US2346778A - Portable hand held electric tool - Google Patents

Description

April 18, 1944. w, MITCHELL PORTABLE HAND HELD ELECTRIC TOOL Filed Oct. 16, 1942 I5 Sheets-Sheet l INVENTOR. WHY/F 6mm Mfr/9271 A TTOENE Y.

April 18, 1944. w. G. MlTCHE LL PORTABLE HAND HELD ELECTRIC TOOL Filed Oct. 16, 1942 5 Sheets-Sheet 2 /4 T TO/PNE Y.

April 18, 1944. w G MITCHELL 2,346,778

PORTABLE HAND HELD ELECTRIC TOOL Filed Oct. 16, 1942 5 Sheets-Sheet 5 Patented Apr. 18, 1944 PORTABLE HAND uELn ELECTRIC TOOL Walter George Mitchell, Aurora, 111., asaignor to Independent Pneumatic Tool Company, Chicago. 111., a corporation of Delaware Application October 16, 1942, Serial No. 462,245

14 Claims.

In my co-pending application Serial No. 462,244, filed October 16, 1942, I have shown and claimed a portable hand held electric drill or similar tool adapted for industrial purposes and having a sturdy skeleton metal frame supporting the tool motor and the spindle and the tool housing and its handle made of a plastic material to give lightness in weight and compactness to the tool for ease in handling and balance in one hand and use over extended periods in production work without unduly tiring the operator holding the tool.

The general purpose and object of my invention is to provide a tool of the character referred to in which the housing consists of sheet metal sections oi.the required size and shape, preferably of comparative light gauge sheet steel, to protect and enclose the operative parts of the tool and withstand wear to a better advantage than the plastic materialand to provide the tool with a metal housing and handle member.

In accordance with my invention the housing cover for the motor and the frame and the handle at the rear end of the tool are in the form of separable half section's divided longitudinally of the tool to facilitate and cheapen their manufacture and provide for the convenient connecting of the switch device for the motor with the motor circuit and the supply cable in assembling the tool by having the switch device supported by one of the handle sections independently of the supply cable.

A further object of my invention is to provide the motor cover sections of the housing with integral tongues at their front ends to interlock with notches in flange formations on the frame and the gear casing, respectively, to hold the cover sections in connected relation with said frame and casing, the cover section over the easing overlapping the forward ends of said tongues.

A further object of my invention is to have the bracket which supports the switch device within the tool handle secured to one of the handle sections to facilitate mounting the switch device with the handle and connecting its terminals with the motor circuit and the leads of the supply cable before the handle sections are brought into closing and handle forming relation in assembling the tool.

A further object of my invention is to provide the bracket with an opening or way to. slidably mount the trigger block which operates the switch device from the exterior of the handle so that the entire switch device-including the trigger block may be assembled on one handle section before it is closed thereover.

A further object of my invention is to have the locking plunger for the trigger block supported by the portion of the bracket which slidably mounts the trigger block so that the lock may be assembled in the switch unit before closing the handle sections.

Other and further objects of my invention will appear from the following specification taken in conjunction with the accompanying drawings in which- Fig. l is a side elevational view of a portable hand held electric drill constructed in accordance with my invention:

Fig. 2 i a rear end view of the tool with portions of the handle sections broken away and in section, respectively, to show the overlapping flange connection therebetween;

Fig. 3 is a cross-sectional view taken on the line 3-3 of Fig. 1 to show the interiltting tongues and notches to be hereinafter described;

Fig. 4 is a fragmentary sectional view taken on the line 4-4 of Fig. 3 to show a detail of construction;

Fig. 5 is a similar sectional view taken on line 5-5 of Fig. 2 to show a further detail of construction;

Fig. 6 is a longitudinal sectional view of the tool with parts in section and elevation, respectively, said section being taken on line 6-8 of Fig. 8;

Fig. 7 is a cross-sectional view taken on line l-J of Fig. 6;

Fig. 8 is a top plan view of the tool with the outer housing broken away and in section, re spectively, to show in particular the laterally disposed tongues at the forward end of the cover sections for the tool motor;

Fig. 9 is an enlarged fragmentary sectional view at one of the tongues to more clearly show the interlock of the latter with the associated flange or wall members on the gear case and the motor supporting frame, respectively;

Fig. 10 is a cross-sectional view with parts in elevation taken on line ilil0 of Fig. 6 to show the switch device for the tool motor and its operation trigger block the latter being shown in its normally outwardly projected position;

Fig. 11 is a similar view or the trigger block and its locking plunger, the latter being shown in locking engagement with the trigger block for holding the switch closed;

Fig. 12 is a horizontal sectional view with parts. in elevation taken on line i2-l2 of Fig. 6 to show the cable clamp and the ground connection thereof with the switch supporting bracket with-* in the tool handle;

,Fig. 13 is a fragmentary side view of one of the half sections of the tool housing to show the locking tongues thereon;

Fig. 14 is a side view of the switch supporting bracket removed from the tool; and

embodiment illustrated, the housing for the tool comprises cover and handle sections in the form of sheet metal stampings, as before mentioned, to give the tool lightness in weight and com pactness in size for balance and ease of handling in one hand over extended periods in production work without fatigue to the operator using the tool. Moreover, the comparative light gauge sheet metal housing may replace the now restricted aluminum casings heretofore employed for these tools, while retaining the tool relative small, light weight and of the full power of the previous tool.

The support for the tool motor comprises an integral U-shaped, study skeleton metal frame 4 having substantially parallel arm portions 5, 5 rigidly connected at the opposite ends of the frame by end walls I, B, the same as disclosed and claimed in my co-pending application aforesaid. As defined in said application and as shown herein, the end wall portion 1 of the frame provides a support for the ball bearing unit 9 for the rear end of the armature shaft H] of the rotor ii of the tool motor. The latter has a stator l2 fitted within the frame arms 5, 6 and secured thereto by fastening screws i3, i3 a shown in Fig. 6.

The stator 52 has a rotative connection with the frame arms 5, 5 in the manner described and claimed in said co-pending application. Briefly, this connection is depicted in Fig. 7 herein and comprises arcuate surfaces l4, l4 on-the frame arms to engage the complementary curved edges f5, l5 of the stator plates having fiat side edges l6, 16 which when turned into opposition to the frame arms allow for the lateral shifting of the stator into and out of the frame 4 through either of its open sides in assembling and disassembling of the stator with respect to the frame.

The reducing gear section 2 of the tool comprises a gear casing i1 providing a chamber It to accommodate the gear train which drives the tool spindle ts from the motor shaft ill. The spindle I9 is journaled within the gear casing I! and is equipped at its outer end with a chuck 20 as shown. The gear casing I1 is a metal casting in one piece and has its rear end wall 2| conforming with and secured to the front wall member 8 of the motor supporting frame 4 by screws 22 as shown in Figs. 3 and 4. As shown in Fig. 4, the rear face of the wall 2! is recessed at 23' to seat the frame wall 8. As in my said co-pending application, the wall 8 has a rin formation integral with the outer ends of the framearms 5, 6 and extends on opposite sides thereof to provide a seating surface on it front face, for the casing wall 2! and a shoulder 24 on its rear side for the front edges of the cover sections for the tool motor. The frame ring 8 also has a center opening 25 to receive the interfitting part of the casing wall 2| and to pass the armature shaft l0 and rotor II.

The motor shaft It) extends into the chamber l8 through th gear case wall 2|, the latter supporting a ball bearing unit 28 for the front end of said shaft it! as shown. The gear train comprises a pinion 21 on the shaft ID in mesh with an intermediate gear wheel 28 driving a pinion 29 which meshe with a gear wheel 30 on the spindl shaft IS. The gear case ll has a tubular extension 3! at the front end of the tool.to mount the spindle l9 and its ball bearing 32. The outer end of the extension 3| is externally screw threaded to mount a screw cap 33 which engages over the bearing unit 32 to hold the latter in place and to clamp the sheet metal cover section 34 over the gear housing I] and against the front face of its end wall 2|. The gear housing I'I mounts a shield member 35 to retain lubricating grease within the chamber I8 for the gears as described and claimed in my other co-pending application Serial No. 475,367, filed February 10, 1943.

The part of the housing providing the motor cover and the handle for the tool comprises a pair of separabl half sections 36, 31 divided longitudinally of the tool and each including an integrally connected half of the cover and the handle, respectively. In short, each half section 35, 31 is a one-piece metal stamping forming one half of th motor cover and the adjoining half of the tool handle as shown. For reference purposes, the cover halves are marked 36a, 31a and the handle halves are marked 36b, 31b, respectively. These halves when assembled fit along their. longitudinal edges, the half section 36 having a marginal flange 38 overlapping the other half 3'! from the inside as shown in Fig. 2. I

As shown in the drawings, the combination cover and handle sections 35, 31 are shaped to conform to the tool parts which they respectively cover and provide, the cover sections 36a, 31a being inbulged form to enclose the motor and its supporting frame 4. The handle sections 36b, 31b are channeled shaped in crosssection to enclose the rear end of the frame 4 and the motor brushes 39, 39 carried thereby for the motor commutator 40 as indicated in Fig. 6. The handle sections 36b, 31b are also shaped to provide a hollow depending pistol grip portion 4| for the tool extending below the motor covers 36a, 31a and the frame 4 as shown. The handle sections of the tool are secured to the frame wall I by screws 42, 42. The latter mount spacers d3 interposed between the frame wall I and the rear walls of the handle sections. At the screws 42, the wall sections of the handle members 36b, 31b are dished as at 44, 44 to countersink the screws 42 and interfit in recesses provided in the associated spacers.

The front edge of each cover section 36a, 31a

while the upper and the lower tongues 45 fit in the upper and the lower notches 48. In this respect, the upper and the lower tongues on the two cover sections 36, 31 fit together in side by side relation and the notches 48 are wide enough to receive them as detailed in Fig. 8. The notches in the wall members 6 and 2| ar peripheral notches to readily receive the tongues in assembling the parts and to have the tongues hook over the wall member 2| as shown in Fig. 9. The tongues are .held in place by their resiliency and the over-lapping of the front cover 34. The latter is inserted in place over the front end of the tool after the side sections 36, 31 are applied. The wall members 8 and 2| provide the flange formations for the tongues as expressed in the claims.

The tool contains a rotary fan element 49 splined on the motor shaft l within the cover sections 36, 31 of the housing. The screws l3 carry a baille ring 5|! which provides the rear side of the fan chamber and fitting against the inner side of the cover sections 36, 31 deflects the incoming air to the center intake of the fan as indicated by the arrows in the drawings. Spacer sleeves 55a, 500 on the screws l3 dispose the baffle plate 50 forwardly of the front loops (not shown) of the stator winding 5|. The fan 49 is rotated by the tool motor and creates a flow of air over the motor to cool the same. The air flow is from the rear to the front of the tool, the handle and the cover sections 36, 31 having air intake and discharge opening therein for the fan. The intake openings 52 are in the cover sections 360., 31a adjacent to the handle sections, while the discharge openings 53 are at the front end of the cover sections at the periphery ,of the fan in the form of slots between the tongues as shown.

The cover sections 36a, 31a have inside metal channels 54, 54 spot-welded thereto to hold the stator l2 in place and to provide for an air flow at the sides of the motor.

The handle sections 36b, 31b provide a chamber 55 Within the grip portion 4| of the handle to accommodate the switch device 55 for the motor and its supporting bracket 51. The latter is fashioned of sheet steel in the form shown in Figs. 14 and 15, and from which it will be noted that the bracket has an upright wall 58 extending the full height of the bracket and spot-welded to the fiat side wall 59 of the hendle section 36b as shown in Fig. 11.. The bracket wall 58 has a side flange 60 shaped to fit in part about the switch device 56 and secured thereto by a screw 6| threaded into a tapped boss 62 on the rear side of the switch case. The latter carries a superstructure 63 on its front side mounting a switch actuating lever 64 on a fulcrum rod 65 about which is a coiled spring 66 which normally moves the free end of the lever forwardly. The lever 64 is of the bell-crank type having one arm co-acting with the spring actuated switch mechanism to close the switch and supply an operating current to the tool motor when the lever is moved inwardly. On the release of the lever, the switch action automatically opens the switch to stop the motor and returns the outer end of the lever 64 to its outermost position as shown in Figs. 6 and 10. The switch device is of a conventional type obtainable on the market.

The trigger block 61 for closing the switch is slidably mounted at the pistol grip portion 4| of the tool handle on the front side thereof just below the motor section I as shown herein. To support the trigger block 61, the bracket 56 has a front flange formation 68 providing a rectangular opening or slide-way 69. The formation 68 extends to the outer walls of the handle sections 36b, 8122, the latter having cut-out portions 10, 10 on the opposite sides of their line of division to provide an opening for the trigger block 81 as shown in Figs. 6, 10 and 11. The trigger block may be either a solid or a cored metal member rectangular in shape to fit, without turning, within the slide-way 69. The trigger block 61 is engaged at its inner end with the lever 64, the actuating spring 66 of which normally projects the trigger block outwardly for accessibility exterior of the handle. A lug 1| on the upper inner end of the trigger block 61 takes into a notch Ila in the bracket section 68 to limit the outward projection of the trigger block by the spring 65 and to hold the trigger block from dropping out of the handle. The front end of the trigger block is curved to fit the operator's finger and the slide-way 68 of the bracket 56 is connected with the upright wall 58 by an intervening flange portion 12.

At the lower end of the bracket 56 is provided an inwardly extending integral portion 13 pro viding a foot for the bracket within the tool handle and an anchoring lug for the cable clamp 14. The latter is in the form of a split band and is secured to the lug 13 by a screw 15 a shown in Fig. 12. The cable 16 is embraced by the band 14 within the handle chamber 55, the cable extending into said chamber through an opening 11 in the closing end wall portions 18, 18 of the handle sections 36b, 31b at the lower or butt end thereof. A' protecting grommet 19 is fitted about the cable within said opening. The latter has an equal part in each end wall portion 18, 18 on opposite sides of their meeting edges.

The handle sections 36b, 312) at the pistol grip 4| are rigidly connected in the assembled too1 by a cross-bolt as shown in Fig. 12. The cable 16 contains the supply leads 8|, 8| for the motor circuit and the ground lead Bla. The latter is connected to the foot end 13 of the bracket 55 by the cable clamp screw 15. This grounds the motor through the cable and protects the operator holding the tool from shocks due to accidental grounding of the motor circuit without the need and expense of housing the tool wholly in insulating material or insulating the motor from the sheet metal housing sections.

The slide-way formation 68 of the bracket 56 has an aperture 82 on its side wall 83 opposite to the wall 58 to mount a locking plunger 84 for the trigger block 61. The plunger carries a push button 85 at is outer end and is biased outwardly by a spring 86. The latter normally keeps the inner headed end 81 of the plunger in a longitudinal groove 88 in the adjacent side portion of the trigger block 61. The button 85 works through an opening 89 in the handle section 311) for accessibility from the exterior of the tool...

done, the operator releases the inward pressure on the trigger block 61 and the switch lever spring 65 projects the trigger block forwardly bringing the head 9| of the cross-pin 90 over the headed inner end of the plunger holding both depressed and the switch closed for continued running of the tool motor. Pressing inward on the trigger block 61 releases the plunger 84 and its spring 88 projects the plunger outwardly whereupon the trigger block when released will be projected to its outermost position to open the switch and stop the motor which is the normal condition of the tool.

The handle section 31b has a rear tongue formation 93 to close a notch 94 im the matching handle section 36b when the parts are assembled. This recess 94 provides for access to the switch holding screw 6| when securing the switch case to the bracket 56 after welding the latter in place.

In assembling the tool, the motor and spindle mechanism are mounted in respect to the frame 4, whereupon the handle and cover section Bl mounting the switch device 56 and the bracket 51 is brought sufficiently close to the frame and motor assembly so that the brush leads from the motor may be connected to the short wires fixed to the top terminals of the switch case. Then the cable I6 has its supply and ground leads secured to the lower terminals of the switch case and to the bracket, respectively. This completes the motor circuit and the other housing section 35 is applied to enclose the assembled parts. The

screws 42 are then applied and the front cover 34 is secured in place over the tongues 45, as to finish the job.

The tool shown and described has the power required for industrial uses and with a supporting frame 4 and sheet metal covers may be kept light in weight and sufficiently small in size to be held and manipulated in one hand without undue tire to the operator over extended periods. The tool due to its construction and design is strong, sturdy and eficient for drilling and kindred op= erations. The details of construction and arrangement of parts shown and described may be variously changed and modified without -iLTTIli from the spirit and scope of my invention, except as pointed out in the annexed claims.

I claim as. my invention:

1. A portable hand held electric tool having a rotatablespindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle and having a flange formation at the front end of the frame, a housing for the tool having a cover section about the motor and the frame and a handle at the rear end of the tool,

said handle being secured to the rear end of the frame and holding the cover in enclosing relation about the motor and the frame, said cover having forwardly extending tongues at its front end fitting over the flange formation on the frame for holding the cover in connected rela tion therewith, and a switch device for the motor carried by and operable from the exterior of the handle.

2. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle and having a peripherally notched flange formation at the front end of the frame, a housing for the tool having a cover about the motor and the frame and a handle at the rear end of the tool, said handle being secured to the rear end of the frame and holding the cover inenclosing relation about the motor and the frame, said cover having forwardly extending tongues at its front end fitting over the flange formation on the frame in the peripheral notches therein, means carried by the frame and overlapping the tongues for holding the same in said notches. and a switch device for the motor carried and operable from the exterior of the handle.

3. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle and having a flange formation at the front end of the frame, a housing for the tool having a cover about the motor and the frame and a handle at the rear end of the tool, said cover and handle being comprised of separable half sections in the form of sheet metal stampings divided longitudinally of the tool, said handle sections being secured to the rear end of the frame and the cover sections having forwardly extending tongues engaging over the flange formation on the frame, means carried by the frame and overlapping the tongues for holding the same in connected relation with the frame, and a switch device for the motor carried by and operable from the exterior of the handle.

4. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle and having a peripherally notched flange formation at the front end of the frame, a housing for the tool having a cover about the motor and the frame and a handle at the rear end of the tool, said'cover and handle being comprised of separable half sections in the form of sheet metal 'stampings divided longitudinally of the tool, said handle sections being secured to the rear end of the frame and the cover sections having forwardly extending tongues engaging over the flange formation on the frame in the notches therein, .a front cover for the spindle carried by the frame and overlapping the tongues for holding the same in said notches, and a switch device for the motor carried by and operable from the exterior of the handle.

5. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle and having a peripherally notched flange formation at the front end of the frame, a housing for the tool having a cover about the motor and the frame and a handle at the rear end of the tool, said housing being comprised of separable half sections in the form of sheet metal stampings divided longitudinally of the tool, said handle sections being secured to the rear end of the frame and the cover sections having forwardly extending tongues engaging over the flange formation on the frame in the notches therein, a fan element within the cover and driven by the motor for cooling the same, intake and discharge openings for the fan in the handle and cover sections, respectively, the intake openings being disposed towards the. rear end of the motor and the discharge openings being in the form of slots in the front edges of the cover sections between the tongues thereon, and a switch device for the motor carried by and operable from the exterior of the handle.

6. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame Within the tool providing a support for the motor and the spindle, a housing forthe tool having a cover about the motor and the frame and a handle at the rear end of the tool, said housing being secured to the frame and comprised of separable half sections in the form of sheet metal stampings divided longitudinally of the tool, said handle having a hollow depending pistol grip portion extending below the cover and the ame, a switch device for the motor mounted Within the grip portion of the handle, and a trigger block slidably mounted with respect to the forward part of the handle below the cover and the frame for operating the switch device.

'7. A portable hand held electric tool having a rotatable spindle and an electric motor for drivhandle sections providing a hollow depending ing the same, a skeleton metal frame within the tool providing a support for the motor and the spindle, a housing for the tool secured to the frame and having a cover about the motor and the frame and a handle at the rear end of the tool, said housing being comprised of a relatively light self-sustaining material supported by the frame and having a hollow depending pistol grip portion for the handle extending below the cover and the frame, a switch device for the motor lo cated within the grip portion of the handle, a bracket therein to support the switch device, and a trigger block slidably carried by the bracket and accessible from the exterior of the handle for operating the switch device.

8. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle, a housing for the tool secured to the frame and having a cover about the motor and the frame and a handle at the rear end of the tool, said housing being comprised of a relatively light self-sustaining material supported by the frame, said handle having a hollow depending pistol grip portion extending below the cover and the frame, a bracket secured within the grip portion of the handle and having a forwardly extending portion toprovide a slide-way, a switch device supported within the handle by said bracket, and a trigger block mounted in said slide-way for operating the switch device.

9. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle, a sheet metal housing for the tool having a cover about the motor and the frame and a handle at the rear end of the tool, said handle being secured to the rear end of the frame and having a hollow depending pistol grip portion extending below the cover and the frame, a switch device for the motor located within the grip portion of the handle, a bracket supporting the switch device within the handle and secured thereto, and a trigger block and a supply cable for the tool, both extending into the handle, for operating the switch device and supplying a power current to the motor, respectively, said cable having a ground lead connected to said bracket and the latter having a slide-way to support the trigger block. 10. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle, a housing for the tool carried b and secured to the frame and comprised of separable half sections in the form of sheet metal stampings divided longitudinally of th tool and providing a cover about the motor and the frame and a handle at the rear end of the same, the

pistol grip portion extending below the cover and the frame and having upright'walls, a switch device for the motor located within th grip portion of the handle, a bracket therein to support the switch device and secured to one of the handle sections, a trigger block for operating the switch device and extending into the handle through an opening therein, one half of said opening being in each wall section, said bracket having a slide-way to support the trigger block, and a supply cable for the motor extending into the handle at the lower end of the bracket and clamped thereto.

11. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle, a housing for the tool secured to the frame and comprised of separable half sections in the form of sheet metal stampings divided longitudinally of the tool and providing a cover about the motor and the frame and a handle at the rear end of the tool, the handle sections providing a hollow depending pistol grip portion extending below the cover and the frame and having closing end walls at the butt end of thehandle, a switch device for the motor located within the grip portion of the handle, a bracket secured therein to support the switch device, a trigger block slidably carried by the bracket to operate the switch device, and a supply cable for the motor extending into the handle at the lower end of the bracket and clamped thereto, the butt end of the handle having an opening for the cable formed in part in each of the closing end walls of the handle sections.

12. A portable hand held electric tool having a rotatable spindle and an electric motor for driving th same, a skeleton metal frame within the tool providing a support for the motor and the spindle, a housing for the tool mounted on and secured to said frame and having a cover about the motor and the frame and a handle at the rear end of the tool, said handle having a hollow depending pistol grip portion extending below the cover and the frame, a switch device for the motor located within the grip portion of the handle, a bracket supporting the switch device within th handle and having an extension forming a slideway, a trigger block at the handle for operating the switch device and carried by th bracket in said slideway, and a spring biased plunger carried by the slideway and cooperating with the trigger block for releasably locking the samein switch closing position.

13. A portable hand held electric tool having a rotatable spindle and an electric motor for driving the same, a skeleton metal frame within the tool providing a support for the motor and the spindle, a housing for thetool carried by and secured to the frame and comprised of separable half sections in the form of sheet metal stampings divided longitudinally of the tool and pro viding a cover about the motor and the frame and a handle at the rear end of the tool, the handle sections providing a hollow depending pistol grip portion extending below the cover and the frame, a switch device for the motor located within the grip portion of the handle, a bracket secured therein to support the switch device, a trigger block for operating the switch device and carried by the bracket, and a cross-member within th handle and engaged with thehalf sections thereof for securing the-same together at the switch device. 9

14. A portable hand held electric tool having a rotatable spindle and anvelectric motor for driving the same, a. skeleton metal frame and a casing within the tool respectively supporting the motor and the spindle, said casing and the frame being secured together at the front end of the frame and having registering peripheral notches therein, ahousing f0t-.th Q tOOl having a handle at the rear end of thetofiql and a front cover for 10 handle.

the casing and a motor cover about the motor and the frame, the handle being secured to the rear end of the frame and the motor cover having forwardly extending tongues engaging in the registering notches in the casing and the frame, said front cover being secured to the casing and overlapping the tongues for holding the same in said notches, and a switch device for the motor carried by' and operable from the exterior of the WAL'I'ER GEORGE MITCHELL.

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