US3589157A

US3589157A - Die mechanism for rolling threads on screw blanks

Info

Publication number: US3589157A
Application number: US795405*A
Authority: US
Inventors: Joseph A Tabor
Original assignee: Russell Burdsall and Ward Corp
Current assignee: Russell Burdsall and Ward Bolt and Nut Co; Russell Burdsall and Ward Corp
Priority date: 1969-01-31
Filing date: 1969-01-31
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29

Abstract

Die mechanism for rolling a thread on the shank of a screw blank to form offset thread segments in the screw thread, the faces of a pair of oppositely disposed die members having conventional thread rolling grooves and one of said die members having a die insert in its face, the die insert having grooves to form the offset thread segments, the bottoms of the grooves in the die insert being shifted axially from the bottoms of the grooves in the face of the die member which has the die insert.

Description

United States Patent Inventor Appl. No, Filed Patented Assignee Joseph A Tabor Greenwleh. C onn.

Jan. 31. I969 Division of Ser. No. 765.595. Oct. 7. 1968. Pat. No. 3.459.250. which is a continuationin-part of Ser. No. 630.887. abandoned. June 29, [971 v Ruse", Burdsall 8 Ward Bolt and Nut Company Port Chester, N.Y. 7

Original application Oct. 7. 1968, Ser. No. 765,595, new Patent No. 3,459,250, Continuation-impart 0! application Ser. No. 630,887, Apr. 14, 1967. Divided and this application Jan. 31, 1969, Ser. No. 795,405

DIE MECHANISM FOR ROLLING THREADS ON SCREW numxs 13 Claims, 14 Drawing 11 11.5. c1 12/90. 72/469 IL c1 13216 11/00 Field 61 Starch 72/88, 90. 469

[56] References c1164 UNITED STATES PATENTS 2.161.610 6/1939 Boggild 12/90 3,308,645 3/1961 Hampton.... 72/469 3,429,161 2/1969 Morse.... 12/46 3,452,375 7/l969 Gabbey 72/469X Primary Examiner-Milton S. Mehr Anomey--Furman Rinehart ABSTRACT: Die mechanism for rolling a thread on the shank of a screw blank to form offset thread segments in the screw thread, the faces of a pair of oppositely disposed 'die members having conventional thread rolling grooves and one of said die members having a die inse1t in its face, the die insert havinggrooves to form the offset thread segments, the bottoms of the grooves in the die insert being shifted axially from the bottoms of the grooves in the face of the die member which has the die insert.

3589;157- UJUNZSIQZI 32:31 2 c? 4 F/G.'4 v 5,

li/ I174.

FIG. 5 i u "I? l g j! H 1 I u (is v I FIG. 5A

DIE MECHANISM FOR ROLLING THREDS ON SCREW" BLANKS now abandoned filed Apr. 14, I967.

This invention relates generally to metal threaded fasteners and more particularly to die mcchanism for rolling a thread on the shank ofa screw blank,

7 In said application Ser. No. 765,595 as filed (the disclosure of which is to be deemed to be incorporated 1 herein by reference), there is disclosed and claimed, inter alia, a prevailing torque lockserew wherein the thread on the shank of the screw is deflected in such manner as to provide one or more offset thread segments of substantial arcuate length in the thread, which offset segments are located intermediate the leading end of the threaded shank and the trailing end of the thread, said offset thread segments throughout their arcuate lengths lying at the same helix angle as the helix angle of the remainder of the thread and certain thread-rolling die mechanism for rolling the thread on the shank of a screw blank. I

This application is a division of said application Ser. No. 765,595 and is directed to the die mechanism for rolling a thread on the shank of a screw blank; the die mechanism comprising a pair of oppo itely disposed thread rolling die members for simultaneously acting upon opposite sides of the shank, one of said die members being movable relatively to FIG. 9 is a fragmentary view to larger scale showing the die insert positioned in its slot in the stationary die of FIG. 4;

FIG. I0 is a view largely diagrammatic to illustrate the profile of the grooves of the insert for forming the cluster of offset thread segments on the screw thread of FIG. I to 3 of the insert of FIG. 6 to 9;

FIGS. II and I2, respectively, a face view and top plan view of the travelling thread rolling die to operate in conjunction 0 with the stationary die shown in FIGS. 4 to 9; and

the other, the first of said die members having a slot therein at its trailing end portion to receive a die insert, the face of the second of said die members having grooves, the ridges and bottoms of which are of conventional profile, which ridges and bottoms have a predetermined helix angle and pitch, the face of the first die member having grooves of the same profile,

helix angle and pitch as the face of the second die member, an insert shaped to fit in said slot and having one or more grooves in its face having the same helix angle as the helix angle of the grooves in the slotted die member for forming one or more offset thread segments in the thread rolled on said shank, the ridges of the grooves in said die insert registering with and forming straight line continuations with the ridges of the grooves in the face of the slotted die member, the bottom or bottoms of the grooves in the face of said die insert being offset from the corresponding bottom or bottom: of the groove or grooves in the face of said slotted die member, the lengths of the die insert groove or grooves being dimensioned to correspond to the length of the locking offset segment or segments to be formed in the screw thread on the shank of the screw.

Although the novel features which are believed to be characteristic of the invention are pointed out in the annexed claims, the invention itself as to its objects and advantages and the manner in which it may be carried out may be better understood by reference to the following more detailed description, considered in connection with the accompanying drawings, forming a part hereof, in which:

FIG. I is a view in elevation of a screw produced by the die mechanism made in accordance with the invention in which the thread segments of adjacent pairs of offset thread segments are offset axially toward each other;

FIG. 2 is a view on line 2-2 of FIG. I;

FIG. 3 is a view in elevation of the screw shown in FIG. I turned 90 from that shown in FIG. I; the screw being screwed into the threaded bore ofu work piece;

FIG. 4 is a face view ofa stationary thread rolling die showing a slot for insertion of a thread rolling insert for forming the offset thread segments;

FIGS. 5 and 5A are, respectively, a top plan view and an end view of the die shown in FIG. 4;

FIGS. 6, 7 and 8 are, respectively, a face view, an end view, and a top plan view of the insert for the slot shown in FIG. 4;

' FIG. I3 is a view in perspective to illustrate the operation of the thread rolling dies.

In said application Scr. No. 765,595, it is pointed out that the offset thread segments may be offset in downward direction (i.e. in a direction toward the leading end of the screw); in an upward direction (i.e. direction toward the head or trailing end of the screw); or, some of the thread segments may be offsetin downward direction and others in an upward direction; and in some instances, particularly if the screw is short in length, a screw embodying the principles of the invention may have a thread having only one free spinning turn at the leading end of the thread and only one or two turns of the thread having an offset segment intermediate the leading free spinning end portion and trailing end of the thread,

The threaded fastener herein described is rcferredto as a screw, but it will be understood that the term is intended to comprehend the term bolt or other product having an external thread. I

Referring to FIGS. 1, 2 and 3, there is illustrated a screw I20, having a head I2] to accommodate a suitable wrenching tool, a threaded shank I22 and thread I23, the successive thread turns being indicated by reference characters I23a to I23q. Located intermediate the leading end and trailing end of the thread 123 is a plurality of vertically aligned offset thread segments 124a, b, c, d, e, each of which is offset downwardly, and offset thread segments 125b, c, d, e, each of which is offset upwardly. These offset thread segments have a substantial, arcuate length and they form a cluster of offset segments 127. The arcuate length, i.e., the circumferential length L of these locking offset segments may be within the range of 5 percent to 50 percent of the circumference ofa turn of the thread. The depth d of the offset of the locking segments should be less than half of the pitch p of the thread and may be any suitable amount up to about 35 percent of the pitch in. certain instances. As shown in FIG. I, the thread segments are offset an amount which is l5 percent of the pitch of the thread. By making the arcuate length of the offset segments longer, a greater frictional and spring action locking effect may be obtained and by decreasing the length, a decreased locking effect may be obtained. Also, by increasing the depth of the offset of the thread segments a greater locking effect may be obtained. By decreasing the depth, a lesser locking effect may be obtained. Also, by increasing or decreasing the number of thread turns that have offset thread segments, the locking effect may respectively be increased or decreased.v

The threaded part of the screw shank may be considered as having a free spinning, leading end portion 128 in which the thread is conventional and undeflected; a trailing end portion 130 in which the thread turns do not have offsets and are conventional and undeflected; and a locking portion 129, located intermediate portions I28 and 130; the cluster 127 of offset segments being located in the intermediate locking portion I29. It is significant to observe that the crest portions of the offset segments in the cluster I27 of offset segments are at the same helix angle along their entire lengths, as the helix angle of the remaining undistorted portion of the thread I23, the thread I23 being conventional, except for the offset thread segments. And the crests of all the thread turn including the crests of the offset thread segments, lie in an imaginary right cylinder. The axial width We of the crest p rtions of the thread I23, including the offset segments, as shown, is uniform. That is, the crests are not blunted as might be caused by certain punching tools. In some instances, however, it might be possible to roll threads on the shank with offset seg ments where the crests of the thread might not be of uniform width throughout the length of the entire thread. it will be observed that the screw, as shown, has a constant major diameter throughout the axial length of the threaded portion and the crestsof the turns of the thread are uniform in axial width. It will be understood, of course, that if the screw has a tapered leading end, the threads at the leading end portion of such a screw may not have fully formed thread turns and the thread turns of the tapered portion will progressively increase in radial width in a direction toward the head end of the screw and the crests of the partially formed thread turns will decrease in axial width. Accordingly, it will be understood that it will be i i the effective threaded portion beginning at the trailing end of the tapered portion of such a screw and ending at the trailing end of the thread which will have constant crest and root diameters; i.e., constant major and minor diameters. The consequence of having the offset segments at the same helix angle as the helix angle of the remainder of the thread is that when the screw is screwed home into locking position into a mating conventionally tapped bore, the offset segments, when'offset exerts a spring action force downwardly on the upper flank of that same turn of the female thread. Also, it is within the contemplation of the that in certain instances the cluster of offset segments may consist of only one pair of offset segments offset toward each other.

Referring now more particularly to FIG. 3, illustrating the shank of the screw 120 turned home in a conventionally tapped bore 131 of a workpiece I32, it will be seen that downwardly offset segment 124a exerts a spring action force downwardly on the upper flank 1350 of the female thread turn "1b of female thread 141. The upwardly offset segment 125!) of the thread 123 exerts an upward spring action force on the lower flank 13617 of turn Id of the female thread, and the downwardly offset segment 124!) of the pair (125b, 1241:) of offset segments exerts a downward spring action force on the upper flank 1356 of the same turn Id of the female thread in a lateral direction diametrically away from the cluster I27 of offset thread segments and this causes both the upper and lower flanks of the male thread I23 in the arc B to engage the upper and lower flanks of the female thread M1 in that are diametrically opposite the cluster of offset segments with greater friction than is the case of a conventionally threaded screw in a conventionally threaded female bore. HO. 3 is somewhat exaggerated to illustrate this clearly. Thus, the screw as illustrated in H08. 1, 2 and 3 has an enhanced fric- 4 tional locking effect in addition to the locking effect due to the cluster 127 of locking offset thread segments.

FIGS. 4 to 13 illustrate the thread rolling dies and manner of offsetting the locking thread segments in certain turns of the thread to form the cluster of offset segments in which the thread segments of adjacent pairs of segments are offset in axial direction toward each other. Referring to FIG. 13, there is illustrated a travelling thread rolling die 150 and a stationary thread rolling die ISI for use in a known thread rolling machine. The screw blank 120a is rolled between these dies in conventional manner. The die faces are suitably formed to perform the function offorming the thread on the shank of the screw with offset segments as shown in H6. I. In the-rolling operation the die 150 is moved to the right as indicated by arrow 152, causing the screw to roll between the stationary and travelling dies in the direction of arrow 152.

The face 157 of the stationary die 151 (see FIG. 4) is provided with milled thread rolling grooves [574 of conventional configuration or profile. the slope and pitch of which cor- I respond to the helix angle and pitch of the thread to be formed on the shank of the screw. However, the stationary die is provided with a cutout or slot 155. This slot has a vertically disposed leading end 155a, and the top and bottom sides 15512 and 155; slope at an angle parallel with the grooves l57a of the face 157. That is, the slot 155 slopes at an angle equal to the helix angle of the thread-The slot 155 is dimensioned to accommodate an insert I56 which is snugly fitted into the slot 141. This, in effect, causes the pair of offset segments, 124b,

125!) to resiliently and frictionally squeeze that thread turn of the female thread between that pair 124b, [25b of offset se'gmentsto provide an effective locking means to inhibit loosening of the screw in the tapped bore 131 after the screw is driven home in the female threaded bore. The pairs of offset segments 124e, 1254:, and 124d, 1254, and l24e and 125:, function in the same way as the pair of offset segments 124b, 125k; that is, the downwardly offset segments exert forces downwardly on the upper flank of the mating turn of the female thread and the upwardly offset segments exert forces upwardly on the lower flank of the mating turn of the female thread so that alternate thread turns of the female thread, as shown in FIG. 3, are resiliently gripped between pairs of offset thread segments of the male thread to effectively lock the screw from loosening itself as a result of vibration or other analogous loosening forces. THat is,the alternate thread turns of the female thread are resiliently clamped between a pair of the spring action offsetthread segments of the screw. Yet, the screw may be turned to loosen and remove it when desired by using s suitable wrenching or turning tool.

in the embodiment illustrated in FIGS. 1, 2 and 3, there is also a locking action or effect in addition to that afforded by the offset thread segments, when the screw is driven home in a conventional female threaded bore. The resulting forces due to the spring action of the offset segments 1244:, b, c, d, e, and offset segments 125b, c, d, eon the female thread, also act on the shank of the screw in a lateral direction toward the l80 I55, which is sometimes referred to as pocket .155. The insert 156 has a length corresponding to the length of the slot and a width Wb to provide a snug fit. The leading end of the insert is provided with grooves 1544 of the same amount of pitch as the grooves 1570 of the face of the die 151, the length Lg of the grooves 154a corresponding to the length L- of the offset thread segments (see FIG. I). It will be observed that the insert is of generally rectangular shape and the thread rolling grooves 154a run parallel with the top edge 1554 and the bottom edge 155a. However, the end edge [55f of the insert is not perpendicular to the bottom edge 155:, but is slightly inclined. so that this edge 155] lies flush with the end of the die .151, when the insert is positioned in its sloped slot 155. Consequently, whenthe thus shaped insert is fitted into the insert slot I55, (which slopes at an angle equal to the helix angle of the grooves 1570) the groovesl54a of the insert then lie at the same helix angle as the grooves 157a. However, the bottoms of the grooves 1540 are offset from the grooves 157a as described 2.: further detail hereinafter. The number of thread forming grooves in the insert corresponds to the number of offset thread segments desired in the finished screw. The trailmilled grooves 161a having the same helix angle and the same pitch as the grooves 1570 in the face 157 of the stationary die 15!. A relief or cutout portion at the'trailing or leave-off end of the travelling die 150 is not necessary as the threaded screw is separated from the diesl50, 151 at thelea off end almost instantaneously after thecluster of offset thread segments are formed so that once the offset thread segments are rolled in by .1 the die insert of the stationary die, the formed offset segments will not be disturbed.

Referring now to FIG. 10, there is shown in more or less dia- Q grammatic fashion in further detail and to larger scale, a profile of the thread rolling grooves [54a of the insert 156 (see also HO. 6 to 8). An insert properly dimensioned and made according to this profile (FIG. 10), will form the offset thread segments "do to HM and l25b to 125a (see FIGS. l to 3) in the thread I23 of the threaded shank 122 of the screw. Broken line 165 represents the profile of the conventional grooves 157a on face 157 of the stationary die 151. The apices 1660 to 166 of the grooves 154a are conventional and are the same as, and register with, the spices of the grooves 157a of face 157 of the stationary thread rolling die. This is, the apices 166a to 166 register with the apices of the grooves 157a when the insert is inserted in slot I55, so that the apices of the insert form continuations of the apices 157a in straight line relationship. Sometimes the rolling of the blanks in the thread rolling dies may cause a chipping of the ridges of the dies. To avoid or inhibit such chipping of the apices of the grooves 157a and the apices 1660 to 166] of the insert where they join, it is desirable to bevel or round off slightly the meeting ends of these apices or ridges. This also minimizes any shearing action of the ridges of the dies on the rolled thread. The apices 1660 to l66j,

which may also be referred to as the ridges of the grooves of the die will, of course, form the root 167 of the thread 123 of the screw in the thread rolling operation. The root 167 of the thread of the screw is conventional and the minor diameter of the shank of the screw I20 is constant throughout the axial length of the threaded portion of the shank. The bottoms of the thread rolling die will, of course, form the crests of the thread of the screw. The bottoms 1680 to 1681' of the grooves of the insert, which will form the crests of the offset thread segments of the screw, are shifted axially from the profile of the conventional grooves in a manner now to be described; the

profile of the conventional or standard grooves (comprising bottoms and apices or ridges) being indicated by broken line- 165 in FIG. 10. Broken line 1654 represents the profile of a conventional screw thread.

To lay out the profile of the grooves in the insert, the height it (see FIG. 10) of the profile of the grooves of the conventional grooves is divided into an apex or n'dge portion 170a, a bottom portion "tie, and an intermediate portion l70b. As

- shown, the height II is divided into three portions l70al70b,

"0c; the profile of the normal or conventional grooves being indicated by broken line 165. The pitch Pfrom apex to apex of the grooves is normal or conventional. These apices 1660 to 166] form the root I67 of the screw thread H3 in the thread 1 rollingopcration. Thus, the root 167 is normal or convenv tional and the root diameter of the threaded portion of the screw is constant. However. the bottoms (1680 to 168:) in the portion "0c of the grooves are shifted axially from the conventional profile 165; the bottoms 1680, c, e,'g, i, (in the one third portion l70c)being shifted axially toward the lower end i of the insert (i.e., toward the leading end of the screw to be formed) and the bottoms 168b, d,f, h (in the one third portion l70c) being shifted axially toward the upper end of the insert (i.e., toward the head or trailing end of the screw to be formed). The bottoms of the grooves in the portion l70c are each shifted axially in the direction mentioned above by an amount indicated at 1710 and WM. As shown, the bottoms (in the one third portion l70c) are shifted from the normal or conventional (indicated by broken line 165) a certain amount of the pitch P (see FIG. 10). As shown, the bottoms are shifted a distance from normal which amount is l5 percent of the pitch 1; that is, the bottoms are shifted a distance indicated at "In and 1711:. However, the bottoms may be shifted a distance within the range of 3 percent to percent of the pitch P, depending on the kind of metal ln the screw to be formed; the size of the thread and locking characteristics desired in the finished thread. Having shifted the bottoms to the desired positions on the profile (FIG. 10); the apices 166a to 166] (in the one third portion 170a) and the bottoms 168a to 1681' (in the one third portions l70c) are joined by substantially straight lines 1690 to l69r( in the intermediate one third portion l70b); the connection lines I690 to l69r. being merged with the apices and bottoms of the grooves in a As shown in FIG. I0, the height in form the apex of the hot- I tom of the groove to the apex of the ridge-ofv the groove, has been divided into three equal parts (ridge portion l70abottom portion 170:: and intermediate portion 1701)), but the proportional heights of these portions, l70a, b, 1:, may be varied depending on the kind of metal that is to be used to make the screw, the size and kind of thread and the locking effect desired. For example, the height of the bottom portion l70c, which is to form the crest portions of the offset thread segments ,in the thread of the screw, and the height of the ridge portion non, which is to form the root portionsvof the thread where'the offset segments are located, may be within the range of one quarter to one half the height 11, measured from the apex of the bottom portion to the apex of the ridge portion of a groove of the insert.

There is an advantage in having the height in the portion 170p substantial because this increases the surface area along the offset thread segments of the screw which engage and fric-. tionally contact the flanks of the female thread in the tapped bore of the workpiece. This surface area distributes the frictional locking forces over a larger surface area than an offset thread which is deflected from conventional in a manner such that the deflected portion of the thread contacts the flanks of the female thread inonly a single line of contact.

Referring, for example, to the slopes of the flared sides I72, 173 and 174, 175 of bottoms 168a and 168d in the portion l70c (see FIG. 10) as typical of the bottoms of the grooves of the insert 156, it will be noted that sides I72, 173, 174, 175 of the bottomal68el68d lie parallel to the adjacent broken "line 165 which indicates the profile of the conventional grooves flared

sides

172a, 173a, 174a, 1750 of the crest portions l24cl25c of the screw I20 lie parallel with adjacent slopes of broken line 1654, representing the profile of a conventional screw thread. Consequently, when the screw is screwed into a mating tapped female bore (see FIG. 3) the sloping

sides

173a, 174a of the offset thread segments 124e, 125:: contact the flanks of the female thread turn 14! f of thread 141 in an area over the entire surface of the width and circum ferential length of the contacting offset thread segments so that the frictional contact between the female thread and offset thread segments of the screw extends over a substantially larger surface area than would be the case if the offset thread.

segments contacted the adjacent flanks of the female thread in only a single line of contact.

lnasmuch as the bottoms of the grooves of the thread rolling dies produce the crests of the thread of the screw, when the screw thread is rolled on the screw blank, it is common practice to provide a blank which has a diameter equal to the pitch diameter of the threaded screw to be formed. The effect or results of rolling the thread on the screw blank by use of the insert 156 is illustrated at the right of HG. 10. It will be seen that the thread segments are offset in a manner corresponding to the bottoms of the grooves of the insert. Offset thread segments l24bl2$b provide a pair of threadlsegments which are offset toward each other; and offset segments 124e, 125a; 124d. HM; and 124e, 125a provide like paris of segments which are offset toward each other (see also FIG. 3). The thread 123 is normal or conventional except for the offset thread segments. Thus, the screw 120, illustrated in FIG. t, has a constant minor diameter and a constant major diameter throughout the axial length of the threaded portion of the shank. Hence, the apicesof the crests of the turns of the in the illustrative embodiments shown in the drawings, the thread is shown as a conventional V thread, but it will be understood that the principles of the invention may be applied to other forms of thread. Also, it will be understood from the foregoing description that the insert may be made to have one or more bottoms which are axially shifted from conventional profile in upward direction (i.e., toward the head end of the screw) or in a downward direction (i.e., toward the leading end of the screw).

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intentiomin the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What i claim:

1. Thread rolling die mechanism for forming a screw thread on the shank of a screw blank to produce a prevailing-torque lockscrew having offset thread segments, which comprises a pair of oppositely disposed thread rollingdie members for simultaneously acting upon opposite sides of the shank, one of said die members being movable relatively'to the other, the first of said die members having a slot therein at its trailing end portion to receive a die insert, the face of the second of said die members having grooves, the ridges and bottoms of which are of conventional profile, which ridges and bottoms have a predetermined helix angle and pitch, the face of the first die member having grooves of the same profile, helix angle and pitch as the grooves of the face of the second die member, an insert shaped to have a snug fit'insaid slot and having a plurality of grooves in its face of the same helix angle as'the grooves in the face of said slotted die member for forming a plurality of locking offset thread segments in the screw thread formed on said shank, the ridges of the grooves of said die insert registering with and forming straight line continuations of the ridges of said grooves in the face of the slotted die member, the bottoms of the grooves in the face of said die insert being offset from the corresponding bottoms of said grooves in the face of said slotted die member by an amount within the range of 3 percent to 35 percent of the pitch mea- 7. Thread rolling die mechanism according to claim 4, in whichthe offset bottoms of the grooves constitute about one third of the height of the grooves. I

8. Thread rolling die mechanism according to claim 5, in which the bottoms of the grooves of said slotted die are offset from the bottoms of the grooves in the face of said first die member an amount about l5 percent of the pitch measured from apex to apex of the ridges of the grooves of the die insert.

9.'Dic mechanism according to claim 6, in which the offset bottoms of the grooves in the face of said die insert are offset an amount about l5 percent of the pitch measured from apex to apex of the ridges of the grooves in the face of the die insert. I 10. Thread rolling dic mechanism for forming a screw thread on the shank of a screw blank to produce a prevailingtorque Iocltscrcw having a threaded shank which has a free spinning'leading end portion, a trailing end portion and a locking portion having at least one offset thread segment intermediate said leading and trailing end portions, which mechanism comprises a pair of oppositely disposed thread rolling die members for simultaneously acting upon opposite 'sides of the shank, one of said die members being movable sured from apex to apex of the saidridges of the grooves in said die insert, the lengths of the die insert grooves being dimensioned to correspond to the lengths of the locking offset thread segments to be formed in said screw thread.

2. Thread rolling die-mechanism according to claim I, in which the bottoms of the grooves are offset from the corresponding bottoms of the grooves in the face of said first die member an amount about percent of the pitch measured from apex to apex of the ridges of the grooves of the die insert.

3. Thread rolling die mechanism according to claim I in which the length of the grooves in the face of the insert is within the range of 5 percent to SOIperccnt of the circumferential length of a turn of the screw thread on the shank of the screw.

4. Thread rolling die mechanism according to claim I, in which the offset bottoms of the grooves in the face of the insert constitutes one quarter to one half of the height of the grooves measured from the lowest point of the bottom to the highest apex point of the grooves.

5. Thread rolling die mechanism according to claim 1, in which'the bottoms of at least one adjacent pair of grooves in the face of said insert are offset from each other in opposite axial directions so that said pair of grooves of the insert form a pair of offset locking thread segments in the screw thread segments are offset axially toward each other. i

6. Die mechanism according to claim 1, in which the lengths of the grooves in the face of the insert are within the range of 5 percent to percent of the circumferential length of a turn of 1 the screw thread on the shank of the screw, and the offset bottoms of the grooves of the insert constitutes one quarter to one half the height of the grooves measured from the lowest point of the bottom of the grooves to the highest point of the apex of the grooves.

formed in said locking portion of said screw thread.

relatively to the other. one of said die members being stationary and having a slot therein at'its trailing end portion to receive a die insert, the other of said die members being reciprocatable and having a facehaving grooves, the ridges and bottoms of which are of conventional profile, the face of the stationary die member havingfgrooves of the same profile, helix angle and pitch as the grooves of the face of said reciprocatable die member, an insert shaped to have a snug fit in said slot mounted in said slot and having a givengroove in its face of the same helix angle as the grooves in the face of a said stationary die member, registering with and lying in straight line relationship with the ridges of said given groove in the face of said insert, the bottom of said given groove in the insert being offset in an axial direction from the corresponding adjacent groove in the face of said stationary die member by an amount within the range of 3 percentto 35 percent of the pitch measured from apex to apex of the ridges of the grooves in the face of said stationary die member, the length of said offset bottom of said given insert groove being dimensioned to correspond to the length of the offset thread segment to be 11. Thread rolling mechanism according to claim' 10, in which the bottom of said given groove in said insert has a length-within the range of 5 percent to 50 percent of the cireumfcrence of a turn of the thread to beforrned on said shank.

12. Thread rolling mechanism according to claim it, in which the offset bottom of the said given groove of the insert'is offset an amount which is about l5 percent of said pitch and the height of the offset bottoms is about one third of the height of a groove measurcdfrom the apex of the bottom to the apex of the ridge of the groove. I

[3. Thread rolling die mechanism for forming a screw thread on the shank of a screw blank to produce a prevailingtorque lock screw having at least one offset locking thread segment intermediate the leading and trailing ends of the thread on the shank, which comprises a pair of oppositely disposed thread rolling die members for simultaneously acting upon opposite sides of the shank, said die members being movable relatively to each other, one of said die members having a slot therein at its trailing end to receive a die insert, the faces of saidtwo die members having grooves, the ridges and bottoms of which are of conventional profile, .the ridges and bottoms of the grooves in the faces of said two die members I the highest apex point of the groove, the length of said offset bottom being dimensioned to correspond to the length of the said locking offset thread segment to be formed in said screw thread.

Patent No.

lnventofls) 7 Column 2,

Column line l5,

Column line 69 Column line 33,

Dated June 29 1971 Joseph A. Tabor It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

line 7, after "12" insert --are after "i.e." insert --in a-.

"turn" should be --turns-.

after the first "the" insert -invention--.

FORM PO-105O (10-69) Column 3, line' 64, "IHat" should be -That.

Column 3, lin'e 68, "5" should be -a.

Column 5,' line 11, "spices" should be --apices.

Column 5, line 12, "This should be --That-.

Column 5, line 43, after l70a" insert Column 6, line 46, after "bore" insert ---l3l.

Column 6, line 67, "paris" should be -pairs-.

Column 7, line 66, after the second "thread" insert wherein the offset thread segments in that pair of offset thread-- {Claim 5) Column 8, line 33, after "member," insert --the ridges in the face of the stationary die member {Claim 10) Signed and sealed Chi a ZJth day of April 9?? {SEAL} fittest some? GOTTSCHALK Commissioner of Patents

Claims

1. Thread rolling die mechanism for forming a screw thread on the shank of a screw blank to produce a prevailing-torque lockscrew having offset thread segments, which comprises a pair of oppositely disposed thread rolling die members for simultaneously acting upon opposite sides of the shank, one of said die members being movable relatively to the other, the first of said die members having a slot therein at its trailing end portion to receive a die insert, the face of the second of said die members having grooves, the ridges and bottoms of which are of conventional profile, which ridges and bottoms have a predetermined helix angle and pitch, the face of the first die member having grooves of the same profile, helix angle and pitch as the grooves of the face of the second die member, an insert shaped to have a snug fit in said slot and having a plurality of grooves in its face of the same helix angle as the grooves in the face of said slotted die member for forming a plurality of locking offset thread segments in the screw thread formed on said shank, the ridges of the grooves of said die insert registering with and forming straight line continuations of the ridges of said grooves in the face of the slotted die member, the bottoms of the grooves in the face of said die insert being offset from the corresponding bottoms of said grooves in the face of said slotted die member by an amount within the range of 3 percent to 35 percent of the pitch measured from apex to apex of the said ridges of the grooves in said die insert, the lengths of the die insert grooves being dimensioned to correspond to the lengths of the locking offset thread segments to be formed in said screw thread.

2. Thread rolling die mechanism according to claim l, in which the bottoms of the grooves are offset from the corresponding bottoms of the grooves in the face of said first die member an amount about 15 percent of the pitch measured from apex to apex of the ridges of the grooves of the die insert.

3. Thread rolling die mechanism according to claim 1 in which the length of the grooves in the face of the insert is within the range of 5 percent to 50 percent of the circumferential length of a turn of the screw thread on the shank of the screw.

4. Thread rolling die mechanism according to claim 1, in which the offset bottoms of the grooves in the face of the insert constitutes one quarter to one half of the height of the grooves measured from the lowest point of the bottom to the highest apex point of the grooves.

5. Thread rolling die mechanism according to claim 1, in which the bottoms of at least one adjacent pair of grooves in the face of said insert are offset from each other in opposite axial directions so that said pair of grooves of the insert form a pair of offset locking thread segments in the screw thread segments are offset axially toward each other.

6. Die mechanism according to claim 1, in which the lengths of the grOoves in the face of the insert are within the range of 5 percent to 50 percent of the circumferential length of a turn of the screw thread on the shank of the screw, and the offset bottoms of the grooves of the insert constitutes one quarter to one half the height of the grooves measured from the lowest point of the bottom of the grooves to the highest point of the apex of the grooves.

7. Thread rolling die mechanism according to claim 4, in which the offset bottoms of the grooves constitute about one third of the height of the grooves.

8. Thread rolling die mechanism according to claim 5, in which the bottoms of the grooves of said slotted die are offset from the bottoms of the grooves in the face of said first die member an amount about 15 percent of the pitch measured from apex to apex of the ridges of the grooves of the die insert.

9. Die mechanism according to claim 6, in which the offset bottoms of the grooves in the face of said die insert are offset an amount about 15 percent of the pitch measured from apex to apex of the ridges of the grooves in the face of the die insert.

10. Thread rolling die mechanism for forming a screw thread on the shank of a screw blank to produce a prevailing-torque lockscrew having a threaded shank which has a free spinning leading end portion, a trailing end portion and a locking portion having at least one offset thread segment intermediate said leading and trailing end portions, which mechanism comprises a pair of oppositely disposed thread rolling die members for simultaneously acting upon opposite sides of the shank, one of said die members being movable relatively to the other, one of said die members being stationary and having a slot therein at its trailing end portion to receive a die insert, the other of said die members being reciprocatable and having a face having grooves, the ridges and bottoms of which are of conventional profile, the face of the stationary die member having grooves of the same profile, helix angle and pitch as the grooves of the face of said reciprocatable die member, an insert shaped to have a snug fit in said slot mounted in said slot and having a given groove in its face of the same helix angle as the grooves in the face of said stationary die member, registering with and lying in straight line relationship with the ridges of said given groove in the face of said insert, the bottom of said given groove in the insert being offset in an axial direction from the corresponding adjacent groove in the face of said stationary die member by an amount within the range of 3 percent to 35 percent of the pitch measured from apex to apex of the ridges of the grooves in the face of said stationary die member, the length of said offset bottom of said given insert groove being dimensioned to correspond to the length of the offset thread segment to be formed in said locking portion of said screw thread.

11. Thread rolling mechanism according to claim 10, in which the bottom of said given groove in said insert has a length within the range of 5 percent to 50 percent of the circumference of a turn of the thread to be formed on said shank.

12. Thread rolling mechanism according to claim 11, in which the offset bottom of the said given groove of the insert is offset an amount which is about 15 percent of said pitch and the height of the offset bottoms is about one third of the height of a groove measured from the apex of the bottom to the apex of the ridge of the groove.

13. Thread rolling die mechanism for forming a screw thread on the shank of a screw blank to produce a prevailing-torque lock screw having at least one offset locking thread segment intermediate the leading and trailing ends of the thread on the shank, which comprises a pair of oppositely disposed thread rolling die members for simultaneously acting upon opposite sides of the shank, said die members being movable relatively to each other, one of said die members having a slot therein at its Trailing end to receive a die insert, the faces of said two die members having grooves, the ridges and bottoms of which are of conventional profile, the ridges and bottoms of the grooves in the faces of said two die members having the same helix angle and pitch, an insert fitted in said slot for forming said offset thread segment in said thread, said insert having at least one thread-segment-offsetting-groove in its face having the same helix angle as the grooves in the faces of said pair of die members, the ridges of said insert groove registering with the ridges in the face of said slotted die member and forming straight line continuations of said adjacent ridges, the bottom of the said thread-segment-offsetting-groove in the face of said die insert being axially offset from the bottom of the adjacent groove in the face of said slotted die member by an amount within the range of 3 percent to 35 percent of the pitch measured from apex to apex of the ridges of the grooves in the faces of said die members, said offset bottom having a height within the range of one quarter to one half the height of said grooves measured from the lowest point of the bottom to the highest apex point of the groove, the length of said offset bottom being dimensioned to correspond to the length of the said locking offset thread segment to be formed in said screw thread.