Butt-contact Speed Control Trigger Switch

Abstract

A self-enclosed trigger switch adapted for mounting within the handle of a portable electric tool such as a drill, saw or the like. The switch has a housing mounting a slidable trigger to be depressed by the forefinger of the user to start the tool and control its speed. The housing encloses a two-pole butt-contact on-off switch and a thyristor speed control circuit. The housing has three sections including two inter-fitting base halves and a frame. The two base halves form a center compartment therebetween in which the speed control circuit is mounted. The frame clamps the two base halves together and forms with the opposite sides of the respective base halves left and right side compartments in which the respective butt-contact sets of the double-pole switch are mounted for actuation by the trigger. The frame also mounts the trigger for reciprocal sliding movement along the top of the two base halves to control both the switch and speed control circuit.

Description

BACKGROUND OF THE INVENTION

Speed control trigger switches have been known heretofore.

In one version, a sliding bridging contact switch and a variable resistor are arranged side-by-side at the top of the base and the movable contacts thereof are spring biased within recesses in the trigger for closing the switch and reducing the resistance when the trigger is depressed. In such version, a thyristor speed control circuit is housed within an open-top compartment in the base which is closed by a terminal board on which the switch contacts and variable resistor are mounted.

In other versions, two sliding bridging contact switches are used in place of the single sliding bridging contact switch mentioned in the first version above for double-pole use to control both sides of the power line, either along or together with a variable resistor mounted on a vertical plane therebetween and a speed control circuit mounted within the base. In such versions also, the slidable contacts of both the switches and the variable resistor are spring biased within recesses in the trigger for actuation thereby.

While these prior switches have been useful for their intended purposes, this invention relates to improvements thereover.

SUMMARY OF THE INVENTION

This invention relates to butt-contact speed control trigger switches.

An object of the invention is to provide an improved self-enclosed trigger switch.

A specific object of the invention is to provide a trigger switch with improved switch contacts and arrangement thereof.

A more specific object of the invention is to provide an improved speed control trigger switch that is simpler in construction and easier to assemble without sacrificing efficiency of operation.

Another specific object of the invention is to provide a self-enclosed double-pole speed control trigger switch that has fewer parts.

Another specific object of the invention is to provide a double-pole speed control switch having the switch poles connected on the power line side of the speed control circuit which adapts it for ready conversion to a single-pole switch by merely omitting the parts of the second pole in assembly.

Another specific object of the invention is to provide a double-pole speed control switch constructed so that all of the electrical connections are either welded or held in engagement by spring pressure to insure reliable electrical contact.

Another specific object of the invention is to provide a speed control switch with improved butt contacts that can be assembled onto the base halves and are held thereon by their contact bias springs to facilitate final assembly of the base into the frame without danger of these contacts falling off.

Another specific object of the invention is to provide an improved double-pole speed control switch wherein the two poles of the double-pole switch are housed in respective compartments within the insulated housing separate from the compartment housing the speed control circuit thereby to afford adequate electrical clearances and to avoid dielectric problems particularly under conditions of high humidity and accumulation of arc contaminants.

Another specific object of the invention is to provide an improved double-pole speed control switch constructed so that the speed control circuit is completely disconnected from the power line in the switch-off position to insure against dangerous line-to-line short circuits within the switch in the event of component failure causing catastrophic failure of other components when the switch is off.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged left side elevational view of the speed control trigger switch with the left side of the frame broken away along line 1--1 of FIG. 3 to show the first pole of the two-pole switch, the shunting contact and connectors in the left compartment;

FIG. 2 is a right side elevational view of the housing and part of the trigger of the switch of FIG. 1 with the right side of the frame broken away along line 2--2 of FIG. 3 to show the second pole of the 2-pole switch and connectors in the right compartment;

FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 1;

FIG. 4 is a sectional view taken substantially along line 4--4 of FIG. 3 to show the speed control elements mounted in the center compartment;

FIG. 5 is a top view of the left one of the two base halves shown in FIG. 4 minus the sliding contact for the resistor;

FIGS. 6, 7 and 8 are views like FIG. 1 showing the first pole of the double-pole switch and shunting contact and in sequential positions of switch closed, speed control circuit shunted, and contact cleaning motion completed as the trigger is depressed, respectively; and

FIG. 9 is a schematic circuit diagram of the butt-contact speed control trigger switch and of its connection to a portable tool motor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-9, there is shown a self-enclosed speed control trigger switch constructed in accordance with the invention. As shown therein, the switch comprises a spring biased trigger 2 mounted for linear sliding movement in a switch housing. This housing comprises a frame 4 and a pair of base halves designated as left base L and right base R, respectively, most clearly shown in FIG. 3. This frame clamps the two halves of the base together and also clamps slidable rear portion 2a of the trigger on top of the base so that finger engaging portion 2b extends forwardly for depression by the forefinger of the user.

To form a center compartment 6 for the speed control components, the left and right base halves L and R are provided with upper and lower ledges La and Ra, respectively, as shown in FIG. 3, each abutting the other base half. Ledge Ra extends toward the left flush with the bottom of the base and is provided with a pair of slightly shortened ribs Rb, one at each of the forward and rear ends thereof, the left ends of which press against the two lower corners of heat sink 8 and hold it fixed against the wall of left base L. Ledge La extends toward the right against base R at a location a short distance below the top of the base to provide a confined space above this ledge for resistor strip 10 and its sliding contact 12 as shown in FIG. 3.

This ledge La and base R are provided with means holding them in registration with one another to prevent them from moving in any direction in a vertical plane as seen in FIG. 3 while the surrounding frame holds them from spreading apart. This means comprises a pair of spaced projections Lb and Lc on the edge of ledge La as shown in FIG. 4 that enter complementary slots in the wall of base R, and a single projection on the wall of base R that enters slot 14 between projections Lb and Lc.

Heat sink 8 is provided with a flat, substantially rectangular body portion that is pressed flat against the wall of left base L within center compartment 6 and T-shaped upper portion integrally formed thereon whereby it is suspended from ledge La. The stem 8a shown in FIG. 4 of this T-shaped portion extends up through lateral slot 14 that divides ledge La into two parts, and the cross bar 8b of this T-shaped portion is bent 90.degree. to the right as shown in FIG. 3 to lie flat in a shallow groove in the upper surface of this ledge to provide a "collector rail" type electrical connector 8b along which movable contact brush 12 of the variable resistor runs when the trigger is moved.

To insure good electrical contact at all times, movable contact 12 is provided with four resilient fingers as shown in FIG. 3 having downwardly bowed portions at their contacting end as shown in FIG. 4, two of which slide on resistor strip 10 and the other two of which slide on connector 8b to maintain the resistor slider connected to the heat sink as shown schematically in the circuit diagram in FIG. 9. The mounting end of this movable contact 12 is bent upwardly as shown in FIG. 4 and is frictionally held in a slot in the trigger, as shown in FIGS. 1 and 3, for movement with the trigger.

The heat sink is provided with a number of sheared tabs 8c as shown in FIG. 4 to provide a fixture for defining the location of and holding thyristor package 16 in place while its anode is soldered to the heat sink. Thus, the heat sink, which is made of electrically conducting metal of good heat conducting type such as copper, forms the anode terminal for the silicon controlled rectifier SCR of the SCR-DIAC package 16 enclosed in broken lines in FIG. 9. The heat sink is provided with a notch at its upper forward corner as shown in FIG. 4 to provide electrical clearance for lateral tab 18a of the shunting switch stationary contact 18.

One pole of the double-pole switch includes stationary contact 20 and movable butt contact 22 shown in FIG. 1, this pole being the left pole of the switch and being mounted in the left side compartment as hereinbefore described. The other pole of the double-pole switch includes stationary contacts 24 and movable butt contact 26 shown in FIG. 2, this pole being the right pole of the switch and being mounted in the right side compartment as hereinafter described. Movable butt contact 26 engages a connector 28 whereby it is connected to a power line as shown in FIG. 9.

As shown in FIG. 1, the left side compartment is defined by a forward wall Ld, a rear wall Le and a bottom wall Lf. The bottom wall is provided with a pair of large apertures Lg and Lh, one at each end thereof, through which bare wires or flat connector tabs are inserted to connect the speed control circuit to an external power supply and load such as a tool motor. Forward wall Ld cooperates with projection Lj to provide a retaining slot for stationary contact 18 which is held fixed to the base by a linear flat connector spring strip 30. One end of spring strip 30 is held in a slot in the base formed so as to bias the other end of the spring strip against the downwardly extending connector portion of stationary contact 18.

The other stationary contacts and like connector including stationary contact 20 in the left compartment and stationary contact 24 and connector 28 in the right compartment are similarly held between wall Le and projection Lk, wall Rc and projection Rd, and wall Re and projection Rf, respectively, and cooperate with spring strips 32, 34 and 36, respectively, to provide so-called "press-in" lead connectors whereby bared, soldered ends of stranded wires or flat tabs can be connected by mere insertion through apertures Lg, Rg and Rh, respectively, and aperture Lh and can be removed by insertion of a release tool beside the wire to pry the spring strip loose therefrom to release the wire. In this connection, it will be noted that apertures Lg and Lh in FIG. 1 and corresponding apertures Rg and Rh in right base R shown in FIG. 2 are large enough to admit such flat connector tabs and release tool.

As shown in FIGS. 1 and 3, left base L is provided with a central aperture Lm through which movable butt contact 22 in the left compartment is connected to the heat sink in the center compartment. The lower end of a helical compression spring 38 rests on a bottom sill Ln at this aperture as shown in FIG. 3 and has a connector cap 40 over the upper end of this spring. This cap is formed of electrically conductive material such as copper and has four strips extending down from its upper cap to surround the spring. The left and right strips have outward bulges as shown in FIG. 3 so that frame 4 pressing on the left bulge keeps the right bulge in good contact with heat sink 8. As will be apparent, this helical compression spring 38 biases movable butt contact upwardly while the outward bias on the left and right strips of cap 40 maintain spring pressure contact between the movable butt contact and the heat sink to insure a good electrical connection.

In the right side compartment, the lower end of a similar compression spring 42 rests on a similar sill or seat and biases movable butt contact 26 upwardly as shown in FIG. 2.

As shown in FIG. 9, thyristor package 16 contains an SCR and a diac D, the latter being a bidirectional triggering device that functions as hereinafter described to fire the SCR into conduction. This diac is connected to the gate of the SCR internally within the integrated circuit package. This diac is connected at its other side through a connecter strap 44 as shown in FIG. 4 to the rear end of resistor strip 10. For this purpose, connector strap 44 is provided with a reentrant loop having a bias whereby it grips the rear end of ledge La so that the protuberance at its upper end presses with a spring force onto resistor strip 10 for a good electrical connection. Strap 44 is kept spaced from heat sink 8 by a ledge Lo as shown in FIGS. 4 and 5. Wire 16a coming from the diac is electrically welded to the downwardly projecting end portion of connector strap 44. One lead 46a of a capacitor 46 is also similarly welded to connector strap 44. The other lead 46b of this capacitor is similarly welded to lateral projection 18a of stationary contact 18. The cathode lead 16b of the SCR is also similarly welded to lateral projection 18a. As will be apparent, left base L is provided with an aperture through which lateral projection 18a of stationary contact 18 extends into the central compartment.

A thin insulating film 48 is placed behind the capacitor to insulate it from the heat sink in the event the insulating coating on the capacitor should chip or in the event solder peaks are left on the capacitor which would otherwise short-circuit it to the heat sink. This insulating film has a lateral bend beneath ledge La as shown in FIG. 3 to hold it in place.

As shown in FIGS. 1 and 2, helical compression springs 38 and 42 bias movable butt contacts 22 and 26 into closed positions and the trigger is provided with cam surfaces for operating these movable butt contacts. Butt contact 22 is a flat piece of electrically conductive metal such as copper and is provided with a center slot in its lower edge into which connector cap 40 is seated. A shoulder 22a at its rear end underlies stationary contact 20 and forms a first pole of the double-pole switch for connecting one power line PL1 to the speed control circuit as shown in FIG. 9. A shoulder 22b at its forward end underlies stationary contact 18 and forms a shunting contact for by-passing the speed control circuit for full speed operation as shown in FIG. 9.

Movable butt contact 26 is like butt contact 22 except that is has only one circuit closing contact at its forward end and its rear end forms a connector always in engagement with connector 28. Thus, butt contact 26 is provided with a like seat at its lower center for spring 42. Shoulder 26a at its forward end underlies stationary contact 24 and forms the second pole of the double-pole switch for connecting the other power line PL2 to the motor as shown in FIG. 9. A shoulder 26b at its rear end constantly engages the underside of connector 28 to which the other power line is to be connected.

As shown in FIG. 1, movable butt contact 22 is provided with a pair of upwardly projecting cam followers including a rear cam follower 22c directly in front of rear shoulder 22a and a forward cam follower 22d directly behind forward shoulder 22b. These two cam followers are pressed against the trigger by helical compression spring 38.

As shown in FIG. 2, movable butt contact 26 is similar to butt contact 22 just described and is provided with rear and forward cam followers 26c and 26d, respectively, corresponding to those in FIG. 1, although only forward cam follower 26d is used. However, this right side butt contact is nevertheless made identical to the left butt contact fo facilitate production and reduce the number of different parts.

As shown in FIG. 9, line PL1 is connected to stationary contact 20 and line PL2 is connected to connector 28. The motor M is connected between stationary contacts 18 and 24 as shown in FIGS. 1, 2 and 9. This motor may be of the universal type or the like that is usually employed in portable tools.

The trigger is provided with means for actuating the left and right movable butt contacts. For this purpose, the lower surface of linearly slidable portion 2a of the trigger is provided with a left cam 2c shown in FIG. 1 for operating cam follower 22c to close the left pole of the on-off switch and a right cam 2d shown in FIG. 2 for operating cam follower 26d to close the right pole of the on-off switch. Cam 2c is at the rear end of the trigger because it operates rear cam follower 22c. Cam 2d is spaced forwardly of the rear end of the trigger because it operates forward cam follower 26d.

The angles of these cams 2c and 2d are arranged so that the right pole of the double-pole on-off switch closes first and opens last relative to the left pole thereof. For this purpose, cam 2c is provided with a 30.degree. slope relative to the horizontal bottom of the trigger whereas cam 2d is provided with a 45.degree. slope relative to the lower surface of the trigger and the starting point of cam 2d, that is, the lower end of its slope, is positioned so that butt contact 26 starts closing slightly ahead of butt contact 22. Thus the right pole 24, 26a starts closing first due to the advanced start of slope 2d and closes first due to the steeper slope 2d than the left pole. This is done so that all arcing will be confined to the left pole 20, 22a that is equipped with a drive spring 50 for imparting cleaning motion to left contact 22.

The trigger is provided with a third cam 2e on its lower surface at the left side as shown in FIG. 1 for closing the shunting contact 18, 22b. This cam is spaced from cam 2c so as to operate cam follower 22d near the end of the trigger depression stroke, after the variable resistor 10 has been reduced to minimum value, for the full speed operation as shown in FIG. 7.

The order in which the several cams operate the cam followers is as follows. On initial pull-back of the trigger, right pole 24, 26a shown in FIG. 2 closes followed closely by closure of left pole 20, 22a of the on-off switch as shown in FIG. 6. This causes motor M in FIG. 9 to be connected in series with the SCR across lines PL1 and PL2 to start the motor running at a slow speed. Further pull-back on the trigger increases the motor speed as brush 12 slides to the left in FIGS. 2 and 9 to reduce the resistance in circuit. Such reduction in resistance causes capacitor 46 to charge to the triggering value of voltage sooner on each positive half-cycle of the supply voltage. Each time such value is reached, diode D suddenly conducts to transmit a pulse of current into the gate of the SCR to render the latter conducting. The SCR then conducts for the remainder of the positive half-cycle of supply voltage and stops conducting when its anode voltage decreases to near zero. Thus, the lower the resistance, the longer the current pulses, relative to the intermediate off intervals, that are applied to the motor and the higher the speed.

This speed increase continues until the resistance is decreased to its minimum effective value. Further pull-back on the trigger causes shunting switch 18, 22b to be closed by cam follower 22d riding on cam 2e as shown in FIG. 7 to shunt the speed control circuit. As a result, full A.C. voltage is applied to the motor for full speed.

As shown in FIG. 1, the linearly sliding portion 2a of the trigger is provided with a vertical slot 2f for retaining a drive spring 50. This spring is made of a flat narrow strip bent back at its upper end which is pinched together, inserted in the slot and allowed to spread so that it frictionally held therein. This bent-back end has a short outward angle at its extreme end to form a tooth for biting into the forward side of slot 2f to aid in retaining it in the slot. The lower end of this drive spring extends down substantially coextensive with cam 2c so that cam follower 22c rises in the space behind this lower end of the drive spring when the on-off switch is closed.

Final pull-back of the trigger causes drive spring 50 to engage cam follower 22c and to move butt contact 22 a short distance toward the rear against abutment Lk as shown in FIG. 8. This is the aforementioned cleaning motion. This movement of the butt contact causes shoulders 22a and 22b thereof to rub stationary contacts 20 and 18, respectively, to break any film formed thereon due to deterioration caused by arching, thus to maintain the contacts in condition to make a good, low resistance electrical contact each time they close. Further contact cleaning motion occurs when the trigger is subsequently released to return to its off position. When the trigger returns from the position shown in FIG. 8 to the position shown in FIG. 7, cam follower 22d rides down along cam 2e. The angle of this cam 2e is directed so that it acts on cam follower 22d to slide butt contact 22 forward against abutment Lj. This causes shoulders 22a and 22b of the butt contact to rub stationary contacts 20 and 18, respectively, to maintain them clean.

Further return of the trigger to the position shown in FIG. 6 causes shunting contact 18, 22b to reopen and causes cam 2c to engage cam followers 22c. If the butt contact has not slid all the way forward by this time, cam 2c acting on cam follower 22c will slide in the rest of the way against abutment Lj, thus providing cleaning action on contacts 20, 22a.

It will be apparent that movable butt contact 22 has now been moved a small amount clear of abutment Lk into readiness for drive spring 50 to move it rearward at the end of the next pull-back stroke of the trigger.

These small amounts of cleaning motion increase the number of reliable switch operations from about 15,000 to over 100,000 reliable operations. This cleaning action assures consistent low contact resistance and thereby lower contact operation temperature.

Since right pole butt contact 26 closes first and opens last, no arcing can thereat. Therefore, a drive spring like left pole drive spring 50 is not normally needed therefor and the cost can be reduced by omitting it. This omission becomes possible by the structure whereby the right pole closes first and opens last. However, a slot 2f' is provided for such drive spring on the right side of the trigger as shown in FIG. 2 so that it can be readily included in those few instances where the switch must be used in extremely dusty or dirty conditions, if needed.

The trigger is also provided with a groove 2g at its upper rear portion for accomodating a helical trigger return spring 52 as shown in FIG. 3. One end of this spring abuts the forward end of this groove and the other end thereof abuts the rear wall of frame 4 and this spring is in compression to return the trigger to its forwardly-extended off position as shown in FIG. 1.

To limit the return motion of the trigger, the top wall of frame 4 is provided with a pair of laterally aligned catches 4a, one at each of the left and right sides, and the trigger is provided with a pair of elongated notches 2h shown in FIGS. 1 and 3 providing clearance for the associated catches through the extent of trigger movement, these notches terminating at their rear end in laterally aligned walls 2j butting the respective catches to limit forward motion of the trigger.

An undercut shoulder 2k is provided in the left side of the trigger as shown in FIG. 1 and the frame is provided with an integral sleeve 4b partly shown in FIG. 3 that supports a spring-biased lock button in the usual manner for catching on the shoulder to lock the trigger in full speed position.

The frame is also provided with a pair of snap-in apertures 4b and 4c for receiving lateral projections Lp and Rj, respectively, when the juxtaposed base halves are inserted into the frame. These projections are provided with an angular top surface to cam the sides of the frame outwardly sufficiently to allow these projections to enter the latching holes.

To assemble the switch, the parts are first assembled on the left and right halves of the base and on the trigger with the exception of resistor slider 12. The trigger and its return spring are then spaced in the frame, using grease to hold the return spring in place and the trigger is locked in depressed position by the lock button. Slider 12 is then inserted in its slot in the trigger. The two halves of the base are then pinched together and inserted into the frame until the projections snap into the holes.

The double-pole speed control switch as hereinbefore described is adapted for ready conversion to a single-pole speed control switch as a convenient cost saving in those applications where a double-pole switch is not required. The switch being constructed so that the two poles are connected on the line side of the speed control circuit, the conversion to single-pole merely requires omitting of the parts of the right pole. This includes stationary contact 24, connector 28, movable butt contact 26, contact bias spring 42 and spring strips 34 and 36 shown in FIGS. 2 and 9. The corresponding side of the motor must then be connected to power line PL2 by a wiring nut.

While the apparatus hereinbefore described is effectively adapted to fulfill the objects stated, it is to be understood that the invention is not intended to be confined to the particular preferred embodiment of butt-contact speed control trigger switch disclosed, inasmuch as it is susceptible of various modifications without departing from the scope of the appended claims.

Claims

I claim:

1. A self-enclosed double-pole trigger switch comprising:

a switch operating trigger including a return spring normally biasing said trigger into its off position from which it can be actuated to its on position by the fore-finger of the user;

a switch housing comprising:

an insulating base;

a frame mounting said trigger for movement along the top of said base;

a pair of open-top compartments in said housing under-lying said trigger;

butt contact means in said compartments, said butt contact means comprising:

first stationary contacts mounted on said base within the corresponding compartments and each having an electrical connector for connecting said stationary contact to an external circuit;

movable butt contacts guided by the walls of their compartments for tiltable movement in vertical planes;

and a pressure spring at the center of each said movable butt contact biasing one end of said movable butt contact toward engagement with said stationary contact to provide the required contact pressure when the contacts are closed;

and means providing electrical connections from said movable butt contacts to said external circuit comprising:

a pair of connectors continuously in engagement with the respective movable butt contacts;

one of said butt contact means further comprising:

a second stationary contact mounted on said base within the corresponding compartment for engagement by the other end of the associated movable butt contact under the force of its pressure spring and having an electrical connector for connecting said second stationary contact to said external circuit;

and cooperating cam and cam follower means on said movable butt contacts and on said trigger for tilting said movable butt contacts away from said stationary contacts when said trigger is released to its off position and for allowing said pressure springs to tilt first ends of the movable butt contacts closed to said first stationary contacts on predetermined movement of said trigger when actuated to said on position and to tilt the other end of one of said movable butt contacts closed to said second stationary contact on further movement of said trigger.

2. The invention defined in claim 1, wherein said cooperating means comprises:

a laterally offset cam follower on each movable butt contact extending from its open-top compartment into the path of the trigger above said base;

and a cam on said trigger for each said cam follower for engaging said cam follower to tilt said movable butt contact against the force of said pressure spring in response to trigger actuation.

3. The invention defined in claim 1, wherein:

said insulating base comprises a pair of cavities, one on each side thereof;

and said frame comprises a skirt surrounding said base and embracing said cavities to form said open top compartments in which said butt contacts means are mounted.

4. The invention defined in claim 1, wherein said electrical connectors together with said pair of connectors comprise:

a pair of load terminal connectors across which a load device may be connected and a pair of line terminal connectors for connecting said switch across an electrical power source whereby the double-pole switch affords connection and disconnection of both sides of the power source to the load.

5. A self-enclosed double-pole speed control trigger switch comprising:

a return spring biased trigger adapted for operation by the forefinger of the user;

a frame mounting said trigger for movement therein and having a base-embracing portion;

a switch base comprising a pair of insulating base halves held fixed within said base-embracing portion of said frame with their tops abutting said trigger and defining with said frame left and right, open-top, switch compartments, respectively;

said insulating base halves defining therebetween a central compartment separated from said left and right compartments;

switch means comprising a double-pole butt contact on-off switch having one pole thereof in each of said left and right compartments;

each said switch pole comprising a pair of stationary contact-connector members mounted in spaced slots in the respective base half within the associated compartment, and a movable butt contact including a central bias spring biasing opposite ends of said butt contact into closure with said stationary contact-connector members, and a pair of laterally offset cam followers on said movable butt contact extending up through the open top of the associated compartment into the path of said trigger;

cams on said trigger engaging predetermined cam followers of the two movable butt contacts of said double-pole switch to afford tiltable closing and opening of one or both ends of said movable butt contacts with respect to said stationary contact-connector members when said trigger is operated;

a thyristor speed control circuit mounted in said central compartment and comprising a variable resistor having its resistor strip mounted at the upper portion of said central compartment and a movable brush contact mounted in a slot in said trigger and movable therewith to vary the amount of resistance in said speed control circuit, and means adapting said speed control circuit and a motor for connection to and disconnection from an electrical power source by the two poles of said double-pole switch.

6. The invention defined in claim 5, wherein said switch means comprises a shunting switch comprising:

one of the stationary contact-connector members of one of said pairs thereof mounted in a slot in one of said switch compartments;

one of the laterally offset cam followers on the associated movable butt contact extending up from the open top of the associated switch compartment into the path of said trigger;

one of the cams on said trigger spaced from the other cams to afford tiltable closure of said shunting switch near the end of the trigger stroke;

and means connecting said shunting switch to shunt said speed control circuit.

7. The invention defined in claim 6, wherein said thyristor speed control circuit comprises:

a thyristor triode having main conduction terminals and a gate;

a triggering device connected to said gate;

a heat sink to which said thyristor triode is mounted by connecting one main conduction terminal thereto;

a firing capacitor in said central compartment;

a connector having spring pressure engagement with said resistor strip, and leads from said capacitor and triggering device having welded connections to said connector;

a tab on said shunting switch stationary contact connector member extending into said central compartment and leads from said capacitor and the other main conduction terminal of said thyristor triode being welded thereto;

and spring pressure means connecting the movable butt contact associated with said shunting switch to said heat sink.

8. A self-enclosed double-pole speed control trigger switch comprising:

a return spring biased trigger adapted for operation by the forefinger of the user;

a frame mounting said trigger for movement therein and having a base-embracing portion;

a switch base comprising a pair of insulating base halves held fixed within said base-embracing portion of said frame with their tops abutting said trigger and defining with said frame left and right, open-top, switch compartments, respectively;

said insulating base halves defining therebetween a central compartment separated from said left and right compartments;

switch means comprising a double-pole butt contact on-off switch having one pole thereof in each of said left and right compartments;

each said switch pole comprising a stationary contact including a wire connector portion mounted in a slot in the respective base half within the associated compartment, and a movable butt contact including a bias spring biasing said butt contact into closure with said stationary contact, and a cam follower on said movable butt contact extending up through the open top of the associated compartment into the path of said trigger;

cams on said trigger engaging the cam followers of the two poles of said double-pole switch to afford closing and opening of said contacts when said trigger is operated;

a thyristor speed control circuit mounted in said central compartment and comprising a variable resistor having its resistor strip mounted at the upper portion of said central compartment and a movable brush contact mounted in a slot in said trigger and movable therewith to vary the amount of resistance in said speed control circuit;

at least one of said base halves comprising a pair of abutments limiting rubbing movement of the movable butt contact on the associated stationary contact to afford limited cleaning movement therebetween;

a resilient drive member mounted on said trigger to engage said cam follower following closure of the associated contacts to slide said movable butt contact on the associated stationary contact for cleaning motion at the extreme end of the trigger stroke;

and the associated cam on said trigger being effective on return movement of the trigger to slide said movable butt contact on said associated stationary contact in the reverse direction for additional cleaning motion.

9. The invention defined in claim 8, wherein:

one of said cams on said trigger is provided with a position and angle so as to cause closing of its associated switch pole before than and reopening after the other switch pole so that said other switch pole which is provided with said resilient drive member takes up all the contact arcing.

10. The invention defined in claim 5, wherein:

one of said base halves comprises a ledge within the upper portion of said central compartment to provide a shallow channel at the top of said base separated from said left and right compartments;

said resistor strip mounted flat on said ledge for engagement by said movable brush contact.

11. A self-enclosed speed control trigger switch comprising:

a return spring biased trigger adapted for operation by the forefinger of the user;

a frame mounting said trigger for movement therein and having a base-embracing portion;

a switch base comprising a pair of insulating base halves held fixed within said base-embracing portion of said frame with their tops abutting said trigger and defining with said frame left and right, open-top, switch compartments, respectively;

said insulating base halves defining therebetween a central compartment separated from said left and right compartments;

switch means comprising a double-pole butt contact on-off switch having one pole thereof in each of said left and right compartments;

each said switch pole comprising a stationary contact including a wire connector mounted in a slot in the respective base half within the associated compartment, and a movable butt contact including a bias spring biasing said butt contact into closure with said stationary contact, and a cam follower on said movable butt contact extending up through the open top of the associated comaprtment into the path of said trigger;

cams on said trigger engaging the cam followers of the two poles of said double-pole switch to afford closing and opening of said contacts when said trigger is operated;

a thyristor speed control circuit mounted in said central compartment and comprising a variable resistor having its resistor strip mounted at the upper portion of said central compartment and a movable brush contact mounted in a slot in said trigger and movable therewith to vary the amount of resistance in said speed control circuit;

each said stationary contact of the double-pole switch being mounted at one end of the associated compartment, and the respective connector portions of these two stationary contacts being arranged for connections in the two sides of an alternating current circuit connecting power through said speed control circuit to a motor;

a shunting contact consisting of a third like stationary contact including a wire connector portion mounted in a slot in the other end of one of said switch compartments and means connecting the shunting switch formed by said third stationary contact and the associated movable butt contact across said speed control circuit;

a connector member consisting of a fourth member similar to said stationary contacts including a wire connector portion mounted in a slot in the other end of the other one of said switch compartments and arranged for connecting the associated movable butt contact in said A.C. circuit; and each said movable butt contact comprising an elongated member biased at its center and having a second cam follower thereon;

one of said movable butt contacts being electrically connected to said speed control circuit and being operable to engage at one end thereof the stationary contact of one pole of said switch on initial operation of said trigger to connect said speed control circuit to said power, and to additionally engage the stationary contact of said shunting switch at the other end thereof by action of said second cam follower and said third cam on further operation of said trigger to by-pass said speed control circuit;

the other movable butt contact being operable to engage the stationary contact of the other pole of said switch at one end thereof on initial operation on said trigger while remaining constantly in engagement with said connector member at the other end thereof.

12. The invention defined in claim 11, wherein:

said double-pole switch may readily be converted to a single-pole switch by omitting in assembly the stationary contact, connector member, movable butt contact and its bias spring from the corresponding switch compartment and instead connecting the corresponding side of the load and power line directly together.

13. The invention defined in claim 5, wherein:

the wire connector portions of the two poles of said double-pole switch are adapted to be connected to the two sides of an alternating current power source;

and said switch comprises means for connecting said speed control circuit in series with a load between the two poles of said double-pole switch so that said speed control circuit is completely disconnected from the power source when said switch is off.