US3390376A - High performance collet for electrical connectors - Google Patents

Description

June 25, 1968 I J. A. NAVA 3,390,376

HIGH PERFORMANCE COLLET FOR ELECTRICAL CONNECTORS F 7; INVENTOR.

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BY ,qw w, ATTORNEYS June 25, 1968 J, A. NAVA 3,390,376

HIGH PERFORMANCE COLLET FOR ELECTRICAL CONNECTORS Filed March 5, 1967 4 Sheets-Sheet 2 Fi-Z ff 47 46a 54 55 44 46 INVENTOR.

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BY ATTORNEYS J. A. NAVA June 25, 1968 HIGH PERFORMANCE COLLET FOR ELECTRICAL CONNECTORS Filed March 5. 1967 4 Sheets-Sheet 4 Y w 5 M u m lb w /ddc INVENTOR. Jaaa/w 4. Alm/4 By rw-h; nrt/rw ATTORNEYS United States Patent 0 3,390,376 HIGH PERFDRMANCE COLLET FOR ELECTRICAL CGNNECTORS Joseph A. Nava, Villa Park, Ill., assignor to The Pylelglational Company, Chicago, Ill., a corporation of New ersey Filed Mar. 3, 1967, Ser. No. 620,408 11 Claims. (Cl. 339-217) ABSTRACT OF THE DISCLGSURE An electrical connector comprisingan insulator block, registered :bores extending through the block and collets mounted Within the bores for receiving electrical contacts and for securely holding and positioning the contacts within the bores. Each of the collets is generally tubularly shaped and comprises a circumferentially continuous cylindrical sleeve and a plurality of flexible and resilient fingers projecting axially from one end of the sleeve. The collet is formed by a machining operation rather than a stamping or punching operation in order to provide special radial and axial cross-sectional configurations, particularly with respect to the fingers.

Background of the invention The general field of art to which the present invention pertains is that of rmulti-pin electric-al connectors and a more specific field of ar-t is that of collets or contact mountings for securing the pins or electrical contacts of `an electrical connector within the contact-receiving bores thereof.

Multi-pin or multi-contact electrical connectors are widely used in numerous applications. They comprise in most instances a pair of insulator blocks through which are formed `a number of axially registered pairs of bores An electrical contact or terminal is carried in each bore. Each pair of axially registered bores houses a pair of mating contacts which come together in electric circuitmaking relation upon assembly of the insulator blocks.

One electrical contact or terminal widely used is known as the pin type, and each pair of such contacts comprises a male member which is partially inserted into the bore of a mating female member. Generally, all of the male members are carried in one insulator block and all of the female members in the other block. This rule is not rigorously followed, however, and furthermore there are electric terminals other than the pin type used in the electrical conncctor art. It is not uncommon for a single electrical connector to employ as many as 30 or more pairs of electrical contacts. The contacts are generally inserted from the back sides of their respective insulator blocks, the opposite or front sides :being identified as those facing the other insulator block in the assembled connector. The individual contacts are connected to suitable conductors such as wires at the back sides of the blocks.

The male members usually protrude out of the bores of their insulator block, whereas the female members usually reside entirely within the bores of their block. By the simple expediency of bringing the two insulator lblocks together into abutting or assembled relation a multitude of electric circuits corresponding to the number of pairs of male and female contacts can be simultaneously completed. When the two blocks are separated all of the circuits are broken.

Means are provided for mounting the male and female contacts within the bores of their respective insulator blocks. Such mounting means should preferably be capable of withstanding the substantial forces that may be applied to the contacts in the Iassembly and disassembly of lCC the connector many times without failure -or breakage thereof.

The contact mounting means generally comprises a plurality of collets inserted respectively into the bores of the insulated blocks. In order to prevent the contacts from being pushed toward the back sides of the insulator blocks during assembly of the connec-tor, i.e., when the male members yare inserted into tne female members, tne collets are each provided with a plurality of radially inwardly extending tines or fingers having shoulders, edges or other stop surfaces for abuttingly eng-aging complemental surfaces formed on the contact members. Collets are generally used for this service -because yof the ease with which the contacts can -be removed for serv-ice, replacement or the like. Merely by inserting a tubular contact removal tool around the contacts and into the bores from the front sides of the insulator blocks, the tines can be spread radially outwardly in the bores and the contacts can then be easily removed from the bores.

In many applications of electrical connectors of the type described hereinabove the individual male and female contact members are quite small and the size of each of the contact-mounting collets is particularly diminutive. oftentimes the collets are about inch in length and j/16 inch or smaller in diameter. The tines or fingers which are formed on the collets to engage and restrict axial movement ofthe contacts may be extremely small.

As a result, the collet tines or fingers of collets heretofore known in the electrical connector art can undergo a relatively small number of assembly cycles. Each time the two insulator blocks of la connector are re-assembled, and -the male contacts are pushed into the female contacts, substantial forces are imposed on each of the little tines of the collets in preventing the male and female contacts from moving toward the back side of their respective insulator blocks.

Prior art connectors of which I am aware have a contact removal capability of about 50 to 60 times. In other words, the contacts can be disassembled from the insulator blocks by opening the collets, with an appropriate tool, and re-assembled after servicing the contacts, a total of 50 to 60 times. This low contact removal capability is generally due to the inability of the small tines of the collets to withstand the fatigue stresses resulting fro-m repeated fiexure.

The tines may fail in several different ways. First of all, due to the forces imposed thereon they may take a permanent deformed set, thus precluding snug engagement with the shoulders of the contacts. In addition the tines may fracture due to fatigue or overstress. Because of this low contact removal capability of the collets, applications of electrical connectors are generally restricted to those which require infrequent disassembly and assembly. As a matter of fact, as a result of collet failure many government and industry specifications require a contact removal capability of only ten times. To greatly increase the contact removal capabilities of electrical connectors without diminishing any of the advantages which attend the use of collets is a principal object of the present invention.

Summary of the invention Briefly, the present invention relates to an electrical connector comprising an insulator block having collet and contact receiving bores extending therethrough. The collets, rather than being made of flat sheet-form material, are machined to a special configuration.

Each of the collets comprises a cylindrical sleeve and a plurality of circumferentially spaced contact-engaging fingers (or tines) projecting axially from one e'nd of the sleeve to jointly surround a contact when the contact is inserted into the collet.

Each. of the iingers comprises a major portion adjacent the sleeve, a radially inwardly inclined beam portion extending from the major portion and a head portion at the distal end of the beam portion.

The head portion of each of the lingers comprises a contact engaging surface formed on the radially inner side thereof to provide, in combination with the contact engaging surfaces of the other head portion, a circumferentially surrounding holding surface for the contact,

The fingers are also flexible from the points at which they join the sleeve and throughout the beam length from such joints to the contact engaging surface at the head portion, whereby the contact engaging surfaces formed on the head portions are radially movable or spreadable from a free state diameter, which is less than the diameter of the engaging surfaces of the contacts, to an assembled state diameter which is equal to the diameter of the engaging surfaces of the contact. The fingers, in addition, are capable of further iiexure, whereby the head portions are radially movable or spreadable, with an appropriate tool, from the assembled state diameter to a diameter suiiiciently larger than the contact engaging surface diameter so as to release the Contact and allow its removal from the collet.

Cooperating means are formed on the collets and the walls of the bores for snap-locking the collets within the bores. In addition the collets include a radial cross-sec tional thickness at the beam portions of the fingers which is less than that at the head portions of the fingers. The diameter of the inner peripheral wall of each of the fingers is less at the head portion than at the major portion. The `beam portion of each of the fingers extends radially inwardly at an angle to the axis of the collet which lies within a predetermined range both when the head portion of the finger is at its free state diameter as well as at its assembled state diameter. Other features include fillets at the junctions of the beam and major portions and the beam and head portions of each of the fingers.

Electrical connectors equipped with collets constructed in accordance with the principles of the present invention and incorporating features described hereinabove and hereinafter have been carefully tested in terms of the number of times which the contacts can be disassembled and assembled without collet failure. Connectors so constructed have removal capabilities in excess of 5,000 times, or more than 80 to 100` times the contact removal capabilities of the connectors of the prior art.

In view of the foregoing it is an object of the present invention to provide a multi-contact electrical connector having unusually high contact removal capabilities, for example, in the order of 5,600 times or more.

Another object of the invention is to provide such an improved electrical connector without eliminating or diminishing the advantages which attend the use of collettype contact mountings.

Another object is to provide a collet having high durability and high fatigue resistance characteristics.

Another object of the invention is to provide a collet capable of withstanding many times more contact removals than those of the prior art without substantially increasing the size of the collet.

Another object of the invention is to provide a collet wherein the stress distributions throughout the tines or fingers thereof is reasonably smooth, with stress concentrations limited to about 1.2 times the normal stress and wherein a good correlation exists between the stresses and bending moments of the fingers to provide optimum iiexure characteristics and high fatigue resistance.

Still another object of the invention is to provide a collet having fingers constructed so as to hold a contact more securely and resist buckling or skew when subjected to an axial load imposed by the contact.

Many other features, advantages and additional objects ot' the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheets of drawings, in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative example only.

Brief description of the drawings FIGURE 1 is a fragmentary cross-sectional view of an insulator block of an electrical connector constructed in accordance with the principles of the present invention and having a machined collet of this invention mounting a male electrical contact in a bore extending through the block.

FGURE 2 is a side elevational view of the collet shown in FIGURE 1.

FIGURES 3 and 4 are respectively left and right end views ofthe collet shown n FIGURE 2.

FIGURES 5-7 are substantially force vector diagrams useful in explaining the forces imposed on the fingers of a collet constructed in accordance with this invention.

FiGURE 8 comprises an enlarged fragmental vertical sectional view of the collet shown in FIGURES 1-4 and a graph showing the stress and bending moment along the active portion of one linger of the collet.

FIGURE 9 is similar to FIGURE 1 but illustrates another embodiment of a collet constructed in accordance with this invention, half of which collet is shown in section and the other half of which is shown in elevation.

FIGURES l0 and 11 are respectively left and right elevational end views of the collet shown in FIGURE 5.

Description 0]" the preferred embodiments Referring to FIGURE l an insulator block of a multicontact electrical connector is indicated generally at reference numeral 10. The block 10 has formed therein a plurality of bores which extend from a front side or wall 11 of the block 10 to a back side or rear wall 12, one of said bores being indicated at 13.

Bore 13 is formed by a bore wall 14 having an annular ridge 16 formed integrally therewith and projecting radially inwardly therefrom. The ridge 16 comprises a cylindrical side wall 17 and a pair of axially spaced radial end walls 18 and 19.

Extending through the bore 13 is an electrical contact 20. Although the principles of this invention are applicable to any type of contact or terminal, the contact illustrated in the drawings is of the pin type, and more particularly a male pin electrical contact. In most connector assemblies all of the contacts in one insulator block are male contacts. A companion insulator block carries a corresponding number of female contacts in axially aligned relation to the male contacts such that when the two insulator blocks are brought together all of the male contacts of the one block (for example, block 10) engage the female contacts of the companion block in mating relation, as will be understood by those skilled in the art.

The contact 20 comprises a cylindrical shank 21 and an enlarged-diameter contact head 22 at one end of the shank adjacent the front Wall 11 of the block 10. A concentric reduced-diameter stud 23 projects forwardly from a front wall 24 of the contact head 22 and is received in a complementary sized bore of a female Contact member of the companion insulator block in the assembled condition of the connector.

The contact 20 is retained in the bore 13 by means of a contact mounting member or collet 26. The outer diameter of the contacts 20 is less than the diameter of the bore 13, and the collet 26 serves not only to center or concentrically align the contact 20 within the bore 13, but also to restrict axial movement of the contact backwardly toward the rear wall 12 of the block 10 after the contact has been inserted into the collet 26. The contact 20 may be prevented from moving forwardly or toward the front wall 11 of the block 1t) by a conductor terminal attached to the shank 21 which overlies the block rear wall l2, as will be understood by those skilled in the art.

The collet 26 is generally tubularly shaped and comprises an annular or cylindrical circumferentially continuous sleeve 27 at one end thereof adjacent the block rear wall 12. The sleeve 27 comprises an outer peripheral wall 28 and an inner peripheral wall 29 and a pair of radial end walls 30 and 31. Formed integrally with and projecting axially forwardly from the end wall 30 are a plurality of circumferentially spaced fingers indicated respectively at reference numerals 32, 33, 34 and 35.

Since the fingers 32-35 are identical to one another only finger 32 will be described in detail and all of the reference numerals applicable thereto are equally applicable to the fingers 33-35.

In radial cross-section finger 32 is substantially segmentally cylindrically shaped along its entire axial length. As shown in FIGURES 1-4, finger 32 comprises an outer peripheral wall indicated generally at 36 and an inner peripheral wall indicated generally at 37. The diameters and shapes of' portions of the walls 36 and 37 along the axial length of finger 32 differ from one another and will be described in detail hereinafter.

The finger 32 may be conveniently described as comprising three structurally and functionally different portions along its axial length, a major portion 38, a beam portion 39 and a head portion 40. The major portion 38 is formed integrally with the sleeve 27. The beam portion 39 is axially forward of the major portion 38, that is, toward the front wall 11 of the insulator block 10. The head portion 40 is axially forward of the beam portion 39 adjacent a distal end 41 of the finger 32.

An important function of the major portion 38 is to retain collet 26 within the bore 13. An important function of the head portion 40 is to engage and to concentrically stabilize the contact 20 within the bore and to restrict axial movement of the contact rearwardly within the bore. Important functions of the beam portion 39 are to connect the head portion 40 to the major portion 38 in a manner so as to provide a radially inward bias to the head portion 40, to resist buckling as the contact head 22 imposes a load on the head portion 40 and to resist fatigue and other failure modes which could result from metal working uneven stress distributions and excessive bending.

Finger 32 (as well as fingers 33-35) is resiliently fiexible so that the head portion 40 is radially movable. Before the contact 20 is inserted into the collet 26 the fingers assume free state positions as illustrated in the dashed lines at 32 in FIGURE l. After the contact 20 is inserted into the collet 26 the fingers are urged radially outwardly to assembled state positions thereof as shown in the solid lines of FIGURE 1.

The major portion 38 of the finger 32 comprises spaced parallel outer and inner peripheral walls 42 and 43 and beam portion 39 comprises functionally spaced outer and inner peripheral walls 44 and 45. The head portion 40 comprises an outer peripheral wall 47 and a stepped inner peripheral wall which includes a pair of radially spaced panallel portions 48a and 48h and an inclined portion 48C. A radial wall 49 forming a shoulder surface interconnects wall portions 48a an-d 48h.

A fillet 46 is formed integrally with and interconnects the major and beam portions 38 and 39 and another fillet 46a is formed integrally with and interconnects the beam and head portions 39 and 40. The fillet 46 comprises a radial end wall 55 facing the end wall 30 of the sleeve 27, and the complementarily shaped ridge 16 formed on the bore wall 14 is received in the recess bounded by walls 55, 30 and 42. i

To mount the contact 20 within the collet 26 the head end 22 of the contact is first inserted into the collet sleeve 27 through the end of bore 13 which opens to the block rear wall 12. The contact 20 is then urged further into the collet 26 until the contact head 22 engages and spreads the fingers 32-35 and a radial back wall E0 of the contact head 22 moves past the radial walls 49 of the finger head portions 40. The fingers then snap radially inwardly to the positions thereof shown in FIGURE 1 wherein the radial back wall 50 of the contact head 22 provides a shoulder surface in abutting engagement with the shoulder surfaces 49 of the fingers 32-35.

When the contact 20 is mounted in assembled relation in the collect 26 the inner peripheral wall portions 48a of each of the nger head portions 40 are in engaging relation with the adjacent surfaces ofthe contact shank 21. Similarly, the inner Peripheral wall portions 48h of each of the finger head portions 40 are in engaging relation with the adjacent surfaces of the contact head 22.

As noted hereinabove, a principal object of the present invention is to provide a collet having a contact removal capability flar in excess of the contact removal capability of the collets or contact mounting members of the prior art. Failure of the fingers (or tines) of the prior art collets results, generally, during flexure of the collet fingers in order to release the contacts from the collet and allow its removal from the connector.

In most instances, the forces required to fiex the fingers create stresses in the beam portion of the fingers which closely approach the yield strength of the material of which the fingers `are made. It is well known that all metals are crystalline, and that repeated stress will result in the mechanism of fatigue failure which occurs when the endurance limit of the material is exceeded. This phenomenon occurs during repeated stress, even though under static conditions, the normal stress may be well within the yield streng'h of the material.

The collet 26, however, constructed in accordance with the principles of this invention, is capable of withstanding a vastly increased number of contact removal and reinsertion operations. The collet 26 is machined so that the thicknesses of portions thereof differ from one another and the entire configuration of the collet and the contours and dimensions of its various portions are carefully selected and controlled. This is in contrast with the fabrication methods of the prior art wherein the collets are generally merely stamped from sheets of fiat stock, or machined, wth regard only to the static stresses of the collet structure.

The collet 26 may be rnade of beryllium copper which affords good resilient fiexibility to the fingers 32-35. As noted, the fingers 32-35 impose a radial inward bias on the contact 20 in the assembled state thereof.

A graphic illustration of this force as well as the other forces which may be imposed on the fingers 32-35 are shown in the force diagrams of FIGURES 5, 6 and 7, wherein reference numerals similar to those shown in FIGURES 1-4 Kare used where applicable to indicate similar portions of the collet 26.

Assume that a male contact 20 is seated in a collet 26 and that an axial force indicated at F is being imposed on the shoulder 49 of the head portion 4t). This force may result from mating of the male contact 20 with a complemental female contact, or from any undesirable encounter with another body. An equal and opposite force F is imposed on the wall 55 of the fillet 46. As a result of the axially offset relation of these forces and of the included angle between the beam portion 39 and the axis of the contact 20, equal and opposite radial forces C and C are imposed respectively on the shoulder 49 and the wall 55. A compressive force F is imposed on the beam portion 39. Forces C and C' may be calculated through the equation where D and L represent respectively the distances with which F and F and C and C are offset with respect to one another, reference being made to FIGURE 7.

The force C is augmented by a similarly directed force P caused by the deflection of the finger 32 from its free state to its assembled state disposition which occurs when the contact 20 is inserted into the collet 26. Forces T and T result from imperfections in the petpendicularity of contract radial wall t) and collet radial wall 49 related to the axial center line of Contact 2t) and collet 26. These imperfections may result in an out of perpendicularity as great as Vxhen force F is imposed, as noted previously, a force T, proportional to F in the ratio of the tangent of 15, tends to radially displace the collet linger 32, in opposition to forces C-l-P and Cl-P.

In accordance with the principles of the present invention the fingers 32-35 are constructed so that with respect to each the force P|C which tends to urge the finger against the contact 2li is always at least twice as great as is force T which tends to spread the linger.

It has been determined that optimum results lare obtained when the distance L is within a range of between 4 to 9 times the distance D. Further, the median diameter of the shoulder 49 in the assembled state thereof should be at least 1.1 times the median diameter thereof in the free state. The median diameter of the abutment wall 5S should be at least 1.3 times the median diameter of the shoulder 49 in the assembled state of the collet. The beam portion 39 should extend at an angle to the axis of the sleeve 27 in a range of between 5-10 in the free state thereof and in a range of between 3-5 in the assembled state thereof.

The iillet 46 between the major and beam portions 38 and 39 not only increases the radially inward bias of the finger 32 as the lingers spread from its free state to its assembled state configuration, but also greatly improves the stress distribution at this highly critical junction.

The bending moment and stress distribution of linger 32 (as well as ngers 33-35) are shown graphically in FIGURE L8. The bending moment shown in the graph is that which occurs along the length of the linger 32 after it has been spread from its free state to a deflected position which will allow the contact 2t) to be removed from collet 26. The deflection in this example is .013. The Stress is that which occurs along the length of the spread finger under the influence of the bending moment.

It is noted that while the stress increases at the junction of the major and beam portions 38 and 39, this increase or concentration of stress is limited to about 1.2 times the normal stress. In the collets of the prior art stress concentrations occur far beyond this 1.2 limitation and are often causes of the relative low contact removal capabilities of the prior art collets.

Referring again to FIGURES 1-4, the fillet 46 comprises, in addition to the radial end wall 55, an outer peripheral wall 51 which extends substantially parallel to the major portion 38, and a transition wall 52 which interconnects the peripheral wall 51 and the outer peripheral wall 44 of the beam portion 39. The transition wall 52 is inclined toward the axis `of the collet 26 at an angle greater than the angle of inclination of the beam portion 39 and comprises an arcuately shape-d section 53 adjacent the outer wall 44 of the beam portion 39.

The tillet 46a comprises a radially outwardly inclined transition Wall 54 which interconnects the outer Walls 44 and 47 of the beam and head portions 39 and 40, respectively. The transition wall 54 includes an arcuately shaped section 56 immediately adjacent the outer wall 44 of the beam portion 39.

As noted, the sleeve 27 is circumferentially continuous. Each of the fingers 32-35 comprises apair of longitudinal end walls 57 and 5S which extend in circumferentially spaced parallel relation to the longtiu- dinal end walls 57 and 58 of adjacent fingers. The facing longitudinal end walls 57 and 58 of adjacent lingers are interconnected by an arcuately shaped wall 59.

When the collet 26 is inserted into the bore 13 of the insulator block; 10, the head portions 40 olt the fingers 32-35 are squeezed together sufficiently to enable the head portions to pass through the ridge 16 projecting inwardly from the bore wall 14. The collet 26 is then pushed forwardly from the back wall 12 of the block 10 into the bore 13 and as the transition walls 52 of the fingers 32-35 abut the end wall 19 of the ridge 16, the fingers 32-35 are wedged together to enable the fillets 46 to move past the inner wall 17 of the ridge 16. As soon as the radial end walls 55 of the fillets 46 have passed axially forwardly of the end wall 18 of the ridge 16, the lingers 32-35 snap radially outwardly and the collet 26 is snaplocked in the bore 13. Once the collet 26 is locked in the bore 13 it is ready to receive one of the contact members 20'.

Portion 48C of the inner wall 48 of each of the head portions 40 is tapered to receive a complementary tapered nose of a tubularly shaped contact removal tool. As it will be understood by those skilled in the art, the tool may be inserted into the bore 13 from the front side 11 of the block 10 to spread the fingers 32-35, whereupon the contact 20 can be removed from the back side 12 of the block 10. The diameter of the bore wall 14 is sutiicient to enable the fingers 32-35 to be spread radially outwardly an amount necessary to move the wall 49 out of axial registry with the wall 50 of the Contact 20.

Another embodiment of a collet constructed in accordance with the principles of this invention is shown in FIGURES 9-11 wherein parts similar to those shown in FIGURES 1-4 are identified by the reference numerals used in FIGURES 1-4 with the prefix l added.

Thus the collet 126 is mounted in a bore 113 of a connector insulator block 11i). The collet 126 has four fingers 132-135 projecting from a circumferentially continuous sleeve 127. A major difference between this embodiment, however, and the embodiment of FIGURES 1-4 resides in the arrangement for mounting the collet within the u bore.

The major portion 138 of each of the fingers 132-135 comprises an outer peripheral wall 142 and a radial wall to receive the walls 117 and 118 of the ridge 116, but the back wall 119 of the ridge 116 abuts a radial wall 16) of a radially outwardly projecting protuberance 161 formed on the major portion 138, rather than the front wall 30 of the sleeve 27 as shown in the other embodiment.

The protuberance 161 also comprises .a peripheral wall 162 of substantially the same diameter as the wall 151 of the tillet 146, and another radial wall 163 spaced axially rearwardly of wall but axially forwardly of the forward wall 130 of the sleeve 127.

In this arrangement the groove which receives the ridge 116 (and which is bounded by walls 117, 155 and 163) is spaced further forwardly of the circumferentially continuous sleeve 127 than in the embodiment of FIGURES 1-4.

As a result the fingers 132-135 are more easily urged into the bore 113 since the wedging surfaces or transition walls 52 are farther from the point at which the lingers 132-135 pivot about the sleeve 127.

An end portion 164 of the sleeve 127 is ared outwardly to facilitate insertion of the head 122 of the contact 120` into the collet 126. In other respects the collet 126 is similar to collect 26 of FIGURES 1-4.

Although minor .modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably come within the scope of my contribution to the art.

I claim as my invention:

1. A tubular machined collet for insertion into a rigid bore of an electrical connector for receiving and securing therewithin an electrical contact comprising,

a cylindrical sleeve portion,

a plurality of resilient contact-securing lingers projecting generally axially in one direction from said sleeve portion and bendable radially outwardly from a free state configuration to a bore-inserted contact-sccuring conguration,

said fingers each comprising, in lprogressively axially spaced relation with respect to said sleeve portion,

a ,major portion, a beam portion and a head portion having first, second and third inner and outer Aperipheral wall means, respe-ctively,

said first and second inner peripheral wall means having adjacent ends joining one another, the adjoining end of said first inner peripheral wall means extending axially and the adjoining end of said second inner peripheral wall means sloping radially inwardly in said one direction from said first inner peripheral wall means,

said second outer peripheral wall means sloping radially inwardly in both the free state and the bore-inserted contact-securing configuration of said finger in parallel relation to said second inner peripheral wall means, and

'a projection forming an abutment wall extending radially outwardly of said first outer peripheral wall means in axially spaced relation to said sleeve portion for providing with said sleeve portion and said first outer peripheral wall means in the outer periphery of said collet circumferential groove means for receiving a complementarily shaped ridge in the bore `of the connector for locking the collet axially in both directions in the bore,

said third inner peripheral wall means providing a substantially radially extending shoulder surface on said head portion facing the projecting end of said finger for receiving in abutting engagement a cooperating shoulder formed on a head of the electrical contact and a contact-head surrounding surface extending axially from said shoulder surface for surrounding the head of the electrical contact.

2. The collet as defined in claim 1 wherein said projection comprises a fillet including a radially inwardly and axially extending transition wall interconnecting said first and second outer peripheral wall means and including an arcuately shaped concave section immediately adjacent said second outer peripheral wall means to enhance stress distribution and to increase fatigue resistance and durability of the collet in the area of the junction of the major beam portions of said fingers.

3. The collet as defined in claim 1 and including a radially outwardly land axially extending transition wall interconnecting said second and said third o-uter peripheral wall means,

said transition wall being concave throughout a substantial portion of the axial extent thereof to enhance stress distribution and to increase fatigue resistance and durability of the collet in the area of the junction of the beam and head portions of said fingers.

4. The collet as defined in claim 2 wherein the thickness of said fillet in a radial plane is in the range of between 1.2 and 2.3 times the thickness of said beam portion in a radial plane.

5. In a collet for retaining an electrical contact in a connector, made of machinable material, the improvement of inner and outer surfaces of revolution forming together with one another and characterized by,

a first shoulder projecting in one radially transverse ydirection from one of said surfaces,

a second shoulder spaced axially from said first shoulder and projecting in an opposite radially transverse direction from the other of said surfaces,

an interconnecting beam section extending axially and radially between said shoulders,

said first and second shoulders being radially spaced at an unstressed position `so that axial forces applied thereto will develop la countermoment counteracting bending moments tending to render said beam section unstable, and transition portions connecting said first and second shoulders at corresponding inner and outer surfaces to said beam section without significant discontinuities,

said inner and outer surfaces at said beam section 'and at said transition portions comprising means disposed in such configurative relationship with respect to one another that the stresses in such beam section and said transition portions will be so smoothly distributed that stress concentrations will be limited to no more than 1.2 times the normal stress.

6. The collet as defined in claim 5 wherein said shoulders are subjected to oppositely acting and axial forces and wherein the vaxial distance between said shoulders is within a range of between 4 to 9 times the radial distance between the lines of said forces acting on said shoulders.

7. The collet as defined in claim 5 wherein said second shoulder is imovable radialy outwardly from a free state position to a contact-inserted position and wherein the median diameter of said second shoulder in the contact-inserted position thereof is at least 1.1 times the median diameter thereof in said free state position.

8. The collet as defined in claim 5 wherein said second shoulder is movable radially outwardly from a free state position to a contact-inserted position and wherein the median diameter of said first shoulder is at least 1.3 times the diameter of said second shoulder in said contact-inserted position thereof.

9. The collet as defined in claim 5 wherein said beam section is bendable radially outwardly from a free state configuration to a contact-inserted configuration and wherein said beam section extends at an angle to the axis of said collet in a range of between 5-10 in the free state configuration thereof and in a range of between 3-5 in the contact-inserted configuration thereof.

10. The collet as defined in claim 5 wherein said transition portions comprise concavely-shaped wall surfaces enhancing the distribution of stress at the areas of juncture of said shoulders and said beam section.

11. A tubular machined collet for insertion into a rigid bore of an electrical connector for receiving and securing therewithin an electrical contact comprising,

a cylindrical sleeve portion,

a plurality of resilient contact-securing fingers projecting generally axially in one direction from said sleeve portion and bendable radially outwardly from `a free state configuration to a bore-inserted contact-securing configuration,

sa1d fingers each compr1s1ng, 1n progressively ax1ally spaced relation with respect to said sleeve portion, a major portion, a beam portion and a head portion having first, second and third inner and outer peripheral walls, respectively,

said first and second inner peripheral Walls having adjacent ends joining one another, the iadjoining end of said first inner peripheral wall extending axially and the 'adjoining end of said second inner peripheral wall sloping radially inwardly in said one direction from said first inner peripheral wall,

said second outer peripheral wall also sloping radially inwardly in both the free state and the bore-inserted contact-securing configuration of said linger, and

a projection forming an abutment wall extending radially outwardly of said first outer peripheral wall in axially spaced relation to said sleeve portion for providing with said sleeve portion and said first outer peripheral wall in the outer periphery of said collet circumferential groove means for receiving a complementarily shaped ridge in the bore of the connec- 1 l 1 2 tor for locking the collet axially in both directions stress concentrations therein when assembled in the in the bore, connector and when securing a contact therewithin said third inner peripheral Wall `providing a subby smoothly distributing stress to maintain concenstantially radially extending shoulder surface on trations at all points along the axial extent thereof said head portion facing the projecting end of 5 no greater than 1.2 times the normal stress.

said finger for receiving in abutting engagement a cooperating shoulder formed on a head of the References Clted electrical contact and a contact-head surround- UNITED STATES PATENTS ing surface extending axially from said shoulder 2,477,849 8/ 1949 Adams 339-217 surface for surrounding the head of the eleclo 3,221,292 11/1965 Swanson et a] 339-217 trical Contact, 3,229,244 1/1966 Bachman 339-217 said abutment Wall and said shoulder surface be- 3,246,281 4/ 1966 Cunningham 339-217 ing spaced axially and radially from one another and being subjected to oppositely directed axial FOREIGN PATENTS forces, 15 936,926 9/ 1963 Great Britain. said projection further comprising an axially extending transition Wall sloping radially inward- MARVIN A- CHAMPION, Primary Examiner- 1y t0 Said Sfod Outer Peripheral Wall, R. s. sTRoBEL, Assistant Examiner. said lingers compr1sing means configured to minimize

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