Douglas Edward Bise.

BACKGROUND

The present invention pertains to a drill bit assembly useful for drilling boreholes in mines for inserting bolts whereby the insertion and fixing of the bolts in the bore holes helps increase the stability of the coal wall (coal rib), as well as increase the stability of the roof of a mine. More specifically, the present invention pertains to a stepped drill bit assembly useful for drilling boreholes of a special geometry in mines for inserting bolts wherein these boreholes cooperate with a threaded bolt to overcome problems inherent with the occasional collapse of the borehole upon the removal of the drill steel.

One of ordinary skill in the art of underground coal mining has knowledge of the basic the techniques to develop a mine shaft. During mining in an environment where the coal seam is high and unstable, miners often have to drill boreholes in the coal walls (ribs) and position bolts therein so as to stabilize the same. Further, during the formation of the mine shaft the miners typically drill boreholes in the roof of the mine shaft wherein each borehole receives a bolt, which is fixed in the borehole. The bolts in the ribs and in the roof provide for and increase the stability of the mine to reduce the potential for a mine collapse. Patent documents like U.S. Pat. No. 6,886,645 B2 to Bise et al. (assigned to Kennametal Inc.) provide a basic description of borehole drilling and affixing the bolts in the boreholes. Applicant hereby incorporates by reference the above-identified patent document.

A number of drill bit designs can be used to impinge the earth strata and drill the borehole. Exemplary patent documents include U.S. Pat. No. 6,915,867 to Bise (assigned to Kennametal Inc.) and U.S. Pat. No. 6,945,340 B2 to Bise et al. (assigned to Kennametal Inc.). Applicant hereby incorporates by reference herein each and every one of the above-identified patent documents.

There are a number of different designs for a bolt and its corresponding structure. The following patent documents are exemplary of these designs: U.S. Pat. No. 5,885,031 to White, U.S. Pat. No. 2,854,824 to Curry et al., and U.S. Pat. No. 3,941,028 to Lobello et al. Applicant hereby incorporates by reference herein each and every one of the above-identified patent documents.

Other patent documents show articles used in the formation of a borehole and/or the stabilization of the mine: U.S. Pat. No. 6,468,010 to Sager et al., U.S. Pat. No. 7,033,117 to Ludwig et al., and U.S. Pat. No. 7,789,589 to Bayerl et al. Applicant hereby incorporates by reference herein each and every one of the above-identified patent documents.

In drilling boreholes, removal of the drill steel is a common occurrence. On occasion the borehole collapses upon the removal of the drill steel. After a borehole collapse, it can be very difficult, and sometimes impossible, to insert a resin cartridge or a mechanical expansion shell into the borehole. This is especially the case for the collapse of a borehole in the coal wall (or rib). Such difficulties are disadvantageous to the formation of the mine shaft, and hence, the overall mining operation. To overcome this situation, there has been developed a bolt, which has a threaded section, used in conjunction with a borehole that has a special geometry. The special geometry borehole has two different regions each with a different transverse dimension (or diameter). The interior region of the borehole has a reduced transverse dimension (or diameter) and the exterior region of the borehole has an enlarged transverse dimension (or diameter). The dimensioning of the bolt is such that the threaded section engages the earth strata surrounding the interior region, which has the reduced transverse dimension. Therefore, if the borehole collapses, the bolt can still push through the earth strata and engage the interior region of the borehole.

In order to best use the combination of the bolt with the threaded section and the special geometry borehole, it would be highly desirable to provide a drill bit assembly that can in one drilling operation drill the special geometry borehole. It would also be highly desirable to provide a drill bit assembly that can in one drilling operation drill the special geometry borehole in a dry drilling environment. Finally, it would also be highly desirable to provide a drill bit assembly that can in one drilling operation drill the special geometry borehole in a wet drilling environment.

SUMMARY

In one form thereof, the invention is a wet drill bit assembly for cutting a borehole in the earth strata wherein the borehole has an interior portion with a reduced transverse dimension and an exterior portion with an enlarged transverse dimension. The drill bit assembly comprises an axial forward spade-style cutting member, which has a spade hard cutting member with a first transverse cutting dimension. The assembly further includes an axial rearward reamer cutting member, which has a hard insert with a second transverse cutting dimension. The axial forward spade-style cutting member is axial spaced apart from the axial rearward reamer cutting member. The first transverse cutting dimension is less than the second transverse cutting dimension.

In yet another form, the invention is a dry drill bit assembly for cutting a borehole in the earth strata of a mine wherein the borehole has an interior region with a reduced transverse dimension and an exterior region with an enlarged transverse dimension. The drill bit assembly comprises an axial forward cutting member having an axial forward hard cutting insert with a first transverse cutting dimension and an axial rearward hard cutting insert with a second transverse cutting dimension. The axial forward hard cutting insert is axial spaced apart from the axial rearward hard cutting insert. The first transverse cutting dimension is less than the second transverse cutting dimension. The dry drill bit assembly further includes an elongate sleeve adapted to receive cutting debris from the operation of the axial forward hard cutting insert.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawing figures which form a part this patent application:

FIG. 1 is a sectional representation of a mining machine having a drill bit assembly attached thereto whereby the mining machine provides rotational movement and upward thrust to the drill bit assembly;

FIG. 1A is side view of a first specific embodiment of the drill bit assembly useful in a wet drilling environment;

FIG. 1B is a side view of the drill bit assembly like the drill bit assembly in FIG. 1A;

FIG. 2 is a sectional view of the rearward reamer cutting member with the hard insert attached thereto and a pair of set screws exploded away from the rearward reamer cutting member;

FIG. 3 is a sectional view showing the first specific embodiment of FIG. 1A at the completion of the drilling of a special geometry borehole in the earth strata of an underground mine;

FIG. 4 is a side view of the cutting member, which comprises a cast body and a plurality of hard inserts, of a second specific embodiment of the drill assembly, which is useful in a dry drilling environment;

FIG. 4A is a side view of the cutting member like that cutting member shown in FIG. 4;

FIG. 4B is a side view of the cast body of the cutting member of FIG. 4 with the hard inserts removed;

FIG. 5 is a side view of another specific embodiment of the drill bit assembly which is useful in a dry drilling environment wherein the axial forward hard cutting insert has a larger cutting diameter relative to the diameter of the mediate helical region and a longer mediate helical region than the specific embodiment of FIG. 4;

FIG. 5A is a side view of the drill bit assembly like the drill bit assembly shown in FIG. 5;

FIG. 6 is a sectional view showing the specific embodiment of FIG. 5 during the initial drilling of the special geometry borehole in the earth strata of an underground mine; and

FIG. 7 is a sectional view showing the specific embodiment of FIG. 5 at the completion of the drilling of the special geometry borehole in the earth strata of an underground mine.

DETAILED DESCRIPTION

Referring to the drawings, FIG. 1 shows a representative environment in which the specific embodiments of the drill bit assemblies operate. The environment is a coal mine which has an earth strata generally designated as 20 and a mine shaft 21 which has a mine roof 22. A drill bit assembly generally designated as 24 is in operative attachment with a mining machine 26. The mining machine 26 provides rotary power and upward thrust to the drill bit assembly 24 to enable it to drill a borehole 30 in the earth strata 20. The drill bit assembly 24 is shown in the process of drilling a borehole in the earth strata. Further, a bolt 28 is shown affixed in the other borehole 32. U.S. Pat. No. 6,886,645 to Bise et al., which has been incorporated by reference herein, illustrates such a mining environment.

FIG. 1A, as well as FIG. 1B, illustrate one specific embodiment of the drill bit assembly 40, which is useful in a wet drilling environment. The skilled artisan is familiar with a wet drilling operation wherein fluid is used to cool the drilling operation and flush drilling debris away from the vicinity of the drilling. Drill bit assembly 40 comprises an axial forward spade-style cutting member 42, a round section of tubing 44, a hexagonal mediate adapter 46, a rearward reamer cutting member 48, and a hexagonal section of tubing 50. The reamer cutting member 48 is shown alongside the other components. However, as will described hereinafter, in actuality, the reamer cutting member 48 is between and connects to the adapter 46 and the hexagonal tubing 50.

Referring to the axial forward spade-style cutting member 42, there is a cutting member body 54, which an axial forward end 56 and an axial rearward end 58. The axial forward spade-style cutting member 42 has an enlarged dimension head portion 60, which contains a transverse slot 62, adjacent to the axial forward end 56. The axial forward spade-style cutting member 42 further has a threaded reduced dimension shank portion 64 adjacent to the axial rearward end 58. The threaded reduced dimension shank portion 64 can be one-half inch (1.27 centimeters) in diameter. The cutting member body 54 contains an axial fluid passage 66, which travels from the axial rearward end 58 until its terminates at the outlet opening 68 through which fluid exits in a spray. The spray is used to cool the drilling operation and flush drilling debris away from the vicinity of the drilling. The axial forward spade-style cutting member 42 further includes a spade hard cutting insert 70, which is received and typically affixed by brazing in the transverse slot 62. The spade hard cutting insert 70 can be a 22 millimeter spade insert. The spade hard cutting insert 70 is made from a hard material such as, for example, cemented (cobalt) tungsten carbide. The spade hard cutting insert 70 as a cutting diameter equal to “A”.

The round section of tubing 44 has a tubing body 74, which has an axial forward end 76 and an axial rearward end 78. Tubing body 74 has an axial fluid passage 80, which extends through the length thereof. Fluid can travel through the fluid passage 80. The axial fluid passage 80 has a threaded forward passage region 82 at the axial forward end 76 of the tubing body 74. Round section of tubing 44 can have an outside diameter (O.D.) equal to three-fourths of an inch (about 1.91 centimeters) and an inside diameter (I.D.) equal to ⅜th of an inch (9.5 millimeters).

The hexagonal mediate adapter 46 has a hexagonal adapter body 90, which has an axial forward end 92 and an axial rearward end 94. The hexagonal adapter body 90 has an axial fluid passage 96 that runs the axial length thereof. The hexagonal mediate adapter 46 is attached at its axial forward end 92 to the round section of tubing 44. Fluid can travel through the fluid passage 96. The adapter 46 can be a ⅝th inch (1.41 centimeters) hexagonal dimension and about 4 inches (10.16 centimeters) in length to provide stability.

Referring to FIGS. 1A, 1B and 2, the rearward reamer cutting member 48 has a reamer body 100, which has an axial forward end 102 and an axial rearward end 104. The reamer body 100 is a modified 1⅜th (3.49 centimeters) vacuum body. Reamer body 100 has a central axial hexagonal bore 106, which comprises a reduced diameter section 112 adjacent the axial forward end 102, and an enlarged diameter section 114 adjacent the axial rearward end 104 of the reamer body 100. As shown in FIG. 1B, the reduced diameter section 112 defines a ¾th inch (1.91 centimeters) hole. The reamer body 100 contains a plurality of notches (or shoulders) 118, each of which carries a hard insert 120 so that there is a plurality of hard inserts 120. These hard inserts 120 are shown shaded in FIG. 1B and can be 1⅜th inch (3.49 centimeters) carbide reamers. Typically, the reamer body 100 has at least three hard inserts 120, which are equi-spaced about the circumference of the reamer body 100. Even though not illustrated, it is apparent that the cutting diameter of the rearward reamer cutting member 48 is equal to “B”, which is twice the cutting radius “B1”. Here, the cutting diameter “A” (e.g., 22 millimeters) is less than the cutting diameter “B” (e.g., 35 millimeters). The reamer body 100 contains a pair of threaded holes 124 in the side wall thereof. Each threaded hole 124 receives a threaded set screw 126.

The hexagonal tubing 50 has a hexagonal tubing body 130, which has an axial forward end 132 and an axial rearward end 134. Hexagonal tubing 50 can be a ⅞th inch (2.24 centimeters) hexagonal tubing with an outside diameter (O.D.) equal to ⅞th inch (2.24 centimeters) and an inside diameter (I.D.) equal to ⅝th inch (1.41 centimeters). Although not illustrated in FIG. 1A, the drill bit assembly 40 attaches at the axial rearward end 134 of tubing 50 to a mining machine, which provides rotary power and upward thrust to the drill bit assembly 40. An axial fluid passage 136 runs along the length of the hexagonal tubing body 130. Fluid can travel through the passage 136.

In reference to the assembly of the wet drill bit assembly 40, the forward spade cutting member 42 attaches in the threaded forward passage region 82 at the axial forward end 76 of the round tubing body 74. The threaded attachment is made tight and secure so that the axial forward spade-style cutting member 42 remains connected to the round tubing 44.

As will become clear, especially from FIG. 2, the tubing 50 and the adapter 46 slide together with the adapter 46 being inside the tubing 50 so that the reamer 48 is retained thereon. More specifically, the axial forward end 132 of the hexagonal tubing body 130 passes into the enlarged diameter section 114 of the axial hexagonal bore 106 until it impinges against the shoulder 116, which is the transition between the enlarged diameter section 114 and the reduced diameter section 112 of the axial hexagonal bore 106. The hexagonal mediate adapter 46 passes through the reduced diameter section 112 of the axial hexagonal bore 106 of the reamer body 100, and then into the axial fluid passage 136 of the hexagonal tubing body 130. One should appreciate that the hexagonal mediate adapter 46 provides additional mass so as to improve the overall stability of the wet drill bit assembly 40. Upon complete assembly, the round tubing 44 is within the reduced diameter section 112 of the axial hexagonal bore 106 of the reamer body 100. To secure the assembly, the set screws 126 are tightened against the external surface of the round tubing 44 and the external surface of the hexagonal tubing 50. The overall wet drill bit assembly 40 is in an assembled condition in which all of the components are securely connected together.

Referring to FIG. 3, which shows the wet drill bit assembly 40 during the drilling of the special geometry borehole 142 in the earth strata 138 of an underground mine. In this regard, the borehole 142 has an interior region 144 of the borehole 142 and an exterior region 146 of the borehole 142. The interior region 144 of the borehole 142 is farther away from the mine surface than is the exterior region 146 of the borehole 142. The an interior region 144 of the borehole 142 is drilled by the axial forward spade cutting member 42, which has the smaller cutting diameter “A”. The exterior region 146 of the borehole 142 is the result of an initial drilling by the axial forward spade-style cutting member 42 and then the cutting by the rearward reamer cutting member 48, which has the larger cutting diameter “B”. The resultant borehole has a special geometry comprising the two different regions, i.e., an interior region 144 of the borehole 142 and an exterior region 146 of the borehole 142, each with a different transverse dimension (or diameter). The interior region 144 of the borehole 142 has a reduced transverse dimension and the exterior region 146 of the borehole 142 has an enlarged transverse dimension.

Referring to FIGS. 4, 4A, 4B, 5 and 5A, the dry drill bit assembly 150 comprises a cutting member shown as 152, a vacuum chuck 154, a section of hexagonal tubing 156, and an elongate sleeve 158. As will be described hereinafter, the elongate sleeve 158 functions as a debris collector for the drilling operation and to provide stability for the drill bit assembly 150. There is a structural difference between the embodiment of FIG. 4 and FIG. 5 wherein for the embodiment of FIG. 5, the axial forward hard cutting insert has a larger cutting diameter relative to the diameter of the mediate helical region and a longer mediate helical region than the specific embodiment of FIG. 4.

The cutting member 152 includes a monolithic cast body member 170 that has an axial forward end 172 and an axial rearward end 174. The monolithic cast body member 170 has a leading cutting region 176, which contains a transverse slot 178. An axial forward hard cutting insert 212 (which can be a 22 millimeter spade insert) is positioned with the slot 178. The axial forward hard cutting insert 212 has a bottom surface 214, a V-shaped top surface 216 and opposite side edges 218. The axial forward hard cutting insert 212 has a cutting diameter “C” (see FIG. 4). In FIG. 4A, the cutting diameter “C1” can be equal to 22 millimeters.

The monolithic cast body member 170 further has a mediate helical region 180, which contains helical flights 182. A plurality of hard carbide edging inserts 238 are located at the peripheral edge of the helix. The helical flights 182 can be a double scroll that ends in carbide inserts. The length “G” of the helical flight region 180 can be between 12 inches (30.48 centimeters) and 16 inches (40.64 centimeters).

The monolithic cast body member 170 also has a mediate cutting region 188. The mediate cutting region 188 includes a slot 190. An axial rearward hard cutting insert 222 is positioned within the slot 190. The axial rearward hard cutting insert 222 has a bottom surface 224 and a top surface mediate portion 226, which is generally parallel to the bottom surface 224. The top surface further has opposite angled top surface portions 228, 230. The axial rearward hard cutting member 222 further has opposite edges 234. The axial rearward cutting member 222 has a cutting diameter equal to “D” (see FIG. 4). Here, cutting diameter “C” (e.g., 22 mm) is smaller than cutting diameter “D” (e.g., 35 mm). There should be an appreciation that the axial rearward hard cutting member 222 can be a ⅜th inch (0.95 centimeters) carbide insert cut off at the tip shown by the dashed lines in FIG. 4A. Cutting edge of the axial forward hard cutting element 212 is axially spaced forward a distance “G” of the axial rearward hard cutting insert 222.

Cast body member 170 has a base region 202, which has a shoulder 204. The base region 202 further contains a dust port 206, a hole 208, and a central volume 210.

The vacuum chuck 154 (a 5522 vacuum chuck) has a chuck body 242, which has an axial forward end 244 and an axial rearward end 246. The chuck body 242 has a central passage 250. The vacuum chuck 154 includes a spring detent clip 248.

The hexagonal tubing 156 (C-C tubing) includes a hexagonal tubing body 256, which has an axial forward end 258 and an axial rearward end 260. The hexagonal tubing body 256 has an axial central passage 262.

Referring to FIG. 5, the elongate sleeve 158 has an elongate sleeve body 268, which has an axial forward end 270 and an axial rearward end 272. The elongate sleeve body 268 has an enlarged axial forward section 276 adjacent the axial forward end 270. The elongate sleeve body 268 further has a reduced axial rearward section 278 adjacent the axial rearward end 272. A transitional section 280 joins together the enlarged axial forward section 276 and the reduced axial rearward section 278. The enlarged axial forward section 276 has an inside diameter equal to “E”. The reduced axial rearward section 278 has an inside diameter equal to “F”. The elongate sleeve 158 can be made of brass and functions as a dust (debris) catcher and a drill stabilizer.

There is a spring clip 300 (or a spring steel friction clip as shown in FIG. 5A) that has a clip body 302 comprising a forward leg 304 and a rearward leg 306. The clip body 302 has a hexagonal aperture 308 therein.

In reference to the assembly of the dry drill bit assembly 150, the cutting member 152 receives the vacuum chuck 154, and the hexagonal tubing 156 also receives the vacuum chuck 154. Prior to beginning the drilling operation, the elongate sleeve 158 surrounds the dry drill bit assembly 150. The spring steel friction clip 300 engages the hexagonal tubing 156 thereby providing an abutment so the elongate sleeve 158 will not slide down the hexagonal tubing 156 past the point of the abutment. The location of the clip 300 can be adjusted to be selectively positioned along the tubing 156 so as to fit a specific drilling situation.

FIG. 6 is a sectional view showing the dry drill bit assembly 150 during the initial drilling of the special geometry borehole in the earth strata of an underground mine. More specifically, the leading cutting region 176, which includes the axial forward hard cutting insert 212, has cut or drilled a borehole. The borehole is a pre-selected depth into the earth strata and has a reduced diameter, which corresponds to the cutting diameter “C” of the forward hard cutting insert 212. The initial drilling operation generates drilling debris, which falls down the borehole such that the elongate sleeve 158 collects the drilling debris. A vacuum is at the dust port so as to suck or draw the drilling debris away from the vicinity of the drilling operation. It is at the point shown in FIG. 6 of the drilling process that the mediate cutting region 188, and in particular the axial rearward hard cutting insert 222, will engage the earth strata upon the upward movement of the drill bit assembly 150.

FIG. 7 is a sectional view showing the dry drill bit assembly 150 at the completion of the drilling of the special geometry borehole in the earth strata of an underground mine. The special geometry borehole has an interior portion with a reduced transverse dimension (or diameter) and an exterior portion with an enlarged transverse dimension (or diameter), which corresponds to the drilling diameter “D” of the axial rearward hard cutting insert 222. As one can appreciate, the basic aspects of the formation of the special geometry borehole are the same for the dry drill bit assembly 150 as they are for the wet drill bit assembly 40. Upon the removal of the drill bit assembly 150 from the completed special geometry borehole, the borehole is ready to receive the threaded bolt.

The patents and other documents identified herein are hereby incorporated by reference herein. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or a practice of the invention disclosed herein. It is intended that the specification and specific embodiments are illustrative only and are not intended to be limiting on the scope of the invention. The true scope and spirit of the invention is indicated by the following claims.