US2759705A - Rock drills with inserted cutting edges - Google Patents

Rock drills with inserted cutting edges Download PDF

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US2759705A
US2759705A US284747A US28474752A US2759705A US 2759705 A US2759705 A US 2759705A US 284747 A US284747 A US 284747A US 28474752 A US28474752 A US 28474752A US 2759705 A US2759705 A US 2759705A
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drill
sleeve
cutting edges
rod
drill rod
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US284747A
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Bjorkman Gustaf Erik
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B10/00—Drill bits
    • E21B10/36—Percussion drill bits
    • E21B10/40—Percussion drill bits with leading portion

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  • This invention relates to rock drills or rock drill bits having cutting edges preferably formed of hard inserts brazed or otherwise secured in place.
  • Rock drills especially those having hard inserts frequently give trouble due to breakage of the steel at or about the head owing to the deformation the steel of the drill rod has undergone in swelling it to a form required to support the inserts and also due to the subsequent heat treatment to which it must be subjected.
  • Drill bits separable from the drill rod have, therefore, been used, said bits carrying the hard inserts, but in this case the difiiculty has been to attach the bit to the rod in a satisfactory manner.
  • a further difiiculty has been experienced when a cruciform shape of cutting edge has been made, owing to the necessary restriction of the metal in the body of steel to hold the inserts.
  • the object of this invention is to provide a cruciform type of drill bit preferably with hard inserts brazed or otherwise fixed in position.
  • the rock drill is provided with a cutting edge at the end of the drill steel and further cutting edges are carried in a separate bit in the form of a ring or sleeve, the drill steel and the sleeve being preferably mutually tapered and united by frictional engagement.
  • the drill steel and sleeve are so cut that they fit snugly together without the aid of screws or other conventional attaching means.
  • the combined cutting edges have a somewhat cruciform pattern.
  • the water holes are located to direct water to the cutting edge or edges.
  • One or more of the cutting edges may be formed by hard inserts.
  • the drill rod is bumped up to form a swelling or enlarged cross sectional area some distance back from the normal cutting edge.
  • Said enlarged area tapers backwardly at a suitable angle to leave the end of the steel substantially in its normal size and shape.
  • the maximum diameter of the enlarged area is smaller than the reaming size of the finished bit to allow clearance for sludging. It will be understood that the swelling will taper both ways therefore leaving no shoulder. It will be apparent from Figures 1 and 3 that the swelling or area having an enlarged cross section constitutes the medial portion drill rod.
  • the drill rod tapers from its medial portion to its narrower terminal portions.
  • Fig. I is a section of the cutting end of a drill penetrating into a hole in rock
  • Fig. II is a bottom plan view of the drill shown in Fig. I;
  • Fig. III is a side elevation of the cutting end of a drill showing a modification
  • Fig. IV is a bottom plan view of the drill shown in Fig. III.
  • drill rod 1 is shown as a normal round rodof hollow steel having a hollow core 2.
  • a diametrical cut 6 is made at the end 3 for the recep tion of a hard insert 7 which will normally extend at least the full width across the diameter of the steel and may be slightly longer to provide a reaming side edge.
  • the end 3 of the drill rod 1 may be finished off as a normal chisel bit as shown.
  • the insert 7 when used would normally block the hollow core 2 or water hole and, therefore, a subsidiary hole 8 is made to come out on the side of the drill at right angles to and just below the bottom of the insert 7.
  • the further cutting edges for the bit according to this invention are formed on a sleeve 9 having a tapered bore 10 to fit the forward portion 4 of the enlarged portion of the drill 1.
  • Its outside shape may be circular with a diameter sutlicient to give it strength to resist bursting under the wedging effect of the taper.
  • it usually has, as shown, two or more winged extensions 11. If two extensions 11 are provided as shown in Fig. II, they are formed diametrically opposite one another and have a diametrical dimension equal to the diameter of the required drill hole. In any case said diameter will be larger than the diameter of the enlarged portion 4 of the rod 1.
  • the end of the drill rod 1 and the sleeve 9 may have their cutting edges formed directly thereon, but usually and as shown, these parts are slotted for the reception of hard inserts 12 and the surface of'the sleeve is frequently given a chisel bit form.
  • - Said inserts 12 may extend the-full width of their respective wings 11 or remain somewhat short as shown in Fig. I.
  • the two members namely the drill rod 1 having a hard insert 7 at its end 3- and an enlarged portion 4 some'little distance from its end, and a sleeve 9 with cutting edges and/or inserts 12, are fitted together as' shown in Figs. I and III.
  • the sleeve 9 fits the taper 4 at the end 3 of the drill 1 so that its end 13 is located substantially at the point 14 of the largest diameter of the swelling.
  • a second water hole 15 will preferably open directly opposite the inside of the cutting edges, that.
  • the assembled drill does not give a truly cruciform pattern, but rather the form of two chisel bits with theircuttingedges at an angle to one another, as shown in Fig. II, but with the centre one occupying a fraction of the total width of the cutting face.
  • the centre or drill rod 1 may project from the top of the sleeve 9 any suitable distance as shown in Fig. I, which distance may vary from practically nothing to the width of the drill rod 1 or even more.
  • the middle portion may be made to act as a centre bit during drilling operations.
  • Such a drill bit tends to keep the drilled hole straight.
  • the rock around the edge is more easily broken away than when the whole face is struck by the full cruciform face of a drill of the same size and, therefore, the expense of providing inserts 12 instead of cutting edges formed directly on sleeve 9 may be avoided.
  • Figs. III and IV show aghtodification in which the ring9 has four wingslland inserts: 12..-
  • the number may be three ifidesiredoranyother con venient number. In thesefi'gur'esthe endI3 of thedrill rod 1' projects only a short distance from. the. sleeve 9.
  • the construction makes a very. strong. drill bit..
  • the sleeve 9 may be soldered or brazed in place by a soft solderorother easily fusible metal.
  • Round hollow drill'steel has been used in the bit described, but any other type. of'steel' having an hexagonal or other cross section may also lie-used.
  • the sleeve 9 aswell as the drill rod' 11 and the wings 11 are individually shaped to conform. about the cutting edges 7' or 12" to a chiselbit or wedge shaped endface,
  • the wedge shaped end portions ofthe sleeve being designated by' the reference character17. They may also be made to conform to a cruciform or any other type of multiple cutting bit.
  • the cutting edge 7 on the drillrod guides the drilling operation.
  • the radial cutting edges 12 disposed on" the wings not the sleeve 9' at a distance from the drill rod leave a ring portion 16,'shown most clearly in Figure I, about the drill rod.
  • Each end portion 17 is disposed between the radial cutting edges 12 and the drill rod.
  • the end portions 17 ofthe sleeve crush or crumble this ring of rock as the drilling proceeds downwardly.
  • This invention provides a drill bit with hard inserts in which the rod-behind the bitis strengthened and the body of steelaround the" inserts-is strongly supported and in which the centralpart of the drilling blow is transmitted through a: hard insert and a length of unbroken or homogeneous metal.
  • a rock drill comprisinga drill rod, the medial portion of said drill ro'd having a greater'cross-sectional area than the terminal portions, said rod tapering forwardly andrearwardl'y'frorn'saidimedial portion to a point spacedf'rom said terminal portions; acentral cutting edge disposed 4 at the forward end of said rod, said cutting edge having a length substantially equal to said end of said drill rod, a removable sleeve having a bore complementary to said tapered portion of said drill rod and frictionally engaged with said forward tapering portion of said drill rod, wings extending laterally from said sleeve, the forward portion of each of said wings being wedge shaped to provide a radial cutting edge laterally disposed from said drill' rod and advanced forwardly from said sleeve and theportions of said sleeve betweenv said radial cutting edges and said drill rod being wedge shaped whereby in use a ring of uncut material is formed between said central cutting edge and said radial cutting edges which is
  • a rock drill comprising a hollow drill rod, the medial portion of said drill rodv having a; greater cross-sectional area than the terminal portions, said rod tapering forwardly and rearwardly from said medial portion to a point spaced from said terminal-portions, a diametrical slot disposed across the forward end ofsaid rod, a hard insert accommodated within said slot to provide a central cutting edge, said central cutting edge having a length substantially coextensive with the diameter of said forward end of said drill rod, a removable sleeve having a bore complementary to -said tapered-portion of said drill rod and frictionally engaged with said forward tapered portion of said drill rod, wings extending laterally from said sleeve, the forward:portion ⁇ ofeach of said wingsbeing Wedge shaped and provided wtih a radial slot, a hard insert accommodated withineach of said.

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  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Mining & Mineral Resources (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Fluid Mechanics (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Earth Drilling (AREA)

Description

I INVENTOR 'u fc rf 5470516710 Wig/$517, M, Ma 7Wz$w ATTORNEY G. E. BJORKMAN ROCK DRILLS. WITH INSERTED CUTTING EDGES Filed April 28. 1952 Aug. 21, 1956 F/EJU United States Patent ROCK DRILLS WITH INSERTED CUTTING EDGES Gustaf Erik Bjiirkman, Nufiield, Springs, Transvaal, Union of South Africa Application April 28, 1952, Serial No. 284,747
Claims priority, application Union of South Africa May 1, 1951 2 Claims. (Cl. 255-63) This invention relates to rock drills or rock drill bits having cutting edges preferably formed of hard inserts brazed or otherwise secured in place.
Rock drills especially those having hard inserts, frequently give trouble due to breakage of the steel at or about the head owing to the deformation the steel of the drill rod has undergone in swelling it to a form required to support the inserts and also due to the subsequent heat treatment to which it must be subjected. Drill bits separable from the drill rod have, therefore, been used, said bits carrying the hard inserts, but in this case the difiiculty has been to attach the bit to the rod in a satisfactory manner. A further difiiculty has been experienced when a cruciform shape of cutting edge has been made, owing to the necessary restriction of the metal in the body of steel to hold the inserts.
The object of this invention is to provide a cruciform type of drill bit preferably with hard inserts brazed or otherwise fixed in position.
According to this invention the rock drill is provided with a cutting edge at the end of the drill steel and further cutting edges are carried in a separate bit in the form of a ring or sleeve, the drill steel and the sleeve being preferably mutually tapered and united by frictional engagement. In other words, the drill steel and sleeve are so cut that they fit snugly together without the aid of screws or other conventional attaching means. The combined cutting edges have a somewhat cruciform pattern. The water holes are located to direct water to the cutting edge or edges. One or more of the cutting edges may be formed by hard inserts.
In a preferred form of the invention the drill rod is bumped up to form a swelling or enlarged cross sectional area some distance back from the normal cutting edge. Said enlarged area tapers backwardly at a suitable angle to leave the end of the steel substantially in its normal size and shape. The maximum diameter of the enlarged area is smaller than the reaming size of the finished bit to allow clearance for sludging. It will be understood that the swelling will taper both ways therefore leaving no shoulder. It will be apparent from Figures 1 and 3 that the swelling or area having an enlarged cross section constitutes the medial portion drill rod. The drill rod tapers from its medial portion to its narrower terminal portions.
An example of the cutting end of a drill according to this invention is illustrated in the accompanying drawing in which:
Fig. I is a section of the cutting end of a drill penetrating into a hole in rock;
Fig. II is a bottom plan view of the drill shown in Fig. I;
Fig. III is a side elevation of the cutting end of a drill showing a modification, and
Fig. IV is a bottom plan view of the drill shown in Fig. III.
2,759,705 Patented Aug. 21, 1956 In the drawings the drill rod 1 is shown as a normal round rodof hollow steel having a hollow core 2.
A little distance back from the end 3 of the drill rod it is bumped up to make the tapered swelling or enlarged area 4 and then tapers rearwardly at 5 to the normal diameter of the rod 1.
A diametrical cut 6 is made at the end 3 for the recep tion of a hard insert 7 which will normally extend at least the full width across the diameter of the steel and may be slightly longer to provide a reaming side edge. The end 3 of the drill rod 1 may be finished off as a normal chisel bit as shown. I
The insert 7 when used would normally block the hollow core 2 or water hole and, therefore, a subsidiary hole 8 is made to come out on the side of the drill at right angles to and just below the bottom of the insert 7.
The further cutting edges for the bit according to this invention are formed on a sleeve 9 having a tapered bore 10 to fit the forward portion 4 of the enlarged portion of the drill 1. Its outside shape may be circular with a diameter sutlicient to give it strength to resist bursting under the wedging effect of the taper. In addition it usually has, as shown, two or more winged extensions 11. If two extensions 11 are provided as shown in Fig. II, they are formed diametrically opposite one another and have a diametrical dimension equal to the diameter of the required drill hole. In any case said diameter will be larger than the diameter of the enlarged portion 4 of the rod 1.
The end of the drill rod 1 and the sleeve 9 may have their cutting edges formed directly thereon, but usually and as shown, these parts are slotted for the reception of hard inserts 12 and the surface of'the sleeve is frequently given a chisel bit form.- Said inserts 12 may extend the-full width of their respective wings 11 or remain somewhat short as shown in Fig. I.
To form the required drill the two members namely the drill rod 1 having a hard insert 7 at its end 3- and an enlarged portion 4 some'little distance from its end, and a sleeve 9 with cutting edges and/or inserts 12, are fitted together as' shown in Figs. I and III. The sleeve 9 fits the taper 4 at the end 3 of the drill 1 so that its end 13 is located substantially at the point 14 of the largest diameter of the swelling. A second water hole 15 will preferably open directly opposite the inside of the cutting edges, that. is, as shown, the inside ends of the inserts 12 in the sleeve 9.- The assembled drill does not give a truly cruciform pattern, but rather the form of two chisel bits with theircuttingedges at an angle to one another, as shown in Fig. II, but with the centre one occupying a fraction of the total width of the cutting face.
The centre or drill rod 1 may project from the top of the sleeve 9 any suitable distance as shown in Fig. I, which distance may vary from practically nothing to the width of the drill rod 1 or even more.
In use the middle portion may be made to act as a centre bit during drilling operations. Such a drill bit tends to keep the drilled hole straight. Also, once the centre is cut the rock around the edge is more easily broken away than when the whole face is struck by the full cruciform face of a drill of the same size and, therefore, the expense of providing inserts 12 instead of cutting edges formed directly on sleeve 9 may be avoided.
It will be noticed that in Fig. I the portion 16 of the rock around the drilled hole is not directly struck by'the cutting edges 7 or 12. The reason is that it has been found in practice and when drilling most types of rock, the drilling will go faster if the ring portion 16 is left to break away without any direct impact from the cutting 3. edges 12. In most cases the width of the rock forming the ring IGshould'be about 7 3 of an inch.
Figs. III and IV show aghtodification in which the ring9 has four wingslland inserts: 12..-
The number may be three ifidesiredoranyother con venient number. In thesefi'gur'esthe endI3 of thedrill rod 1' projects only a short distance from. the. sleeve 9. The construction makes a very. strong. drill bit..
There is another advantage, common to the various constructions namely, that if the middle cutting edge 7, that is the one on the.drill'rod,,breaks,.the sleeve 9 may be knocked olf and'used' on another drill. rod 1', and vice versa if it'is the sleeve 9 which becomes broken.
With this invention during drillingoperations-the. blow on the di'ill'i's transmitted to the drill" face directthrough unbroken. metal by the centre. cutting edge 7 which acts as a. pilot drill. If desired, the sleeve 9 may be soldered or brazed in place by a soft solderorother easily fusible metal.
Round hollow drill'steel has been used in the bit described, but any other type. of'steel' having an hexagonal or other cross section may also lie-used.
The sleeve 9 aswell as the drill rod' 11 and the wings 11 are individually shaped to conform. about the cutting edges 7' or 12" to a chiselbit or wedge shaped endface,
the wedge shaped end portions ofthe sleeve being designated by' the reference character17. They may also be made to conform to a cruciform or any other type of multiple cutting bit.
In operation the cutting edge 7 on the drillrod guides the drilling operation. The radial cutting edges 12 disposed on" the wings not the sleeve 9' at a distance from the drill rod leave a ring portion 16,'shown most clearly in Figure I, about the drill rod. Each end portion 17 is disposed between the radial cutting edges 12 and the drill rod. The end portions 17 ofthe sleeve crush or crumble this ring of rock as the drilling proceeds downwardly. Thus this disposition of'radial cutting edges, a central cutting edge, and a non-cutting crumbling portion on the lateral forward'portion of the wingsbrings'about a rapid and efiicient cutting.
This invention provides a drill bit with hard inserts in which the rod-behind the bitis strengthened and the body of steelaround the" inserts-is strongly supported and in which the centralpart of the drilling blow is transmitted through a: hard insert and a length of unbroken or homogeneous metal.
I claim:
1. A rock drillcomprisinga drill rod, the medial portion of said drill ro'd having a greater'cross-sectional area than the terminal portions, said rod tapering forwardly andrearwardl'y'frorn'saidimedial portion to a point spacedf'rom said terminal portions; acentral cutting edge disposed 4 at the forward end of said rod, said cutting edge having a length substantially equal to said end of said drill rod, a removable sleeve having a bore complementary to said tapered portion of said drill rod and frictionally engaged with said forward tapering portion of said drill rod, wings extending laterally from said sleeve, the forward portion of each of said wings being wedge shaped to provide a radial cutting edge laterally disposed from said drill' rod and advanced forwardly from said sleeve and theportions of said sleeve betweenv said radial cutting edges and said drill rod being wedge shaped whereby in use a ring of uncut material is formed between said central cutting edge and said radial cutting edges which is crushed by the Wedge shapedport'ions of the sleeve.
2. A rock drill comprising a hollow drill rod, the medial portion of said drill rodv having a; greater cross-sectional area than the terminal portions, said rod tapering forwardly and rearwardly from said medial portion to a point spaced from said terminal-portions, a diametrical slot disposed across the forward end ofsaid rod, a hard insert accommodated within said slot to provide a central cutting edge, said central cutting edge having a length substantially coextensive with the diameter of said forward end of said drill rod, a removable sleeve having a bore complementary to -said tapered-portion of said drill rod and frictionally engaged with said forward tapered portion of said drill rod, wings extending laterally from said sleeve, the forward:portion\ofeach of said wingsbeing Wedge shaped and provided wtih a radial slot, a hard insert accommodated withineach of said. radialslots and disposed from said drill rod. to provide aplurality. of radial cutting edges, said radialcutting edgesbeing. advanced forwardly from said sleeve, and the portionof each wing disposed. between said radialcutting. edge andsaid drill rod being wedge shaped, whereby in'use a ring of uncut material is formed between said central cutting edge and said radial cutting.
edges which is crushed by the portion of said sleeve disposed betweenisaid radial cuttingedges and said drill rod.
References Cited in the file of this patent UNITED STATES PATENTS 740,906 Owen Oct. 6, 1903 1,035,270 Thomas Aug. 13, 1912 1,096,134 Sims May 12, 1914 1,169,369 Wakfer Jan. 25, 1916 1,277,970 McKenzie M Sept. 3, 1918 1,415,619 Akins- May 9, 1922 2,310,288 Hokanson Feb. 9, 1943' FOREIGN PATENTS 143,600 Australia Sept. 27, 1951 337,785 France: Mar. 1, 1904 397,144 GreatBritain Aug. 14,1933
US284747A 1951-05-01 1952-04-28 Rock drills with inserted cutting edges Expired - Lifetime US2759705A (en)

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3952819A (en) * 1975-03-10 1976-04-27 A & W Deep-Well Drilling, Inc. Fatigue resistant anvil bit for percussion rock drill
US3960223A (en) * 1974-03-26 1976-06-01 Gebrueder Heller Drill for rock
US3993147A (en) * 1976-01-19 1976-11-23 Dresser Industries, Inc. Taper lock removable stem for raise bit
US4069878A (en) * 1976-03-08 1978-01-24 Reed Tool Company Raise drilling bit with detachable stem
DE2752544A1 (en) * 1977-11-24 1979-05-31 Sandvik Ab Rock drill boring head - has enlarged end carrying four button headed hard metal cutting inserts around larger central insert
US4275796A (en) * 1978-02-20 1981-06-30 Gebruder Heller Verwaltungsgesellschaft Mit Beschrankter Haftung Rock drilling tool
US4294319A (en) * 1978-05-16 1981-10-13 Karlheinz Guergen Cutter head for rotary percussion drills
US4304312A (en) * 1980-01-11 1981-12-08 Sandvik Aktiebolag Percussion drill bit having centrally projecting insert
DE3136464A1 (en) * 1980-09-24 1982-06-16 Kennametal Inc., 15650 Latrobe, Pa. "DRILLING CHISES, ESPECIALLY GROOVING CHISELS FOR BLASTING BOLTS AND CUTTING INSERT FOR SUCH CHISELS"
US4613003A (en) * 1984-05-04 1986-09-23 Ruhle James L Apparatus for excavating bore holes in rock

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US740906A (en) * 1902-07-22 1903-10-06 David Awst Owen Rock-drill attachment.
FR337785A (en) * 1903-12-16 1904-04-25 Res Advanced sounding device
US1035270A (en) * 1911-05-05 1912-08-13 Thomas J Thomas Drill.
US1096134A (en) * 1913-08-04 1914-05-12 Stephen W Sims Well-drilling tool.
US1169369A (en) * 1916-01-25 Samuel Peck Drill.
US1277970A (en) * 1917-10-15 1918-09-03 Norman J Mckenzie Drilling-bit.
US1415619A (en) * 1921-03-18 1922-05-09 Edwin J Akins Drilling bit
GB397144A (en) * 1932-01-14 1933-08-14 Joseph Robbins Curtis Improvements in or relating to rock-drills
US2310288A (en) * 1939-07-17 1943-02-09 Eidco Inc Drill bit

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1169369A (en) * 1916-01-25 Samuel Peck Drill.
US740906A (en) * 1902-07-22 1903-10-06 David Awst Owen Rock-drill attachment.
FR337785A (en) * 1903-12-16 1904-04-25 Res Advanced sounding device
US1035270A (en) * 1911-05-05 1912-08-13 Thomas J Thomas Drill.
US1096134A (en) * 1913-08-04 1914-05-12 Stephen W Sims Well-drilling tool.
US1277970A (en) * 1917-10-15 1918-09-03 Norman J Mckenzie Drilling-bit.
US1415619A (en) * 1921-03-18 1922-05-09 Edwin J Akins Drilling bit
GB397144A (en) * 1932-01-14 1933-08-14 Joseph Robbins Curtis Improvements in or relating to rock-drills
US2310288A (en) * 1939-07-17 1943-02-09 Eidco Inc Drill bit

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3960223A (en) * 1974-03-26 1976-06-01 Gebrueder Heller Drill for rock
US3952819A (en) * 1975-03-10 1976-04-27 A & W Deep-Well Drilling, Inc. Fatigue resistant anvil bit for percussion rock drill
US3993147A (en) * 1976-01-19 1976-11-23 Dresser Industries, Inc. Taper lock removable stem for raise bit
US4069878A (en) * 1976-03-08 1978-01-24 Reed Tool Company Raise drilling bit with detachable stem
DE2752544A1 (en) * 1977-11-24 1979-05-31 Sandvik Ab Rock drill boring head - has enlarged end carrying four button headed hard metal cutting inserts around larger central insert
US4275796A (en) * 1978-02-20 1981-06-30 Gebruder Heller Verwaltungsgesellschaft Mit Beschrankter Haftung Rock drilling tool
US4294319A (en) * 1978-05-16 1981-10-13 Karlheinz Guergen Cutter head for rotary percussion drills
US4304312A (en) * 1980-01-11 1981-12-08 Sandvik Aktiebolag Percussion drill bit having centrally projecting insert
DE3136464A1 (en) * 1980-09-24 1982-06-16 Kennametal Inc., 15650 Latrobe, Pa. "DRILLING CHISES, ESPECIALLY GROOVING CHISELS FOR BLASTING BOLTS AND CUTTING INSERT FOR SUCH CHISELS"
US4361197A (en) * 1980-09-24 1982-11-30 Kennametal Inc. Blast hole grooving bit and wear resistant compact
US4613003A (en) * 1984-05-04 1986-09-23 Ruhle James L Apparatus for excavating bore holes in rock

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