US3163872A - Method of forming spiral thread lock - Google Patents

Description

Jan. 5, 1965 ROSAN ETAL 3,163,872

METHOD OF FORMING SPIRAL THREAD LOCK Original Filed July 25, 1960 3 Sheets-Sheet 1 I a6 48a.

INVENTOR.

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INVEN TOR .Zs K7607! a. db arm/1M5? Jan. 5, 1965 J. RosAN ETAL METHOD OF FORMING SPIRAL THREAD LOCK 3 Sheets-Sheet 3 Original Filed July 25. 1960 INVENTOR. I I o se Krsarz BY J7Z ertJZi/ [z 75m? MUG/EVE? amma United States l atent O 3,163,872 WTH'SD F FORMING SPIRAL THREAD LGCK Jose Rosin, San Juan Gapistrano, and Albert Jack La Torre, Santa Ana, Calif assignors to Rosz'm Engineering Corporation, Newport Beach, Calif., a corporation of California Qriginal application Juiy 25, 1960, Ser. No. 45,855, now Patent No. 3,081,808, dated Mar. 19, 1963. Divided and this application Aug. 28, 1961, Ser. No. 134,282 9 Claims. (Cl. -86) This is a division of application Serial No. 45,055, filed July 25, 1960, which issued into Patent No. 3,081,808 on March 19, 1963.

The present invention relates to a method of making a threaded insert with a spiral thread lock. This invention finds particular usefulness in making the inserts described in the aforesaid Patent No. 3 ,081,808.

The present inserts ditfer from all prior inserts in that they have a side wall of less radial thickness than that found in any prior inserts. The present inserts are further characterized by having higher strength characteristics, greater hardness and greater ductility than is found in any prior inserts. It has been found that very thin walled inserts made in accordance with the teachings disclosed hereinafter, will develop a holding power markedly superior to that of previously known, relatively thick walled inserts of the same internal size.

Inserts made in accordance withthe principles of the present invention and having internal and external threads are designed so that the external threads are one size larger than the internal threads; the external threads preferably being made less than full standard depth in order to provide an uninterrupted thin-walled, radially flexible column between the internal and external threads.

One of the principal features of the present inserts is that the inserts made by this method not only embody means for permanently locking the inserts against rotation in the threaded bodies or members in which they are mounted, but also may embody internal locking threads for preventing a bolt, stud, or other. fastener mounted therein from becoming loose under conditions of excessive vibration. In this connection, the internal lock is formed by slightly depressing the root of one or more convolutions of the external thread in a spiral pattern conforming to said one or more convolutions to correspondingly modify the internal thread by reducing its diameter to form locking threads providing an interference fit with any fastener mounted therein.

Another advantage of the present invention is that the internal locking threads can be formed at any desirable point along the length of the inserts, or the inserts may be provided with locking threads at a plurality of points along their length.

Accordingly, the principal object of the invention is to provide a method of making a one-piece lockable insert, and a method of providing an internal locking thread in an insert.

Another object is to provide a method of making an insert having internal locking threads and flexible side walls providing unusually high wear resisting characteristics enabling a fastener to be mounted in and removed from the insert a great number of times without damage to the internal locking threads, and without reducing the effectiveness of the locking action of the internal locking threads.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a greatly enlarged quarter sectional view of an insert embodying the principles of the present invention;

FIG. 2 is a plan view of the insert of FIG. 1;

3,163,872 Patented Jan. 5, 1965 FIG. 3 is a fragmentaryvertical sectional view through a body having a threaded bore that is counterbored at its outer end and adapted to receive the insert of FIG. 1;

FIG. 4 is an elevational view, partly in section, of. an

insert having an internal thread lock and a modified driving groove arrangement;

FIG. 5 is a quarter sectional view of an insert of the type shown in FIG. 1, but modified to include axially spaced internal locking threads;

FIG. 6 is an elevational view of a standard stud threaded at both ends; I

FIG. 7 is a view showing the stud of FIG. 6 mounted in the insert of FIG. 5, the insert being shown in crosssection;

FIG. 8 is a diagrammatic vertical sectional view of an insert of the type shown in FIG. 4 disposed between the plate dies used for rolling the locking thread in the insert; a

FIG. 9 is a greatly enlarged diagrammatic view illustrating a portion of the insert of FIG. 8 and a portion of the die that rolls the root of an external thread to form the internal locking thread, the latter being indicated in dotted lines;

FIG. 10 is a diagrammatic sectional view illustrating a step in another method of rolling the external thread prior to forming a locking thread within the insert;

FIG. 11 is a diagrammatic sectional view illustrating the step of rerolling the external thread to form the internal locking thread;

FIG. 12 is a greatly enlarged diagrammatic view of a portion of the insert and die that rolls the internal locking thread. 7

Referring to FIGS. 1 and 2, the new insert is generally identified by the numeral 10 and comprises a tubular body 12 provided with external threads 14 and internal threads 16. The external threads 14 have a major or crest diameter indicated by the dimension A, and a minor or root diameter indicated by the dimension B. The external threads 14 are shallower in depth than a standard thread of the corresponding size and pitch, so that the diameter B of the thread root 15 is larger than the root diameter of a standard size thread, as will be explained more fully hereinafter. The internal threads 16 have a major or root diameter indicated by the dimension C and a minor or crest diameter indicated by the dimension D. The diameters C and D correspond to those of a standard size thread. In other words, the internal threads 16 are preferably unmodified in order that they can receive any fastener provided with corresponding standard threads.

The insert 10 has a radial wall thickness E equal to /2(B-C) that is substantially less than has been provided heretofore in inserts of the same general type. Such thin wall construction has been made possible by forming the insert 10 with external threads 14 one size larger than the internal threads 16, and preferably modifying the external threads 14 by making their depth substantially less than standard depth.

According to the present invention, the external threads 14 have a radial depth less than the standard depth. The use of a modified external thread makes it possible to maintain a continuous thin wall or column 18 of minimum thickness E throughout the internally threaded length of the insert. The insert 10 has a counterbore 20 at its upper end 22 of a depth equal to about twice the pitch of the external threads 14, but this depth may be varied as desired. The counterbore 20 is formed by a cylindrical wall 24 and a beveled Wall 26 extending on an angle of 45. The wall 24 has a. diameter F that is preferably a feW thousandths of an inch larger than the root diameter C of the internal threads 16, so that a thin expandable wall 28 having a radial thickness of a dimension G is provided at the outer end of the insert.

Thus, the expandable wall 28 is slightly thinner than the column wall 18.

The internal threads 16 are intersected by six longitudinal V-shaped grooves 30 defining a hexagon shaped recess within the insert and adapting the threads 16 to be engaged by a hexagonal drive member of corresponding shape and'size for driving the insert into a threaded bore. The sides 32 of the grooves 39 intersect an angle of 120-", and the distance across the flats of the hexagon has the dimension LFIG. .2. The diametrical distahce between the apices of the grooves 39 is represented by the dimension J. The grooves 30 need not extend for the full length of the inser-t 10 and may be terminated at any desired depth; The external threads 14 in the region of the counterbore 20 are knurled or longitudinally serrated through at least two convolutions to provide relatively sharpte'eth 34 for engaging a surrounding body to form a permanent lock therewith. The teeth 34 have sides of volu'te shape due to the formation thereof by serrated rollers (not shown). The lower end of the insert 10 is chamfered internally and externally on an angle of about 30, as indicated at 36 in FIG. 1. The knurling operation raises the crest of the threads 14 in forming the teeth 34, so that the diameter K across the points of the teeth is a few thousandths of an inch greater than the original crest diameter A.

As has been indicated. above, it is preferable to make the external threads 14 shallow, or of less than standard depth. In accordance with the present invention, it is also preferred to make the threads 38, FIG. 3, in the insert-receiving bore 40 in a parent body 42 less than standard height, in view of the following:

If theshallow-depth external threads "14 are used with an unmodified bore thread, excessive torque would be required to mount the insert 10 in the bore, due to the interference between theorests of the bore threads and the root of the external threads 14. In addition to excessive torque, there would be the possibility of distorting or crushing the thin-walled inscrt'while it is being mounted in the bore. In the, case of mounting the insert in Plexiglas, Lucite and other plastic materials, the excessive stress concentration would cause crazing in the plastic. In order to avoid the foregoing 'difiicnlties, the bore 40 to receive the insert 10 is drilled with a tap drill of a dimension larger than would normally be used in providing a bore to be tapped for a standard thread corresponding to the size of the external threads 14 on the insert. Accordingly, and as is shown in FIG. 3,

the body of parent material 42 is drilled to provide the bore 40 having a dimension L. The outer endof the bore 40 is provided with a counterbore 44 having a cylindrical Wall 46 of a diameter M and a beveled wall 48 extending on an angle of about 30. The diameter M is such as to receive the locking teeth 34 with a mini? mum of radial clearance. Hence, the diameters K and M are made almost equal.

It is not essential that the bore .40 be 'counterbored since the present insert can be used with a bore that is threaded throughout its length. In such case, the points of the teeth 34 may engage the root of the threads, but this would not be objectionable since the teeth would ream out the root to make their own way, if necessary. In either instance, the diameter L of the drilled bore 40 is made greater than the crest diameter of the corresponding standard thread size, so when threads, 38 are tapped in the bore 40, the crests are truncated. as indicated at 48a in FIG. 3, respectively.

The diameter of the bore threads 38 is such that the crests 48a do not engage the root 15 of the external threads 14 of the insert 10. The clearance thus provided eliminates stress concentration in these areas. Thus, it is simpler and more practical, in the interest of providing the thin wall 18 in the insert 10, to adapt the bore 40 in the body 42. to receive a modified external thread 14 (by using an oversize tap drill for the bore 40) rather 4 than modifying the internal threads 16 of the insert 10 so that only special fasteners could be used therewith.

It will be understood, of course, that the advantages of the insert 10 can be realized by following the less desirable practice of making the internal threads 16 shallow and using a standard external thread 14.

In making the insert 10, a solid rod or bar of stock (not shown) of suitable met-a1 is center-drilled at one end, and a portion of the end is rough turned and then finished to the desired outside diameter A, as can be readily visual: ized. The external threads 14 are then rolled into a predetermined length of the rod. From one of three convolutions of the threads 14 at the threaded extremity of the rod are next knurled to form the teeth 34, The rod is then rough drilled to provide a bore 16a and the finished counterbore 2-0. The bore 16a is then finish.- reamed to the minor diameter D of the internal threads 16. The rod is then cut oil by a parting tool at the end of the threaded portion remote from the teeth 34. The work piece is then finish-faced, and internally and externally chamfered as, shown at 36,.at the end remote from the counterbore 20.

The cut off work piece in the foregoing state is then rough-tapped to remove a major portion of the metal that will form the internal threads 16, and is then broached to provide the driving grooves or flutes 30. The internal thread 16 is then finish-tapped, completing machining of the insert 10 of FIG. 1, which is then heat-treated to give it a hardness of 40 to46 on the Rockwell C scale.

It will be noted from the foregoing that the teeth 34 are formed before'the bore 16a is drilled and the counterbore 20 is formed. This procedure assures good knurling without distorting or damaging the insert material.

FIG. 4 illustrates a modified form of insert 49. The insert 49 also differs from the inserts previously described herein in that it is provided with a unique internal IQCk'. ing thread 50 located at a point about midway of the height of the insert and extending through about 1 /2 convolutions of the internal 51 The internal look: ing thread 50 provides a loci; for any threaded fastener that is mounted thereon. The manner which the loch-1 ing thread 50 is formed will be described in detail later.

FIG. 5 shows an insert 52, similar to the insert 10, but :wherein the root of the external thread 14 has been depressed at longitudinally spaced points to provide two internal. locking threads 50. The locking threads 50 are preferably located beyond the second convolution Of the internal lead thread 16 in order to enable a fastener to have a substantial start in the insert enga ing before the locking thread 50. Any number of locking threads 50 may be provided in the insert, depending upon the length. of the insert. It will be obvious, of course, the more locking threads that are provided, the greater will be the torque resistance oflfered by the insert to backing out of a fastener. The use of two locking threads, as shown, doubles the locking elfect of the single thread shown in FIG. 4.

The insert 52 is especially adapted to be used with a standard stud '53 of the type shown in FIG. 6, which has threads 54 and '55 at its opposite ends. FIG. 7 shows the insertSZ mounted upon the threads 54 at the lower. end of the stud 53. The internal locking threads '50 effectively lock the stud 53 against turning, so that when the insert 52 is locked in a parent body, the stud 53 may be removed without backing the insert out of the pawn bQdY- More? over, any fastener, such as a nut, mounted upon the threads .55 can be removed without backing the stud 5 3 out of the insert 52.

The locking threads 54} are preferably formed in the insert 49, FIG. 4, after it has been otherwise completely machined and heatstreated to harden the same. This has the advantage that the dimensions of the locking thread 50 can be held to close tolerances since no size deviation is introduced by subsequent heattreatnient. The lock: ing threads 50 are formed by a cold-rolling operation.

FIG. 8 diagrammatically illustrates the manner in which the locking thread 50 is formed. Thus, an insert such as the insert of FIG. 1, is placed between a pair of die-rolling plates 56 and 57. The plate 56 is similar to the plate originally used to roll the shallow external thread 14, except that the thread forming ridges 58 are ground off so that they do not engage the root of the external thread 14, but clear the same by a few thonsandths of an inch. No change is made in thesides of the ridges 58. Hence, they engage and support the flanks of the thread 14 against distortion during the rolling of the locking thread 50.

The die-plate 57 is positioned on the opposite side of the insert 10 and is provided with a single ridge 59 located at the point where the locking thread 50 is to be formed in the insert. The ridge 59 is of slightly greater height than the ridges on the die-plates previously used to form the threads 14 and may have the configuration of a die for forming a thread of standard depth. The sides of the ridge 59 are preferably parallel with the flanks of the threads 14 but may be relieved slightly to permit drawing in of the metal during rolling. The difference in angle may be about one degree at each side, so that the angle of the sides of the ridge 5? is about 58, compared with the 60 angle of the threads 14. The foregoing relation is diagrammatically shown in FIG. 9 wherein a portion of the insert 10 and a portion of the die-plate 57 are shown to greatly magnified scale. It will be noted that the face of the ridge 59 is narrower than the root 15 of the thread 14 so that a distinct, depressed, spiral pattern groove 6% having the contour shown in dotted lines is formed in the rotor.

During the rolling of the locking thread 58, the dieplate 56 supports the flanks of the thread 14 to prevent distortion thereof, while the die-plate 57 applies pressure to the insert 10 to depress the root 15 inwardly about .001", or more, depending on the diameter of the insert, to the depth indicated by the dotted line 64 As the dieplate 57 is pressed toward the insert 10 and moved relative thereto, the ridge 59 in depressing the root 15, as indicated above, will cause a corresponding portion of the internal thread 16 to be deformed inwardly to reduce its crest diameter and form a locking thread 59, the typical distortion and contour of the internal threads 16 being indicated by the dotted line 61. In view of the fact that the external threads 14 and the internal threads 16 have a diiferent pitch, the rolling of the root 15 of the external thread effects a slight change in the lead of the locking thread 50, as illustrated, which enhances the locking action of the thread.

During the rolling of the locking thread 51), the insert 10 is preferably rotated through about 1 /2 turns, so that locking thread 50 extends through about 1 /2 convolutions of the internal threads 16. The locking thread 50 may extend through two convolutions, but preferably not less than one. Extending the locking thread 56) through an angle in excess of 360 will avoid unequal pressure on the locking thread and insure a uniform resistance to rotation of a fastener throughout the periphery of the fastener. Consequently, a uniform torque is required to turn the fastener relative to the locking thread 50.

One of the unique features of the locking thread 5t combined with the resilient, ductile side wall construction of the present insert is that the insert is capable of breathing or yielding and expanding when the locking thread is engaged by a fastener. Torque tests have shown that the present insert has the unexpected and unusual characteristic of requiring breakaway torque equal to the drive torque applied to the fastener, and in some instances the breakaway torque has exceeded the drive torque. In prior fasteners, the breakaway torque is ir1- variably only a minor fraction of the drive torque. Hence, the present insert is far superior to all prior inserts in resisting loosening under conditions of severe vibration.

FIGS. 10, 11 and 12 diagrammatically illustrate another method of forming a locking thread 50 in the insert 10. FIG. 10 illustrates one end of a piece of bar stock X having a center drill Y formed in one end thereof and engaged by a lathe center Z, the latter being shown in dotted lines. The external thread 14 is formed in the bar stock by one or more rollers or dies 62. The die 62 shown has ridges 63 that roll the major portion of the length of the external thread 14 to the desired shallow depth. A single ridge 64 on the die 62 is of less height than the remaining ridges 63, so that about 1 /2 convolutions, indicated at 65, are shallower than the remaining root portions 15 of the external thread 14.

The additional machining operations on the insert 10, described in connection with FIG. 8, are then performed upon the bar stock X, so that the resulting insert 16X has the structure illustrated in FIG. 11. The insert 10X is heat-treated to harden the same in the same manner as the insert 10. After heat-treating, the external threads 14 are rerolled by a cold-rolling operation to form the internal locking thread St). The rerolling is preferably effected by die plates 56'. and 57 which, as in FIG. 8, do not engage the teeth 34 of the serrated threads. These die plates have ridges 58' all. of which are of the same height, so that during the rerolling operation, the shallow root portion 65, see FIG. 12, is depressed inwardly from the position indicated in dotted lines to the full line position marked 65', which corresponds to the depth or root diameter of all of the remaining external threads 14. During the rerolling operation, both die plates 56 and 57 cooperate to effect displacement of the root portion 65, and simultaneously support the flanks of the remaining external threads 14 against distortion. As the die plates 56 and 57' apply pressure to press the root portion 65 inwardly, the ridges 58' cause a corresponding portion of the internal thread 16 to be deformed inwardly to reduce its crest diameter and form the locking thread 50, the distortion of the internal threads it being indicated by the dotted lines 61. The rolling of the root portion 65 of the external thread 14 effects a slight change in the lead of the locking thread 50, as shown, which enhances the locking action,

The method of forming the locking thread 50 illustrated in FIGS. 10, 11 and 12 has the advantage over the method illustrated in FIGS. 8 and 9, of providing an external thread 14 wherein the root diameter is uniform throughout the length of the insert.

It will be understood that any one of the internally threaded inserts disclosed herein can have one or more locking threads formed in the interior thereof. It will also be understood that while certain inserts have been shown mounted in a bore of a certain type, any given insert can be mounted and used in any other type of bore shown herein.

It will also be understood that the principle of making the external thread larger than the internal thread by one thread size is applicable to both fine threads and coarse threads. However, by way of illustration and not limitation, the following example is given relative to a finethread insert having a 4 inch internal thread with 28 threads per inch, and a inch external thread with 24 threads per inch. Such an insert will have the following principal dimensions, which should be considered in connection with FIG. 1, and'with the understanding that they will vary within acceptable tolerances:

It will be noted from a comparison of the minor diameter B of the external thread 14 with the major diameter C of the internal thread 16 that the side wall 18 of the insert is about 0.0117" thick. In the smallest and thin nest inserts made in accordance with this invention, it is preferred to maintain a minimum side wall thickness of not less than 0.008" with a preferred minimum thickness of 0.011. It is to be understood, however, that this side wall thickness will vary with the sizes of internal and external threads employed in the inserts. Hence, the minimum thickness may exceed 0.020" in some inserts, but in any event, the side wall thickness in each insert will be substantially thinner than in prior inserts of the same internal thread diameter.

Other typical thread combination sizes of internal and external threads that may be used for the present insert are. as follows:

Inches 0.25

Minimum Standard Mini- Internal External Modified Root mum Thread Thread Root Dia. Int. Wall Size Size Dia. Thd. Thick- Ext. (Inches) ness Thd. (Inches) (Inches) -32 4-28 0.2120 0. 1900 0. 0110 54-28 ")1 e-24 0. 2735' 0. 2500 0. 0117 it e--24 %24 0. 3355 0. 3125 0. 0115 24 Z4 a-20 0. 3960 0. 3750 0. 0105 '}i (r20 r20 0. 4580 0. 4375 0., 0102 l-ZO Mo-2 4 0. 5240 0. 5000 0. 0120.

In the above table, column 1 indicates the size of the internal thread of the insert; column 2 the size of the external thread; column 3 the minimum root diameter of the external thread in inches, which is less than standard; column 4 the standard root diameter of the internal thread in inches; and column 5 the minimum wall thickness of the insert in inches. It will be noted that the minimum wall thickness shown is 0.0102" and that for the sizes shown, the wall thickness varies from 0.0102" to 0.0120"; It will be clearly understood that these wall thicknesses will varydepending upon the variations in allowable tolerances for the given threads, between'ma-ximum and minimum. In any event, the wall thickness of any given insert made in accordance with the principles of this invention will be less than that of prior inserts of the same internal thread size.

The inserts disclosed herein may he made of any suitable material. It has: been determined that a stainless steel known in the metallurgical field as Armco'174P H is an ideal material for use in making the present inserts. Another stainless steel known inthe industry as Armco 1710PH may be used where a non-magnetic material is desired for the insert. Certain aluminum alloys can also he used, including the well known aluminum alloy identified as 2014T6. The, latter may be used where a hard, light-Weight insert is desired. In this, connection, the present thin-walled inserts made of stainless steel are characterized by their surprising lightness. For example, 1000 stainless steel inserts having a /4-28 internalthread and a 71 -24 external thread, weigh only 2.7 lbs. The use of stainless steel and aluminum alloys is further preterable because of their corrosion resistant properties.

A steel alloy, A.I.S.I. #4130, has also been tound satisfactory. Although it does not have corrosion resistant 8 properties, it does have the strength characteristics of the above stainless steels.

The stainless steel materials mentioned above are particularly well suited for use in making the present thinwalled inserts for the reason, that they can be heat-treated to give the inserts the desired high hardness, high ductility and high modulus of elasticity required without rendering the same brittle or introducing other undesirable charac teristics.

One of the preferred stainless steel materials for making the present inserts Armco 17-4PH has the following physical properties at room temperature:

Ultimate tensile strength 190,000 lbs, p.s.i.

(pounds per square. inch). Yield .02% 170,000 p.s.i. Double Shear 130,000 p.s.i. Elongation in two inches 10%.

Reduction of cross sectional area in test piece 37.5 to Rockwell hardness (C Scale) 40 to 46.

A single internal locking thread of 1 /2 convolutions provides torque and pull-out resistance that far exceeds the requirements of Military Specifications N-25027 (ASG),

Actual tests have also shown that the internal lock thread is capable of maintaining torque resistance meeting specifications even after 600 cycles of insertion and removal of bolts from the insert. This extremely long life of the locking thread 50 is believed to be attributable to the hardness of the material of the insert and tothe fact the side wall 18 of the insert is thin and resilient, enabling said side wall to flex outwardly when the locking thread is engaged by a fastener, rather than remaining rigid and causing excessive wear on the fastener threads and locking thread.

Any of the inserts disclosed herein can have more than one locking thread formed therein, if desired.

While several methods of making a one-piece lockable insert having an internal locking thread have been disclosed herein, it will be understood that minor variations may be made therein without departing from the principles of the invention or the scope of the annexed claims.

We claim:

1. The method of making a threaded insert with, an internal lock, comprising the steps of: forming external and internal threads in a metal body with the external thread one size larger than the internal thread and with a Wall thickness between the root diameters of said internal and external threads of not less than .008"; heat treating the body to harden the same; and cold-rolling in a spiral pattern through at least one convolution, the root portion only of said external thread which is disposed opposite a crest of an internal thread so as to depress the same to a depth below the original root diameter of said thread, whereby to displace corresponding portions of the internal thread to reduce the crest diameter thereof to provide an internal locking thread.

2. The method of making an insert as defined in claim 1, including forming the external thread to a. depth sub.- stantially less than the depth of a standard thread of the same diameter and pitch.

3. The method of making a threaded insert, with an internal lock, comprising the steps of: forming an external thread on a metal body of a depth substantially less than that of a standard thread of the same major diameter and pitch; forming a standardthread interiorly of said body of a size to provide a thin: wall portion between said external and internal threads; heat treating the body to harden the same; and cold-rolling in a spiral pattern through atleast one convolution, the root portion only of said external thread which'is disposed opposite a crest of an internal thread so as to depress the same to a depth below the original root diameter of said thread, whereby to displace corresponding portions of the internal thread to reduce the. crest diameter thereof to. provide an internal peripheral locking thread.

4. The method of making a hollow insert, comprising the steps of: forming standard threads on the interior of the body of the insert; forming threads on the exterior of said body to a depth substantially less than the depth of a standard thread of the same diameter and pitch; and depressing the root of the external thread which is disposed opposite a crest of an internal thread through at least one convolution of the external thread.

5. The method of making a threaded insert, with an internal lock, comprising the steps of: forming an external thread on a metal body: forming a thread interiorly of said body; heat treating the body to harden the same: and cold-rolling in a spiral pattern through at least one convolution of the root portion of said external thread which is disposed opposite a crest of an internal thread so as to depress said root, thereby displacing a corresponding portion of the internal thread to reduce the crest diameter thereof to provide an internal, locking thread.

6. The method of making a threaded insert with an internal lock, comprising the steps of: forming an external thread on a metal body of a depth substantially less than that of a standard thread of the same major diameter and pitch with 1 to 2 convolutions of shallower depth than the remaining threads; forming a standard thread interiorly of said body of a size to provide a thin wall portion between said external and internal threads; heat treating the body to harden the same: and cold-rolling in a spiral pattern the root portion only of said 1 to 2 convolutions of said external thread which is disposed opposite a crest of an internal thread so as to depress said root to a depth equal to that of said remaining external threads whereby to displace corresponding portions of the internal thread to reduce the crest diameter thereof to provide an internal locking thread.

7. The method of making an insert as defined in claim 1, including the step of supporting the flanks of the external thread against distortion during the cold-rolling of the root portion of said external thread.

8. The method of making an insert, as defined in claim 1, in which the external and internal threads are formed on a stainless steel body and said body is heat treated to a hardness of to 46 on the Rockwell C scale.

9. The method of making an insert, as defined in claim 1, wherein the rolling of the root portion of the external thread is confined to approximately one and one-half convolutions of said root portion through about one and onehalf convolutions.

References Cited in the file of this patent UNITED STATES PATENTS 1,692,497 Furlan Nov. 20, 1928 2,444,145 Rosan June 29, 1948 2,791,787 Neuschotz May 14, 1957 2,795,221 Braendel June 11, 1957 3,065,983 Flumerfelt Nov. 27, 1962 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNm 3,163,872

January 5, 1965 Jose Rosain et al Itis hereby certified that error appears in th ent requiring corr e above numbered patection and that the said Letters P corrected below.

atent should read as Column 3, line 67, strike out respectively"; column 5, line 32, for "rotor" read -root column 10, lines 18 and 19,

rough about one and one-half convolutions".

Signed and sealed this 5th day of- October 1965.

SEAL) Attest:

ERNEST W. SWIDER \ttesting Officer EDWARD J. BRENNER Commissioner of Patents

Claims (1)

1. THE METHOD OF MAKING A THREADED INSERT WITH AN INTERNAL LOCK, COMPRISING THE STEPS OF: FORMING EXTERNAL AND INTERNAL THREADS IN A METAL BODY WITH THE EXTERNAL THREAD ONE SIZE LARGER THAN THE INTERNAL THREAD AND WITH A WALL THICKNESS BETWEEN THE ROOT DIAMETERS OF SAID INTERNAL AND EXTERNAL THREADS OF NOT LESS THAN .008"; HEAT TREATING THE BODY TO HARDEN THE SAME; AND COLD-ROLLING IN A SPIRAL PATTERN THROUGH AT LEAST ONE CONVOLUTION, THE ROOT PORTION ONLY OF SAID EXTERNAL THREAD WHICH IS DISPOSED OPPOSITE A CREST OF AN INTERNAL THREAD SO AS TO DEPRESS THE SAME TO A DEPTH BELOW THE ORIGINAL ROOT DIAMETER OF SAID THREAD, WHEREBY TO DISPLACE CORRESPONDING PORTIONS OF THE INTERNAL THREAD TO REDUCE THE CREST DIAMETER THEREOF TO PROVIDE AN INTERNAL LOCKING THREAD.

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