US2168102A - Drill bit - Google Patents

Description

Aug. l1, 1939.

` P. H. NAST DRILL BIT Filed Nov. 30, 1958 2 Sheets-Shes@ 1 us 1, 1939- P. H. NAST 2,168,102

DRILL BIT FiledA Nov. 3o, 1938 2 sheets-Sheet 2 l `Patented Aug. 1, V1939 PATENT OFFICE DRILL Brr Paul H. Nast, Royal Oak, Mich., assigner to Sullivan Machinery Company, a corporation ,of

Massachusetts Application November 30, 1938, Serial No. 243,215

20 Claims. .This invention relates todrill bits, and more particularly to improvements in rock drill bits of l of certain advantages over ordinary drill bits ofv They are much more v the integral-shank type. readilyv portable. Less money is tied up in drill steel. They are relatively inexpensive, making it 10 possible for them to be discarded after becoming worn, or, more often, after they have been resharpened `a few times by grinding. -Whensuitably designed, they require no very expensive resharpening equipment and can be resharpened l by grinding, without reforging operations.

In such bits, it is therefore highly desirable to shape the cutting surfaces so that the bit can bec resharpened by grinding on a conventional grinding wheel, thereby minimizing the expense of regosharpening equipment.

' It is also desirable to provide cutting edgesof such shape and so arranged that the bit may not only have relatively great strength and inherent wearing qualities, but also operate very efllciently,

25 whereby a' hole may be drilled with relatively great speed and to a relatively great depth, be, fore the bit becomes dull.

One difficulty in drill bits of the shapes more commonly used is that withthem there is a rapid 30 loss of gauge, and a consequent need, particularly when the gauge is lost very rapidly, of starting a hole much larger than the desired diameter of the bottomed hole. Furthermore, in manydrill bits the working end of 'the bit -is so formed that cer- 35 tain points or projections4 are either not sufficiently protected from carrying an excessive part of the' work of drilling, and so dull rapidly, or portions may be so formed that fracture occurs.

An object of the invention is to provide an im- 4 n proved rock drill bit of the impact type having an improved working face formed with edges so shaped and arranged as to overcome the diilculties encountered by ordinary drill bits. It is. another object of my invention to provide anim- 45 proyed vdrill bit, and particularly to provide an improved drill bit which by reason of ease of resharpening and unusual durability will be especially adapted to detachableV drill bit constructions. Yet another object is to provide an :.u improved drill bit having improved edges of such shape and so arranged as. to increase the cutting efficiency thereof to a marked degree. Still ,an-

other object is to provide, in a drill bit oi' the above character, improved working surfaces and 5;, edges so thatrapid -wear and breakage of the bit ment andseveral modiilcations which inven- 'bodiment my invention.

(Cl. Z55-64) due to fracture of sharppoints or projections either at the extremities of the edges orrat the bit periphery, are substantially reduced. Another object is to provide a drill bit whose resharpening may be wliolly and readily performed by grind- 5 ing operations and 'which will require a minimum number of different types bf grinding operations and a minimum amount of handling during the grinding operations. It is another object of my invention to provide a drill blt which can be sharpened with great ease with the use of a single lgrinding wheel and, in certain embodiments wholly, and in others mainly, though not wholly,

by relative movement between said bit and the' grinding wheel in a direction only tangential tov the circle of rotationof the periphery of the grinding wheel. A still further object is to provide an improved drill bit having chopping edges ofA rugged construction and of arcuate extent adapted to the workthey areucalled upon to perform, and providing adequate clearance space for the discharge of cuttings produced, and having cuttingfedges also proportioned to the amount of work they are called upon to rform, in a very advantageous manner. Anot r object of the invention is to provide an impr ved drill blt having cutting and chopping edges so related to each other with respect to planes perpendicular to the bit axis as to insure most effective cooperation and maximum durability and rapidity of drilling. Still another object is to provide an improved drill bit which, while cutting away the material to be drilled very effectually across the inner portion of the hole, may at the same time chop away the material at or near the outer edge or periphery of the hole and prevent theifeby rapid loss of gauge of the bit and decrease in cross sectional area of the hole, and, due to less rapid rounding oi! `of the end of each: cutting edge or portion of thebit, postpone for a relatively long time the tendency towards sticking of the bit in the drill hole. These and other objects and advantages of the invention'will, however, hereinafter more fully appear in'the course of the tollowing description and as more particularly pointed out in the appended claims.

In the accompanying drawings there are shown, for 'purposes of'illustration a preferred embodition may assume in practice.l

Inthese drawings, 4 Fig. 1 is a view, in side elevation, of a detachable drill bit incorporating, in a preferred emthe bit so that the arcuate chopping edges lie slightly inside of the bit periphery, makes it possible to avoid all danger of fracturing off of the chopping edges or of portions thereof, and yet these edges lie nearenough to the annular zone of the extreme ends of the cutting edges to protect the latter from excessive work. The outwardly vand forwardly inclined surfaces 8 of the chopping edges are shown in the present embodiment of. the invention as plane surfaces.

It will be observed that there is shown in Fi'gs. l to 5 inclusive, an embodiment of the invention which provides a cutting' action of unusual effectiveness and which is enabled to perform its function better and to stand up longer, due to the,

originally shaped, and resharpened, with great.

ease with a suitably shaped grinding wheel and with a minimum of handling during the grinding operation and with a minimum of loss of gauge in resharpening. By arranging the relatively inclined wedge-shaped surfaces terminating in the cutting edges 6, 6 and the inclined surfaces 8, 8 terminating in the arcuate chopping edges, in the manner disclosed, it is' possible to sharpen the cutting edges by two grinding operations simply `by passing the bit straight across the wheel face at each side of the bit in a direction substantially parallel to the alined cutting edges 6, 6, and the chopping edges may be formed again by simply grinding back the extremities of the wings 5, 5. 'I'he chopping edges 1, 1 aid in maintaining the full diameter ofthe hole by chopping away the material to be drilled annularly adjacent the periphery of the hole. Accordingly, greater penetration by the edges 6, 6 will be possible, and the ends of these edges will be protected; and the chopping edges not only will perform their function ofmaintaining the diameter of the hole, but also will tend to break away the material in a substantial annulanzone extending inwardly from the periphery of the hole, thereby protecting vthe ends of the cutting edgesl as above indicated, and

-also provide the external fracturing effect hereinabove mentioned so effective in maintaining gauge in deep holes. 'I'he substantial surfaces at the 4periphery of the bit and at the cutting face thereof will very efectually prevent any tendency to rifle and will maintain the bit at all times central of the hole being drilled.

From the foregoing description, it will be obvious that there is provided, by this embodiment of the invention, a highly eflicient, rugged, rapidly cutting and readily resharpened drill bit, possessingv relatively greatadvantages over drill bits of the ordinary type. and also possessing thel advantages of maintenance of full diameter of the drill hole, and maximum delivered energy per unit of cutting-edge length. It will further be noted that by forming the arcuate chopping edges slightly inside the bit periphery, fracture and* under severe drilling conditions, to be very eflec.

tive and under many conditions to far out-perform ordinary bits, such as conventional cross bits, .which have heretofore been recognized as among the most eicient drilling forms; to be `of this charactermay be made inexpensively, and 5 be resharpened easilyand inexpensively.

As variations in the form and .relative location of the teaming' or chopping edges, and in their length relative to the lengths of the cutting edges, are among (though these are not to be `under- 10 stood to be the only) variations within the broad scope of my invention, I shall now describe certain other illustrative embodiments.

Referring next to the species of the invention shown in Figs. 6 t0 9, 4it Will be noted that I 15 l vedge of a transversely-extending wedge-shaped cutting'portion 20. At opposite sides of the cutting,edge I9 are chopping edges 2I`, 2l, these extending at their foremost portions, in 'this embodiment of the invention, into the same plane 25 at right angles to the axis of the drill bit as in cludes the cutting edge I9. In this form of the invention, moreover, the lchopping edges 2| are provided along the intersections of inclined surfaces 22, 22 with the periphery 23, 23.0f the 30 slightly tapered, relatively conical, forward portion 24 of the drill bit. As is common, the drill bit is shown as provided with a rearward portion 25 having a more pronounced taper. It is obviouslyA unnecessary to employ thedouble taper to 35' somewhat flatter, that is to say, they make a somewhat more acute Adihedral angle with a rplane at right angles to the vaxis of the bit, than 40 the'surfaces 26 of the wedge-shaped portion supporting the cutting edge. I9, this being desirable for the purpose of providing adequate support for the chopping edges, though not essential. 'I'he periphery of the bit is relieved at four points 45 as, at 21, by grooves formed between adjacent wings, to-permit.the easy. passage of cuttings and cleansing fluid from the bottom of the hole.' The forward end of this bit will be noted, to summarize, to include .one`diametric cutting edge 50 broken by the cleansing fluid discharge opening .32, andv a 'pair of. choppingedges at opposite sides of the cutting edge, the chopping edges each being in the form of a 'portion of a conic section and each being tangent to a line parallel 55,V

of a dihedral angle whose edge coincides with the cutting edgeand a pairV of preferably but not necessarily somewhat ilatterplane surfaces 65 extending from the rearmost portions of the sides of the cutting edge supporting portion out to the chopping edges.

'I'he form of construction shown in the slightly modifled bit of Figs. 10, 11, l2 and 13 differs from 70 that of thespecies of Figs. 6 to 9 only in that the plane surfaces 22' 22', whichcorrespondsgenerally to the plane surfaces 22, 22 of Figs. 7 to 9, would intersect at their outer edges the cone with whose surface the forward endof the drill coin- Ihe forward 69 4. cides, along lines whose farthest forward point would lie in advanceof the transverse plane at right angles to the axis of the bit which includes the cutting edge. I9. Therefore, since it is not desired to have the chopping edge extend in advance of the cutting edge, a small segment 28 in the same transverse plane with the cutting edge I9 is provided at the forward end'or edge of the chopping portions. Thismerely amounts in effect to providing an initia small blunting which because it is done in advance results in the chopping edges lying further forwardly than they would lie were the blunting to occur through wear to a corresponding degree of dullness of the chopping edges in the species of Figs. 6 to 9.

Each of the forms of my invention may be provided with cleansing fluid passages if desired, and I have shown such at 32 in each of the last two species described. The two forms of the invention shown in Figs. 6 to 9 and in Figs. 10 to 13= inclusive, respectively, can be originally sharpened and re-sharpened with great ease with a suitably shaped grinding wheel, and with a minimum loss of gauge in resharpening. `Of course, these forms are also very readily formable and resharpenable by purely forging operations. Hot milling or other machining processes are also applicable. i

With reference to the embodiment of the 'invention shown in Figs. 14, and 16, it will be observed that theessential difference between this construction and that shown in Figs. 10 to 13 resides in the fact that the cutting-edge sup-V porting wings are relatively still narrower and f' that the angular recesses 21' are made of greater cross-sectional area by reason of the fact that the chopping edge supporting wings do not have parallel sides, but instead are ground back from their outer ends nearly radially instead of lying along parallel chords spaced substantially at opposite sides of the axis of the drill bit.

It will be noted that the cutting edges (the radial or diametrically extending edges) in each of the illustrative embodiments of my invention .are shown as ,spaced by the provision made for cleansing iiuid delivery. Obviously, these edges may be regarded, depending upon the point of view adopted, as eitheralined spaced radial edges,

or as a single diametric edgehaving, in the constructions shown, its center removed.

Since the advantages of my invention have been clearly pointed out in connection with the description of the several species disclosed for purposes of illustration, it is unnecessary to repeat them here.

This application is being flled to take the place of and so that it may be copending with my Iearlier filed applications Serial No. 117,175, filed Dec. 22, 1936, for Drill bits; Serial No. 25,246, fiie June e, i935, for Drin bits; and serial No. 744,298, led Sept. 17, 1934, for Drill bit.

While I have in this application specifically described several forms which my invention may assume in practice, it will be understood that these forms of the same are shown for purposes of illustration, and that the invention may be further modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire Letters Patent is:

l. In a drill bit of the type whichis percussiv 1y actuated and intermittently rotated during its percussive actuation, a bitbody formed with integral pairs of wings arranged in rightto secure by ting-edge portions.

supporting a pair of alined cutting edges ex tending along a'. diametric line and the other pair of said wings each supporting a curved chopping edge lying slightly inside the bit periphery and having an outer curved supporting surface receding rearwardly outwardly and terminating at the blt periphery, said chopping edges generally.,ar cuate both in end and in side elevation, the forward end of the bit, between said alined cutting edges and each of said arcuate chopping edges, bounded mainly by a pair oi.' plane surfaces disposed in the sides of a dihedral langle whose edge is parallel to the alined cutting edges.

2. In a drill bit of the type which is percussively actuated and intermittently rotated dur` ing its percussive actuation, a bit body formed with integral pairs of wings arranged in rightangular relation to eachother at theforward cutting end of the bit, one of said pairs of wings bit periphery, said chopping edges generally arcuate both in end and in sideelevation, the forward end of the bit, between said alined cutting edges and each of said arcuate chopping edges, bounded mainly by a pair of plane surfaces disposed in the sides of a dihedral angle whose edge is parallel to the alined cutting edges, and said alined cutting edges projecting at the forward face of the bit in advance of said chopping edges a distance materially less than the normal penetration of said cutting edges. y

`3. In a drill bit of the type which is percussively actuated and intermittently rotated during its percussive actuation, a bit body having at its cutting end pairs of wings arranged in rightangular relation to each other, the wings of one of said pairs being materially wider than `the wings of the other of said pairs, the narrower pair of wings supporting alined cutting edges extending along a diametric line and the wider pair of wings each supporting adjacent the periphery of the bit a chopping edge curved both when viewed from the front and from the side of the bit, said chopping edges lying slightly inside of the bit periphery and having an outer curved supporting surface receding rearwardly outwardly and terminating at the bit periphery, the forward ends of said narrower wings essentially wedge-shaped, and the forward'surfaces of each of said wider wings inside said vchopping edges disposed substantially wholly in planes edge is parallel to and to the rear of said cut- 4. In a. drill bit of the type which is percusslvely actuated and intermittently rotated during its percussive actuation, a bit body having integral wings and a front" cutting face whose forward-end peripheral portions lie in a surface of revolution whose axis coincides with the axis of the bit, said bit having alined cutting edges extending along a diametric line, said bit further having chopping edges at opposite sides of said alined cutting edges spaced inwardly from they intersection with such surface of revolution of planes making with each other an obtuse dihedral angle whose edgeis parallel to said alined cutting edges, said alined cutting edges whollysupported by certain of the wings .of said bit, and said chopping edges wholly supported by the remaining wings and at the outermost edges of planes disposed as aforesaid, but lying substantially in the wall of a surface of revolution of smaller diameter than the one bounding the wings. a

5.n In a drill. bit of the typewhich is percussively actuated and intermittently rotated during its percussve actuation, a bit body having at its forward end a pair of mutually opposite relatively wide wings and a second pair of mutually opposite relatively narrow wings, the latter at right angles to the former, said narrow wings wedge-shaped at their forward ends to provide alined cutting edges extending diametrically of the bit and said wider wings having forward plane surfaces sloping forwardly and outwardly from the junction of said wide wings with the body of the bit, said wide wings at theirouter extremities terminating in chopping portions having curved cutting edges each of a length arcuately substantially equal to one-half the effective cutting-edge length, said arcuate chopping edges lying slightly insidethe bit periphery and having supporting them curved outer outwardly receding surfaces terminating at the bit periphery.

6. In a drill bit of the type which is percussively actuated and intermittently rotated during its percussive actuation. a bit body having at its forward cutting end integral pairs of wings arranged in right-angular relation to each other, one of said pairs ofvwings supporting alined cutting edges extending along a diametric line and the other pair of said wings each supporting adjacent the periphery of the bit a chopping edge generally arcuate both in end and in side elevation'and positioned to work substantially in the same transverse zone with said alined cutting edges, the forward end of the bit, between said alined cutting edges and each of said chopping edges, bounded mainly by a pair ol planes disposed in the sides of a dihedral angle whose edge is parallel to the alined cutting edgesand spaced from a plane which includes said cutting edges and the axis of the bit a distance equal approximately to one-half the thickness of the wings supporting said cutting edges, said arcuate chopping edges lying slightly inside the bit periphery and having outer supporting curved receding surfaces terminating at -the bit periphery.

7. In a drill bit of the type which is percussively actuated and intermittently rotated during its percussive actuation, a bit lbody having at its forward cutting end integralpalrs of wings arranged in right-angular relation to each other with the wings of each pair diametrically arranged, the wings of one of said pairs each supporting a straight radially extending cutting edge, said edges lying in a common straight line perpendicular to the bit axis and in a plane which bisects the bit, and the wings of the other pair each supporting a single chopping edge whose projection on a plane perpendicular to the bit axis conforms substantially to the arc of a circle lying slightly inside the bit periphery, said bit having provision for the delivery of cleansing fluid therethroughbetween said alined cutting edges, and the forward end of said bit, between said chopping edges, being bounded, save for the portion thereof formed for cleansing 'fluid delivery, by two pairs of planes, the planes of each pair intersecting in a line parallel to the cutting edges, said lines of intersection parallel to each other in a plane perpendicular to the bit axis and i I 5 submnualiyv in the sides of the' wings' which carry the cutting edges, and one plane of one pair intersecting with one plane ofthe other pair in a line including said cutting edges, and said chopping edges having outer curved receding surfaces terminating at the bit periphery.

8. A drill bit of the type which is lpercussively actuated and intermittently rotated during drilling, having at its forward end rectangularly-related pairs of alined wingswhose extremities lie in a common surface of revolution, therwings of one of said pairs supporting alinedcuttig edges ,c

whose outer extremities extend to said surface of revolution, and the wings of the other, yadjacent their outer ends, supporting chopping edges which lie substantially in a surface of revolution lying inside said rst mentioned surface of revolution.

9. A drill bit of the type which is percusslvely actuated and intermittently rotated during drilling, having a pair of oppositely radially extending wings supporting at the forward ends of V-shaped Y edge-supporting portions cutting edges which lie y in a plane bisecting the bit, said wings of a width only suiiicient to support said cutting edges, and said cutting edges extending to. the outermost ends of said wings, said bit having another pair of oppositely extending wings arranged at 'right' angles to the wings of said first pair and supporting at their most forward portions but slight- 1y inside their radially outermost portions chopping edges extending circumferentially of the bit, said latter wings materially `wider than said cutting edge supporting wings -whereby increased arcuate extent of said chopping edges is provided,

the forward surface of saidchopping edge supporting wings sloping inwardly and rearwardly toward the sides of the first mentioned wings, said chopping edges arranged and adapted to cut away the material in an annulus at the periphery of the hole andsaid cutting edges projecting forwardly, throughout their. length, beyond the foremost portions of said chopping edges and also projecting, radially of the bit, beyond the circle struck from a point in the bit axis and including the foremost points in said chopping edges.

10. A drill bit of the type which is percussively actuated and intermittently rotated during drilling. having a pair of oppositely radially extending wingsv supporting at the forward ends of V- shaped edge-supporting portions cutting edges which lie in a plane bisecting the bit, said wings of a width only sufficient to support said cutting edges, and said cutting edges extending to the outermost ends of said wings but separated at their adjacent ends by a substantial space, said bit having a cleansing fluid discharge passage formed within and opening through said space, said bit having another pair of oppositely extending wings arranged at right angles to the wings of said first pair and supporting at their most forwardvportions but slightly inside their radially outermost portions chopping edges extending circumferentially of the bit, said latter wings materially wider than said cutting edge supporting wings and than said space separating the cutting edges and having to the inside of said chopping edges forwardsurfaces which slope inwardly and rearwardly towards the sides of the first mentioned wings whereby respectively increasedarcuateextent of said chopping edges is provided and radially inward pressures directed toward the center of said hole are provided, said chopping edges adapted to' cut away the materia! in an annulus at the periphery of the hole, 15

and said cutting edges projecting forwardly, throughout their full lengths, at least as far as the foremost points in said chopping edges, and extending radially of the bit at their outer ends, further than the distance from the bit axis to the radially outermost points in either of said choppins edges.

11. A drin bit of the type which is percussively actuated and intermittently rotated during drilling having a plurality of radially extending cutting edges formedvat the intersections of forperiphery inwardly and forwardly to said chop-- ping edges.

12. A vrock drill, bit having at its cutting end integral pairs of wings arranged in right-angular relation to each other, one of said pairs of wings supporting av single diametrically extending cutting edge and the other pair of said wings each supporting adjacent the periphery of the bit a chopping edge generally arcuate both in end and in side elevation, the forward end of said bit, between said diametric edge and each of said chopping edges, bounded mainly by a pair of planes disposed in the sides of a dihedral angle whose edge is parallel to the cutting edge.

13. A rock drill bit having at its cutting end pairs of wings arranged in right-angular relation to each other, the wings of one of said pairs being materially wider than the wings of the other of said pairs, the narrower pair of wings each supporting a diametrically extending cutting edge f portion extending to the periphery of the bit, and the wider pair of wings each supporting adjacent the periphery of the bit a chopping edge generally arcuate both in end and in side elevation, the for ward end of said narrower wings essentially `wedge-shaped and) the forward surfaces of said wider wings inside said chopping edges substantially wholly in planes lying in single sides of a dihedral angle whose edge is parallel to and to the rear of said cutting-edge portions.

14. A rock drill bit having at its cutting end integral pairs of wings arranged in right angular relation to each other with the wings of each pair diametrically arranged, the wings of one of said pairs each supporting a straight, radially extending cutting edge, said edges lying in a common straight line perpendicular to the bit axis, and the wings of the other pair each supporting a single chopping edge whose projection on a plane perpendicular to the bit axis conforms substantially to the arc of a circle struck from a center in said bit axis. said chopping edges each curved in side elevation and having their extremities substantially further towards the rear of the bit than their central points, said'rblt having provision for the delivery of cleansing iuid therethrough between said.alined cutting edges, and the forward end of said bit, between said chopping edges, being bounded save for the portion thereof formed for cleansing fluid delivery, by two pairs of planes, the planes of each pair intersecting in a line parallel to the cutting edges, said lines of intersection parallel to each other, in a plane perpendicular to the bit axis, and substantially in the sides of the wings which carry the cutting edges, and one plane of one pair intersecting with one plane of the other pair in a line including said cutting edges.

15. A rock drill bit having at its forward end a body having thereon a pair of `mutually opposite, relatively wide wings and a second pair of mutually opposite, relatively narrow wings, the latter at right angles'tothe former, said narrow wings wedge-shaped at their forward ends to provide a cutting edge extending diametrically of said bit and said wider wings having forward plane surfaces sloping forwardly and outwardly from the junction of said wide wings with the body of the bit, said wide wings at their outer extremities terminating in chopping portions each of a length arcuately equal to at least one-half the effective cutting-edge length.

16. A rock drill bit having at its cutting and integral pairs of wings arranged in right-angular relation to each other, .one of said pairs of wings' supporting a single diametrically extending cutting edge and the other pair of said wings each supporting adjacent the periphery of the bit a chopping edge generally arcuate both in end and in side elevation and positioned to work substantially in the same transverse zone with said cutting edge, the forward end of said bit, between said diametric edge and each of said chopping edges, bounded mainly by a pair of planes disposed in the sides of a dihedral angle whose edge is parallel to the. cutting edge and spaced from a plane which includes said cutting edge and the axis of the bit a distance equal approximatelyto one-half the thickness of the wings supporting said cutting edge. l

1'7. A rock drill bit having at its cutting end integral pairs of wings arranged in right-angular relation to each other with the wings of each pair diametrically arranged, the wings of oneof said pairs each supporting a straight, radially extending cutting edge, said edges lying in a common straight line perpendicular to the bit axis and in a plane which bisects the bit, and the wings of the other pair each supporting a single chopping edge whose projection on a plane perpendicular to the bit axis conforms substantially to the arc of a circle struck from a center in said bit axis, said bit having provision for the delivery of cleansing iiuid therethrough between said alined cutting edges, and the forward end of said bit, between said chopping edges, being bounded save for the portion thereof formed for cleansing fluid delivery, by two pairs of planes, the planes of each pair intersecting in a line parallel to the cutting edges, said lines of intersection parallel to each other, in a plane perpendicular to the bit axis, and substantially in the sides of the wings which carry the cutting edges, and one plane of one pair intersecting with one plane of the other pair in a line including said cutting edges.

18. In a drill bit, a body rotatable upon its axis during percussive actuation and having a substantially circular rearward'portion and a forward portion of oruciform shape whereby four wings `arranged in pairs at right angles to each other are provided, the wings of one of said pairs being relatively wide and the wings of the other of said pairs being relatively narrow, said wider wings having at their outermost extremities chopping edges each arcuate in end elevation and having in side elevation its median portion in ad Vance of its end portions, and said narrow wings providing support for' and having thereon at least one cutting edge extending in the same general direction as said chapping edges, the median i 9,109,109 chopping edges and saidl portion o f each of said cutting edges in their entirety being substantially -co-planar perpendicular to the bit axis. whereby and terminating in a plurality of edges. said eilig including radialcutting edges and su tially peripheral arcuate chopping edges in alternation,

each in a dinerent quadrant from each of the others, xsaid cutting edges/in their entireties andv the most forward portionsv ot said chopping edges being substantially co-pianar perpendicular to the bit axis, and the lateral;etremities of said disposed of said bit @he met choppingedgesbeing nearertothesh'ankofthe'la forwarvdportions'oisaidl g5 20.Arockdrillbitcomprising:ashankrotat of the hole at a transverse zone ablel upon its axis during percussive actuation and-terminating in lfouiedges, said edgesinciudinginalternationradialcuttingedgsperpmdiculartothebitaxisandsubxtantiallype ph from the side of the bit, each 0i laid edges Ain a dinerent quadrant from each ott/he' others', said cutting edges in their entireties and the most ior.

wmcntneedgescftheothmmwaueltonm cutting edges, said bit further having a duid discharge separating said cutting edges, and the extremities

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