US2414191A - Electric switch - Google Patents

Description

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W. B.-COON ELECTRIC SWITCH Filed June 2, 1945 Jan. 14, 1947.

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m@ y L Jan. 14, 1947. w. B. coON ELECTRIC SWITCH /Filed June 2, 1945 2 Sheets-Sheet 2 Patented Jan. 14, 1947 UNITED STATES PATENT FFCE.

ELECTRIC SWITCH Wiliiam E. Coon,

Chicago, Iii.,

assigner to Simpson Electric Company, Chicago, Iii., a corporation of Iliinois ll. Claims. 1

The present invention relates to electric switches and is particularly concerned with electric switches adapted to be used for effecting the switching necessary to connect in circuit the proper instruments, sockets, etc., in a tube tester.

One of the objects of the invention is the provision of an improved electric switch which is very compact, which occupies a minimum amount of space, and which is adapted to be manufactured at a very low cost.

Another object of the invention is the provision of improved electric switches of the class described which have a special type of actuating and indicating member which is adapted to project from a panel to permit the actuation of the switch and to indicate its position at all times.

Another object of the invention is the provision of an improved switch structure of the class described which has a quick make and quick break and which has a wiping action between the contacts of the switch so that the circuits are made and broken with a minimum amount of arcing and so that the Contact resistance is reduced to a minimum.

Although the present switches are particularly adapted to be advantageous for certain uses mentioned above, I desire it to be understood that the switches are also of general application and may lbe used for many other purposes.

Another object f the invention is the provision of an improved electric switch of the class described having a snap action and means for holding the switch in any of its actuated positions but which isalso adapted to be actuated in common with a plurality of similar switches by a single actuating device so that all of the switches may be simultaneously returned to their initial position.

Another object of the invention is the provision of an improved switch structure which is adapted to be embodied in double throw or multiple switches and which may include as many gangs as desired on a single elongated shaft.

Another object of the invention is the provision of an improved switch structure having an improved actuating member and improved indicia whereby the switch has a plurality of diiierent positions but only one of the indicia corresponding to its present position is visible` at any time.

Other objects and advantages of the invention will be apparent from the: following description and the accompanying drawings, in which similar characters of' reference indicate similar parts throughout the several views.

Referring to the drawings of which there are two sheets:

Figure l is a fragmentary sectional view of a panel equipped with a plurality of switches constructed according to the invention and adapted to be returned to initial position by a single actuator;

Fig. 2 is a fragmentary front elevational view of the panel with the switch structures shown in dotted lines;

Fig. 3 is a side elevational view of a switch unit embodying the invention with certain parts shown in section, taken on the plane of the line 3-3 of Fig. 8, looking in the direction of the arrows;

Fig. 4 is a full switch;

Fig. 5 is a similar view showing the switch including two banks of contacts;

Fig. 6 is a sectional view taken on the plane of the line 6 5 of Fig. 3 looking in the direction of the arrows;

Fig. 7 is a side elevational view of the switch of Fig. 3 shown on a scale corresponding to twice the size of the switch;

Fig. 8 is a similar side elevational view of the other side 0i the switch of Fig. 7;

Fig. 9 is an exploded view showing the various parts of the rotating contact member prior to their assembly;

Fig. 10 is a plan view of one of the contacts carried by their rotatable contact member;

Fig. 11 is a fragmentary sectional view of the switch taken on the plane of the line Il-l l of Fig. 8 looking in the direction of the arrows;

Fig. l2 is a fragmentary view in perspective showing the structure of one of the frame members; and

Fig. 13 is another fragmentary view in perspective showing the structure of the other of the frame members.

Referring to Figs. 3, 7 and 8, 20 indicates in its entirety one 0f the switch units embodying the invention, a plurality of which are shown in Fig. 1. The switch unit 23 is provided with a supporting frame which may consist of a pair of frame members 2i, 22 of metal. For example, frame member 2l consists of a strip of sheet metal having a dat body portion 23 which is provided at each end with a laterally turned end ange 24 and an inwardly turned attaching ange 25 carried by the end ange 24.

The attaching anges are located at right angles to the body portion 23 and are provided with threaded -bores 26 for receiving the screw bolts 21 size side elevational view of the (Fig. l) by means of which the switch units are attached tc a panel 28. The end flanges 2 are preferably formed with rectangular slots 29 in their edges, leaving a pair of outwardly projecting lugs 30 for engagement with the other frame member 22.

The frame member 22 may consist of a straight piece of sheet metal each end of which is formed with the inwardly extending rectangular slots 3l adjacent the end, of such a size as to receive the lugs 3l) and the body portion 32 between the slots 3l is Aof sufficient width to be received in the slot 2S of the end flange 24. Thus, when these frame members 2| and 22 are assembled as shown in Fig. 3, the ends of the lugs 3E may be riveted over slightly to hold the frame in assembled relation.

The two frame members 2| and 22 are provided with a pair of aligned cylindrical bores 33, 34 for receiving the stub shaft 35 which carries the rotating actuating disc 36. The length of the stub shaft 35 depends upon the number of banks of contacts that are intended to be employed upon each unit. As shown in Fig, 4, the unit may have one bank. of contacts, or, as shown in Fig. 5, two banks, or any suitable number of banks of contacts may be employed, depending on the number of contacts which it is desired to actuate simultaneously.

The actuating disc 36 preferably consists of a molded member made of a phenolic condensation` compound which is molded about the shaft 35 and about anchoring formations carried by a metal disc 31 that is located in the right face of the actuating disc 36. Metal disc 31 may be secured in place by a screw bolt 38 as shown in Fig. 3 or it may have a plurality of anchoring members cut out of its periphery and bent inward to be anchored in the molded insulation of the actuating disc 36.

The metal plate 31 serves as a part of the snap mechanism and for retaining the switch in its actuated positions and this plate is provided with a central aperture 39 that registers with the aperture 4U in the actuating disc 36.

In addition to this, the metal disc 31 has a plurality of circular apertures 4I-46 (Fig. 8) which are countersunk at their outer end so as to provide a better socket for a steel ball 41 which is located to be received in the apertures lil-45. The ball 41 is carried in a cylindrical bore 43 in the frame member 22, this bore being located at a suitable rad'usfrom the axis of shaft 35 so that the ball is adapted to be received in any of the sockets ll-'i carried by the rotatable actuating member 36. Ball 41 projects from itsV bore t8 in the frame member 22 to engage the.

metal plate 31 on the left, and on the right hand side in Fig 3 the ball is engaged by a leaf spring 49 which urges it toward the rotatable actuating member 36.` l

The leaf spring 39 may be made of any suitable material such as spring brass or bronze, and it comprises an elongated strip of this sheet metal having an enlarged attaching ange i! provided with apertures for receiving the rivets 5I passing through Vthis flange and through the frame member 22 tc secure the leaf spring 49 to frame member 22. The leaf spring extends longitudinally of the frame member 22 and thus has considerable length so that it need not be bent beyond its elastic limit. Its length is such that it projects abovethe end ange 24 of the switch unit, the upwardly projecting portion serving to be engaged by a common actuator which will be further described in respect to Fig. l.

Spring is urges the ball :i1 toward the left but permits the ball to be cammed out of the sockets ii-t6 when the rotatable member 35 is turned. The actuating disc S5 includes a circular body portion 52 in the form of a plate of molded insulation which is provided with a centrally located cylindrical hub 53 and a spring housing flange 5t extending in the same direction as the hub and located near the periphery of the disc 52. The edge 55 of the disc 52 may be rounded and is preferably knurled as shown for convenient engagement with the ngers which actuate the disc by frictional contact.

The cylindrical housing flange 52 may be provided on its cylindrical periphery with numerical indicia indicated at 55 (Fig. 4) showing the position of the switch at any time. The axial length of the hub 53 and housing ange 54 is such that rotatable actuating member 36 may be received between the frame members 2l and 22 where it is rotatably supported by the shaft 35 engaging in bores 33, 34,

The space between the hub 53 and housing flange 5G houses a spiral ribbon spring 51 which is used to urge the actuating member 36 toward its initial position. The frame member 2l carries a metal pin 58 (Fig. 3) riveted in a bore and projecting into a hook 5B which is formed by curling one end of the spring into partially cylindrical form. The other end of the spring has a cylindrical formation 66 which may be slid axially into a cylindrical bore 6| that is formed in the housing flange 54, thus anchoring this end of the spring to the actuating member 36. The strength of the spiral spring 51 is sufficient to rotate the member A35 and its rotatable switch members when the pressure of spring 49 is released, but as long as spring 4S presses the ball enough to alter the position of the rotatable member 35.

In addition to the sockets iii-25 for the ball E11, the plate 31 preferably has an arcuate slot G2 which is of suflicient length to determine the range of movement of the rotatable member 35.

Slot 62 is located to be engaged by an inwardlyA projecting lug 53 which may form a part of frame member 22 (see Fig. 13), being bent inwardly from the frame member 22, to extend into the slot S2. The end Si! of slot G2 determines the limit of rotation in a clockwise direction of the rotatable switch and the end 55 of the slot t2 determines the limit of motion in a contrary direction.

In order to reduce the friction between the end of the insulating hub 53 and the adjacent frame member 2l, a washer 65 is carried by the shaft 35. The left end of shaft S5 (Fig. 3) is provided with one or more non-circular portions 61 such as for example flat surfaces, and the shaft 35 is adapted to actuate a rotatable switch member 68 for each bank of contacts. In Fig. 5 this flattened portion of the shaft 35 has been extended far enough to support two such rotatable switch members 58 and E9.

lThe rotatable switch member 68 is shown with its parts in exploded form in Fig. 9 'and this member preferably comprises a disc 1@ of insulating material such as indurated fiber or a phenolic condensation molding compound.. Disc 1S is provided with the centrally located non-circular aperture 1 l which is complementary to the -exter-j nai shape of the shaft 35 at its .flattened por-,-l

tions'I. The disc T0 is preferably provided with a plurality of partially` circular apertures 'I2 which are substantially rectangular in shape but are arranged along the line of a circle, these slots being adapted to receive the securing members that are carried by a pair of annular Contact members 13, M,

Each annular contact member comprises a flat sheet metal member in the form of an annulus and having a plurality, auch as for example four, inwardly extending radial tabs 'I5 which are bent in an axial direction, the. axial portion being called a securing tab IS and being provided with an axially' extending` slot ll, The securing tabs i6 are wide enough and thickv enough to fit in the slot I2 and theyA are properly located to registerA with four of these slots.

Thus. the annular contact plates 'I3 and 'I4 may .be secured to the opposite sides of the insulating disc 'IB by passing the securing ta'bs TIB through predetermined slots 'I2 and by spreading the axially extending slots il. The annular contact members 'I3 and *Ill are of such size that only the innermost portion of these annular members rests on the faces of the insulating disc lil and thus the annular members 'i3 and 'I4 project beyond the edge 'i3 of the insulating disc 1B. Since the tabs 'I6 may be located in spaced slots 12, the two annular members 'I3 and 'Ill may be insulated from each other and if desired each of these annular members might be used for a contact.

However, in the embodiment of Fig. 3 only the outermost annular member 'i3 has been used for a contact while the other annular member It merely serves as a guide for holding the rotatable switch member 68 upon the shaft 35. This is accomplished by means of the switch contact bank 'i9 (Fig. 7) which carries a multiplicity of xed contacts Bil-25, The contact bank 19 corisists of a plate of insulating material such as a phenolic condensation compound. which is arcuate in shape, the arcuate portion 85 being substantially concentric but spaced from the rotatable switch member 68.

At each end the arcuate portion 85 has an enn largement 8'I provided with apertures for receiving the screw bolts 88 which pass through these apertures and are threaded into the frame member 2 I. An insulating spacer washer 89 is carried by each bolt 88 to space the bank 'I9 properly from the frame member 2i so that the contact annulus 'I4 is spaced from frame member 2l.

Adjacent each end of the arcuate member S there is also an inwardly extending insulating lug Bil, 9| which extends radially toward the insulating disc 'I0 and is of suiiicient thickness to haverv a sliding t between the annular members 'I3 and i4 at the edge I8 of disc l0. It is these lugs 538, 9| which guide the annular members 'I3 and 'M of the rotatable switch member 'lil and hold this switch member on the shaft 35. A third such lug 92 projects radially inward from the arcuate portion 86 between the annularvcontacts 'i3 and 14.

The annular member 'I3 serves as a continuous contact for engaging. the fixed contact member and the xed contact member 85 is located closer to the axis of the shaft so that it will be in engagement with the annulus 13. The other fixed contact eil- 84' are. located. at a greater radius so that they are out of contact with the annulus 'I3 butare positioned toengage a radially'Y extending contact portion 93 which is carried by theannuluszlfiy. x .1. 1 r e r .'z. All of the'contactsg--B may be identical construction and these preferably comprise resilient sheet metal members which are bent back upon themselves at the connector portion Sd which is provided with a T-shaped formation and with an aperture 95 for receiving a connecting wire. At an intermediate point each connector is secured to the arcuate insulating plate 86 (Fig. ll) by a tubular rivet 96 which passes through both the insulating plate and the contact mem ber.

From the tubular rivet 96 each contact extends radially inward, One is bent upward at 91 and the other is bent downward at 98 to give these contact portions a spread. Then the contact por- I tions are bent until theyv extend into engagement with each other at the end portions IBO and each of the corners ISI is bent outward so that the two legs of each contact engage each other but the corners have a spread for the purpose of guiding the contact member 93 carried by annulus 'I3 between them. This spread of the fixed contact portions assures the contact 93 entering between them and wiping across both of the legs of each xed Contact.

Referring now to Figs. 1 and 2, here the panel 23 is provided with a plurality of apertures IEiZ, each aperture consisting of an elongated portion for exposing the knurled edge of the actuatincr disc 3b and each aperture also including a small rectangular portion for exposing an indieating numeral on the hub 54. The threaded bores 26 in frame member 2i serve to receive the l screw bolts 2l which secure the switch units to the rear side of the panel with nothing but the edge of the actuating disc and the indicating numerals exposed on the front side of the panel.

Allof the upwardly projecting end portions of the leaf springs 49 are located in alignment and these are adapted to be engaged by metal discs "i3-|05 (Fig. l) carried by a reciprocating actuating rod I'fll. rhe rod IBS is guided by being slidably mounted in cylindrical apertures in the angle brackets IWI- |539 which are secured to the panel 28 by screw bolts and the discs IGS-HB5 are located on the left side of each leaf spring 49 having reference to Fig. 3.

A helical compression spring Il@ is interposed between the bracket I E8 and a washer I I I on the rod |06, the washer being in engagement with a transverse pin II 2. The coil spring H0 urges the rod |06 toward the left and urges the discs IUS-|05 out of engagement with the leaf springs 49.

A bracket H3 carried by panel 28 has a bell crank H4 pivotally mounted by a rivet IIS with one arm I I6 in position to engage the end of rod |06. A push button II'I is slidably mounted in a threaded plug II8 carried by panel 28 and is confined against outward movement by a transverse pin I I 9. A plunger rod I20 of the push button II'I is located to engage the other arm i2I of the bell crank but a coil spring I22 urges the push button outward into the position of Fig. l. In some embodiments of the invention this spring may be eliminated. as the spring iIIl on the rod IBS may accomplish the` same purpose..

The operation of the switch units and of. the bank. of switch units is as follows: Contact is the common contact which is connected to a commonv lead that is intended to be controlled by the switch and connected to any one of the other contacts B-Bll selectively. When the switch isv inthepositionimwhich contacteer engages.; Contact iitis'on. open circuit with:

respect to the other contacts Ste-84..

If the finger is then appliedto the knurled edge 55V of the rotatable actuating member 36, this will tend to cause this member to rotate and the steel ball 41 will be cammed out of its rst socket 46 and will ride up over the metal member 31 against the tension of the leaf spring i9 which holds the ball in the aperture 48. As the rotatable member 36 moves on farther, the ball will drop into the socket 45 and will tend to hold the rotatable member 36 in this position. In this position the movable contact member 93 engages the contact 84 having been inserted between vthe portions 99 and H10 of that movable contact as shown in Fig. 11.

The resistance toward movement of a ball out of its socket is such that the spiral spring I in the housing 54 of rotatable member 36 cannot overcome the resistance to movement of the ball and the switch is held in this position. I-Iowever, each time the switch is moved a step farther away from the contact 85, the spiral spring 5l is wound up.

The rotatable member 36 may be successively brought into a position in which the steel ball il is retained in sockets 44, 43, e2, and finally 4 I, during which the Contact member 93 will successively engage xed contacts 83, 82, 8i and finally 30 and the movable switch member lil will be retained in any of these positions by the steel ball lil engaging in its socket.

Ii the operator Wishes, he may move the switch backward to any desired position and at any time the position of the switch Will be indicated by the numeral which is exposed at the aperture |02.

There are some'uses of these switch units in which it is desirable to clear the machine or tester and move all the switches back tothe initial position. In such case the arrangement of Figs. 1 and 2 is of great advantage as it is only necessary to push the push button Ill to clear all the switches. This action is as follows:

Push button Il'l rotates the bell crank l i4 clockwise in Fig. 1. Bell crank il@ moves rod lofi toward the right against spring Il. Discs l03--I05 engage the leaf springs 49 of the respective switch units 20, permitting the steel balls 4l in each unit to be cammed out of whichever socket il-d6 the ball happens to be in. Under these conditions the steel ball 41 no longer holds the rotatable actuating member 35 in a xed position and the spiral spring 51 in the housing 5d acts to return the rotatable switch member 'lll to its initial position where the movable contact 93 engages the iixedcontact 35. Thus a mere push on the push button H1 releases all of the switches to return to their initial position. In a tube tester this is of marked advantage because otherwise it would require separate manipulation of each switch unit by the operator.

The present switches maintain their contacts in a bright and low contact resistance condition and they are adapted to be moved to any one of a plurality of positions with a minimum amount of eiort. The present switch may be provided with any number of banks of contacts for simultaneous or successive operation and any number of unitsv may be mounted on a single panel to be releasedand returned to initial position by merely actuating one push button.

The present devices are capable of being manufactured very economically and they utilize a minimum number of separate parts. rIhey may be used for a long period of time without neces'- sity forv repair 'or' replacement of any ofitheirf parts and maybe manufactured so econ'oriii'callyA` 8 that they may be placed within the price range of a vast number of users.

While I have illustrated a preferred embodiment of my invention, many modications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself oi all changes within the scope of the appended claims. v

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

'1. A rotatable switch member comprising a supporting member having a slot, a supporting frame carried by said member and having bearings for a shaft, a rotatable insulating member projecting from said slot for engagement by the fingers of an operator, an annular contact carried by said rotatable shaft and a plurality of fixed contacts carried by said frame and insulated from each other, and a snap retaining means for holding the rotatable insulating member in any of a plurality of different positions, said snap retaining means comprising a ball resiliently mounted on said frame and adapted to be engaged in any one of a plurality of sockets located in said rotatable insulating member, said ball being movable mounted in a bore in said frame and havin-g resilient means urging it toward said sockets.

2. A rotatable switch member comprising a supporting member having a slot, a supporting frame carried by said member and having bearings for a shaft, a rotatable insulating member projecting from said slot for engagement by the fingers of an operator, an annular contact carried by said rotatable shaft and a plurality of fixed contacts carried by said frame and insulated from each other, and a snap retaining means for holding the rotatable insulating member in any ci a plurality of dierent positions, said snap retaining means comprising a ball resiliently mounted on said frame and adapted to be engaged in any one of a plurality of sockets located in said rotatable insulating member, said ball being movabley mounted in a bore in said `trame and having resilient means urging it toward said sockets, said resilient means comprising a leaf spring having a projecting portion to 50 be engaged for releasing the retaining action of said ball.

3. A snap mechanism for retaining a rotatable switch'member in any position to which it is moved comprising a supporting frame, an insu- 55 lating member rotatably mounted in said frame and being provided in one of its ends with a plurality of sockets arranged in a circle, said frame having an aperture adapted to register with any ci said sockets, a retaining ball in said aperture 60 and adapted to engage in said sockets and a leaf spring engaging said ball and carried by said frame and projecting beyond the end of said frame for manipulation to release the ball.

4. A snap mechanism for retaining a rotatable 55 switch member in any position to which it is moved comprising a supporting frame, an insulating member rotatably mounted in said 'frame' frame and projecting beyond the eridof-s'aid frame for manipulation to release the ball, said 9 sockets being formed in a metal plate embedded in said insulating member.

5. A snap mechanism for retaining a rotatable switch member in any position to which it is moved comprising a supporting frame, an insulating member rotatably mounted in said frame and being provided in one of its ends with a plurality of sockets arranged in a circle, said frame having an aperture adapted to register with any of said sockets, a retaining ball in said aperture and adapted to engage in said sockets and a leaf .spring engaging said ball and carried by said frame and projecting beyond the end of said frame for manipulation to release the ball, said sockets being formed in a metal plate embedded in said insulating member, and said metal plate being formed with an arcuate slot for receiving a lug carried by said frame, said lug and slot serving as stops to determine the limits of rotative movement of said insulating member.

6. A snap mechanism for retaining a rotatable switch member in any position to which it is moved comprising a supporting frame, an insulating member rotatably mounted in said frame and being provided in one of its ends with a plurality of sockets arranged in a circle, said frame having an aperture adapted to register with any of said sockets, a retaining ball in said aperture and adapted to engage in said sockets and a leaf spring engaging said ball and carried by said frame and projecting beyond the end of said frame for manipulation to release the ball, said insulating member having an axially extending hub and an axially extending cylindrical housing and a spiral spring tensioned between said insulating member and said frame and located in said housing to return said insulating member to initial position when said ball is released from pressure by said leaf spring.

7. A switch assembly comprising a plurality of switch units carried by a panel, each switch unit having a disc, the edge of which projects through a slot in said panel and each switch unit being provided with a plurality of sockets in said disc engaged by a spring pressed ball carried by the switch unit frame, spring means for returning each switch unit to its initial position, movable contact means actuated by each rotatable disc and xed contacts carried by each switch unit, a reciprocating plunger rod carried by said panel and having discs for engaging a leaf spring carried by each switch unit for urging the ball of each switch unit into its sockets, and manual means for actuating said plunger to relieve all of the balls of the switch units from spring pressure and to permit the first-mentioned springs to return each switch unit to its initial position.

8. In an electric switch unit, the combination of a supporting frame having a pair of fixed frame members provided with bearings for a shaft, a shaft in said bearings and projecting beyond said frame, said shaft having a non-circular formation at its projecting end, a rotatable insulating member of disc shape carried by said shaft for actuating the shaft, an insulating supporting plate carried by said frame adjacent the projecting end of said shaft and having a plurality of fixed contacts, an insulating disc carried by the projecting end of said shaft and rotatable with said shaft, a pair of annular metal members carried by said latter disc and projecting edgewise therefrom to form a groove and a pair of insulating lugs projecting from said insulating plate into said groove to hold said latter insulating disc on the projecting portion of said shaft.

9. In an electric switch unit, the combination of a supporting frame having a pair of xed frame members provided with bearings for a shaft, a shaft in said bearings and projecting beyond said frame, said shaft having a non-circular formation at its projecting end, a rotatable insulating member of disc shape carried by said shaft for actuating the shaft, an insulating supporting plate carried by said frame adjacent the projecting end of said shaft and having a plurality of fixed contacts, an insulating disc carried by the projecting end of said shaft and rotatable with said shaft, a pair of annular metal members carried by said latter disc and projecting edgewise therefrom to form a groove and a pair of insulating lugs projecting from said insulating plate into said groove to hold said latter insulating disc on the projecting portion of said shaft, one of said fixed contacts engaging the annular portion of one of said annular metal members, and the other of said fixed contacts being located farther outward radially to engage a radially projecting contact member carried by said latter annular member.

10. In an electric switch unit, the combination of a supporting frame having a pair of fixed frame members provided with bearings for a shaft, a shaft in said bearings and projecting beyond said frame, said shaft having a non-circular formation at its projecting end, a rotatable insulating member of disc shape carried by said shaft for actuating the shaft, an insulating supporting plate carried by said frame adjacent the projecting end of said shaft and having a plurality of fixed contacts, an insulating disc carried by the projecting end of said shaft and rotatable with said shaft, a pair of annular metal members carried by said latter disc and projecting edgewise therefrom to form a groove and a pair of insulating lugs projecting from sai-d insulating plate into said groove to hold said latter insulating disc on the projecting portion of said shaft, said insulating disc carried by said shaft being provided with a plurality of circular sockets in one of its faces and a spring pressed ball carried n by said frame for engaging in any one of said sockets to resiliently resist rotative movement of said latter insulating disc.

11. In an electric switch unit, the combination of a supporting frame having a pair of fixed frame members provided with bearings for a shaft, a shaft in said bearings and projecting beyond said frame, said shaft having a non-circular formation at its projecting end, a rotatable insulating member of disc shape carried by said shaft for actuating the shaft, an insulating supporting plate carried by said frame adjacent the projecting end of sai-d shaft and having a plurality of xed contacts, an insulating disc carried by the projecting end of said shaft and rotatable with said shaft, a pair of annular metal members carried by said latter disc and projecting edgewise therefrom to form a groove and a pair of insulating lugs projecting from said insulating plate into said groove to hold said latter insulating disc on the projecting portion of said shaft, said insulating disc carried by said shaft being provided with a plurality of circular sockets in one of its faces and a spring pressed ball carried by said frame for engaging in any one of said sockets to resiliently resist rotative movement of said latter insulating disc, said spring pressed ball being engaged by a leaf spring carried by said frame and projecting beyond said frame for manipulation to release the pressure on said ball.

WILLIAM B. COON.

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