US1900553A - Portable motor driven saw - Google Patents

Description

March 7, 1933. G E. HAMPTON 1,900,553

PORTABLE MOTOR DRIVEN SAW Filed Feb. 4, 1931 4 Sheets-Sheet vl March 7, 1933. G. E. HAMPTON PORTABLE MOTOR DRIVEN SAW 4 Sheets-Sheet 2 March 7, 1933. .6, E; HAMFTQN 1,900,553

PORTABLE lao-Toa DRIVEN sAw Filed Feb. 4, 1931 4 Sheets-Sheet A 3 rx j S g5 w *5? 3 l 'o V a March 7, 193g." G. E. HMProN 1,900,553

'PORTABLE MOTOR DRIV/EN SAW Filed Feb. 4, 1931 4 Sheet'sl-Sheet 4 'Nvlvo ff La/2M A TTORNE Y.

yPatented Mar. 1933 being UNITED v,STATI-:s- PATENT horf-'ma GEORGE E. HAMPTON, OF ITTSBUBGH, l1PEN'NSYIN'AN'IA, ASSIGNORTO THE'SYNTRON COMPANY, A CORPORATION 0F DELAWARE PORTABLE KOTOR DRIVEN SAW Application med February 4, 193.1. Serial No. 518,268.

My invention relates to motor driven tools and articularly to portable motor driven circu ar saws.

Among the objects of my invention are the ollowingz--To provide a relatively simple,

light, and compact structure for a motor .driven circular saw of the portable type, in

which the single-piece motor shaft is supported by three ball bearings; to provide a torque-limiting clutch between the motor and the tool, which clutch shall slip with appreciable audible noise in case a predetermined maximum torque is exceeded; to provide a saw arbor or shaft in a housing, the saw shaft rovided with means for preventing the leaage of grease in the housing; to provide a saw-supporting shaft that shall be so mounted asto permit free expansion of one end thereof, while the other end thereof adjacent to the saw is held in a xed position relativel to the housing; to provide a housing for t e saw shaft with means for limiting the. amount of oil or grease which may be placed therein; to provide a relatively sim le and highly eiiicient ball bearing support or the movable guard of the saw; to provide means for ensuring a supply of cleanv air for the motor in case the'saw 1s operating on dusty or dirtywork; to provide a vfreely movable guard for the otherwise exposed portion v of the circular saw, that shall be actuable by the operator when grasping a handle ofthe device; and to provide a plurality'yof normally open switches and means for closing said switches either by the operator in grasping a handle of the device or by the operator when placing the device in proper operative position on material to be operated'on.

Other objects will be apparent in the course of the description of the device, which while describing a s cie embodiment' of my invention is not lntended to be limited thereto, but, particularly in` certain of the' broader elements may be embodied in other motordriven devices. i

In practicin my invention I provide. a, ghaving' a stator" and a rotorl motor housing structure located therein, the shaft of the rotor being in a single piece and being supportthereon at one ond thereof, and between vtwo of the coaxially alined ball bearings. Both ends of the motor housing are provided with suitable airinlet and outlet openings and the rear end of the housing is provided with Ya hood to which may be attached a flexible conduit. The worm on the rotor shaft drives a tionof which is so mounted on the saw shaft as to rotate therewith but free to move a limited distance axially thereon, the two clutch jaws being spring-pressed into operative en'- gagement. The housin surroundin the saw shaft is provided witan oil plug o such construction as to limit the amount of lubri- Vcant which may be placed in the-housing.

Means is also `provided on the saw shaft to counteract the axial flow of` lubricant along thel saw shaft caused by the operation of the worm and of the worm gear.

'The normally upper portion of a circular saw mounted on the saw arbor is protected .by a fixed guard or cover, while the lower otherwise exposed portion of the circular saw is covered by a swinging' guard', mounted on a-portion of the saw structure and concentric therewith, b a form of ball bearing;

The mova le guard is moved initially from' its normal position by linkage actuated by the operator until itis in such position as to be moved further to its extreme position by material to bey operated on. I provide also a relatively simple form of base which may be adjusted for any desired depth of saw cut in 'such manner that it always remains parallel to its original position. The basefmay be Atilted angularly-laterally of the saw.` structure to permit of sawingmaterial at an angle Aother than aright angle relatively toa surface thereof. l 1- I rovide also arelatively'simpleand hi hly ecient safety device for the tool emb yworm gear mounted on the saw shaft which v vshaftis mounted in a housing and supported ing a normally-open motor-circuit-controlling switch located adjacent to or in a handle of the tool, and a second normally-open motorcircuit-controlling switch connected in series circuit with the other switch and actuable to its closed position by an arm which is springpressed outwardly from the base in such manner that it effects closing of the second motorcircuit-controlling switch only when the device or tool and material to be operated on thereby are located in positive operating positions relatively to each other.

In the drawings, f

Figure 1 a top plan view of a portable motor driven saw embodying my invention,

Fig. 2 is a view in side elevation thereof with certain portions shown in section,

Fig. 3 is a view in side elevation of a device embodying my invention showing theposition of certainparts of the structure when 1n positive operatmg conditions,

Flg. 4 is a' fragmentary view taken on the l structure of Fig. 8.

As I lhave already hereinbefore stated, I have elected to lshow the application of the various parts or elements embodying my invention as applied to a portable motor driven circular saw, and I wish itto be understood i that all of the various elements herein set forth as embodying the present invention, may be applied 'to' other forms of power driven tools in which the driving motor may be an electric motor or some other suitable form of 'driving device and that the are also applicable to driven tools other t ana circular saw` and finally that the invention in its broadest` aspect is not llmited to portable tools but is applicable also to the so called stationary tools, which it may be desired to 'equip with completely effective safety control devices to safeguard an operator attending the device or tool.

. Referring initially to Figs. 1, 2, and.3 of

i the drawings, I have there illustrated a portable motor-driven circular saw, designated generally by the numeral 11 and including a motor structure 13, a cover 15 for the u per ofthe saw, a base or shoe 17, a ront dle 19, a second-or top handle 21, and

a swinging saw guard 23.

Referring now to-Fig. 7 of the drawings for further details of the motor structure 13,

it may be noted that there is provided a motor casing 25 which has located therein a stator structure 27, an energizing winding 29, and a plurality of relatively long machine screws 31 to hold the stator assembly in proper operative position against a shoulder' portion' which may be constituted either by an inner flange 33 or by a plurality of peripherally spaced lugs integral vwith the caslng 25.

A rotor 35 is located within the motor structure 13 and is mounted on a rotor shaft 37 which is made of a single piece of suitable steel, that portion thereof supporting the rotor proper being of larger diameter than the other portions thereof.

At the rear end portion thereof vthe casing 25 is shaped to constitute a bearing bracket or support 39 in which there is located a ball bearing 41 of usual construction. At the other end of casing 25 I have provided a saw arbor housing 43, one end portion of which is of such shape and dimensions as to interit with the forward portion of casin 25,-against which it is held by a plurality of s ort machine screws 45. The otherl end of housing 43 is of a reduced diameter, this portion of ameter constituting the greater axially-extending portion, as may seen clearly in Fig.

7 of the drawings.

Two spaced ball bearings 47 `and 49 are supported by the reduced portion of housing 43, the outer ball races thereof being held in proper operative desired manner. he inner ball race of ball bearing 49 is initially loosely located on a portion 51 of shaft 37 and held thereon in a manner to be later set forth. A washer or spacer 52 isthen located against the outer face of the inner ball race and on a ortion 53 of shaft 37 -of reduced diameter. paddle wheel or fan structure 55 is then located on the 'reduced portion 5.3 of shaft 37 having one face plositions in any suitable or' reduced ditions: the inner ball race of bearing 47, worm 57, -paddle wheel 55, washer or spacer 52 against the shoulder of the shaft and the inner ball race of `bearing 49. A suitable lock washer 63 holds the nut 61 in finally adjusted position. *The housing 43 may be provided with an opening in the upper or top portion thereof and a cover 65 of dish shape may be provided to normally close this inspection open- 1125 eferring further to Fig. 7 of the drawings, I have Iillustrated a nut 67 having screw threaded engagement with the other end of shaft 37, a lock washer 69 bein provided to prevent turning of the nut on ne shaft. A

of bearing bracket 39 andA is held in pro er operative position thereagainst by a plura ity of machine screws 73.

I have illustrated a universal type of rotor embodying a commutator 75 and a pluralit of brushes 77 and 79 in suitable holders whic may be supported by a brush holder yoke 81.

In order to prevent lubricant from escaping from the bearing 41 along the shaft 37 and toward the commutator 75, I provide 'a suitable packing 83 around the shaft, together with an oil thrower groove 85 on a bushing 87 located around a portion of the commutator end of shaft 37 A f- The co-operating action of worm '57 and Worm gea-r 89 driven therebywill cause lubricant such as a heavy oil 91 in housing 43 to flow in a predetermined direction, and in the case of the structure herein shown the tendency will be for the lubricant to be forced alon worm 57 toward the rotor 35 and the padle wheel` 55 is provided to counteract this flow of lubricant toward the bearing 49 in order to ensure that the duty to which a packing 93 around shaft portion 37 is sub]ected will not be too severe.

A plurality of openings 95 are provided at the rear end of the motor housing and one or more openings 97 are provided at the forward end of the housing so that a fan 99 mounted on shaft portion 37 and held by a pin 101 will be able tot draw air into and force f it out of the interior of the motor housing.

- end of which is suitably secured-against the end of the motor structure 1,3, as is shown more particularly in Fig. 7 of the drawings.

Referring now to Fig. 5, the worm gear 89 is loosely mounted on a sleeve 107 which in turn is mounted on al saw shaft 109, being `secured thereon by a through pin 111, or by other suitable means. One portion 113 of a jaw clutch coupling is secured against one side ofthe worm gear 89 and is held thereagainst by rivets 115. The second portion 117 of the coupling ismounted on a portion of the sleeve 107 1n `such manner as to be axially movable thereon but `prevented from turning relatively thereto by a key 119. It may be noted also that worm gear 89 fits against a shoulder 121 on sleeve 107 and is held against this shoulder by `a spring ring 123 which lits into thesleeve 107. A helical spring 125 surrounds a reduced portion 127 of coupling portion 117, the vother end of spring 125 fitting against an internally screwthreaded collar 129 which maybe adjusted co-operating faces of the two portions 113 and 117 are of substantially the shape shown in Fig'. 6 of the drawings, that is, the oooperating faces are vserrated, the corners or angles being rounded so that witha given spring tension the clutch will transmit up to a certain load, after which it will slip.

The saw shaft 109 is rotatably supported` in housing 43, which extends at right angles to the motor housin by two ball bearin s 135 and 137. Ball earing 135 is heldin proper operative position against a shoulder 139 ofshaft 109 by the slipped-on s1eeve.107, a paddle wheel 141- being located therebetween as shown more particularly in Fig. 5 of the drawings. The outer ball race of bearing 135 is held in its proper operative position within a cage 142 byV a bearing nut 143 which has external screw threads 'interfitting. with internal'screw threads in a vportion of cage 142. In this manner ball bearingv 135 is held rigidly in a fixed osition on shaft 109 and also in a fixed position in cage 142. A plurality of packing rings 145' are located 'around the outer or saw end of shaft 109 and are held by a suitable metal gasket 147 in order to prevent the outflow of lubricant from cage 142-past the bearing 135.

The outer end of gear housing 43 is open and is covered by a cap member 149 which is coaxial with shaft 109 and which is held in proper operative position by a plurality of short machine screws 151. The inner ball race of bearing 137 is held in fixed position on shaft 109 by a nut 153having screw threaded engagement with a portion of shaft 109, the nut 153 being prevented from turning'by a lock Washer 155.

It may be noted here that the above described construction of the saw shaft or arbor and the parts thereon constitute an assembly that may be built up as a unit and then placedin position within the housing surrounding it. Thus the ball bearing 135 may be located, as described, against the shoulder 139`and in the cage 142, the outer.

ball race being held by nut 143. Then the paddle wheel 141, the sleeve 107 with the Worm/gear 89, the jaw clutchcoupling, the

compression spring 125, the collar 129-and the lock washer 131 thereon, and the ball bearing 137 may be placed in sequence on the shaft 109 and all held in proper axial poly sitions thereon by nut 153.

The cage 142 may then be inserted in an opening in housing 43 from the right hand side as seen in Fig. 5 and be held therein by a plurality of screws 156. The inner surface of cap member149 is made smooth so that the bea-ring may move therein axially thereof-in case of expansion of shaft 109 because of rise of temperature thereo'fafter the de-A vice has been in operation or some time, that is, longitudinal expansion of the shaft 109 is permitted.

I 45 which is The other end of shaft 109 is provided with a flan e abutment 157 and a circular saw 159 is c amped thereavainst by a circular resilient clamping member 161 which, in

'5 turn, is held by a cap screw 163 and a lock washer 165.

The-housing 43 of the gears has associated therewithfas has valready been hereinbefore mentioned, a cover 15 for the upper and larger portion of the circular saw 159. A swinging guard 167 is pivotally mounted for turning movement on an extended portion 169 of cage 142 (see Fig. 5), a hub portion 171 of the swinging guard 167 being provided with an inner' substantially semi-circular l groove 173 to co-operate with a similar groove 175 in portion 169 whereby an annular groove of substantially circular shape in lateral section is provided. Hub portion 171 is rovided with a radial opening 177 to permit of introducing into the groove of lcircular shape a plurality of steel balls of the proper size, the number placed therein being just sufiicient to fill the annular groove to thereby provide a ball bearing for the swinging guard on the extension 169. When the proper number of steel balls have'been placed in the groove a screw threaded plug 179 is fitted into the opening 177 to close the same. Guard 167 is provided with a lug 181 in substantially.

' the position shown in Fig. 2 of the drawings and a tension spring 183 is connected to a part of cover 15 and to'lug 181 to hold the guard in its normal inoperative position, substantially as shown in Fig. 2 of the drawings, where a portion thereof abuts against a stop lug 185 secured against a part of cover 15.

It may benoted that the lower right hand portion offcover 15 isv cut away (see Fig. 2)

40 and a suitable metal screen 187 covers the otherwise open portion to properly protect the saw. A lip-like shield 15a projects from the forward edge of the cover 15 to a point forwardl of the screen 187 so that saw-dust blown through the screen by movement of the saw durin cutting will be deected in a generally orizontal direction, but slightly upwardly, instead of being blown vertically upward where it will obscure the vision of the o erator.

The shoe 17 is adjusts. ly supported relatively to housing 43 by being provided with a pair of s aced upstanding rods 189 and 191 to whic the base is pfvotally connected as by means of a hinge structure co-o rating with each upstanding rod, such a inge structure being shownat 193 in Figs. 1 and 2 of the drawings. Thumb nuts 195 are provided to clamp rods 189 and 191 in apertured portions 197 and 199 made integral with the' gear housing 43.

Means for adjusting the shoe 17 angularly relatively to thev saw., assuming that it has been moved away from the housing to a certain amount, may includel the hereinbefore mentioned hinge structures 193 and a suitable locking shown in Fig. 4 in lend elevation, and in side elevation in Figs. 2 and 3. Ah arcuate portion 201 having an arcuate slot 203 thereinl .(see F ig. 4) has extending therethrough a machine screw 205 fitting into. an adjustable portion of shoe 17. A scale and a mark as shown in Figs. 2 and 3 may be provided on vthe arcuate surfaces of the fixed member 201 and the movableshoe and be properly graduated in mechanical degrees to indicate thel angle of tilt of the shoe. I do not desire, however, to be limited to the precise structure shown, as I may employ equivalent clamping means. f v

The handle portion 19 hereinbefore/ mentioned has located therein a normally-open motor circuit controlling switch of any desired or suitable kind, the handle 207 thereof being located .outside of and closely adjacent to the handle 19. A current conduct- :'ng cable 209 may extend into a part of the handle 19, and be of any suitable or desired length and provided at its other end with a suitable plug to permit of energizing the motorin a manner well known in the art. The switch within the handle 19 is shown more clearly in Figs. 8 and 9 and has two stationary contact members 270 and 271 that are respect'vely connected `to the current conductors of the cable 209.` A` movable contact member 272 cooperates with the stationary contact members to control the motor circuit. The contact member 272 is pivotally mounted in the handle 19 and has toggle connection with the switch lever 207 that is pivotally mounted in the casing at the point 273. A spring 274 anchored at its one end to the switch cas5ng,rand at its other end to the toggle joint serves to yieldably maintain the switchin open position as shown in Fig. 8.

When the lever 207 is moved toward the handle 19, the toggle joint 276 is carried between tension springs 275 whose ends are conmeans, one form of which is nected to the `lever 207 and the movable contact member 272, so that the springs V275 instantially circular openlng 213 with a cover member 215 thereon in order that a thermal- 1 ly-'actuable circuit-controlling switch may be located therein if desired.

A second normally-open motor-circuit-controlling switch is located in a casing 217 at the forward endvof the tool and Iis provided the housing217.

with an actuatin arm 219 located outside of eans for eectin the closin of this switch is located in an may be saidto .constitute a part of the shoe 17 and is shown as including a relatively long bar 221 pivotally mounted at the rear thereof on a pin 223, a spring 225 being provided to yieldngly hold the member 221 in the position shown in Fig. 2 of the drawings where it is resiliently forced out of the plane of the shoe. The forward portion 227 of member 221 is bent upwardly and has a rod 229 secured thereto as by welding, the inner end of rod 229 being so located as to engage arm 219 to actuate the switch of which arm 219 is a part.

Means for effecting initial movement of the swinging guard 167 by an operator includes a link 231 pivotally connected at onev its' end to the switch handle 207 and having other end pivotally connected through a lostmotion slot connection with a swinging arm 233, which is pivotally mounted intermediate its ends inside of cover 15 (see Fig. 5), by a pivot pin 235 moving in an arcuate slot 237. The arm 233 is held in either of its limiting positions by an overcenter spring 239, the link 231 being yieldingly urged to one limiting position shown in Fig. 2, by a spring 241. The upper end of spring 239 is secured to a pin 243 in housing 15 and its lower end is secured to a dog 245 pivotally mounted on the lower end of arm 233, a lug 247 being provided on arm 233 to ,limit the turning movement of dog 245 in one direction.

The various parts of the device: are shown in their normal vor inoperative positions in Fig. 2 of the drawings. The handle 207 of the first motor-controllingswitch is in such position that the switch controlled 'thereby is open. 'The same is true-as Vregards the switch controlledby handle 219. If now an operator desires to use the circular saw on a piece of material 259, (see Fig. 3) he will first pick up the portable saw-assembly by handle 19 and, assumingthat he thereby carries it to the place of operation, he will then grasp handle 21 with the other hand to properly hold and locate the saw assembly with relation to the piece of work or material to be operated on. It may here be pointed'out that the swinging'pivotally-mounted guard 167 is resiliently heldin substantially the position shown in Fig. 2 of the drawings where its forward tip or end portionwould eiectively prevent its being 'turned on its bearing by a piece of wood to be sawed.

It is therefore necessary for the operator to place his fingers around handle 207 and to firmly close them in order to move the handle 207 against the tension of spring 241 and against the pressure of a. spring associatedk with the switch which biases-the iirst motorcircuit-controlling switch to its open position. The turning movement of handle 207 towards handle 19 has two results: first, the switch controlled by handle 207 is closed, and second, a projection 249 on dog 245 en ages a projection 251 ofthe swinging guar and causes it to turnon its pivot bearing and move into a osition indicated by the broken lines 253 in i 3 of the drawings. It may be noted that le projection 249 on dog 245 extends laterally thereof in orderthat it may properly engage the projection 251, the relative positions of these members in one lane being shown in the left hand portion of) Fig. 5 of the drawings.

If now ,the operator presses positively downwardly on -handle 21 so that the forward portion 227 of member 221 engages a piece of wood 259, the pivotally mounted arm 221 will have its forward endc moved upwardly, and upon the operators exerting suf- -ficient pressure on the handle 21, it will be moved into substantially the position shown in Fig. 3 of the drawings, as a result of which their closed positions, the first switch in i handle 19 being closed vby the grip of one of the .hands'of the operator, and the second motor-circuit-controlling switch being closed by positive operatin -engagement between the saw structure, an more particularly the shoe thereof, and material to be operated on.

It is of course necessary for the operator to prevent engagement of the saw teeth with thematerial before the saw blade is being rotated, but as soon as'both motor-circuitcontrolling switches have been closed as set forth above, the-saw will be rotated and forward movement of the device may be effected at a rate of speed as determined by the operator in accordance with the several factors affecting the speed of movement, in a manner well known in the art. As soon as the guard 167, moved into the position shown by the broken lines 253, is engaged by the material 259, it will be turned on its bearing until it has been moved entirely out of the way of the piece of material, that is, into the cover 15. It is obvious that it is necessary for the operator, in a device of the kind herein disclosed, to so hold the device that there will suicient pressure between mem r 221 and material 259 being sawed to ensure that member 221 is maintained in the `position shown inf Fig. 3 of the drawings. For if this.,

is notl the case, the switch controlled byarm 219 will automatically be` opened by reason of spring 225 causing the return of arm 221 to the position shown in Fig. 2, with a consequent opening of the switch controlled by arm 219.

Upon a piece of wood having been completely sawed through the swinging guard 167 Awill move back into the position shown in Fig. `,2 of the drawings, and if this movement is effected before the operator releases his grip on handles 19 and 207, the projection 251 will have moved back into the position shown in Fig. 2 of the drawings, while dog 245 is still in the osition shown in Fi 3 of the drawings. he dog 245 is pivotal y mounted on link 233 so that it may o rate as a pawl and move over the end of projection 251 when the operator releases his grasp on handle 207.

I desire here to point out more particularly the efficacy of the second motor-circuitcontrolling switch and its actuation by member 221. If lthe second switch were not provided and if the operator were to firmly grasp handles 19 and 207 he would close the motor circuit, while at the same time the swinging guard would be moved to such position as would expose a part of the circular saw so that serious injury to the operator might result. If however, the second motor.- circuit-controlling switch is provided, the motor will not be energized even if the operatorA should grasp handles 19 and 207 tightly7 enough to close the first switch. I have pointed out particularly the operation and effect of the second switch as it is obvious that the second switch and its actuating member controlled by the direct positive con- A tact thereof with material to be. operated on when the materialis placed in proper position' relatively to the tool to be operated on thereby, can be a plied to many other motor driven devices w ichare designed and built to operate on various kinds of material. It is only necessary to locate the pivotally mounted arm actuating the second switch, in such manner that material to be operated on will engage the same when placed in proper position to be operated on and,vas noted above,

I believe that this is applicable to many other forms of motor driven devices.

Housin 43 may be lled to a certain hei ht with a lu ricant such as heav oil 91 see Fig. 7) and in order that it shall e impossible to permanently fill housing 43 with an excessive amount of oil, I provide an oil filling' glug 255 as shown at the left hand end of ig. 7. A removable closure 257 Ais provided for the plug `and this must be removed in order to `pour` oil intothe housing 43 and if the tool is resting upon a horizontal surface it is obvious that the amount of oil which will remain in housing 43 is limited to substantiallythe top of oil plug 255. A

Rotor shaft 37 is made in one piece and its inherent frequency of vibration, as a column, is relatively low but it may happen that the speed of rotation is so high that lateral vibration thereof will occur. In order to overcome or counteract this vibration I provide the three caxially alined ball bearings shown more particularly in Fig. 7 of the drawings, two of these ball bearin being located relatively close together anV one on each side ofthe worm 57. I have found, as 'the result of actual tests, that a motor rotor thus supported will operate at speeds on the order of 10,000 R. P. M. without noticeable vibration and I attribute this entirely to the use of three coaxially alined ball bearings su porting a single piece shaft. 4

eferring to Fig. 7 of the drawings, it may be noted that a addle wheel 55 is located on the portion 53 o shaft 37 in order to counteract the tendency of lubricant bein forced toward the ri ht by worm 57 when t e same is rotated. I? the paddle wheel 55 were not provided lubricant would be forcedagainst and throu h ball bearing 49 and the packing 93 would e subjected to excessive o11 pressures and might give way, thereby permitting oil to reach theu motor windings. Substantially the same comments hold in regard to the saw shaft and the addle wheel 141 shown more particularly in ig. 5 of the drawings. The provision of a torque limiting device, shown in Fig. 6 of the drawings, ensures that the motor shall not be overloaded. In a portabletobl ofthis kind there is always a tendency `on the part of an operator to force the tool in order to make speed, and if this is continued for too long a time or to too great an extent, it will inevitably result in a burnout of the motor. The device embodying my invention provides a torque-transmitting de- The swinging guard is provided with a relatively simple and effective bearing, which not only permits the swinging movement pf the guard, but also ensures that the guard will be held in its proper' operative position axially of its support. v It Vmay be noted also that it is relatively easy to adjust the shoe to efect any desired depth of cut ofthe saw by the loosening of the thumb nuts 195, the moving of the shoe, which Vit may be noted, moves parallel to itself, and thena retightening of the thumb nuts.

It is also easy to tilt the shoe by loosening one screw and then tilting the shoe to the desired angle after which the tightening screw 205 may again be tightened.

While I have illustrated and described a s ecilic embodiment of my invention, it is o vious that many of its objects and elements are not limited to the particular device shown in the present application, and I desire, therefore, that the scope of the appended claims shall be limited only by the pertinent prior art.

I claim as my invention 1. In a portable motor driven tool assembly including a handle for the assembly and a driving motor, a motor-circuit-controlling switch located adjacent to the handle to be grasped by the operator in holding and guiding the tool by said handle, a second motorcircuit-controllin switch in series circuit with said first switch, and means for closing said second switch upon pressing' said tool and material to be operated on thereby into close operating engagement.

2. In a portable motor driven tool assembly including a handle and a motor, a normally open motor-circuit-controlling switch adja-l cent to the handle to be closed by the operator in holding and guiding the tool by said handle, a second normally open motor-circuitcontrollin switch in series circuit with said first switc, and means closing said second switch when the tool is'pressed positively and firmly into operatingengagement with materialtobe operated on by said tool.

3. In a portablepower driven tool assembly including a driving member therefor, a cutting tool, a fixed housing for a portion of the tool, a movable guard for another portion of the said tool, a device actuable to initiate movementI of said movable guard Y toward aposition where the tool will be eX- posed, and means preventing a complete swinging movement of the guard by said device, swinging movement of the movable guard bein completed by relative operating movement etween the cutting tool and the material being operated on thereby.

4. In a portable power driven tool assembly including a driving member therefor, a cutting tool, a fixed housing for a portion ofthe tool, a movable guard for another portion of theV said tool, a device actuable to` initiate movement of said movable guard toward' a position Where the tool will be exposed, means preventing a complete swinging movement of `the uard by saiddevice, swinging movement of te movable guard bein completed by relative operating movement tween the cutting tool and the material being operated on thereby, and a power control device actuated I in predetermined relation to movement of the eogu ard.

5. A portable cutting apparatus comprising a unitary assembly including a driving element, a rotatable cutter driven thereby, a

' swingingsguardnpivotally ymounted coaxially of the cutter, means normally maintaining the guard in advance position to shield a given motor.

portion of the cutter. and means whereby it 1s possible to swing said guard only such distance as to expose but a part .of the cutter, swinging movement of the guard being completed by engagement thereof with the material being operated on by the cutter.

6. A portable cutting apparatus comprislng a unitary assembly including a driving member, a cutting element driven thereby, a

movable guard covering a portion of the said element when'in its normally closed position, Ineans actuable in one direction to swing said guard only such distanceas to expose a part of said portion of the cutting element, means for supporting the guard so that swinging movementl thereof will be completed by en-A gagement with the material being cut by the said element, and means causing the guard to return to itsv normal guarding position when the cutting element has been removed from the material, independently of movement of the said actuable means in the opposite direction.

7. Portable cutting apparatusfoomprising y a unitary assembly including, ai driving member, a cutting element driven Ithereby, movable gua rd for said element, means normally maintaining the guard in advanced osition to shield a given portion of the cuttln element, anda device for controlling the driving element and having connection with the guard to eHect movement thereof in opposition tosaid means when the said device' is operated to set the cutting element in operation, the said guard being positioned for engagement with the material operated upon y the cutting element and thereby moved vment thereof in opposition to said means when the said\dev1ce is operated to set the motor in operation, the said guard being positioned for en agement lwith the material operated upon gy the saw and thereby held in retracted position and in disconnected relation to thefsaid device, and means for. restoring the said device and the uard to coout of engagement with the material and the said device moved .,to effect stopping ofthe 9. Portable saw apparatus comprising a unitary assembly including a motor, a saw blade driven thereby, a movable guard for the blade, means normally maintaining the guard in advanced position to shield a given portion of the blade, a manuallyoperable de- 'los operative relation after the guar has passed vice for controlling the motor and having connection with the guard to effect movement thereof in opposition to said means when the said device is operated to set the motor in operation, the said guard being positioned for enga ement with the materlal operated upon by 51e saw and thereby held in retracted position and in disconnected relation to the said device, and means for restoring the said 10 device and the guard to cooperative relation after the guard has passed out of engagement with the material.

10. Portable cutting apparatus comprising a unitary assembly including a driving member, a cutting element driven thereby, a movable guard for said element, means normally maintaining the guard in advanced position to shield a given portion of the cutting element, and means operable to move said guard toward retracted position and disconnectible therefrom upon engagement of the apparatus with the Work, to permit return movement of the guard to advanced position independently able means. v y.

11. A portabley motor driven saw assembly comprising a driving member, a rotatable cutting element, a cover for the upper and rear portions of the cutting element, a screen constltuting a continuation of the coverand positioned to shield a forward portion of the said element, a movable guard normally enclosing the lower portion of the cutting element and having lts upper edges extending into the said cover and screen, mechanism in the cover for moving the said guard rearwardly into'the cover, and means for operating said mechanism. c

12. A portable motr driven saw assembly comprising a driving member, a rotatable cutting element, an imperforate cover for upper and rear portions of the cutting element, a screen constitutin a continuation of the cover and positione to shield a forward portion of the said element, a guard of further movement offtheJ said operv movement of the guard to its advanced position when the cut-ting element has been removed from the material.

In testimony whereof, I have hereunto subscribed my name this 22nd day of J anuary, 1931.

GEORGE E. HAMPTON.

of the cover and positioned to shield/a forward portion of the said element, a guard positioned tshield'the lower portion of the said element, and a deiector extending from the front edge of said cover in a forwardly and upwardly inclined direction from the line of juncture between the cover and the screenl 14. Portable cutting apparatus comprising a unitary assembly including a driving member, a cutting element driven thereby, a movable guard for said element, means normally

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