US 3118026 A
Description (OCR text may contain errors)
Jan. 14, 1964 R. A. PUSCH ETAL 3,118,025
PUSH BUTTON SWITCH STRUCTURE Filed Dec. 22, 1960 2 Sheets$heet 1 n2 no 14 k n4 5 4s I 54 5eF. 4 3 J 3 INVENTORS ROBERT A. PUSCH 42 BY ROY E. WHEELER E \/us ATTORNEY Jan. 14, 1964 R. A. PUSCH ETAL PUSH BUTTON SWITCH STRUCTURE 2 Sheets-Sheet 2 Filed Dec. 22, 1960 IN V EN TORS ROBERT A. PUSCH ROY E. WHEELER ATTORNEY United States Patent M 3,11%,tl26 PUH BUTTUN SWETEH STRUKITURE Robert A. Pusch, Le Roy, and Roy E. Wheeler, Bloomington, EL, assignors to General Electric Company, a corporation of New York Fiied Dec. 22, 10360, Ser. No. 77,576 lb (Itaims. (El. Mitt-46) This invention relates to manually operated electrical selector switches and particularly to a push button switch structure adapted for small size and compact assembly.
Selector switches are mechanisms for making or breaking electrical contacts. The operation may be momentary under actuation, or the actuated condition may be latched. The switch contacts, in turn, control the energization of various electrical or electromechanical devices or motors. Such selector switches have actuator mechanism units that are of the push button or turn button types; the former term is often used to describe both modes of actuation, and is so used hereinafter. These switches also have contact mechanism units, or contact blocks, that are attached to the actuator units to be actuated thereby.
In mounting a plurality of these push button switches on a panel, presently available components generally re quire that they be rather widely spaced in order to ensure ample room for connecting electrical connectors to the contact block. In addition, the operating mechanisms of the available components generally require more than square inches of panel area per unit. This invention is concerned with providing a push button switch that is about half that size or less, for example, this area may be little more than 1 inch square. Moreover, the con struction is intended to permit close spacing between switch units of the order of a quarter of an inch even though each unit is to be accessible for the connection thereto of eight to sixteen wires.
This invention is also concerned with providing a switch including a contact block module that may be combined in various ways and may be attached to and actuated by different kinds of push button actuator units. The actuator units are also arranged to have certain common structural features adapting them to be interchangeable in use with the contact block.
Accordingly, it is an object of this invention to provide a new and improved push button switch construction.
Another object is to provide a new and improved push button switch construction that is small in size and effective and reliable in operation.
Another object to provide a new and improved switch construction including a contact block that is adapted to have a large number of wires compactly and. reliably atached thereto.
Another object is to provide a new and improved switch construction including a contact block that is adaptable to be actuated interchangeably by different types of actuator units.
in carrying out this invention in one preferred embodiment, switch includes .a contact block having a casing divided into a contact portion and a plurality of connector compartments. A plurality of pairs of fixed contacts are mounted in the contact portion of the casing, and an operating member having a contact means is movable therein for selectively en aging the fixed contacts. Electrical conductors are connected to the fixed contacts and terminate in connector elements within the connector compartments. The connector elements are parallel and of the slidingengagement, friction-retaining type. The connector compartments are parallel and open externally on the same side of the casing.
The connector compartments, in the preferred embodiment, are arranged on opposite sides of the contact com- 3,118,026 Patented Jan. 14, 1964 partment, and are open to be accessible at an end of the casing while the contact operating member is accessible for actuation from the other end of the casing.
The casing of the contact block unit, in the preferred embodiment, includes an actuator compartment into which the operating member normally extends. The actuator unit includes a base that is adapted to mate with the contact block casing, one within the other, so that the actuator compartment is effectively enclosed by both units. The actuator base encloses an actuating member that is operative within the actuator compartment to actuate the operating member. The actuating member, in one embodiment, is a rotatable shaft having a cam in the actuator compartment for engaging the operating member. In a second embodiment, the actuating member is a push button mounted for reciprocating translatory movement in and out of the actuator compartment. The operating member is adapted for actuation by the different types of actuating members.
The fixed contacts of the contact block are in the form of bent resilient, metallic strips, each of which is engaged by the contact block casing at three spaced locations to be placed under stress and to be tightly held in place.
The foregoing and other objects of this invention, the various features thereof, as well as the invention itself may be more fully appreciated from the following description when read together with the accompanying drawing, in which:
FIGURE 1 is a perspective View of a push button switch embodying this invention;
FIGURE 2 is a perspective view of a push button switch embodying this invention in which the actuator unit employs a turn button mechanism;
FIGURE 3 is an enlarged sectional view of the push button switch of FIGURE 1 and taken on the line 3-3 of FIGURE 4-;
FIGURE 4 is a sectional view taken on the line t4 of FIGURE 3;
FIGURE 5 is a sectional view of the push button switch of FIGURE 2;
FIGURE 6 is a sectional view taken on the line 66 of FIGURE 5;
FIGURE 7 is a sectional View taken on the line '77 of FIGURE 5; and
FIGURE 8 is an enlarged exploded view in perspective of the contacts in the contact block of FIGURE 5.
In the drawing corresponding parts are referenced by similar numerals.
The push button switch of FIGURE 1 includes an actuator unit 1% and a contact unit, or contact block 12. The actuator unit includes a base 14 of generally cylindrical form. A cylindrical passage 16 extends through the base and is interrupted at its upper end by two annular flanges l8 and 20 that project inwardly at the outer end of the base. A packing gland 22 is mounted in the annular space between the flanges 18 and 20.
The base l-t is mounted on an instrument panel 24 by means of a knurled clamping ring 26 which is internally threaded and fastened to the threaded upper end of the base M. Washers 28, a sealing ring 3t! and a positioning plate 32 are used in a well known manner between the clamping ring 26, the panel 24 and an externally projecting flan e 34 on the base to insure proper clamping and sealing of the base 14 to the instrument panel 24. The positioning plate 32 includes a bent-down lug that fits in a notch in the panel 24 and a tongue that fits in a groove along the base 14 all in a well known manner in order to index the positioning of the base on the instrument panel 24.
Slidably mounted within the passage 16 is a movable actuating member 3%; in the form of a cylindrical rod having an outwardly projecting flange 38 that engages with the flange 18 of the base. The upper end of the actuating member 36 is engageable by the finger of an operator so that it may be depressed, and the lower flat surface 4d of this actuating member 36 functions as a switch actuating surface as is described hereinafter in greater detail. The portion of the actuating member 35 above the flange 38 is guided within the flanges 18 and 22 of the base. The lower portion of this actuating mem ber 36 is guided within retaining ring 42 which has a key-tongue 44 sliding in a groove 46 in the actuating member to prevent rotation thereof in the base 14. A coil spring 48 surrounds the lower end of the actuating member and is seated between the lower surface of the flange 38 and a flange 50 of the retaining ring 42. This retaining ring is fastened in a recess at the lower end of the base 14 by suitable means such as staking of the flange 50. The coil spring biases the actuating member upwardly (which is to the outer side of the instrument panel 24) with the flange 18 providing an upper limit stop. The height of the ring 42 is chosen to provide a lower limit stop for the flange 38, which corresponds to the position of the lower switch actuating surface 4% being substantially even with the lower end of the base 14.
The wall portion 52 of the base 14 below the flange 34 has angularly related flat external surface portions providing an indexing shape and preferably is octangonal in shape to mate with a similar shaped vestibule com partment 54 at the upper end of a contact switch block 12. The contact block 12 is made of an insulating material such as a phenolic resin and formed in two half casings 56, 53 similarly shaped at the upper vestibule compart ment to form the aforementioned octagon shaped wall.
Both casings 56 and 58 of the contact block may con tain the same contact and switch structure. Only the contents of the casing 56 are shown in detail. Modifications of the contents of casing 56 may be provided in casing 58; also, casing 58 may be used without a switch and employed only to provide a closure for casing 56 and to complete the aforementioned vestibule compartment 5%. Casing 56 is formed in a plurality of compartments in addition to the compartment 54. A central contact compartment 6% communicates by means of a passage 62 to a spring compartment 64 in the lower end of the casing. The contact compartment 60 also communicates via passages 66 to upper connector compartments 68 and via passages 7%) to lower connector compartments 72. Except for the aforementioned passages, each of these compartments are separated by walls within the casing. Within the contact compartment 6 a pair of upper fixed contacts 74 and a pair of lower fixed contacts '76 are mounted. The upper fixed contacts 74 are each attached to one arm of an L-shaped metallic strip '73 (FIGS. 3 and 8), the other arm of which is formed as a bifurcated connector tab 80. The L-shaped strip 73 is retained within the casing 56 under tension. That is, the strip 73 is bent resiliently into the necessary L-shape to fit within the compartments 60 and 63 and through the passage 66, and pressed into place. The spring tension of the overbent contact strip 79 holds it in position in the casing 56. There is a three-point clamping of the contact strip '78 when it is in position in the case '76; that is, the contact strip engages the compartment walls of the casing 56 within a recess at the location $2 which backs up the fixed contact '74, at the intermediate location 84, and at the location 8% where the bifurcated connector portion 8b is formed. This three-point clamping of the stressed connector strip firmly retains that strip in position without any other clamping or bonding of the strip required. This clamping of the contact strip '78 is effective to support the fixed contact 74 and the strip 78 against the forces applied during engagement of a switch contact (as described below) and the forces applied during connection and disconnection of a connector element to the bifurcated portion 8% (as discussed below).
The lower fixed contacts 76 are also mounted in the contact compartment es and connector compartment 72 by means of a three-point clamping in a manner similar to that described above for the upper fixed contact '74. The lower fixed contact 76 is attached to one leg of a bent metallic strip 38 retained in a compartment wall recess. The other leg of strip 88 ends in a bifurcated connector tab 96. One of the clamping locations, which retain the strip bent in a stressed condition, is in back of the contact '76 and referenced by numeral 92, a second location is in the connector compartment '72 at the beginning of the bifurcated connector portion 9'8 and referenced by the numeral 94-, and a third intermediate clamping location 96 is at a recess that received a struck out projecting portion 97 of the strip 88. The contact strip 855 is retained within the casing 56 without further clamping or bonding thereof.
A switch operating plunger liiil is slidably mounted within the casing 56. The lower end of the operating plunger 1% extends through the passage 62 into the spring compartment 64 and is biased upwardly by a spring i l-Z seated within the compartment 64 between the lower wall of the casing 56 and a notch formed in the operating plunger 109. The intermediate portion of the operation plunger 1% contains a slot in which are slidably mounted two contact bars 1M and 1% yieldably spaced apart by means of a coil spring 1W8. The contacts at the outer end of the conductive contact bars 194 and lit-6 respectively bridge the upper pair of fixed contacts 74- and the lower pair of fixed contacts 76 when the operating plunger is in its normal upper position and in its actuated lower position, respectively. The upper end of the plunger lbil is formed as an actuating finger which projects into the actuator compartment 54 for engagement by the actuating surface 46 of the actuator 36.
The contact block 12 is assembled by attaching the two casing halves 56 and 58 with an insulating plate 112 therebetween by means of suitable fasteners such as pins 114. The plate 112 extends from the floor of the compartment 54 down to completely cover the other compartments of each casing half. The assembled contact block 12 is secured to the base 14 of the actuator unit 10 by means of fasteners 116 extending through the wall of the compartment 54 and into the lower wall '52 of the base. When so assembled, the height of the actuator compartment 54 of the contact block corresponds substantially to the extent of movement of the actuating member 36, which, in turn, corresponds to an appropriate movement of the operating plunger for switching contact. That is, the operating plunger Nil is moved from its normal upper-contact position to a lower-contact position, with the yieldable connections between the contact bars 164 and 1% providing an appropriate tolerance in this operating movement.
In operation, the actuating member 36 is biased upwardly by the coil spring 48, and the operating member Tilt) is independently biased upwardly by the coil spring 102. Consequently, the actuator unit It) and the contact block 12 may be handled separately and used interchangeably with other units of the same or related types. Yet both springs 4-8 and 162 cooperate in restoring the actuating member 36 to its normal, upper position after having been depressed as a push button by an operator.
The same contact block construction is adapted for use with a push button having a rotatable actuating member or turn button." A turn button actuator unit 12% is shown in FIGS. 2 and 5-7, in which parts similar to those previously described are referenced by the same numerals.
The unit 120 has an actuating mechanism that includes a cylindrical shaft 122 rotatably mounted in a hollow base 124- and formed with the flanges 18, 2b and 34 described above. The shaft 12-2 has a central portion 126 and a reduced upper portion 128 rotatable within the space of the flanges ES, 20 and packing gland 22. A square socket 139 is formed in the top surface of the shaft portion 123,
and mating with that socket is a square stub 132 that is integral with a knurled actuator button 134 having an indicator arrow 135. The stub 132 and button 134 are rotatably retained within a knurled ring clamp 136 by a C-clamp 138. The ring clamp 136 is internally threaded for attachment to the threaded upper end of the base 124 and is adapted for clamping the actuator unit to the panel 24. The relative positions of the stub 132 within the ring clamp 136 and of the socket 1% near the top of the base 124 are such that the stub and socket engage before the threads of the ring clamp and base do. This construction facilitates assembly of the unit in that the operator can feel when the stub and socket are meshed before the threads engage, and the clamp is then movable into position for tightening.
The central portion 126 of the shaft contains 8. diametrical detent passage 140. A single compression spring 142 within the passage presses equally on detent balls 144, 14-6 at either end. The halls 1494, 146 are received within either of two pairs of V-shaped detent recesses 148, 151i and 152, respectively, which are formed in the inner wall of the hollow base 124. A tongue 156 projects radially inward from the wall of the base 124 underneath the flange 18 and into a groove 1558 cut into the shoulder formed at the upper surface of the central shaft portion 126. The remainder of that shoulder bears against the under surface of the flange 18. The shaft 122 is retained in position by means of 'a washer 1611, in which the lower reduced end of the shaft 122 is rotatably mounted. The washer 16f! is retained in position after assembly by means of staking or the like.
Acam disk 162 having a plurality of cams 164 and 166 integrally formed at the lower surface thereof is axially secured to a squared stub at the bottom of the shaft 122. The cam surfaces extend into the actuator compartment 54 of the attached contact block 12 and engage the fingers 110 of the operating plungers 1011 within the two casing halves as and 58. The effective depth of the cam surfaces for full actuation of the operating plungers 111i) is substantially equal to the height of the compartment 54 and to the length of plunger fingers 1119. The earn 164 is illustrated as having two extreme surface levels (low and high) 168 and 170 corresponding respectively to the two extreme positions of the operating plunger in casing 58, and to the pairs of detent recesses 148, 1% and 152, 154, respectively. The cam 166 actuates plunger 1% in casing 56. The tongue 156 and groove 12%? are positioned to provide a limit stop for each of those positions. The cam disk 162 may also be formed with cams (not shown) having an intermediate dwell corresponding to a neutral position of the operating switch bars 1%, 1%. A third pair of detent recesses (not shown) would be provided for that neutral dwell position. Different combinations of such cam surfaces may be used to actuate the operating plungers Hit) of the two casing halves 56 and 53.
In operation, the button 134 is turned in opposite directions to reciprocate the operating plungers 1th? accordingly via the cams 154 and 166. The cams operate within the actuator chamber 54 in a manner that is effective in a somewhat similar way to the depressible push button 36. The contact block 12 is secured to the actuator unit 121? in the same way as to the unit 1d. The formation of the actuator compartment 54 as the larger to receive the actuator base 52 is consistent with the general scheme for smaller dimensions for the actuator unit It) to provide as much room as possible for the operators fingers between units. The actuator compartment 54 is kept free of dust with the base flange 34 overlapping and sealing the top edge thereof.
The operating plunger 1% is constructed with the contact bars 1% and 196 and spring 102 spaced symmetrically along a central axis thereof, and the fixed contacts 74 and '76 are also symmetrically positioned with respect to that axis. The finger 114 however, is formed off-axis, which arrangement permits the finger 11% to be positioned races either closer to the wall of the actuator compartment as shown in FIG. 6 or, in the reverse position, more remote therefrom as shown in FIG. 4. This asymmetrical plunger arrangement permits a more compact and smaller switch construction.
For example, the actuator units 111 and 126 have been constructed with diameters of about one inch, and the square contact block with a side dimension of about one and a quarter inches. In this small size, the cams 1&4 should have as large a turning radius as possible to afford as small a slope as possible for the cam surface within the limited angle of rotation to produce the required actuating movement whereby an operator can readily apply the torque required to turn the actuator and operate the switch. Thus, to optimize the cam turning radius and thereby its slope, especially where more complex cam surfaces are used for switch actuation, the asymmetric finger 11% is close to the wall of the actuator compartment.
In the embodiment of FIG. 3, the necessary space for the coil spring 48 and the retaining ring 42 together with certain minimum wall dimensions and the like for strength leaves an actuating surface 46 of small diameter. This is accommodated by the placement of the asymmetric finger 1111 closer to the center of the actuator compartment 54, where it is positioned to be actuated by the actuating surface 4t Notwithstanding the small size of the contact block 12 and the close spacing of such contact blocks on the mounting panel (say to within a quarter of an inch), the units are accessible for assembly on or removal from the mounting panel. Moreover, a large number of wires may be readily connected to or disconnected from the connectors 8t) and 90. The wires 173 may be secured to resiiient, female pressure connectors 18% made of metallic strips. Arms 182 struck out from one end of the strip are wrapped around one or two wires 178, and arms 184 struck out from the other end are bent around to form two sheaths that slidabiy receive the two branch tabs of the bifurcated connector or 99 and frictionally and resiliently retain that connection. A smaller female connector 186 of the same general construction is dimensioned to be secured to a single wire 1% and to be connected to a single branch of the tab connectors 811 or 9%. The smaller connector is so dimensioned that two can be attached to the two branches of each male connector. The connector strips '78 and he may be formed with female connectors at their ends in place of the bifurcated tab type.
The female connectors 131) or 186 are slidably connected to the male connectors 89 or 9t! Within the respective connector compartments 63 or 72. The compartments '63 for the upper-contact connectors 86? open in the same plane as do the compartments 72 for the lower-contact connectors @11, and thse planes are at different levels. Thereby, the Wire connections are more readily made, and the desired connectors 88 or 911 are readily distinguished. Moreover, Wires connected to adjacent compartments, say compartments 6'? and 72, are sufficiently spaced in a staggered array that there is no danger of accidental contact between adjacent female connectors.
The connector compartments 68 and 741 are in a parallel array as are the connectors 80 and Mt therein, so that the connections may all be made in the small space afforded. Moreover, the eight to sixteen wires coming from the lower end of each contact block 12 are in a parallel compact bundle, which ensures neatness and ease of handling.
The separation of the contact block into compartments provides insulation between all of the conductive elements outside of the contact chamber 69. Moreover, the electrical elements of the two casing halves 56, 58 are reliably insulated from each other by the insulating separator sheet 112.
In a copending application by Pusch et al., and assigned to the same assignee as this application, S.N. 77,748, filed December 22, 1960, Illuminated Push Button Switch,
2 an illuminated switch actuator unit is described that is adapted for use with the contact block of this invention. Certain switch structure described herein is disclosed and claimed in Kane et al. application SN. 77,580, filed December 22, 1960, for Rotatable Switch Actuators and assigned to the assignee of this application.
The above described push button switch construction is effective and reliable in operation as well as small in size. The actuator and contact block units are interchangeable, and a large number of wires may be compactly and readily connected to the contact block.
Various modifications of the foregoing features of this invention may be made, and it is not intended that the scope of the invention be limited to the specific form that is described.
What is claimed is:
1. In combination, a switch contact block having a casing including a contact compartment and a separate pair of electrically separated connector compartments at opposite sides of said contact compartment, said casing including passages connecting said connector compartments in communication with said contact compartment, two pairs of bent resilient conductor strips each supported by said casing in a stressed condition and each having a contact end within said contact compartment and a terminal end in a separate one of said connector compartments, fixed contacts on said contact ends, an operating member reciprocably mounted in said casing having mov able contact means for cooperation with said fixed contacts, the fixed contacts on opposite ones of said strips lying in a pair of spaced parallel planes generally perpendicular to the axis or" reciprocation of the operating member, the terminal ends of said strips extending generally parallel to said axis, said connector compartments opening at the bottom wall of said casing to expose the terminal ends of said conductor strips, said terminal ends including parallel sliding-engagement friction-retaining connectors, a hollow base having a side wall portion with a plurality of angularly related surface portions, and an actuating member mounted in the base for movement relative thereto to efiect reciprocation of said operating member, said casing having walls in telescoping mating engagement with said base Wall portion, the two pairs of opposed connector compartments opening in a pair of spaced parallel planes which are generally perpendicular to said axis.
2. In combination, a switch contact block; an actuator therefor; and means for fastening one to the other; said contact block comprising a casing having a plurality of separate compartments, a plurality of fixed contacts in a first one of said compartments, and an operating member having contact means for engaging said contacts and movable within said first compartment, said operating member extending in one operating condition a certain operating distance into a second one of said compartments of a depth substantially equal to said distance, said second compartment being open at one end face of the casing and enclosed on the sides by walls of said casing forming a certain distinct, indexing shape; said actuator comprising a base having an opening extending between the ends thereof and having walls adjacent one of said ends of a shape to mate with said second compartment walls one within the other and of substantially the same depth, an actuating member movable within said base opening, accessible to an operator at the opposite end of said base, and engaging said operating member within the depth of said indexing shape to provide an effective actuating movement thereof substantially equal to said operating member distance.
3. The combination of claim 2 wherein said actuating member is a push button mounted for reciprocating translatory movement between said base ends an amount substantially equal to said operating distance.
4. The combination of claim 2 wherein said actuator is a rotatable shaft having a cam at said one base end 53 effective to move said block operating member through said operating distance.
5. The combination of claim 2 wherein said operating member includes a plunger rod having a central axis, a contact cross-bar symmetrically positioned with respect to said rod axis and adapted for bridging said contacts, said rod further having a single finger extending into said second compartment, said finger being positioned asymmetrically with respect to said plunger rod axis, said compartments including means for guiding said operating member in either of two positions spaced one hundred and eighty degrees about said axis wherein said finger is close to and remote from said casing walls respectively.
6. In combination, a switch contact block; an actuator; and means for fastening said block to said actuator; said contact block including a casing, a plurality of fixed contacts symmetrically positioned with respect to an axis of said casing, an operating plunger rod mounted for axial movement in said casing, a contact member symmetrically mounted with respect to an axis of said operating rod and movable therewith, said operating rod having a single finger portion asymmetrically positioned with respect to said rod axis, said casing including means for slidably guiding said operating rod for axial movement substantially coaxially therein and with said contact member engageable with said fixed contacts, said guide means being adapted to similarly guide said operating rod in either of two positions in which a portion of said rod finger is on opposite sides of said casing axis and respectively closer to and more remote from a wall of said casing; said actuator including a base having a movable actuating member adapted to engage and actuate said operating rod finger in one of the positions thereof.
7. The combination as set forth in claim 6 wherein said actuating member includes a push button member mounted for reciprocating translatory movement in said base along the axis of said operating rod, and said operating rod is mounted in said position with said finger more remote from said casing Wall.
8. The combination as set forth in claim 6 wherein said actuating member includes a rotatably mounted shaft adapted for turning operation, and a cam adapted to engage the finger of said operating rod and produce axial movement thereof, and said operating rod is mounted in said position with said finger closer to said casing Wall.
9. In combination, a pair of detachably connected switch contact blocks each having a casing including a contact compartment and a pair of spaced connector compartments on opposite sides of the contact compartment, the compartments of each casing opening at a side wall of the casing, a pair of fixed contacts in the contact com partment of each casing, a reciprocable operating member in each casing each having contact means movable relative to said fixed contacts, a separate pair of conductors connected to each pair of fixed contacts and having terminals extending generally parallel to the direction of reciprocation of the associated operating member into said connector compartments, said connector compartments opening at the bottom walls of the casings to expose said conductor terminals, a hollow base having side walls arranged in a selected indexing configuration, an actuating member mounted within the base for movement relative thereto for effecting reciprocation of both of the operating members, said casings having walls in telescoping mating engagement with said base walls when the casings are connected, means securing the casings together with said open side walls in confronting relation, and an insulating barrier between said open side walls to electrically isolate the connector compartments of the two casings.
10. In combination, a pair of detachably connected switch contact blocks each having a casing including a contact compartment and a plurality of connector com partments, the compartments of each casing opening at a side wall of the casing, two pairs of fixed contacts in the contact compartment of each casing, a reciprocable operating member in each casing each having contact means movable relative to the fixed contacts means, a separate pair of conductors connected to each pair of fixed contacts and having terminals extending generally parallel tothe direction of reciprocation of the associated operating member into separate connector compartments, said connector compartments opening at the bottom Walls of said casings to expose said conductor terminals, a hollow base having side walls arranged in a preselected indexing configuration, an actuating member mounted within the base for movement relative thereto to effect reciprocation of both of said operating members, said casings having walls in telescoping mating engagement with said base walls when the casings are connected, means securing the casings together with said open side walls in confronting rela- References Cited in the file of this patent UNITED STATES PATENTS Koertge May 29, 1956 Frank May 29, 1956 Ellis Mar. 7, 1961