US2644671A

US2644671A - Rock drilling bit

Info

Publication number: US2644671A
Application number: US732171A
Authority: US
Inventors: Martell D Ingram
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-03-04
Filing date: 1947-03-04
Publication date: 1953-07-07
Anticipated expiration: 1970-07-07

Description

July 7, 1953 M. D. INGRAM aocx DRILLING BIT Filed March 4,. i947 '7 Shets-Sheet 1' Inventor MarteJ] D. 122 gram.

July 7, 1953 M. D. INGRAM ROCK DRILLING BIT '7 ShetS-Sheet 2 Filed March 4, 1947 2 k qw j 111s AGENT July 7, 1953 D. INGRAM 2,644,671

ROCK'DRILLING BIT Filed March 4, 1947 7 Sheets-$11991; 3

Fig. 7

' [IIViZZOF 'Mariell D. Ingram sat Wm HIS .HGENT.

July 7, 1953 M. D. INGRAM 44, 1

ROCK DRILLING BIT Filed, uarcn 4, 1 947 7 Sheets-Sheet 4 fnz/enzor Martel] D. Ingram WWOQW HISAGENT.

July 7, 1953- M. o. INGRAM.

Rocx DRILLING BIT 7 Sheets-Sheet 5 Filed March 4. 1947 a H [I I m x [N VEN TOR. Mar a 61/0. lz zyram H16 .HGEN'IZ 7 sneetg-she x e INVENTOR. Mar teIIDJ BY 225mm Mg Hag GE T.

M. D. INGRAM ROCK DRILLING, BIT

July 7, 1953 Filed-March 4, 194'? 7 Sheets-Sheet 7 INVENTOR.

Hi3 AGEJVZ,

. 8 I, F ii Martel] .Dlngram BY W Patented July 7, 1953 UNITED STATES PATENT OFFICE This invention relates to improvements in rock bits employed in rotary well drilling, and more particularly to rock bits which may be readily assembled or disassembled for the repair and replacement of the bearings, the rotary cutter elements and other parts connected therewith.

Rock bits have been proposed heretofore which embodied rolling cutters but, for the most part, it has been found that these wear rapidly and *that they do not readily lend themselves to disassembly for the repair or replacement of worn parts, due to the manner of construction. Furthermore, it has been found that certain parts of rock bits wear exceedingly fast as compared with other parts. Therefore, in the present invention, an attempt has been made to correct the defects existing in bits that have been made jheretofore, and to provide other new and'salient features which make possible more efficient operation and more rapid cutting than has hereto- .fore been possible.

The primary object of the present invention is to provide a rock bit structure made of relatively few parts, yet providing a structure that is strong :and sturdy and which may be readily assembled .and disassembled.

Another object of this invention is to provide a rock bit in which the cutter unit is provided 'with bearings adapted to sustain both radial and 1 thrust loads.

Another object of this invention is to provide -a rock bit in which hardened metal inserts may be applied to the cutter teeth thereof, as by welding or by centrifugal casting,

Another object of this invention is to provide a rock bit in which the bowl and wash pipes thereof are provided with a resilient lining, such as rubber or synthetic rubber, to prevent abrasive action thereon.

A still further object of this invention is to provide, in a rock bit, a self-cleaning action for the cutter teeth.

A preferred embodiment of this invention together with modifications thereof are illustrated portion of parts of the bit as shown in Fig. 3, partly in section and partly in elevation;

Fig. 5 is an elevational view of the cutter elements removed from the bit;

Fig. 6 is a sectional view taken on the line 68 of Fig. 3, looking in the direction indicated'by arrows;

Fig. 7 is a view similar to Fig. 1 but of a mod ification of the invention which shows a different method of mounting the cutters and shaft there- Fig. 8 is a fragmentary View of the modified form of the invention, showing the manner of locking the shaft against rotary movement;

Fig. 9 is a perspective view of a wash pipe for directing drilling fluid to a point near the bottom of the well;

Fig. 10 is a sectional view taken on the line Ill-l0 of Fig. 7;

Fig. 11 is a fragmentary view of an end portion of the cutter shaft showing how a lubrication fitting may be temporarily installed thereon so that a lubricant may be introduced into the shaft;

Fig. 12 is a bottom view of the form of bit shown in Fig. 7;

Fig. 13 is a longitudinal sectional view through the cutter elements showing how the various bearings are installed and sealed within the cutter unit;

Fig. 14 is a sectional view taken on the line M--l4 of Fig. 12, looking in the direction indicated by the arrows;

Fig. 15 is a view similar to Fig. 14 but showing a modified form of applying the hard surfacing material to the teeth;

Fig. 16 is a perspective view of the bit body with a quarter section removed therefrom to show the details of construction;

Fig. 17 is a fragmentary sectional view taken on the line l'I-Il of Fig. 16, showing how the drilling fluid may be directed downward;

Fig. 18 is a view similar to Fig. 17 but showing certain of the openings plugged and certain of the other openings having orifices therein so as to direct the fluid laterally therefrom;

Fig. 19 is a view similar to Fig. 10 but showing a modified manner of installing the cutter shafts therein; and

Fig. 20 is an enlarged fragmentary detail, partly in section and partly in elevation, showing the manner of locking the cutter shafts against rotation or longitudinal displacement.

With more detailed reference to the drawings, the numeral I designates the body of a rock bit on which a threaded pin 2 is disposed on the upper end thereof, which threaded pin is adapted to be connected to a conventional drill stem in a manner well understood in the drilling art. The body I has a downwardly depending center portion 3 which center portion has a central water course 4 therein and which central water course connects with lateral Water courses 5, 5. The upper end of water course 4 connects with a central bowl portion 5. It is preferable to have the water courses 4and 5, 5 linedwith a rubber lining T and 8, respectively. The bowl 6 is also provided with a rubber lining 9, having a bead 9a engaging top of pin 2.

The bit body I has downwardly depending arms In, I0 disposed on opposite sides th ereof and se cured to the body as by Weldingas indicatedin dot-dash outline in Fig. 1. The welding may be done by any of the various conventional methods of welding, such as flash, electric or acetylene.

Cutters II, II are disposed intermediate the depending center portion 3fand the arms ID, ID. Each of the cutters 11, H has a shaft l2 made integral therewith and protruding outward from either face thereof. It is preferable to have the outer cylindrical surface of" the shaft I? covered v by a hard surfacing material which may be in the form of tungsten carbide applied the leto by welding and said outer surface material ground or machined until a finished surface results, or a hard'sur ac n alloy mate ial f rmin a sleev l3 may be applied to the shaft as by pressing or s r in said sleev therenn Ea h end f he sha t. a a s ot o hard fa in ma e ial a ed in t e cen e ther o to form thrust bearings I4, 14, respectively, for en a me w t com leme tary po s of, h r surfacing material l5 and I6 formed on ,a plane surface within cylindrical races Hand is, which races are formed on depending center portion 3 and the arm H3, respectively; The cylindrical races I7 and [8 have their inner surfaces covered with a lining of hard surfacing material such as tungsten carbide, or a sleeve of hard alloy material may be provided, which sleeve may be pressed or shrunk thereinto, and when ground or finished,

pin bearings

19 and 20 maybe fitted into the respective races so as to support shaft [2' for rotation of the cutter element H. The cylindrical races H and 18 have cylindrical neck portions 2| and 22 respectively, which neck porthe cutter ll will be transmitted directly to' the #4 center of the depending'center portion 3and the center of arm portion" 10 without the neck portions 2| and 22 sustaining the entire load.

By having the neck"portions2l, 22 interfitting with the inner

cylindrical surfaces

23 and 24, a substantially fluid tight'seal will result and which will normally exclude drilling mud or other abrasive matter. The arms H] are welded'to the body I as indicated in Fig. l and when'the various parts of the rock bit are assembled in the relation as shown in this figure, it is impossiblefor the cutters II to become mislocated. When the cutter or bearings are in needof repair, the arms l0, It! may be readily removed with'a cutting e921 9 as u e s,

torch along the line where they were welded, and they may be reassembled after making necessary repairs or installing new parts in the same manner as the bit was originally assembled.

Water course tubes

25, 25 are mounted in the bottom of the bowl 6 in position to direct the drilling mud into the teeth of cutters II, II and, due to the construction of the bit body, these water courses may be brought into close proximi tv t the faces of the gutters for c ean the debris 'frQm between theteethoftheclitters during" the drilling'"'operation; It is preferable to have these

water course tubes

25, 25 threaded 'exteriorly and to have them rubber or synthetic rubber, lined, because this lining resists the abrasive action of the drilling mud. By having the ends of these water courses threaded, they may be inserted or regnpved when worn or as desired, and interchanged with course tubes of different lengths, 'or with tubes having a different type of outlet nozzle openings. It is also preferable for these water course tubes to-be inclined sli htly ng nt a mine a e fo med by the bottom of. the teeth- By hav ng. the dri ing mud striking the ut rs at his an l the teeth. are cleanefd'as the cutte rol s- 3 are opp s te disused. on. either side of t e bit Pq y ,l' an secured hereto as, by W d n and e pa ed ntermed ate arms Cuttgrs 32 and 33 are e oneatedandhave s a t 4 139 a d 3. res ec ively made inte s he ew th 17 1s s fts. 3A. 3.4 nd 3,5,. 3.5. are round and h ve a her ssfa ine m terial an.- plied t t o te ur a es th reo which terial may be Emma efme ined 9 resent a QQQ? h-s Eeli 9 the a ms 3. as a yli driqel e e ms herein he en ave surfaces of Which a s v e th ahard s rfacin iel uc as n s en a ide which facing mate al s semis b lwe d orbs Sleeves of a d 93 materia 35, M 191 may be pressed or shrunk into place, or pressed or shrug]; on the shafts 3 4, 24 and $5, 3.5,.

ylm ri e scs l s is. were f med n depending center port on on opposite si e theren a y nd i re sss 3. s x al ali nment with recess 37 in each respective side. The ers .2 a 3,3. mqunt d n n oller h a es 40 n 4 5,1 as w es e een Eec end f cam haf 3.4. 3.4 and 3. ashes a

hard alloy insert

42, 42, 42, 42 attachedthereto a by we n g ins-ee br el in n o. a rece s. an whi h e a e e...q mn m nta y. hard a oy se 3 3- 43 each cy nd ica bearin recess 31, 3'! and 39, 3,9. These inserts may be fused th t b weld n i c herdallby rts. 43 ay-beio medo un sten carbide.

or other s'ni ab ea esu f 9ie mater alhe tt 3 erect h rolle ime and have wedge-shaped

teeth

44, 44, 4 and

teeth

45, 45, 4 5 iorined t respectively. Irw n be noted from Figs. 3 and 4 that c ter 32 issubstantially longer than cutter 33 sentence seen of the cutters are arranged sp"thalt win the rock 'bitis rotafied'aroiindit 'axisfthe teeth on n e f yim p e l over,'th'at is, the rid'g'je le will "beremoved by the we inner cutter 33 whenthfebitisro The cutters 32, '33 are an I a'rly disposed on axes of approximately fift degrees frd the horizontal with the axes converging atappr i mately the center'o'f the'drillb'itf 'The .upper'po'r sa ly. em e we:

bit body and has rubber or synthetic rubber lined conduits 46 leading from the rubber lined bowl 6 of the bit body The nozzles on the lower ends of these conduits are elongated so as to discharge the drilling fluid along the faces of the teeth to wash them and to keep them free of debris. Teeth cleaning fingers 41 are provided between the rows of

teeth

44, 44, 44 and between the rows of

teeth

45, 45, 45, each of which is a piece of metal attached to the lower portion of bit body and projecting downward in close proximity to the cutter body, as will best be seen in Fig. 6. It is preferable to have the cleaning fingers of greater width than thickness in order that they will be suillciently strong to dislodge rocks which may become lodged between the cutter teeth.

The form of theinvention as shown in Figs. 1 to 6 has arms l0, l and 3|, 3| secured to the body l as by welding and when these arms are welded in place they become substantially an integral part of the bit body and the cutters and 32, 33 cannot be misplaced or lost in the well unless the arms are broken off. The cutters preferably are made each of a singe piece of metal, and each cutter may be replaced by cutting off the arm along the weld line where the arm has been previously welded to the bit body and, in so doing, the bit members are separated into com-, ponent parts, such as shown in Figs. 2 and 4, and if desired new cutters and new bearings may be installed and the bit made serviceable again at very little cost.

A modified form of the invention is shown in Figs. '7 to 18, inclusive, and has a body 5| made of unitary construction having a threaded pin 52 at the upper end thereof for connecting the bit with the drill stem in a manner well understood in the drilling art. Bit body 5| has'downwardly depending center portion 53 which forms a support for the bearings of the roller cutters, as will hereinafter be more fully described.

Arms

54, 54 are oppositely disposed on the bit body 5| (see Fig. 16) and are made integral therewith. Recesses 55 are formed in the bit body 5| to receive

cutters

56, 56, which cutters are mounted on

shafts

51, 51.

Shafts

51, 51 are screw threaded into the depending center portion 53 and are frictionally locked therewith by the ends of said shafts abutting the bottom of the respective threaded holes therein. The

shafts

51, 51 have shoulders thereon which engage

bearings

58, 58 that are of the semi-thrust type.

Bearings

59, 59 are also mounted on the

shafts

51, 51 and may be of the roller type and may seat upon the larger portions thereof. These bearings seat in inner bores of

cutters

56, 55, and hardened

thrust plate bearings

60, 6| are secured to opposite sides of the cutters 5B, 56, as by welding, so as to form cutter units with self-contained bearings. The cutter units may be replaced readily on the job by unscrewing the

shafts

51, 51, putting the cutters in place and replacing the shafts.

Seals 62, which may be made of felt or the like, are provided to retain the lubricant within the

bearings

58 and, 59 and to exclude mud therefrom. Lubricant may be introduced through a conventional fitting 64, such as shown in Fig. 11 which fitting may be attached temporarily in hole 63, and after the lubricant is introduced, the lubricant fitting '65 may be removed and the hole 63 plugged with plug 65 which may be screwed therein to prevent the entrance of foreign matter.

After the shaft 51 is screwed into place a pin 56.may be passed through the perforated head:

'6 of the shaft 51 and its end bent into slot 61 in the arm 54, so as to prevent the shaft from becoming unscrewed.

A dowel pin 68 is adapted to pass through the thrust plate bearing 59, which thrust plate bearing is made of a hardened alloy metal. Each thrust plate bearing 69 is mounted on the inside face of each of the depending arms 54 and doweled so as to prevent rotation of the thrust plate upon rotation of thrust plate 6| which is welded to the cutter 56. A dowel pin 10 secures in like manner a thrust plate bearing 1| in place and prevents rotation-thereof upon rotation of thrust plate 60. These thrust plate bearings 69 and Here detachably secured, respectively, to the inner face of the arm 54 and the outer face of the depending center portion 53 so they may be replacedas may be desired.

It will be appreciated readily that, with a single unitary bit body 5|, the cutters may be renewed readily and replaced on the job without having to provide a new bit body each time the cutters become worn. It has been found that the bit bodies wear over a long period of spectively, which provide an'opening therein to distribute lubricant to the respective bearings. The ends of the

cutters

12, 13 are partially closed by annular thrust plate bearings 12d, 12c and 13d, 136 in the respective bearings. These thrust plate bearings are formed of a hard alloy metal and are in abutting relation with other thrust plate bearings removably attached to the depending center portion 53 on each outer face thereof and to each inner face of depending arms 15, 15. With the shaft 14 passing through openings in the annular thrust plate bearings the openings are closed in substantially tight relation.

By having the ball thrust bearings arranged as-shown in Fig. 10, i. e., bearing 12a at the smaller end of the cutter 12 and bearing 13a at the larger end of the cutter 13, it is possible, by having a pair of shoulders on the shaft 14. to use a single shaft through these

cutter elements

12, 13 that will transmit the thrust toarms 15, 15 through the shaft 14, as the thrust plates 12d, 13d are welded on each corresponding end of the respective cutters so as to engage an en of bearings 12a, 13a, respectively.

The

roller cutters

12, 13 are mounted on the shaft 14, which shaft is drilled todistribute a I lubricant to the bearings. The shaft 14 passes through arms 15 and depending center portion 53. -The

roller cutters

12, 13 are mounted on the bearings 12a, 12b, 13a, 131), as above described, which bearings are sealed in the cutters in substantially the same manner as de-' scribed with respect to the cutters 56. It will be readily appreciated that by removing a nut 16 from the shaft 14, the

roller cutter assemblies

12 and 13 may be removed, as well as the thrust bearing plates, and new ones installed in a few minutes time, more job and with a-inaterial saving both time and money.

Fig. 12 shows one form of-tooth pattern for the teeth of the cutters which is designed to cut over the entire surface of the bottom of the well each time the bit is rotated one complete revolution.

Fig. 13 is a cross-sectional view of the cutter element 56 removed from the bit and showing the manner in which the bearings are retained in spaced relation in the cutter element.

The form of the invention as shown in Figs. 19 and 20 is substantially like the form shown in Fig. 10, "except two

inter-engaging shafts

81 and 82 threadably engage each other at 83 and both shafts are locked against rotation relative to each other and relative to the arms 84. By having the shafts mounted in manner, and formed with shoulders '85, '86 on shafts 8i and 82, respectiveiy, the thrust of the roller cutters, which roller cutters carryinverse spirals, is transmitted by the ball thrust bearings against the shoulders 85, -85 of the shafts 8I, 82 and thence to the arms 85, Eli and to-the body of the bit.

The shafts BI, 82 are drilled and cross-drilled to form openings, which openings are adapted to receive a lubricant which passes into a chamber formed between the bearings therein for lubrication of the bearings.

'It is preferable to have an insert 81 of tungsten carbide or other hard surfacing alloy applied to the leading side of the cutter teeth, as by welding or by centrifugal casting of the cutters withthe hardened tungsten inserts within the casting mold, so as to retard abrasion. The insert is formedsubstantially as a triangular prism, preferably having one right angle corner which seats within a step joint within tooth 88, as will best be seen in Fig. 15, or granular tube tungsten may be applied to the tooth '89 which is formed having a stepped off-set on the leading side thereof, asindicated at 90. 13y having the tooth of this construction, the hard alloy material is supported by a tooth of tough steel and with the projection extending up behind the tube tungsten tip 93, which-may be applied with a welding torch, or tungsten carbide insert "81, the tooth is -not -so likely to fracture and break off at its base, as would be va tooth built up ontirely of hard alloy material.

In the operation of the rock bits herein described, the-bit is-adapted tobe screwed onto the lower end of adrillstem (not'shown) for-rotation by a conventionalrotary drilling; rig in a manner well understood in the drilling art.

The reamer cutters designatedas I I, I I in one form of the inventionand-designated as '56, 55 in another form of the bit, preferably have their axes disposed at an angle of from 24 degrees to 33 degrees above the horizontalwith the cutting edge projecting beyond the outer confines of the bit bodies I and-ELrespectively, so as to givea sizing 'or-reaming action to the wall of'the well being drilled.

'The form of the invention as shown -in Figs. '1 to 6, inclusive, has transversely disposed rolling cutter elements 312,, '33 "that-have their arms disposed approximately from '7 degrees "to 115 degrees above the horizontal. It is preferable to have the cutter-pointsof the transversecutters 32 33 lead the points of the reamer cutters by from one-half inch toone'inch so as to keep the'greater area of the 'hole advancedahead-of the portion to bereame'dbythereaming-cutters. Byihavingthe cutters arrangednn'this manner and-within-the sense I l mi o a le he e g ven. him been foun that a sp d cu ti ac io ult w th a mi m of tr n n the cu t sl 7 Upon r t t onof the 1 1 11 stem and the rock 1 on e ted wit the low r nd thereof, the var ous utte el ments H, H audit, .33 of e m of the invention shown in Figs, 1 to 6, inclusive, are rotated due to their frictional contact with the bottom of the hole being drilled. The cutters" tern on the bottom of the well, and with the out:

ter elements

32, 33 having the teeth arranged as hereinbefore described, they will describe a pat,- tern which cuts over the entire bottom of the well, which will give a true circular hole.

"The mud or fluid is pumped down through the drill pipe into the bowl 6 .of the drill bit and the earth cuttings that are cut by cutter elements I I,, II, 33 will be floated to the top of the well in a manner Well understood in the rotary drilling art.

Byhaving the water or fluid courses disposed in the manner shown herein, the drilling fluid is directed downward into the cutters and to a point immediately adjacent the bottom of the well, which will "keep the cutter teeth cool and lubricated with drilling mudor fluid and will cause the immediate fiotationof the earth formation to the top of the hole.

Angularly disposed recesses are iormedinthe body I between depending arms I0 and BI, so as to enable the mud that is beingdischarged upward to be given-a spiral action. r

The forms of the .bit as ,shown in Figs. 7 "to l8, inclusive, and in Figs. 19 and ,20, operate in substantially the same manner-as described with ;re.- spect to the form illustrated Figs. ;1 to 15,11 elusive.

Having thus described my invention, I claim: 1. In .a rock bit structure for rotary drilling, a bit body having an opening formed therein, a threaded connection on the upper vend of said bit body for connection with a drill stern, roller cutters, arms depending downward from said :bit. body, a roller bearing element mounted on: each of said arms, said roller cutters being journalled in said roller bearing elements for rotary movement about the axis of each respective cutter, conduits formed through said bit body for directing drilling fluid ,to said cutters, eachof said cutters having a shaft -formed integral therewithand having an annular recessformed ineach end of saidoutter and exterior of said shaft to receivesaid roller bearing elements, and a bearing race adjacent each end of each cutter and interfitting there:- within telescoping relation with the annular recesses of said cutters so as to seal said bearing races against the entrance of drilling mud there into. I I

2. 'In a rock bit-structure for rotary drilling, ,a bit body having a"hollowibo dy formed therein, a threaded connection on the upper end of said bitbodyfor connection with a drill stem, roller cutters; arms depending downwardly from said bQdy, a roller'bearing element inounted on each of said arms, said roller cuttersbeing journalled in said rollerbearing elements for rotary movement -ab outthe axis of .each respective cutter, conduits 'formed through said bit body for directing drilling'fluidto said cutters, eachofsaid cutinsa ha ormsdin s a therewith n endthereof and exterior of said shaft to receive said roller bearing elements, an annular rim formed on each of said depending arms in axial alignment with said annular recess formed in the respective cutters so each of said rims will extend inwardly into the respective recess formed in the respective cutters for maintaining the axis of the respective cutter in aligned relation with the axis of its respective annular rim in the respective recess, and a bearing race formed adjacent each end of each cutter and interfitting therewith in telescoping relation with the annular recesses of the cutters so as to seal said bearing races against the entrance of drilling mud thereinto.

3. In a rock bit structure for rotary drilling, a bit body having an opening formed therein, a threaded connection at the upper end of said bit body for connection with a drill stem, said bit body having a depending center portion and depending arms spaced apart and from said depending center portion, bearing races mounted on said arms and on said depending center portion, rolling elements in said races, a roller cutter mounted between each of said arms and said depending center portion and journaled at its respective ends in said bearing races for rotary movement of each respective cutter about its axis, said bearing races having hard surfacing ma terial, such as tungsten carbide thereon, which hard surfacing material is machined to a smooth finish for engagement with said rolling elements.

4. In a rock bit structure for rotary drilling, a bit body having an opening formed therein, a threaded connection at the upper end of said bit body for connection with a drill stem, said bit body having a depending center portion and dea bit body having an opening formed therein,

athreaded connection at the upper end of said bit body for connection with a drill stem, de-

pending arms spaced apart and from said depending center portion, roller cutters, bearing races in said arms and said depending center portion, rolling bearing elements in said races, said rolling bearing elements jouralingsaid roller cutters between said arms and said dependin center portion for rotary movement of saidroller cutters about their respective axes, and said bearing races having sleeves of hard alloy material fitted thereinto and so finished as to present a smooth interior finish for said bearing elements to roll upon.

5. In a rock bit structure for rotary drilling, a bit body having an opening formed therein, a threaded connection at the upper end of said bit body for connection with a drill stem,'. said bit body having a depending center portion and depending arms spaced apart and from said center portion, roller cutters, bearing races in said arms and said depending centerportion, rolling bearing elements in said bearing races, said rolling bearing elements journaling said roller cutters between said arms and said depending arms on said bit body which arms are spaced apart, a bearing race in each of said arms, rolling bearing elements in each of said'races,

said races having hard surfacing material, such for-engagement with said rolling bearing elements, and roller cutters having an axial projection extending from each end thereof and journalled in said rolling bearing elements.

'7. In a rock bit structure for rotary drilling, a bit body having an opening formed therein, a threaded connection at the upper end of said bit body for connection to a drill stem, arms mounted on said body and depending downwardly therefrom and spaced apart, a depending center portion mounted between said arms, roller cutters, an axial projection on each end of each of said roller cutters and forming an axis there- 'for, bearings in said arms and said depending center portion for journaling said axial projections of each of said cutters, a hard material insert on the outer end of each of said axial projections adapted to be in complementary abutting relation with a hard material insert in each of said arms.

MARTELL D. INGRAM.

References Cited inthe file of this patent UNITED STATES PATENTS Number Name Date 250,385 Parsons Dec. 6, 1881 1,729,063 Bull Sept. 24, 1929 1,908,049 Reed May 9, 1933 1,990,007 Sperry Feb. 5, 1935 2,017,834 Hummel Oct. 15, 1935 2,043,142 Zublin June 2, 1936 2,049,047 Brownlee July 28, 1936 2,063,012 Catland Dec. 8, 1936 2,087,500 Catland July 20, 1937 2,116,561 Crum May 10, 1938 2,143,909 Crum Jan. 17, 1939 2,155,040 Fisher Apr. 18, 1939 2,160,852 Gouthey June 6, 1939 2,168,060 Catland Aug. 1, 1939 2,168,192 Carleton Aug, 1, 1939- 2170320 Catland Aug. 22,1939 2,171,057 Crum Aug. 29, 1939' 2,174,102 Catland Sept. 26, 1939 2,279,129 Pennington Apr. 7, 1942 2,336,029 Ogarrio Dec. 7, 1943