US1529616A - Relay contact and method of making the same - Google Patents

Description

March 10, 19 25 1,529,616

F. L4 DODGSON RELAY CONTACT AND METHOD OF MAKING THE SAME Filed Jan. 13, 1919 2 Sheets-Sheet 1 E rs "tum: Q! /7 23 24 A TTORNE I March 10, 1925. 1,529,616

F. DODGSON RELAY CONTACT AND METHOD OF MAKING THE SAME Filed Jan. 13, 1919 2 Sheets-Sheet 2 INVENTO BY M/ I ATTORNEY Patented Mar. 10, 1925.

UNITED STATES PATENT OFFICE.

FRANK L. DODGSON, OF ROCHESTER, NEW YORK, ASSIGNOR TO GENERAL RAILWAY SIGNAL COMPANY. OF GATES. NEW YORK. A CORPORATION OF NEW YORK.

RELAY CONTACT AND METHOD OF MAKING THE SAME.

Application filed January 13, 1919.

To all whom. it may concern Be it known that l, FRANK L. DonosoN, a citizen of the United States, and resident of the city of Rochester, in the county of Monroe and State of New York, have invented a new and useful Relay Contact and Method of Making the Same, of which the following is a specification.

This invention relates to an improved construction of a contact for relays used in railway signaling systems, and to a method of making such an improved contact.

It is important to have low resistance between the contacts of relays used in railway signaling systems, especially contacts in motor circuits where the resistance of the contact, if high, constitutes a large proportion of the total resistance. It has been proposed to obtain such low contact resistance by employing metal In metal contacts, but such contacts are objectionable because the arcing or sparking, gcncrally occurring upon separation of the contacts, causes the contact surfaces to become pitted or roughened, thus increasing the contact resistance and necessitating frequent renewal. Moreover, the interruption of current often draws an arc across the relay contacts as they separate, sufficient in some instances to cause the metal to metal contacts to actually fuse together,something which cannot be tolerated in railway signaling systems, because safety requires actual separation of contacts at the proper time. The metal to metal con tacts in railway signaling relays are specially susceptible to such fusing because the force tending to cause separation of the contacts is small. Lightning and other heavy current discharges accentuate this ditliculty, so that the olriectionable features of metal to metal contacts has led to the use of carbon, graphite, or some similar refractory material for one or both of the contacts. Graphite to metal contacts, however, have the disadvantages that the contact resistance is high and often variable.

\l'ith these considerations in mind. it is contemplated. according to this invention. to provide a relay contact in which the actual making and breaking of the circuit will occur between metal and graphite. while the flow of current: in the circuit will take place through the low resistance of a metal to Serial No. 270.970.

metal contact. Such a construction gives the desired low resistance for conducting the current, and at the same time provides for the satisfactory making and breaking of the circuit.

I am aware that it has been heretofore suggested to make and break circuits be tween carbon to metal contacts, as in the well known circuit breaker: but the application of this idea to the delicate relays used in railway signaling, presents a number of diilicuit problems, which it is the purpose of my invention to solve. The contacting parts in a relay must be light, bccause of the small amount of energy avail able for operating them. For example, in the relay in which 1 am familiar the operat ing force for each pair of contacts is only about one ounce. Yet, the contacts must have a substantial and rugged construction suflioient to Withstand long service under wide variations of temperature and atmospheric conditions.

Also, the requisite operating characteristics of railway signaling relays, together with the small size of parts and the small amount of operating force available, imposes certain limitations upon the construt. tion not found in other circuit controlling devices. In a relay contact, one member should he resilient so as to make a good firm contact with the other member. and also to cause a scraping or abrasion of the contact surface of said other member as the contact members are hrtmght together. It likewise important to have a spring action at the contact members of a relay so as to provide an initial pressure, when the relay s energized, tending to force the armature away, or in other words, assist in the dropaway of the armature. The small amount of operating force available, for exam ne. only one ounce per pair of contacts), requires that the resiliency or springaction for accomplishing these two functions should be con'ihined and derived from the same member. This is EUPUHII'JllSliKtl in the relays with which I am familiar. by making one contact member resilient and shaping it such that it rubs across the contact fa e of the other contact member during the closing movement, the resiliency of this same mcm her affording the desired spring action both For kicking ofi' the armature when the relay is deenergized and for making good coir tact. lVhen an attempt is made to incorporate with such a contact construction the l'unctions of making and breaking the circuit between graphite and metal, while maintaining the circuit between metal and metal, it will be evident that a still further spring action is required, for the reason that the initial contacting between the graphite and metal contacts, upon energization of the relay, must give way to permit the contacting of metal to metal contacts, while on the other hand, upon deenergization of the relay, the contacting between graphite and metal must follow up and succeed the break ing of the contact between metal and metal. ll? it is attempted to obtain this latter spring action from the resilient contact member, it found that the duty imposed is too great for satisfactory and reliable operation These limitations impose conditions upon the construction of a Contact suitable for re lays used in railway signaling which are not found in ordinary circuit breakers and simi lar devices.

Also, the requirements or performance of relays, especially in the breaking of circuits, are also extremely exacting. The parts r;lt0llltl be constructed so there is no chance of binding or sticking, since stately requires the separation of contacts at the proper time, even though the force tending to produce separation is very small. Furthermore, any construction meeting these requirements should also be one which can be made by ordinar manufacturing methods by average skilled abor.

One of the principal objects of this invention, is to provide a relay contact having those essential and desirable characteristics, which is simple, practical, and reliable in its operation, and which will withstand long service under severe operatin conditions.

After a satisfactory construction of a relay contact has been determined, it is found that the making of its delicate parts, and the assembly and fastening together of these parts in the relation requiret'l, together with proper clearances for satisfactory operation, presents a number of diliicult problems; and a further object of my invention is to devise a method of making a relay contact oil the character described which can be practiced rtliriently by average skilled labor, and which can be used commercially to produce a relay contact hav ng the desired teaturcs oi construction and operation.

Uiher objects and advantages or my in xeution will appear the drscription prti gresses; and the novel features oi the invention will be pointed out in the appended claims.

in descriijing the invention in detail. reference will be made to the accompanying drawing, in which is illustrated a preferred physical embodiment of the invention, in which like reference characters refer to corresponding parts in the several views, and in which:

Fig. l is a view in side elevation of a relay of well known construction, showing a contact embodying my invention applied thereto;

Fig. 2 is a view in end elevation of the relay shown in Fig. 1;

Fig. 3 is an enlarged section of a contact cn'ibodying my invention, taken substantially on the line 3--3 in Fig. l and looking in the direction indicated by the arrow a, the parts of the contact being in the open position corresponding to the deenergized condition of the relay;

Fig. 4 is a fragmentary section, similar to Fig. 3), showing the parts in the closed position, corresponding to the energized condition oi the relay;

Fig. It illustrates in perspective the separate parts of the contact disassembled;

Fig. (3 is a perspective vicvv ol' the apparatus used in accordance with my invention to assemble and fasten together the parts of the relay contact;

Fig. 7 is an enlarged vertical section through the apparatus shown in Fig. (3;

Fig. 8 is an end view of the stopper plunger forming a part of the apparatus shown n Fig. 7; and

Fig. 9 is a perspective view of another part of the apparatus illustrated in Fig. T.

Referring tirst to the general construction of the well known type of relay shown in Figs. 1 and 2, this relay comprises the usual pair oi coils L with a back strap :2, and pole pieces 3 fastened to a coil support t, all of these parts being supported by the top plate 5 ol the relay casing. This casing consists of the metal top plate a hastplate 6, and glass walls or sides T, \Yllllll are clamped between the top plate and the base plate by screws o. The armature .l of the relay is pivotally supported at one edge to downwardly extending lugs it) integral with the coil support l. A number of contact lingers 11 are fastened to the armature l) with interposed pieces 12 of insulating material. Each contact linger 11 is provided at one end with resilient contact pieces 1 and l-t which are adapted to cooperate with lixcd back and trout contacts. respectively. 'lhcse front and back contacts are in the form of binding i iost's R and F. with which the parts actually touching the contact pieces 13 and it are associated. The oppw site end of each contact tinger 11 is clro trically connected by a flexible condurtor if to a binding post secured to and ii striated troin the top plate I. have shown my invention applied particularly to the construction of the trout contact or binding post F. Referring to Figs. 3 and 4, the front contact post F comprises a stem 16, which is screw threaded for part of its length at one end and which has an enlarged head or holder 17 at its lower end. The base portion of the holder 17 is squared and fits without turning: in a groove in the bottom of a block 18 of insulating material Whichextends across the under side of the top plate 5. The stem 16 extends through a larger hole in the top plate 5 and through a bushing it) of insulating material. A sleeve 19 of treated silk or similar insulating material surrounds the stem 16 and insulates it from the metal top plate 5: and the whole front contact post 1 is clamp-ed in place by a nut 21. (Fig. 1). the post being provided with the usual nuts 22 for attaching wires.

The holder 17 of the contact post F has an axial cylindrical cavity formed therein. the lower end of which is counterbored to receive a contact member or button 2?, of carbon. graphite, or other refractory llltt' terial. This button 23 is formed with a lower cylindrical portion slightly less in diameter than the counterbore in the holder 17, and with a smaller guiding collar, and is bored axially to fit freely and snugly around a contact pin24 of silver or other good contact material. This pin 2i has a thin cylindrical head 25 at the lower end: and in the lower end of the graphite button 23 is a cylindrical recess which is slightly deeper than the thickness of said head of the pin. The upper end of the contact pin 2-4 is fastened to the holder 17. and between the bottom of the cavity in said holder and the button 23 is interposed a lightcompression coil spring 26, which tends to urge the but ton 23 downward to the position, shown in Fig. 3, where the head 25 of the pin 24 limits further movement, and the lower contact surface of the button 23 is below the contact surface of the head 25.

I prefer to make the contact finger 11 of brass or similar good conducting material of the requisite stiffness, the contact piece 1 and pin 24 of coin silver or other highly conductive and non-corroding material. and the button of graphite or other refractory material having good conducting properties.

One of the important features of the invention is the Way of fastening the contact pin 24 to the holder 17. The upper end of the pin 24: extends into an axial bore in the holder 17; and the upper end portion of said pin is reduced in diameter. so as to leave a shoulder which bears against the bottom of the cavity in the holder IT. This upper end portion of said pin 24 is formed with gripping edges or shoulders. preferabl 7 formed by a circumferential groove 27; an when the pin 24 is in place this groove 27 is aligned with a transverse hole 28 in the holder 17. After the parts are properly positioned. as hereinafter explained, solder 29 is run in the hole around the upper end of the pin 24. thereby securely fastening the pin in place.

lVith the relay deencrgized,the parts of the contact device assume the nositions shown in Fig. 3, the sprinf 26 having moved the graphite button 23, guided by the pin it, to its lowermost position, where the lower face of the head 25 of said pin is above the lower face of the button 2;}. lVhen the relay is energized, and its armature fl is attracted, the front contact piece 1;} of the contact linger 11 move upward y and makes contact first with the graphite button 23. The pressure of the spring 2:; on the button 23, however. is made slight and less than the pressure whi h the contact linger exerts, so that the button is moved upward until the pressure of the contact finger falls directly upon the enlarged head :25 of the contact pin :24. thus establishing a direct metal to metal connection from the contact finger 11 to the binding post F. This position of the parts is shown in Fig. 4.

Vhen the relay is again deenergljizcd. its armature and its contact fingers are c turned to their lower position by their weight. During; this movement. the but 33, being! urged downward by the sprin will follow up the downward movement of the contact piece 3. C(uiscuucutiy. the con tact piece 13 first leaves contact with the head of the pin 24-. thereby separating the metal to metal contacts but leaving: the cir cuit completed through the graphite button '23; and then, when the downward 'l ollovvaip movement of the button 23 is arr s d by the head 25 of the pin 24 (sec Fl: :1). the contact piece 13 finally breal-cs contact the button 23. thereby illicl'l'lll iiilig the cur rent between graphite and metal. Thus. it will be, evident that my invention provides a construction in which the initial hm JiEw final breaking of the circuit takes p tween a refractory material and a while the circuit is established \hio low resistance of a metal to metal to it will be observed that the con iruction described is simple and compact. 'liie graphite button .2 3 and the contact pin it are combined into a unitary 41 ructurc adaptcd to cooperate with a single metal contact piece. The spring: action. demanded to bring about the breaking" and lllilix'lllgj oi the i'li' cuit between graphite and metal. i derived from the sprin; "26. indepeiulently of the resiliency of the contact piece i i. thereby dividing the duties imposed upon the parts and satisfying: the limitations of ii llll lion previously explained. The from contact post l embodying the invention. can be readily applied to any of the pre ent types of relays. and if desired. may be an and metal.

act

aligned, the plunger 30 is again projected to hold the assembled parts of the contact post firmly in the proper position.

It will be noted from Fig, 7 that the spacing member S bears against the pin 24, the

shoulder of which in turn bears against the bottom of the recess in the holder 17. This positions the pin 2i lengthwise of the con tact post F in the relation desired to adapt it for incorporation in a i nnplete relay. The pin 2i is positioned AIL-1137' in the exact relation desired by reason of being guided by the button 23, which in turn is positioned accurately with regard to the holder 17 by the thin collar 44; on the spacing member S. It will be evident that the primary factor de termining the precise axial alignment of the pin desired, provided the parts are other wise within the narrow limits readily attaincd in ordinary manufacturing, is the clearance between the graphite button 23 and the holder 17, such as to permit the but ton to slide easily without any chance of binding. This desired relation is what is obtained by the spacing member After the parts are in position, a short cylindrical piece of solder all is inserted in the upper end of the hole in the holder 17, this piece of solder being long enough to stick out slightly when resting on the pin The holder 17 now heated, preferably by the flame of a torch or similar heating appliance, the flame being applied as indicated at 47 in Fig. 7. The operator watches the projecting upper end of the piece of solder 4-6 carefully, and as soon as this piece of solder melts and disappears, an additional piece of solder 4:8 is also dropped in, and the flame withdrawn. The parts are then allowed to cool, or are cooled artificially by a blast of air. if desired, and the contact post removed and inspected. If solder can be seen from the lower end of the hole 28, it is known that a proper joint has been made. The fact that solder has run past the 'pin 24-, proves that this solder must have formed around the groove 27 in the end portion of this pin. and also that the solder must have been hot enough to make a good joint.

The purpose of putting in the piece of solder ltiinto the holder 17 before heating it, is to provide a simple and reliable way of determining when the holder 17 has been heated sufliciently to properly melt the solder. Obviously, overheating should be avoided, because it is liable to distort the parts and injure the spring 26. The stopper plunger 38 prevents the solder from running out of the hole 28, and since this plunger is made of aluminum, the solder will not stick to it. The cross cuts 39 in the upper end face of the stopper plunger 38 afford vents to allow the heated air or gases to pass out from the hole 28 without interfering with the desired movement of the solder. The apparatus illustrated provides for the assembling of one contact post, but obviously several similar base blocks may be used in gangs, if desired.

This application is a continuation in part of my prior application, Serial No. 226,708, liled April a 1918.

Although I have particularly described the construction of one physical embodiment. of my invention, and explained the operation and. principle thereof; nevertheless, I desire to have it understood that the form selected is merely illustrative, but does not exhaust the possible physical embodiments of the idea of means underlying my in vention.

l'Vhat I claim as new and desire to secure by Letters Patent of the United States, is:

l in a relay for railway signaling, a contact construction comprising, an insulated contact post having a cup-shaped end, a metallic pin fixed to said post within its cupshzmed end and extending axially thereof, said pin having an enlarged head at its outer end, a carbon button partially enclosed within the cup-shaped end of said post and sun rounded and guided by said pin, said button having a recess in its outer end to receive the enlarged head of said pin, this recess be ing deeper than the thickness of said head a compression coil spring within the cupshaped end of said post and acting to press said carbon button outward to a definite position determined by the engagement of the head of said pin with the bottom of the recess in the button, and a movable contact fin ger having a flat resilient contact piece at its end engaging the button before and after engagement with the pin during movement of the finger toward and away from the post respectively, whereby electrical contact between the finger and post is broken between carbon and metal and is maintained between metal contacts.

2. In a relay of the type described, a contact arrangement comprising, an insulated contact post having a cylindrical recess in its outer end, a pin of highly conductive material fixed to said post and extending axially thereof within said recess, a carbon button. of general cylindrical shape having an axial bore to receive said pin, a spring within said recess acting to press said button outward, means limiting the outer position of said button to a point where its contacting face is beyond that of said pin, a contact finger having a resilient flat contact piece at its free end disposed at an acute angle to the axis of said button and pin, said finger being movable with respect to the post to cause electrical contact between said button and contact piece of the finger before and after contact between the pin and the contact piece as the finger is moved toward and away from the post, respectively, the angulit) lar disposition of the contact piece causing it to slide over the contacting surfaces or said button andpin, whereby a rubbing engagement of metal-tonietal contacts is employed for i'naintaining circuit connections while the circuit is broken by the rubbing engagen'ient of metal to-carbon contacts.

In a contact construction for relays of the type shown and described, a stationary contact post having a recess, a :arbon button within said recess formed with a circumferential shoulder to engage the post around said recess, a metallic pin tired to said post and passing through an axial hole in said button, said pin having an enlarged head at its outer end, the button having a recess in its outer face to receive the head of said pin, the cooperation of the button with the head of the pin limiting the outer movement of the button, means urging said button outward and a movable contact member engaging both the button and pin and exerting a pressure sufiicient to force the button inward and permit the meaning of a direct metal-to-nietal contact between said member and the enlarged head of said pin.

4. A relay for railway signaling having, in combination, a movable contact finger carried by the armature of the relay, a fixed metallic pin, and a movable graphite button surrounding said pin and spring pressed toward said contact linger. said pin and but ton being both arranged to cooperate with said linger, said parts co-acting to make and break the circuit between the contact finger and the graphite button and to maintain the circuit through the contact linger and the metallic pin.

A relay for railway signaling having, in combination, a movable contact finger carried by the armature of the relay, and a contact post for cooperating with said contact finger, said post comprising a stem having an axial recess therein, a movable member of conducting refractory material in said recess, and a metallic member of highly conductory material attached to said stem, said movable member being yieldingly biased into position to make contact first and last with said contact finger as the latter is moved toward and from the contact post, whereby the circuit is made and broken between a metal and a refractory material and is maintained between metal and metal.

6. In a relay, the combination with a mom able contact finger, a contact post tor cooperating with said finger and provided with an axial recess, a carbon button in said recess movable lengthwise of the post, a spring enclosed in the recess and pressing the button outward, and a fixed metallic contact member of highly conductive material coacting with said button to limit the outward movement thereof to a position in which the contact face of the button is nearor the contact finger than that of the metallic contact, whereby the contact finger engages the button and the metallic contact in succession as it. moved to its attracted position.

7. A graphite-metal contact for relays comprising a fixed metallic pin, a movable graphite button surrounding said pin, and resilient means tor urging said button to a position where its contacting face is beyond the contacting face of said pin.

8. A graphiteanetal contact for relays comprising a circular pin of highly conductive material, a movable graphite bub ton surrounding said pin and guided thereby, said pin and button coacting to limit the movement of the button to a position where the contact face thereof is beyond that of the pin, and a compression coil spring acting to urge said button to its projecting position.

9. A graphiteanetal contact for relays con'iprising a silver pin formed with an enlarged head, a graphite button surrounding said pin and movably guided thereby, said button having a recess in one end face adapt-- ed to receive the head of said pin, and a spring yieldingly holding said button prw jected against the head of said pin, the con tacting end face of said button when projected being beyond the contact surface of the head ol said pin.

10. A cont-act post for relays comprising a stem and an enlarged head having an axial recess therein, a metallic pin attached at oniend to said head and extending out of the recess lengthwise of the post, a graphite button surrounding the pin and partially enclosed in said recess. and a. compression coil spring in said recess tending to move the button outward, said button being limited in its outward movement to a position where its contacting face is beyond the outer end face of the pin.

11. A contact construction for relays cone prising a post, a metallic pin extending axially of the post and fastened thereto at one end, a graphite button guided by said pin, said pin being adapted to cooperate with said button and limit the movement thereof to a position where its contacting face is beyond that of the pin, and a spring acting to move the button outward.

12. A contact construction tor relays comprising a contact post, a metallic pin haring one end portion thereof roughened and extending into a bore in said post, said post having a hole therein intersecting said axial bore and filled with solder which embraces the roughened end portion of the pin and holds it in place, a movable graphite button surrounding the pin, and means for resiliently urging said button to a position where its contacting face is beyond that of the pin. 13. A contact construction for relays in which a metallic contact pin is fastened at ill) tit)

one end to a contact post by solder in a hole in the post extending transversely of the axis of the pin and which embraces gripping edges formed on the end portion of said pin.

14. In a relay, the combination with a vertica ly movable contact finger, a contact post for cooperating with said finger and provided with an enlarged head having an axial recess therein. a button of conducting refractouv material in said recess and yield ingly projected outward to a limited extent lengthwise of the post, and a fixed metallic member of highly conductive material havinc its contact face within the limits of the outer contacting face of said button. said contact face of said metallic member being in a horizontal plane above that of the but' ton while the button is in its projected po sition.

15. In a relay. the combination with a movable contact linger having a resilient contact piece at one end. a contact post comprising a stem adapted to be fastened to the top plate of the relay, a fixed metallic pin of relatively low resistance attached to said stem and provided with a contact face at its lower end. a spring. and a movable *arbon button supported by said pin and normal y positioned by said spring so as to be engaged first by said contact piece as the finger is attracted. said contact piece on the finger being: inclined with respect to the faces of said stem and button so as to rub over them as the finger is attracted 16. A contact post for relays comprisin; a stem adapted to be attached to the top plate of the relay. a metallic contact member attached to said stem. a carbon lmtton movable lengthwise of the stem and having its outward movement limited by said metallic member so as to have its contact face beyond that of the metallic member. and a spring acting to press said button outward.

1T. contact post for relays comprising: a stem adapted to be attached to the top plate of the relay and provided at one end with an enlarged head having a recess therein. a carbon button in said recess in vable lengthwise of the stem. a metallic contact member secured to said stem and adapted to limit the outward movement of the carbon button and position it with its contact face beyond that of the metallic member. and a sprin; enclosed in said recess for press in; said button outward.

19. A contact post for relays comprising a stem adapted to be attached to the top plate of the relay. a carbon button carried by said stem and movable lengthwise thereof. a metallic contact member fastened to said stem and having a contacting part within the limits of the outer contact face of said button. said button having a recess in its contact face to receive said contacting part of the metallic member. and a spring for pressing said button outward.

19. A contact post for relays comprising a stem having an axial recess therein. a

'arbou button in said recess. and movable lengthwi e of the stem. said button having an axial bore lcng'thwiic thereof. a spring enclosed in the recess and acting to press said button outward. a metallic member o highly conductive material attached to said stem. said metallic member passing through the bore in said button whereby said button and metallic member are disposed with their contact faces one within the limit of the other. and means whereby the outv; rd movement of the button is limited so as t position its contact face normally outside f that of the metallic member.

2t). A contact post for relays comprising a stem having an enlarged head with a downwardly opening axial recess therein. a carbon button in said recess and biased to move downward lengthwise of the stem to a prwtetcrminc l project ed position. and a metallic member of highly conductive ma terial attached to said head with its contact face within the limits of and above the con tact face of the button in it lmver proje ted position.

.21. contact post for rciays. comprising a stem screw threaded f r part of its length at one end and having an enlarged head at its other end: said enlarged head havin j a cylindrical cavity formed therein which i:' counter-bored at one end: a condu tive bu ton of refractory material adapted to l'ai t I lit in the couuterlmre f said cavity. said button having" a hole pa sing therethrmua'h which is counterbortal at one end: a metal lic pindle of relatively low resistance ex tending through said reces and rigidly ecured to said stem. said spindle having;- a shank adapted to pass through the hole in said button and also having an enlarged head at one end adapted to fit loosely in the counterborc in said button and to loosely hold said button in position. the thickness of the head of said spindle being less than the depth of the countcrbore in said button: and a spring. housed in said cavity and adapted to spring); press said button ontward in one direction. the movement of said button being limited by the under side of the head of said spindle.

22.11) a relay. the combination with a movable contact linger having a resilient contact piece at its outer end. of a statioiu ary contact post cooperating! therewith and comprising a fixed metallic member of highly conductive material. a movable member of conducting refractory material. and a spring. said movable member being normal- 1y projected by the spring into position where its face nearer said contact piece than the metallic member. the tension of llt) said spring being less than that of the contact piece, whereby the contact piece makes contact successively with the refractory member and the metallic member.

23. The method of making graphite-metal contacts for relays of the type shown and described in which a small contact pin is fastened at one end to a contact post and a graphite button is guided by said pin and partially embraced by parts of the post, said method consisting in positioning the pin in proper relation to the contact post by holding the button in alignment with the adjacent parts of the post embracing it with an intervening space for clearance, and then fastening the pin to the post in the position thus established.

24. The method of making graphiteanetal contacts tor relays of the type shown and described. in wihch a small pin with a roughened end portion tits loosely in a bore in a post intersected by a transverse hole in said post, said method consisting in assembling and holding the pin in the proper relation to the post. heating the post, and then running solder into the transverse hole around the roughened end portion of said pin.

25. The method of making grzqtihite-metal contacts for relays of the type shown and described. in which a small pin with a roughened end portion tits loosely in a bore in a post intersected by a transverse hole in said post, said method consisting in assem bling and holding the pin in proper relation to the post, inserting a piece of solder into one end of the transverse hole with part of the solder sticking out in sight, and then heating the post until the solder melts and disappears.

26. The method of making grapl1itemctal contacts for relays of the type shown and described, in which a small pin with a roughened end portion tits loosely in a bore in the post intersected by a transverse hole in said post, said method consisting in assembling and holding the pin in proper relation to the post, covering one end of the transverse hole in the post with a vented stopper, and then running solder into the other end of said transverse hole around the roughened end portion of said pin.

27. A contact construction for relays colnprising, a stationary metallic contact. a movable contact member ot refractory lnateriat having a recess therein to receive the coin tacting portion of said metallic member, and a movable finger for engaging said metallic contact and said refractory member, the contact between said finger and metallic member being broken in a substantially closed chamber formed by the recess in said member of refractory material.

28. Contact construction for relays, comprising a stationary metallic contact, a movable finger arranged to engage said contact. and a movable conducting refractory mene ber partially enclosing said stationary contact and co-operating with the finger to form a closed chamber around the contacting portions of said finger and stationary contact when contact between the latter is broken.

FRANK L. DODGSON.

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