US2148805A - Method of making oil hole drills - Google Patents

Description

Feb. 28, 1939.

s. A. coesDuu.

METHOD OF MAKING OIL- HOLE DRILLS Fild May 9,1938 I 3 Sheets-Sheet 1 11v VENTOR 5Zzz4r'Z 62554 222: BY

I Y A TTORNEI Feb. 28, 1939.

S. A. COGSDILL METHOD OF MAKING OIL HOLE DRILLS Filed May' 9, 1938 3 Sheets-Sheet 2 INVENTOR jie'iydrz f2 d'dgsd'z'll B Y I I I A T T ORNE Y5.

Patented Feb. 28, 1939 UNlTED STATES" mrrnon or PATENT OFFICE MAKING OIL HOLE Application May 9, 1938, Serial No. 206,865

2 Claims.

This invention relates to oil hole drills and particularly to a method of making the same, the principal object being the provision of such method by the practice of which oil holedrills of superior characteristics may be. manufactured in an economical manner.

Objects of the invention include the provision of a method of making an oil hole drill in which the b nk may be formed with spiral flutes prevlous to the step of providing the oil holes therein; a method of making an oil hole drill eliminatlng the necessity of rifle drilling; a method of making an oil hole drill in which the oil holes in an initial stage of operation are formed by milling or otherwise providing a groove opening onto the exterior surface of the drill blank in parallel relation with respect to the usual flutes; a meth- 0d of making an oil hole drill including the steps of forming a groove in a drill blank and thereafter working the metal of the blank at and ad- I jacent the'periphery thereof into the outer portions of the groove to cl'ose it, thereby providing an oil hole within the blank; and a method of forming an oil hole drill including the steps-of spirally fluting a blank, providing one or more grooves opening onto the exterior surface of the blank and extending in approximate parallelism with respect to a marginal edge of at least one of the flutes, and then acting upon the blank to work the metal thereof at and adjacent the exterior surface thereof into the outer portion trate suitable examples of oil hole drills formed in accordance with the present invention, illustrating various steps in the operation of forming the drills and suitable apparatus for use in forming the same, I

Fig. 1 is a partially broken side elevational view of an oil hole drill of the type having a cylindrical or straight shank;

Fig. 2 is a fragmentary partially broken side elevational view of an oil hole drill having a tapered shank;

Fig. 3 is a transverse sectional view taken throughthe fluted portion of a blank'suoh-as is provided in accordance with'the present invention in the formation of drills such as illustrated in Figs. -1 and 2; Fi 4 is a view similar to Fig. 3 but illustrating a subsequent step of operation in the forming of the drill;

Fig.- 5 is a fragmentary side elevational view of a drill lank after the operation illustrated in- Fig. 4-has been completed;

- Fig. 6 is a more or less diagrammatic view taken transversely through a drill blank such as iilusl0 trated in Fig. 5 and illustrating a subsequent step of operation thereon in which the metal of the blank is causedto close the outer edges of the grooves formed by the operation illustrated in Fig. 4 thereby to form oil holes in the drill;

Fig. 7 is a transverse sectional view through a completed drill formed in. accordance with the present invention 'and constitutes a slightly enlarged transverse sectional view taken through the fluted portion of the drill shown in Figs. 1 or 2;

Fig. 8 is a fragmentary side elevational view of an oil hole drill arranged for side feeding of liquid into the oil holes thereof;

Fig; 9 is an end elevational view, partly in section, of an apparatus by means ofwhich the operation illustrated in Fig. 6 may be suitably accomplished; I

Fig. 10 is a partially broken plan view of the apparatus shown in Fi 9;

Fig. 11 isa side elevational view of the appsratus shown in Figs'. 9 and 10, certain parts thereof being broken away to better illustrate the construction and parts being shown in section.

Drills of the type employed for cutting metal I and having one or more passages therethrough for conveying a stream of liquid to the point of the drill are. commonly known as oil hole drills although in many cases'liquid which is actually caused to flow through the drill does not consist 4o of oil. In the majority of cases, however, theliquid actually used will serve as a lubricant for the drill even though the lubricant consists of water, either plain or with the addition of soda,

, as is commonly employed in cutting steels, 4s

-- wrought and malleable iron, aluminum and other soft alloys, or it may be other aqueous drilling compounds such as are commonly; sold on the market. Such liquid has an additionally imporl tant function in more or less heavy production so drilling, namely that of a coolant, it thus serving to cool the cutting edge of the drill and prevent it from becoming over-heated, thus permitting the. v drill to maintain its proper cutting edge for a greater length of time than would otherwisebe u 35 thereof desired'in the final product.

possible. Particularly in drilling relatively deep holes the flow of such liquid through a drill has an additional important function of serving to carry away the chips out of the drill opening, thus preventing the chips from packing up in the hole and endangering breakage of the drill, as Well as eliminating the necessity of repeatedly removing the drill from the opening to clear the drill and opening of chips during the drilling opelation.

It will be understood that oil hole drills are usually identical in substantially all respects to ordinary drills except for the provision of the oil hole or holes therein. In other words they are usually of the spirally fluted type having two or more spirally arranged flutes and corresponding lands and usually provided with the conventional ,body clearance back of the margin or cutting edge thereof. The drills may be of the conventional or so-called straight shank type or of the conventional taper shank type. While the present invention is applicable to such drills regardless of the number of flutes provided therein, for the purpose of simplicity in illustration and description drills of the two flute type only will be referred to, the application of the present invention to drills having a greater number 91' flutes being readily apparent to those skilled in the art upon the disclosure herein. a

The conventional method of forming oil hole drills is to form a drill blank with a pair of opposed flutes in opposite sides thereof but with the flutes straight and parallel to the axis of the blank as dlfierentiated from the spiral conformation The drill blank with these straight flutes in it is then rifle drilled from one end thereof to the other end thereof to provide the oil holes, these holes, because of the straight conformation of the flutes in the blank at this stage of operation, thus being arranged in parallel relation with respect to the flutes. After the oil holes are drilled the fluted end of the blank is then twisted so as to impart to the flute the desired helix angle. Drills constructed in accordance with this practice are necessarily relatively expensive to produce because of the'time and labor involved in drilling the elongated oil holes in the blank, the relatively high percentage of breakage of the drills employed in drilling the oil holes, the labor and care required in twisting the drill blank into the desired spiral conformation, and for other reasons well understood to those skilled in the art.

Another type of oil hole drill construction has been suggested and in which the drill blank is initially spirally fluted in the usual manner and then a groove is milled or otherwise formed in each land of the drill spirally thereof in parallel relation with respect to the lands, a small tube is then disposed in the bottom of each of the grooves and the remaining portion of the groove is filled in usually with a brazing material until that part of the groove not occupied by the tube is completely filled with such material. The drill blank reaching such condition may then be machined in a conventional way to bring it to completed condition. This last typeof oil hole drill has not proven commercially satisfactory for the reason that by its use the torsional strength of the drill is considerably reduced and the chips formed during the drilling operation in working around the drill tend to stick in the brazingmaterial exposed on the surface of the drill at the outer end of the groove and thus pack together, endangering breakage of the drill, and the brazing material also tends to tear out in part, leaving a rough surface restricting escape of the chips and further tending to cause the same to packaround the drill.

In both of the conventional methods above described it is substantially impossible or at least commercially impractical to employ them in the production of oil hole drills smaller than 2; of an inch in diameter, particularly where the drills are of such length as compared to their diameter as to come within the classification of long drills. The reason is that in drills produced by the first method it requires a relatively long hole to be drilled by a relatively small diameter drill making it substantially impossible to prevent run out of the drill and involving a large number of breakages of the drills employed for drilling the oil holes. the slot required for reception of the oil hole tube makes it altogether impossible to employ the method on smaller drills and on those slightly larger reduces the torsional strength of the drill to such an extent as to render them unsuitable for use.

Drills made in accordance with the present invention may be produced at a materially smaller cost than in either of the two methods previously described; the present invention is applicable to the manufacture of oil hole drills of a diameter materially smaller than possible in accordance with previous practices, and this regardless of length; and tests indicate that the resulting drillv itself is of greater strength torsionally than drills constructed in accordance with previous practices. i

In accordance with the present invention the drill blank is provided with the flutes desired in the finished drill and which fiuteswill, of course, usually be spirally arranged around the axis of the drill. One or more relatively deep grooves are provided in the outer peripheral surface or lands of the drill blank, preferably in the same spiral relation as the flutes therein and preferably in parallel relation to a marginal edge of the corresponding flute. These grooves and the flutes may be formed simultaneously with each other or either one prior to the other. The grooves thus formed thus correspond in a measure to the grooves formed in the drill blank according to the second conventional method above described and which insuch conventional method is adapted to receive a tube which will later serve as an oil hole. In the broader aspects of the present invention the groove or grooves thus formed in accordance with the present invention in'the drill blank may also serve to receive such a tube. but inasmuch as its use would be more or less superfluous and is not required for the practice of the present invention it will ordinarily not be employed. Regardless of whether or not such tube is employed the. blank thus fluted and grooved is subjected to a suitable operation whereby metal of the drill blank at and adjacent the lands thereof is caused to flow or otherwise be displaced towards the center of the groove or grooves adjacent the periphery of the blank and so as to completely close the outer edges of such grooves without causing the bottom portions of the grooves to be likewise closed. As will be apparent by this operation the grooves are automatically formed into peripherally walled openings open only at the opposite ends of the drill blank, thus provid ng the oil holes desired in the finished product. the metal at the surface of the lands into the The operation of displacing- In the second method the relative size of open edges or tops of the grooves may be employed for simultaneously forming part or all of the usual body clearance provided in suchv drills back of the cutting edges or margins, this metal flowing or displacing steps thus serving a dual purpose. Once the open edges of the grooves have been closed the drill blank may be completed in accordance with conventional practice.

It may be mentioned that while the step of closing the open edges of the grooves as above described in accordance with the present invention in the broader aspects of the invention may be accomplished in any suitable manner as for instance by peening, swaging or the like, it is preferably accomplished by a suitable rolling operation and-by the use of which the surface layer of metal over part or all of the body clearance area of the drill is compacted and densified. This 'densiflcation of this surface portion of the drill tices of the present invention in this respect has a greater resistance to breaking under torsional strains than ordinary types of drillsnot provided with oil holes and constructed from the same material. The present invention, however, is not concerned with the drill itself as an article, but

only to the method of manufacturing the same.

Referring to the drawings and particularly to Fig. 1 a drill is shown comprising a body indicated generally at 20 and a shank 22, the shank 22 inthis case being a so-called straight or cylindrical shank. The body 20 is provided with a pair of diametrically opposite conventional flutes 24'arranged spirally of the axis of the drill, there being a corresponding number of lands 26 separating. the flutes 24. The lands 26 are each provided with a cutting edge or margin 28 along holes 20a.

that edge thereof more advanced in the intended direction of rotation and the remainder of the lands are radially inwardly relieved with respect to such margin or cutting edge to provide the usual body clearance. That portion of the body 2001' the drill between the flute 24 and below each land 26 is provided with a so-called oil hole'30, the oil holes 30 extending from the point 32 of the drill in the same" spiral relation as the flutes 24 into the shank 22 where they open into enlarged centrally arranged openings or pockets 34 provided therein. It will, of course, be understood that in actual practice the chuck or other fixture which receives and supports the shank 22 of the drill is provided with suitable means for applying a suitable liquid to the interior of the opening 34 from which it will flow through the oil holes 30 to the point32 of the drill forthe purposes above described.

v A modified-arrangement for introducing liquid The drill illustrated in.Fig. 21s substantially identical to the drill illustrated in Fig. 1 except for' the shank portion thereof. Accordingly, like numerals illustrate like parts except that such ance with conventional practice.

numerals bear a prime mark. The shank 22' in this case instead of being cylindrical is tapered or formed as the frustur'n of a cone and its extreme'end is provided with a tang 36 in accord- The oil'holes 30 in this case instead of opening into an enlarged opening or pocket in the shank .22 are each connected adjacent the junction of the main body 20 with the shank 22' with a corresponding straight opening 38 extending in axially parallel relation through the length of the shank 22' and opening on the outer end of the tang 36. As will hereinafter be obvious it makes no difference what type of shank is provided on a drill orwhatmethod is followed in supplying liquid to the oil holes in the drill in accordance with the present invention, but for the purpose of ease in description only, unless otherwise specified, it will hereinafter be considered that the type of drill shown inFlg. l is the one referred to in the following description.

As previously mentioned it makes no difference in accordance with .the broader aspects of the present invention whether or not the flutes and grooves. are formed simultaneously with each other, whether the flutes are formed previouslyto the grooves, or whether the grooves are formed previously to the flutes and this fact is to be kept in mind, in thefollowing description and claims even though, for'the reason of simplicity in description, it will be assumed that the flutes are formed first and thegrooves afterwards.

In making the drill shown inFig. 1 a suitable length of cylindrical stock is first prepared, corresponding in length and diameter to the desired finished drill. In such cases this piece of stock may comprise, for instance, a body portion corresponding to the body portion 26 of high speed steel and a shank portion corresponding to. the

shank 22 of low carbon or other suitable steel.

vention the flutes 24 may be first formed straight, .and likewise the grooves, and that the body of the drill later twisted to the desired spiral, but inasmuch as this would involve an additional and unnecessary step it will be assumed that the flutes 24 will be formed in the blank in the same spiral relation as desired in the finished product by any suitable or conventional method as, for instance, by a milling operation. In such case after the flutes 24 are formed in the blank the cross-sec-.

tlonal conformation of the'body portionof the blank will he that illustrated in Fig. 3.

The next operation is to. form one or more grooves 4|! in the blank and which may be accomplished in any suitable manner as, for in-' imately equal to half the radius of the blank.

The bottom of the grooves 40 are preferably rounded or'of semi-circular conformation and the width of the grooves 40 equal to the diameter of the oil hole desired in the ultimate product particularly where, as is desirable, no separate oil hole tube is to be employed. As illustrated in Flg. 5 the grooves 40 extend from the point 32 into that end of the shank 22 which joins the body 26 and, being centrally located with respect to their corresponding lands 2B are, accordingly, arranged in spiral formation in approximate par allelism with the adjacent margins of the flutes 24. 1

The next operation consists in working the metal adjacent the surface of the lands 26 into the outer edges ofthe grooves 40 so as to completely close such outer edges while still leaving the inner or bottom portions of the grooves 411 open thereby to provide oil holes. If for any reason whatever it is desired to employ oil hole tubes, it will be understood that these tubes would be positioned in the bottoms of the grooves 40 previous to the operation of closing the outer edges of the grooves disclosed in Fig. 6.

In the broader aspects of the present invention the metal at and adjacent the surface of the lands 26 may be worked inwardly towards the corresponding grooves 40 to close the outer edges thereof in any desired manner as long as the operation effects the purpose of closing the outer edges of the grooves. The working or flowing of the surface metal-of the lands 26 to close the grooves is preferably accomplished by a rolling operation as illustrated in Fig. 6. In carrying out this operation a pair of rollers 42, each peripherally shaped to accurately fit one of the grooves 24, are engaged in the grooves 24 and are pressed firmly toward one another therein. The purpose of the rollers 42 is twofold in that they not only serve to guide and turn the blank in its passage therethiough but also, where located sufficiently 'close to the metal displacing rollers aid in preventing displacement of the metal of the blank into the flutes 24 during the rolling operation. A second pair of rollers 44 are provided in alternate relation with respect to the rollers 42. The rollers 44 are each provided with a concave sectioned peripheral portion 46 of a curvature preferably corresponding with the curvature of that portion of the final product providing the body clearance back of the cutting edge or margin 26, and bevel side faces 48. Means are provided. for urging the rollers 44 toward one another.

It will be appreciated that when the rollers 44 are'flrst brought into engagement with the lands 26, they will bear against the corresponding lands 26 only at the junction of the curved faces '46 with the bevel faces 48, this being because of the fact that under such circumstances the radius ofthe faces 46 will be less than the radius of the outside diameter of the blank. Accordingly, when pressure is applied to the rollers urging them toward one another there will be a tendency for the metal between the outer margins of the curved faces 46 to be crowded centrally inwardly and because the rollers 44 are arranged centrally of their corresponding grooves 40, to crown such metal into the open outer edges of the grooves toclose the same. With suitable pressurethusl'applied to the rollers 44 the blank is drawn between ers 42 and 44 until the rollers 44 have been imbedded in its surface a sufficient extent to completely close the outer ends of the grooves and thereby provide the oil holes .30 therein as well as to provide a suitable amount of body clearance over the width of the rolls 44.

After the operation disclosed in Fig. 6 is completed the drill blank is removed from between the rollers 42 and 44, the opening 34 may be machined in the shank 22 and suitable holes drilled through its bottom end to connect the interior thereof with the oil holes 30, and where only one margin 28 on each land 26 is desired and as ordinarily will be the case in connection with the drills for drilling metal, the projecting portion of the land at its trailing edge may be removed as indicated in Fig; '7, and the drill hardened, ground or otherwise acted upon to bring it to its final con dition.

It will, of course, be understood that where the form of construction shown in Fig. 8 is desired, the rolling operation disclosed in connection with Fig 6 will close the grooves 40 over all their length except that small end portion thereof in the shank which is adapted to later form the inlet openings 35, and in such case no subsequent op-- eration of drilling through the free end of the shank to provide communication with the correspondingends of the openings 30a is required.

It may be stated at this point that where the operation disclosed ,in Fig. 6 is properly carried out, the metal which is displaced over the open ends of the'grooves 4b to form the openings all is so densified and compacted, as will be appreciated by those-skilled in the art, as to impart a materially added stiffness to this portion of the drill. This is particularly true where this metal is worked cold, in other words where no artificial heating of the drill blank is resorted to during the operation disclosed in Fig. 6, and tests have shown that under such conditions the resistance of the drill to breakage under torsional strains is smaller drills, it may be found necessary to preheat the drill blanks before the operation described in Fig. 6 is carried out so as to enable a proper flow of the metal over the open end of the grooves to be obtained. The temperatures to which the blank is heated in such case is preferably approximately those temperatures to which the material from which the drill body is made requires for usual normalizing treatment. It will be understood, however, that even though it is necessary to bring the drill blank to a suitably high temperature before the operation illustrated in Fig. 6 is carried out, the surface portion of the lands which is displaced into the outer edges of the grooves 40 will be densified or compacted in a manner similar to'that occurring when the operation is carried on cold. It may also be noted that the line along which the metal is joined at the outer ends of the grooves will be substantially imperceptible in the finished product and that the entire surface portions. of the lands will be hard and smooth in the finished product so as not to engender packing of chips in operation.

Although forming no part of the present invention, in Figs. 9, 10 and 11 apparatus of a type suitable for carrying out the step of operation illustrated in Fig. 6 is shown. This apparatus is a machine including a flat base 50. At one end outer ends of which bear against the lower ends of the base 50 is a sub-base I extending centrally across which is an integral upwardly extending wall 52 having triangularly shaped webs 58 at its opposite ends extending between it and the sub-base 5I. A pair of upwardly extending post members 54 are vertically adjustably secured to the forward face of the wall 52, as viewed in Fig. 8, at opposite ends of the wall, by bolts 55 through slots 55 in the post members. The upper ends of the members 54 are provided with aligned horizontal openings 51 in each of which a plunger 58 is slidably received. The plungers 58 are each of its corresponding roller 44 which is pivotally mounted thereon by means of a suitable pin- 68. 1 The posts 58 are so maintained by the respective collars 59 and pins 62 that the corresponding rollers 44 are arranged for contact with the drill blank passing between' them at an angle corresponding to the helix angle of the flutes in the drill blank.

A pair of supports I0, one fixed to, the wall 52 and the other directly to the sub-base 5| respectively above and below the axes of the posts 58 are provided with aligned openings 12 therein the axes of which may be arranged in intersecting relation with respect to the axes of the openings 54 but which as shown are arranged slightly ofiset therefrom to insure ample clearance between the rollers 44 and 42. Each of the supports I0 threadably receive a post I4, the posts I4 extending towards one another and having their adjacent ends coned and slotted as at I6 for reception of the corresponding rollers 42 which are supported thereon by means of pins I8. The

posts I4 are turned in their supports 10 so as to cause their respective rollers 42 to be skewed an amount to correspond with the "spiral of the flutes 24 in the particular drill blank to be acted upon and they are locked in this rotatably adjusted position by means of lock nuts 80 and set is provided. Each end of the wall 52 is provided with an outwardly projecting centrally slotted support 84, vertically offset from the centers of the posts 58 and in which a lever 88 is pivotallymounted midway between its endsby means of a pin 80. The upper end of each lever 88 extends over the outer end of the corresponding post 58 and is there provided with an adjusting screw 90 adapted to bear against the outer end of the corresponding post 58 centrally thereof. The screws 82 may be locked in their adjusted posi- .tion by means of lock nuts 94. As will be best observed from an inspection of Fig. 10 the levers 88 extend downwardly at an angle and their lower ends lie outwardly of'corresponding webs' 58 arranged at opposite ends of the sub-base 5|. Between the webs 88 a pair of spaced bosses 98, best shown,in'Fig.'9. are arranged on the sub-base 5| and aligned openings are provided in the webs 1 58 bosses 88. In the thus aligned openings in each web 58 and its corresponding boss 88 is axially slidably received a post or pin I00 the of the corresponding levers 88.

Rotatably supported upon a pin I02 between the bosses 88 in eccentric relation with respect to the posts I00 is a cam member I 04. The cam I member I04 is an axial type of cam, that is its peripheral portions which extend between the opposed ends of the posts I00 vary in thickness in a circumferential direction. The cam I04 is provided with an operating lever I06 which upon being operated to rotate the cam I04, will have the tendency to move the posts I00 outwardly where the cam I04 is turned to bring a portion of increasing thickness between them. Thus it will be understood that if the cam I04 is turned by the handle I06 to bring a narrow portion of the cam between the opposed ends of the post I00,

screws 92 will move the posts 58 and consequently the rollers 44 toward each other.

As indicated in Figs. 9 and 10, at the end of the base 50 opposite the apparatus thus described is secured a support IIO provided with an opening II2, preferably rectangular in section, disposed with its axis in the same horizontal plane as the axes of the posts 58 and with its axis in the same vertical plane as the axes of the posts N. A rack H4 is reciprocably received within the opening II2 andwithin the support I I0 lies in mesh with a pinion I I6 secured to a shaft I I8 having bearing in the support H0 and receiving at its outer end a hand wheel I20. As will be apparent rotation of the hand wheel We acting through the shaft IE8 and gear H3- Will cause reciprocation of the rack H4 in the opening IE2.

The inner end of the rack H4 is provided with a suitable anti-friction bearing 22, preferably of the combined radial and thrust type,,upon which is rotatably mounted a chuck I24 of a type suitable for receiving and holding the shank end of a drill blank with the axis of he drill blank in a horizontal plane including the axes of the posts 58 and in a vertical plane including the axes of the posts I4.

With the apparatus thus described and assum-- ing that it is desired to employ it to carry out the operation previously described in connection with Fig. 6, a drill blank of the stage of completion illustrated in Fig. 5 is secured at its shank end within the chuck I24 at a time when the chuck I 24 has been moved to or adjacent the extreme limit of its movement in a direction to the right as viewed in Figs. 9 and 10. The handle I I06 of the cam I04 is then moved so as to permit the rollers 44 to be separated from each other .a required amount to permit insertion of the drill blank between them. It may be assumed that the posts 14 have previously beenadjusted so as to place the rollers 42 at an angle corresponding to the flutes 24 of the drill blank and soas to be closely received within such flutes and that theposts 58 have been previously adjusted to bring the rollers 44 at an "angle corresponding to the angle of the flutes 24 in the drill blank. The hand wheel I20 is then operated tocause the outer end of the drill blank to be inserted bedesired amount, and then the hand wheel I20 is turned to cause the drill blank to pass axially between the rollers 42 and 44, the rollers 42 acting through the flutes 24 to turn the blank about 5 its axis and the rollers 44 acting upon'the lands of the drill blank to displace the metal in the previously described manner in a direction. tending to close the open ends of the grooves 40. The drill blanks may be caused to pass back and forth between the rollers 42 and 44 any desired number of times required to obtain the full penetration of the rollers 44 into the drill blank, the cam I04 being turned at the end of each pass to obtain a further penetration. In the smaller size of drill one or two passes at the most may be all that is required to obtain the desired penetration of the rollers 44, the number of passes required usually increasing with increased diameter of the drill.

It will be understood that the other operations required on the drill blank to bring it to its completed form may all be of a conventional nature and, accordingly, do not require a showing of the apparatus designed to effect them.

It will be understood that the specific method of and apparatus for closing the outer edges of the grooves 40 in the blanks described are illustrative of only one method among many which may be found suitable for use'for carrying out this particular step of the present invention and, accordingly, the present invention in its broader aspects is not to be interpreted as being limited to this specific method and apparatus of closing the aforementioned grooves. be understood thatjormal changes may be made in the specific steps and sequence of steps of operation described, as well vas apparatus for carrying out such steps, without departing from the spirit or substance of the broad invention, the scope of which is commensurate with the appended claims.

What I claim is:

1. In the formation of an oil hole drill, the step of forming a generally cylindrical blank Patent NO. 25 148 ,8 5"

Accordingly, it will CERTIFICATE or CORRECTION.

STUART A. COGSDIIL. It is hereby certified that error appears fl n the printed specification having a plurality of spirally arranged angularly spaced flutes in the outer surface thereof and a correspondingly spirally arranged groove in at least one of the lands between a pair of said flutes, then working at least a portion of the surface layer'of said land first in a generallycircumferential direction toward the center of said groove and then radially of said blank while the walls of said groove are totally unsupported, said groove being of sufiicient depth whereby the said working of said surface layer closes the open side of said groove without completely filling said groove, that portion of said surface thus worked being exclusive of the cutting edge of said land whereby said portion of said land thus worked provides a relief for said drill behind said cutting edge.

2. In the manufacture of an oil hole twist drill including a metal displacing operation between rolls, the steps of operating upon a cylindrically shaped metal blank to provide a plurality of spirally arranged flutes therein, operating upon said blank to provide a groove in a land thereof between an adjacent pair of flutes and for a length commensurate with. the length of said flutes, inserting said blank between said rolls, forcing said rolls radially inwardly against the surface of the lands of said blank with at least one of said rolls in bridging relation with respect to said groove while the walls of said groove are totally unsupported, efiecting relative reciprocation between said blank and said rolls axially of said blank and simultaneously guiding said blank for rotational movement about its axis through cooperation with said flutes whereby to radially contract the dimension of said blankv between said rolls and urge a portion of the metal acted upon by said rolls into the open edge of said groove'to close the same, said groove being of such depth that said rolling operation closes the open edge thereof Without closing the bottom thereof.

STUART A. COGSDILL.

February as, .19 9.

of the above numbered patent requiring -'correction follower Page i first.

column, line 65, for the word "crown"read crowd; and second colunn', line 52, for "temperatures" read temperature; and'that the saidLetters Patent should be read with this correction therein" that the same may. conform the record of the case in the -P'atentoffice. v I I I Signed and sealed this 18th day of li r11, A.Ia.- 1959--.

(Seal) 'HenryVan Arsdale Acting commutator-er Patente-

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