US2781431A - Electric switches and parts therefor - Google Patents

Description

mamas Feb. 12, 1957 u. F. CARTER 2,781,431

ELECTRIC SWITCHES AND PARTS THEREFOR Filed Aug. 5, 1953 2 Sheets-Sheet 1 Feb. 12, 1957 u. F. CARTER ELECTRIC SWITCHES AND PARTS THEREFOR 2 Sheets-Sheet 2 Filed Aug. 5, 1953 INVENTOR dl rze/ .3 (brt' r I n I I; A1-r EZY nrncrnrc swrronns AND PARTS THEREFOR Uriel E. Carter, Milwaukee, Wis., assignor to Cutler- Hammer, Inc., Milwaukee, Wis a corporation of Delaware Application August 5, 1953, Serial No. 372,568

14 Claims. (Cl. 200-83) This invention relates to electric switches and parts therefor; and although not limited thereto, the invention relates more particularly to switches automatically operable in response to an external condition.

An object of the invention is to provide an electric switch having an improved snap operating mechanism and improved contact actuating structure.

Another object is to provide an improved form of electric switch operating with a snap action in response to an external condition.

Another object is to provide a switch which will be rugged and dependable in operation and which is inexpensive to manufacture.

A further object is to provide an electric switch of the character described which may be readily assembled and adjusted.

Other objects and advantages of the invention will hereinafter appear.

T he accompanying drawings illustrate an embodiment f the invention which will now be described, it being understood that certain modifications in respect of structural details may be made therein without-departing from the spirit of the invention or the scope of the appended claims.

in the drawings,

Figure l is a top plan view, partly in section, of a switch embodying the invention;

Fig. 2 is a rear elevational view of the switch illustrated in Fig. 1, as indicated by the arrows at 22;

Fig. 3 is a cross sectional view taken on line 33 of Fig. 1, and looking in the direction of the arrows;

Fig. 4 is a cross sectional View of a portion of the switch illustrated in Fig. 1, certain of the parts thereof being shown in elevation; and

Fig. 5 is a view in elevation of a preferred form of the contact members employed.

Referring to the drawings, the U-shaped switch frame is generally designated 1% and comprises a base plate 11 States Patent having a pair of like, parallel, upwardly extending side as best illustrated in Fig. l.

A bracket 16 (Fig. l) is secured near the upper edge and on the rearward side of plate 13 toward the snapacting mechanism. This bracket 16 has an outwardly turned end 17, adjacent to wall 12 (Fig. 1:), the extreme outer portion 18 of which is of reduced width. Portion 18 is inserted into a perforation 19 (Fig. 2 at one end of a leaf spring 20. The other end of spring 20 is notched at 21 to accommodate the reduced central portion of a 2,781,431 Patented Feb. 12, 1957 nut 25. Nut 25 is turned upon a small bolt or screw 26 which extends rearwardly from plate 13 at a point near wall 12a. As the nut 25 is turned in opposite directions, respectively, the notched end of spring 21 is moved toward or away from plate 13, said nut 25 being lockable in any adjusted position thereof by a second nut 25 (Fig. 1).

The central portion of spring 20 is constrained against excessive movement away from plate 13, and the end of spring 26 is prevented from becoming disengaged from the end 18 of bracket 16, by a portion 27 of bracket 16. This portion 27 extends rearwardly from the top edge of bracket 16, over the upper edge of spring 20, and then downwardly and forwardly, as indicated at 27 and 27', respectively, in Figs. 2 and 3.

Except for leaf spring 20, nut 25, screw 26, and end 17 of bracket 16, the switch is substantially symmetrical about a plane parallel with and midway between side walls 12 and 12 A pair of like angle pieces 34) and 3% (Fig. 2) are secured, as for example by welding, to the lower end portion of plate 13, in such manner that portions 31 and 31 thereof, respectively, Figs. 1 and 2, are opposed and extend rearwardly from plate 13. The lower central portion of plate 13 between angle pieces 30 and 30 is cut away at 32, 32 (Figs. 2 and 3) to accommodate a main or range coiled compression spring 35. This spring is held in place at its upper end by a nut 36 and a threaded member 37. The nut 36 has a lower gland portion which extends axially into the upper end of the spring 35 and has an upper portion 38 against which the upper end of spring 35 bears. The nut 36 is internally threaded to accommodate threaded member 37. The upper end 39 of the latter is of reduced diameter and forms a shoulder at dd, Fig. 3. The plate 13 is otfset forwardly to form a central vertical arch 41, Figs. 1 and 3, which accomodates the upper end 39 of member 37. A washer 42, Figs. 1 and 3, disposed on shoulder All) bears against the lower edge of arch 1 and the lower edge of bracket 16. The top end 39 of member 37 is kerfed to permit rotation of threaded member 37 by means of a screwdriver. The upper portion 38 of nut 36 is provided with extensions 43, 43, Fig. l, which. engage plate 13 and prevent said out from turning. Thus, rotation of member 37 in opposite directions, respectively, causes the nut to move vertically and vary the degree of compression of spring 35.

The lower end of spring 35 bears against a spring gland 50 which in turn bears against the rib 51 (Fig. 3) of a lever 52. Lever 5'2 has two like arms 53 and 53 (Fig. 2) which are pivoted at their respective lower ends about a pivot member 54, Figs. 2 and 3, secured, as for example by spot welding, to the base plate 11. The pivot points of member 54 are located rearwardly of the rib 51, as shown in Fig. 3. The arms are interconnected at their lower ends by a connecting member 55, Fig. 2, in which rib 51 is formed.

Arms 53 and 53 are disposed between wall 12 and portion 31 of angle piece so, and between wall 12. and portion 31 of angle piece Sit respectively. Also, arms 53 and 53 extend beyond angle pieces 36 and 30 respectively. The upper free ends of arms 53 and 53- are connected, in this instance, by a cross piece 56, Figs. 1 and 2. A forwardly projecting tab 57, Figs. .1, 2 and 3, on member 56 is adapted to engage leaf spring 2% at a point intermediate the ends of the latter. The upper free end of lever 52, Fig. 2, is swingable about pivot member 5 in the plane of symmetry of the switch toward and away from plate 13. Main spring 35, bearing against gland 50, and thus against rib 51, tends to pivot the free end of lever 52 toward plate 13 so that tab 57 engages leaf spring 20. The operating position of lever 52 is determined by the compressive force of the compression spring 35, which is adjusted by rotation of threaded member 37; by the resilience of spring which is adjusted by rotation of nut (Figs. 1 and 2), and by an operating force applied at the center of spring gland and to which the switch is responsive. A pin 61 (Fig. 3), which is riveted to gland 56, extends through an opening 62 in the connecting member and connects the central portion 63 of gland 50 with the central portion of a piston 60. Piston is disposed for reciprocation in an opening formed in the base plate 11. The lower face of the piston 60 extends below the lower face the base plate 11. A pressure assembly comprising a hollow base 64, appropriate fittings 65, and a flexible diaphragm 66, is bolted or otherwise fastened to be pressure tight against the bottom of the base plate 11. Pressure applied to the interior of base 64 through an opening 67, forces the diaphragm 66 upwardly to lift the piston a ainst the force of spring 35 and thus pivot the free end of lever away from plate 13.

A second lever 70 is pivoted, at notches 71, 71 formed in its upper edge, in cooperating notches 72 formed in portions 31 and 31 of angle pieces 30 and 3%, respectively. The lower free end of lever 78 extends substantially toward the pivot 54 for lever 52 and is provided with cars 73, 73 extending from each side thereof. Each car 73 is perforated at 74 (Fig. 2) to accommodate the lower end of a respective one of a pair of coiled tension springs 75, 75. These springs extend upward between arms 53 and 53 and outwardly of portions 31 and 31 of angle pieces 36 and 30*. Their upper ends are hooked in notches 76 in the upper edge of cross-piece .56. The springs 75, are stretched so that lever 7 6 is firmly biased against its pivot points on portions 31 and 31'" of angle pieces 30 and 30 respectively.

The free end of lever 70 is further provided with a square perforation 77 on each side thereof inwardly of the respective perforations 74, 74. A leaf spring 78 is attached to lever 70 by a rivet 79. The spring 73 lies flat against the lever and its ends, which are notched, extend beyond the perforations 77, 77.

The contact and terminal assemblies are mounted on a base 80 molded from suitable insulating material. The base 80 extends substantially all the way from wall 12 to wall 12 and is held by a pair of machine screws, one of which is shown at 81 in Fig. 1, against the forward side of plate 13 and against the base plate 11, as best illustrated in Fig. 3.

The rear wall of the base 30 is recessed to freely accommodate the main spring 35. The front face of the base 80 has formed therein a generally rectangular recess the bottom of which is stepped to provide a lower step 82 and an upper step 83. Four stationary contact members 84, 84, 85 and 85 (see Fig. l) are held by machine screws 86 (Figs. 4 and 5) to the upper step 83 so that one end of each extends over the lower step 82 (Figs. 4 and 5). The latter end of each contact member is provided with a contact tip. The other end of each stationary contact member is provided with a terminal assembly comprising a U-shaped clamp 87 and a machine screw 88. The latter slidably extends through the clamp 87 and is threadedly engaged with the stationary contact member. Separator sections 89, which are molded as part of the base, separate the respective combined contact and terminal members. Suitable indicia is marked on a beveled face 80 (Fig. 3) of the base 86 in the vicinity of the respective terminals to identify each terminal. Said beveled faces extend rearwardly and upwardly preferably at a 45 degree angle with respect to the base plate 11 so that said indicia may be read as well from the front or the top of the switch.

A pair of movable bridging contactors 91 and 92 (Figs. 1, 4, and 5) are disposed rearwardly of the stationary contact members. is provided with contact tips properly spaced for cooperative engagement with the tips of stationary contacts 84 Bridging contactor 91, Figs. 1 and 4, i

and 84, respectively, Fig. 1. Bridging contactor 92, Fig. 5, is provided with contact tips likewise spaced to engage the tips of stationary contacts 85 and 85", respectively. Each bridging contactor has a central perforation 94 the lower part 94 of which is wider than the upper part 94*.

The base 80 is provided with two openings 96, 96, which are alined with a respective one of the bridging contact perforations 94, 94, Figs. 4 and 5, and with a respective one of the perforations 77, 77, Figs. 2 and 4, in lever 70. The rearward portion 56 of each opening 96 is generally square while the forward portion 96 Fig. 4, is circular. A pair of coiled springs 97, 97, Figs. 1 and 4, each bearing at one end thereof against the respective inner ends of the circular portions 96 96 and at the other end thereof against a respective one of the bridging contactors 91 and 92, urge the latter toward contact with the stationary contacts.

Motion of lever 70 is transmitted to the bridging contactors 91 and 92 through a pair of like contactor operator bars 1% and 100, Figs. 2 and 4. .As best illustrated in Figs. 1 and 4, bar 100 comprises a substantially rectangular main body portion 101, a forward neck portion 102, a forward head portion 103, a rearward circular neck portion 104, and a rearward head portion 105. The rearward head portion is elongated vertically and the forward head portion 103 is eiongated horizontally. The rearward end 166 of the body portion 101 (Fig. 4) is circular. For convenience in assembly, the upper and lower faces of the bar 100 are provided with projections 107. Another pair of projections or extensions 1'98, extending laterally from the body portion 191 substantially midway between the projections 5.07 and for ward neck portion 102, are adapted to abut the rear face of base 80 to limit the forward swing of the free end of lever 70.

Contactor actua'tor bar 100 is shown in Fig. 4 in its switch open position. Projections 168 are retracted from the rear wall of base 80 and the forward part of body portion 106 slidably extends through opening 96 in the base 80. The bridging contactor 91, disposed on the forward neck portion 102, is held in switch open position against the bias of spring 97 by the forward head portion 103. At the other end of each bar 160, the rear ward neck portion 104 extends through the respective slot in the adjacent end of leaf spring 78 and the latter bears against the rearward head portion 105.

As lever 70 swings forwardly to close the switch, the spring 78 is carried forwardly on neck 104, Fig. 4, away from head 1&5 until it abuts the cylindrical portion 106 of bar 100. Thereafter, the bar 100 moves forwardly with a snap movement to release the bridging contactor The latter is then urged into engagement of its tips with those of stationary contacts 84 and 84; see Fig. 1. Movement of the bar 100 continues until projections 108 are brought into abutting relation with the rear face of the base 80. This movement carries the head 103 out of engagement with bridging contactor 91. When motion of bar 100 is stopped, spring 78 is flexed until the forward swing of lever 70 is stopped. At the same time the resilience of spring 78 acts to reduce bouncing of the contacts by reducing impact shock and thus minimizes arcing thereat.

In this condition of the switch, with the contacts closed and with the lower free end of lever 76 swung forward,

the free end of lever 52 has a forward position so that tab 57 ('Fig. l) engages the leaf spring 20 and so that the axis of each of the pair of springs 75, 75 is forward of the pivot points of lever 70 in notches 72. Springs 75, 75 which bear against frame 10 through lever 76, angle pieces 30 and 30 and transverse plate 13, urge lever 52 against its pivot 54. As pressure is applied through fitting 65 and opening 67, diaphragm 66 is forced upwardly to lift piston 60. Piston 60 through its pin 61 (Fig. 3) urges spring gland 50 upwardly against the bias of the main spring 35 and away from connecting member 55 of lever 52. But the lower ends of springs 75, 75 are held by lever 74) in a position to the rear of pivot 54. Thus as the gland 50 is moved upwardly the free upper end of lever '52 swings rearwardly. It carries with it the cross piece 56 and the upper ends of springs 75, 75. When the axis of the springs crosses over the pivot point of lever 70, the free end of the latter swings rearwardly carrying spring 78, Figs. 1 and 4, with it. Together they swing rearwardly until spring 78 abuts the head 105, 105 to begin snap rearward movement of bars 100 and 101i. After moving a short distance heads 193 engage their respective bridging contactors-91l and 5 ,2. Thereafter the switch connections are rapidly broken as the bridging. contactors are carried rearwardly against the bias of springs 97, 97; Figs. 3 and 4. When the bridging contactors 91 and 92 abut the lower step 82, the head 103 acts as a stop to prevent further rearward movement of the bar 104 spring 78 and lever 70.

As the pressure on diaphragm 66 is decreased, the bias of main spring 35 causes the upper end of lever 52 to swing forwardly. When the axis of springs 75, 75 again crosses over the pivot point of lever 70, the latter snaps forward to its switch-closed position.

The axes of springs 75, 75 must cross to the opposite side of such pivot points before lever 70 is moved. Thus in practice lever 52 has one angular position in which the lever 70 is snapped to open the switch; but has another, slightly more forward, angular position in which lever 70 is snapped to effect closure of the switch. The downwardly extending outer end 27 of portion 27 of bracket 16 terminates at a point 27 between these two angular positions. Nut 25 (Figs. 1 and 2 is turned so that spring 2%, unless prevented by tab 57, engages such point 27* of portion 27. A preselected pressure, lower than that required to open the switch, is required to close it. The preselected difference in these pressures is the operating differential of the switch.

Upon swinging rearwardly in response to increasing pressure on piston 60, lever 52, 53 withdraws tab 57 from engagement with spring prior to reaching the angular position at which lever 70 is moved to open the switch. In swinging forwardly lever 52, 53 (Fig. 2) effects engagement of tab 5'7 with spring 20 before reaching the angular position at which lever 76 is moved to close the switch. Thus, the spring 2% aids in opposing motion of lever 52, 53 into a position to close the switch. Thus the operating differential of the switch may be increased by turning nut to increase the deformation and thus the pressure of spring 20.

Pivot member 54, member 56 and lever 70 may be formed by punching and stamping from sheet material. When so formed, the sheared ends of these parts are substantially at right angles to the sides thereof. --In the punching and stamping operation in which each is formed, portions of member 54 and lever 79 are tilted, and perforations 74 and notches 76 are upset. A sheared end and one surface of said parts meet at .an edge which provides a knife edge for pivotal movement of levers 52 and 70 and of springs 75, 75. No grinding or other operation is required to form such edges. Such knife edge pivots afford pivotal contact along a single line and therefore materially reduce wearing of the members and insure accurate pressure responsiveness of the switch.

Another important structural feature resides in the shape .of bars 101) and 101 with respect to the shape of bridging contactors 91 and 92, particularly at their perforations 94, 94. Referring to Figs. 4- and 5, portion 94* of perforation 94 is of size to slidably accommodate head 103, whereas portion 94 is of a size to slidably accommodate only neck 192. Thus the bridging contacts may be readily assembled on their respective bars by insertion of heads 103, 103 through portions 94 94 of perforations '94, 94. Each bridging contact member is then 6 moved downwardly on the-neck 102 of its associated bar so that the head 103 engages the bridging contact member on either side of perforation 94. When the assembly is complete, the bridging contact member is prevented from moving upward by the wall portion of base which joins steps 82 and 83.

Wiring for the switch is brought in through knockouts in walls 12 and 12 forward of transverse wall 13. The latter serves to separate the switch into two sections so that the wiring cannot interfere with the switch actuator mechanism. The switch cover 1'10 is generally vU -shaped and is held to the frame in clipped-on relationship by integrally formed punched clips 111, Fig. .3, which engage .the underside of base plate 11. i

I claim:

1. In a condition responsive switch, in combination, a first pivoted lever comprising a member pivoted at one end thereof and having spaced arms extending in like directions from the pivoted end of said member, said arms being joined at their free ends, a second pivoted lever disposed between said arms intermediate the free end of said arms .and the pivot of said first lever, the free end of said second lever extending generally toward the pivot of said first lever, an over-center spring interconnecting said arms and the free end of said second lever, a main spring, means to exert .a force in response to a condition, said spring and said means being operatively connected with said member at pointsremoved from said pivoted end, said first lever being movable to carry said over-center spring over the pivot of said second lever for snap movement of the latter, fixed contacts, movable contacts engageable with said fixed contacts, means to transmit motion of said second lever to said movable contacts comprising a spring mounted for movement with said second lever, and an operating member connected with said second lever for motion therewith in one direction and connected with said spring last mentioned during motion of said second lever in an opposite direction.

2. In a switch responsive to a condition, in combination, a frame having a base and sides extending -in like directions from said base and a separator interconnecting said sides, a first lever disposed Within said frame and comprising a member positioned substantially parallel with said base and pivoted at one end thereof about said base, said first lever further having a pair of spaced arms extending from the pivoted end of said member in like directions with the sides of said frame on one side of said separator, said arms being interconnected at their free ends, a second lever pivoted about said separator intermediate the free ends of said arms and the pivot of said first lever toward which latter pivot the free end of said second lever generally extends, over-centersprings interconnecting the free ends of said arms and the free end of said second lever, a range spring, means'extending through said base for exerting a force. in response to a condition, said range spring and said means engagingopposite sides of said member at points on one side of the pivot of said member, said spring being interposed between said member and said separator, and a fixed contact and carried by said second lever.

3. In a condition responsive switch, over-center mechanism comprising first and second levers each pivoted :at a respective end thereof and having its other end free, an over-center spring interconnecting the free ends 'of said levers, means to rotate said first lever inresponse to a condition through an arc from a first to a second position for snap movement of the free end of said second lever, switch means connected for actuation by the free end of said second lever, a stop having an angular position with respect to the pivot point of said first lever inter mediate such actuating positions of said first lever, resilient means engaging said stop and engageable with said first lever to oppose motion thereof to one of'said actuating positions, and means to adjust the deformation of said resilient means for varying degrees of such opposition.

4. In a condition responsive switch, over-center mechanism comprising a first and a second lever each pivoted at a respective end thereof and having its other end free, an over-center spring interconnecting the free ends of said levers, means to rotate said first lever in response to a condition through an are from a first to a second position for snap movement of the free end of said second lever, fixed contacts, movable contacts engageable with said fixed contacts, a resilient member carried by said second lever, a contact operator having a portion extending through said second lever and connecting with said resilient member, and said operator having another portion thereof resiliently connected with said movable contacts.

5. In an electric switch, a frame comprising a plate having a pair of opposed side walls extending in like directions from opposite sides of said plate, a transverse member interconnecting said side walls, a first lever pivoted about said transverse member and having a free end extending toward said plate, a second lever pivoted about said plate and comprising a pair of arms spaced outwardly of said first lever, said second lever further comprising a member interconnecting said arms, tensioned spring means interconnecting said free end of said first mentioned lever and the arms of said second lever for snap movement of said first lever as said spring means is carried over center by said second mentioned lever, a range spring interposed between said transverse member and said member interconnecting said arms and biasing said second lever for rotation in one direction, pressure responsive means acting against the bias of said range spring, and a switch having a movable contact connected to the free end of said first lever for actuation thereby.

6. For an electric switch, snap acting mechanism ineluding a pivoted lever, a resilient member secured to a 'free end of said lever, a contact operating bar having a portion slidably extending through said lever and said resilient member, said operating bar having a head portion for engagement with one side of said resilient mem ber and further having a portion slidably extendable through said lever and engageable with the other side of said resilient member.

7. For an electric switch, an operating bar having a neck portion and a head portion, a bridging contactor having a central elongated opening formed therethrough, said opening being of a width over a first part of its length to accommodate said head and said neck and a width over another part of its length to accommodate said neck alone, said neck portion being slidably disposed within said first part of said opening, a guide wall for said bridging contactor positioned to prevent movement of the latter to aline said other part of said opening with said head, a pair of stationary contacts each adapted for engagement with said bridging contact member on an opposite side of said opening, and biasing means urging said bridging contact toward the position affording contact with said stationary contacts.

8. A switch comprising a plurality of punched and stamped sheet metal elements with complementary hearing parts, one element furnishing in original punched and stamped condition a knife edge bearing for the other element, the knife edge being the meeting edge of substantially right angle surfaces of a portion of said one element, and said portion of said one element being so disposed thereon as to present the knife edge to the complementary bearing part on the other element for substantially free pivotal movement of, one of said elements on the other in opposite directions from a transient intermediate position.

9. In an electric switch, in combination, fixed and movable contacts, a snap acting lever, mechanism interconnect ing said lever and said movable contacts and comprising a spring carried by said lever and a contact operator extending through. said lever and having a lost-motion connection with said spring, the movable contact having a resilient mounting upon said contact operator.

10. In an electric switch, in combination, fixed and movable contacts, a snap acting lever, condition responsive means operable automatically to transmit motion of said lever to said movable contacts and comprising a leaf-type spring mounted for bodily movement with said lever, and an operating member connected with said lever for motion therewith in one direction and connected with said leaf-type spring during motion of said lever in an opposite direction.

11. In an electric switch, first and second levers each being pivoted about a respective one of a pair of spaced pivots and each having a free end extending substantially in the direction of the pivot of the other, said first lever comprising a pair of members spaced on opposite sides of and extending beyond the pivot of said second lever, resilient means interconnecting the respective free ends of said levers and normally biasing said levers into engagement with their respective pivots, said levers being rotatable about their respective pivots in the same plane and the free end of said first lever being rotatable through an are on opposite sides of the pivot of said second lever for snap action of the latter, a fixed contact, a movable contact carried by said second lever, biasing means normally urging said first lever toward a position on one side of the pivot of said second lever, a resilient member mounted on spaced supports and having an intermediate portion engageable with said first lever over a portion of the arc of rotation of said first lever to oppose action of said biasing means, and means to adjust the tension of said member for different degrees of such opposition.

12. In a condition responsive switch, in combination, a first pivoted lever comprising a member pivoted at one end thereof and having spaced arms extending in like direction from the pivoted end of said member, said arms being joined at their free end, a second pivoted lever disposed between said arms and between the free end of said arms and the pivot of said first lever, the free end of said second lever extending generally toward the pivot of said first lever, spring means interconnecting the free ends of said arms and the free end of said second lever, a main spring, means to exert a force in response to a condition, said spring and said means to exert a force being operatively connected with said member at points removed from said pivoted end, fixed contacts, and movable contacts engageable with said fixed contacts and carried by the free end of said second lever, said first lever being movable between a first and a second position for snap operation of said second lever at different values of the condition and including means to adjust the differential between such values comprising a resilient member engageable with said first lever over a part of the travel of said lever between said first and said second positions.

13. In an electric switch, snap acting mechanism including a snap acting member, means to actuate said mechanism in response to a condition, an operating member having one end thereof operatively connected with said snap acting member, a contact assembly comprising an insulating base having a stepped surface, said operating member slidably extending through a first step of said base, a fixed contact secured to a second step of said base and having an overhanging portion extending over said first step, a movable contact carried by said operating member and being engageable with said overhanging portion of said contact, said operating member and said movable contact having complementary interlocking portions, the surface of said base intermediate said first and second steps being engageable with said movable contacts to maintain said movable contacts in interlocked relationship with said operating member, a resilient member mounted for movement with said snap acting member, said operating member being connected with said snap acting member for snap motion therewith in one direction and being connected with said resilient member for motion therewith during motion of "said snap acting member in an opposite direction.

14. In combination, a frame, a punched and stamped pivot element carried by said frame, condition responsive snap acting mechanism comprising a punched and stamped snap acting lever pivoted about said pivot element, fixed contacts, movable contacts actuated by said lever to engage and to disengage from said fixed contacts, said pivot element and said lever furnishing in original punched and stamped condition a knife edge bearing one for the other, the knife edge being the meeting edge of substantially right angle surfaces of a portion of one of said elements, and said last mentioned element in punched and stamped condition having said portion thereof so disposed thereon as to present the knife edge to the complementary hearing part on the other element for free pivotal movement of said elements relatively to one another in opposite directions from a transient intermediate position.

References Cited in the file of this patent UNITED STATES PATENTS 2,090,526 Eaton Aug. 17, 1937 2,193,129 Furnas et a1. Mar. 12, 1940 2,308,312 Shaw Jan. 12, 1943. 2,314,191 Ayers Mar. 16, 1943 2,375,387 Robbins May 8, 1945 2,505,831 Krieger May 2, 1950 2,507,066 Trautman May 9, 1950 2,574,770 Zeller Nov. 13, 1951 2,616,011 Elliott Oct. 28, 1952 2,658,397 Hollinshead Nov. 10, 1953

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