US2778355A - Demolition hammer - Google Patents

Description

R. G. BOURBON 2,778,355

DEMOLITION HAMMER Jan. 22, 1957 Filed May 12, 1954 4 Sheets-Sheet 1 9 9 1 I N V EN TOR.

91 Oi /jg 1957 R. G. BOURBON DEMOLITION HAMMER 4 Sheets-Sheet 2 Filed May 12, 1954 llll m 1957 R. cs. BOURBON DEMOLITION HAMMER Filed May 12, 1954 4 Sheets-Sheet 5 INVENTOR. Gjozzrdozz 0 6 6 fl H d M 1 M w A .III. 1 9 I J Jan. 22, 1957 R. e. BOURDON 2,778,355

DEMOLITION HAMMER Filed ma 12, 1954 4 Sheets-Sheet 4 INVENTOR. #245196 G fiozzrdazz- DEMOLITION HAlVIMER Russell G. Bourdon, Muskegon, Mich, assignor to The Kaydon Engineering Corp. Muskegon, Mich, a corporation of Michigan Application May 12, 1954, Serial No. 429,344

'5 Claims. (Cl. 125-33) My invention relates generally to hammer mechanisms and particularly to mechanically driven hammers designed for such operations as breaking concrete, drilling stone, driving spikes and like percussion operations and labors.

The class of demolition hammer, to which my invention pertains is to be particularly recognized as distinctcver the familiar pneumatic types, in that the means for driving the hammer mechanism is carried out by a motorized mechanical system in contrast to the pneumatic or hydraulic mechanisms employed in the so called pneumatic hammers.

While I recognize that there have been repeated efiorts in the past to design an improved mechanical hammer for demolition purposes embodying electrically driven means for imparting blows to a chisel or like impact tool, such to my knowledge have not resulted .in a construction which is satisfactorily acceptable in practical application. Various shortcomings have been present in previous hammers of this class to the extent that the industrial world at large employs pneumatic hammers because of their characteristic improved operating dependability over known mechanical styles. As a consequence the hammer of my invention has been devised to overcome the various shortcomings and defects previously experienced in hammers of this class and such is therefore directed to improvements in mechanical demolition hammers.

Briefly, the hammer of my invention embodies several improved principles of operation whereby greater etficiency, operating dependability, improved ruggedness and sustained operating life are obtained. In this regard I employ a V-belt drive intermediate the power element and the driving mechanism which feature does much in the way of eliminating the transmission of vibrational forces from the driving unit to the power element. Additionally, I have included a new and improved insulated style of handle by which the operator may grasp and direct my hammer in use. This feature results in two marked improvements; one, vibrational cushioning between the operator and the hammer is provided and two, safety against electrocution of the operator is gained, as for example when the cutting tool encounters an underground cable or the like. Other features arranged to eliminate or minimize vibrational effects, which normally accompany a mechanical style of hammer, have been embodied .in the driver or impact producing unit of my hammer so that 'repercussion effects from the cutting tool are substantially eliminated or reduced to a workable minimum.

In this vein, my improved driver mechanism is arranged to impart rapid and forceful blows to the cutting tool, and embodies a dynamically and statically balanced rotating mass having a striker projection moveable relative of the mass and cushioned therefrom so that the imparting of blows to the cutting tool is accompanied by minimum repercussion e'fiect while positively delivering a blow to the tool or cutting bit.

The main object of my invention is to provide a new '1' nited States Patent ice and improved electrically driven demolition hammer embodying new concepts and features of construction whereby vibrational effect on the operator is reduced to a minimum and satisfactory and efiicient operation of the hammer is obtained.

Another object of my invention is to provide a mechanical style of demolition hammer embodying an electric drive and in which an improved driver mechanism is employed for imparting rapid and forceful blows to a tool bit with a minimum repercussive disturbance to-the operator and power unit.

' Still another object of my present invention is to provide a new and improved demolition hammer embodying improved safety features from the standpoint of insulating the operator against electrical shock and vibrational effects which normally'accompany the operation of :such a hammer.

A still further object of my invention is to provide a new and improved mechanical style of demolition hamtiter in which belt drive means are employed intermediate the power element and the driver mechanism whereby vibrational transfer between the driver and power elements is reduced to a practical minimum thereby assuring greater life to my hammer mechanism.

A further additional object of my invention is to provide a new and improved bearing means for the rotating hammer or :driver mechanism of my device which cushions the driver against shock by the use of aligning bushings carried in a .resilientmaterial.

A still further object of my invention is to provide an electrically driven, mechanical demolition hammer embodying means for retaining the cutting tool in a nonoperating position when desired, so that the same will not be driven or impacted when withdrawing the same from the work, for example.

Still further it is an object of my ,inventionto provide an electrically driven demolition hammer embodying means for selectively disengaging the impact delivering means 'from the tool bit without the need for deenergizing the electrical motor.

The above and further objects, features and advantages of .my invention will be recognized by those familiar with the art from the following detailed description and specifications therefor, such :being shown in the accompanying drawings illustrating a preferred embodiment of the concepts of my invention.

In the drawings:

Figure 1 is a side elevational view in substantially full cross-section lengthwise, with parts thereof shown in full elevation for demonstrating the arrangement of elements employed in the demolition hammer of my invention;

Figure 2 is a partial cross-sectional view taken substantially along line 2-2 of Figure 1, illustrating in particular the features and mode of operation of the driver mechanism of my new hammer.

Figure 3 is a partial sectional view, along substantially the longitudinal center line of a demolition device similar to that shown in Figures 1 and 2 but showing the features of an alternate construction in which means are embodied for selectively disengaging the cutting tool from the impact delivering means;

Figure 4 is a partial top plan view of the device shown in Figure 3;

Figure 5 is a partial side elevation of the operating handle end of my improved device showing portions of the tool bit release mechanism embodied in the modified apparatus of Figures '3 and -4; and

Figure '6 is a diminished top plan view of the release mechanism shown in Figure 5.

Referring now to the drawings, it will be recognized (from Figure 1 especially), that the demolition device therein shown comprises, generally speaking, the combination of two units, a drive unit 11 and an impact driver unit 12.

In greater particular, the drive unit 11 comprises a substantially cylindrical cast body or housing 15 from one end of which extend two spaced and oblong shaped walls 16, 16 each distinguished at its outer end by a semicircular cut-out portion 17 for receiving one-half of a shocker bushing and roller bearing assembly 18. A central chamber 19 in housing 15 is provided for carrying an electrical motor 20. A ball bearing means 21 for supporting one end of the motors armature shaft 22 is carried centrally of a cap member 23 secured to the upper end of housing 15 by stud bolts 25. A filter member 26 is held outwardly of cap member 23 by ringmember 27 also secured to housing 15 by the stud bolts 25. The filter 26 is arranged to purify air prior to its passage through ducts 28 in housing 15 as caused by the rotation of the motors armature shaft which carries a suction fan 29 adjacent bearing 21. Ventilation and discharge of air from the chamber 19 is by discharge passageways 30, 30 formed in the side Walls of the housing and leading outwardly from the motor chamber 19. The opposite end of armature shaft 22 is supported in ball bearing means 31 located in a transverse wall portion 32 at one end of chamber 19.

Mounted coaxially with the outer end of armature shaft 22 and below Wall 32 is a worm 35 driven by the rotating armature shaft and supported between the bearing means 31 and a second ball bearing means 36 housed in web portion 37 of housing 15. Mounted adjacent and transversely of the axis of worm member 35 is a worm gear shaft 38 carried between spaced bearing members 39, 39 carried in opposite side walls 16 of the housing 15. Small pulley wheels 40, 40 are keyed or otherwise rigidly secured to the outer ends of the worm gear shaft 38, outwardly of walls 16 while a worm gear 41 is fastened centrally on shaft 38 for meshing engagement with worm 35 (see Figure 2).

Attached to opposite side wall portions 42, 42 of housing 15 and adjacent chamber 19, are a pair of cup- like brackets 43, 43 held in place by bolt means 44. Such brackets carry internal rubber cushions 45 which receive shank portions 46 of operating handle members 47, 47. Handles 47 are tubular and right angular in form and support vulcanized rubber grips 48 at their outer ends which cooperate with the insulating bushings or rubber mountings 45, 45 to insulate the operator from electrical shock, in the event that the hammer encounters an electrical conductor in its digging operating, or the like. Further the construction employed in this arrangement serves to reduce the vibrationalefiect on the operator. The two handle members 47, 47 are interconnected outwardly of cap member 23 by a breast plate 50, substantially in the manner shown in Figure l; the plate being fastened to the handle members by means of bolts 51, or the like.

The impact driver unit 12, as best seen in Figure 2, includes a substantially hollow cast metal housing arranged to interfit with housing 15 of the drive unit and having foreshortened side wall portions 56, 56, elongated side walls 57, and 58, a lower end wall 59 and an embossed neck portion 60 projecting from end wall 59. Side wall portions 56, 56 of this housing are formed with an arcuate or semi-cylindrical cut out portion at their upper ends which match and matingly align with the two corresponding cut out portions 17, 17, of the drive unit housing 15. Thus when the two housingslS and 55 are interfitted, the same provide registering cylindrical openings between their abutting ends and on opposite sides of the device which receive and house the shock bushing and roller bearing assemblies 18. The bearings 18 are arranged to support rotatably stub shaft portions 64 related to the hammer mechanism indicated generally at 65; such stub shafts being pressed or keyed into the inner race of the bearing assemblies 18 for rotation therewith.

With particular reference to the bearing assemblies 18, it will be noted that the same bear a unique construction which enables a floating support for the stub shafts 64 cushioning the housing walls 16 as well as the driver or impact hammer 65. To accomplish this unique feature I employ a standard roller bearing assembly 18a which is bonded to a surrounding grommet ring 1812, made of rubber or a similar resilient material, which forms a shock absorbing bushing. An annular metal mounting ring 18c in turn carries the assembled ring and hearing so that the unitary combination so formed can be mounted in the ends of, housings 15 and 55 as described and shown.

The hammer mechanism 65 as shown, comprises a substantially cylindrical metal mass or body 66 cut out intermediate its lateral limits to provide a more or less boomerang shaped recess 67, as best seen in Figure 2 of the drawing. The stub shaft portions 64 are formed in tegrally and coaxially of the substantially cylindrical body 66 of the hammer mechanism. A substantially J-shaped hammer arm 68 curved to fit recess 67 (see Figure 2), is pivotally mounted at one end on an axle 69 extending between side wall portions 70, I'll of the hammer body 66; these walls being separated by the recess 67. In cross section the hammer arm 68 is somewhat semi-cylindrical along its outer face with the exception of a cam projection 71 extending outwardly of its periphery and formed with a flattened face. Such hammer arm 68 is designed to rock about its axle 69 relative to the main body portion 66 of the hammer when the latter is rotated and such two members are separated adjacent the free end of the hammer arm by a compression coil spring 73 having its ends housed in opposed openings 74 and 75 formed respectively inward of the hammer body 66 and hammer arm 68.

Rotation of the hammer mechanism 65 and as a consequence the movement of hammer arm 68 therewith is accomplished by means of combination sheave and fly wheel members 76, 76 located at the extreme ends of stub shafts 64, outwardly of the side wall portions 56, 56 of the driving unit housing 55. Interconnection of fly wheels 76, 76 with the drive unit 11 is accomplished by two V-belt means 77, 77, one of which is mounted over each of the said combined sheave and fly wheels 76 and one of the pulley wheel members 40, 40.

Located immediately adjacent hammer arm 68 and pivotal about one end on an axle member 80 mounted across a rectangular chamber 81 formed within neck portion 60 of housing member 55, is a metal striker member 82 having a striker appendage 83 at one upper corner. Such appendage 83 is arranged normally to engage with the cam projection 71 of the hammer arm member 68 when the hammer body is rotated. A short pin member 84 is disposed across a slotted recess 85 beneath appendage 33 of the striker for connection with one end of a tension spring member 86 disposed in a cylindrical opening 87 formed in neck portion 60 of the driver housing. Spring 86, as best seen in Figure 2, is anchored at its opposite end by a spring retaining plug 88 which seals off the opening 87.

In the form of device shown in Figures 1 and 2, the spring 86 serves to maintain striker member 82 in constant contact with an adjacent shank end portion 90 of a. chisel or tool member 91 mounted for rectilinear reciprocation in a bushing member 92 carried within the lower end of neck portion 60. A tool or chisel retainer ring 93 of conventional design is associated with the neck portion 60 via lateral openings 94, 94 therein and is designed to retain the chisel member in reciprocal association with the neck 60 and bushing 92 therein. An extended shoulder or collar portion 95 on the chisel member 91 is designed to interfere with the chisel retainer ring according to known practice and design to further promote its retention in the device.

Connection of the driver unit to the drive unit is accomp ished by zt fit n5 the Substantially lJ-shaPcd driver housing 55: withhousing of the drive unit, the side wall portions 56, 56 of'l'tousing 55 abutting the walls 16 ,of the drive unit housing. It will further be noted from Figure 2 in particular, that elongated side walls 57 and 58 of housing 55, are arranged to extend along opposite sides of the hammer unit 65. Connection of such walls 57 and 58 with the transverse wall portion 37 of the drive unit housing 11 is by bolt means 97. Also it will be seen that such bolt means 97 are combined with compression spring members 98 which serve as a locking device for the nuts on bolt means 97.

In addition to the two housings 11 and 55, two side plates 99, 9,9 are disposed outwardly of sheave wheels 76 to enelose the same, such being secured to the two housings 1 1 and 55 by means of bolts 100 or other means.

With respect to the design of the hammer unit 65 and the combined sheave and flywheel members 76, '76, the latter are formed to substantially counter-balance the off-center mass distribution of the hammer mechanism caused by cut-out portion or recess 67 in the ham mer body 66 and the rocking movement which accompanies operation of the hammer arm-68. To balance the hammer unit, the fly wheels are formed to counterbalance the system when the hammer arm is at its radially outermost limit of travel, as"indicated by the dotted circle C of Figure 2. In this position the outer swing of the hammer arm is limited by contacting engagement of its surface 101 with surface 102 of the hammer body recess 67. Thus on impact with striker 82, the hammer arm and hammer body are moving together free of vibration and unbalance.

With particular reference to the form of device illustrated in Figures 1 and 2, it will be recognized that the organization of the impact hammer unit and the tool or chisel 91 therein is such that no provision is made for interrupting or halting impulse delivery to the tool bit withoui denergizing the drive motor. Since that arrangement has certain recognizabledisadvantages and shortcomings from the standpoint of convenient operation, the alternate structure of Figures 3 through 6 is presented herewith, i

It will be understood from an inspection of Figures 3 through 6, that the alternate form of device therein shown has provision for disengaging the tool bit from the ina fiuence of the impact hammer unit without the need for shutting off the electrical motor. To this end, the lower end of the driver unit housing 55 (particularly the formcriy described neck portion 60 thereof) has been revised to form an alternate neck structure 106. Neck structure 106 is formed with a substantially lengthwise extending, open-ended, axial bore which bears enlarged bore portions 107 and 108 adjacent its opposite or upper and lower ends, respeetively, A tool bit or chisel 109 is arranged for insertion into this axial bore of the neck portion, the same having a cylindrical collar 110 thereon which registers with the lower enlarged bore portion 108. The shank or upper end 111 of the tool bit is encased within a tubularcap member 112 which slides freely within the upper enlarged bore portion 107. This cap is closed overat its upper end and extends into the interior of housing 55 for engagement with the striker member 82. Since it is my intention that the working parts of the impact driver unit be lubricated preferably with a splash oil system by filling housing 55 with oil, grommet-like seals or O-rings 113' are provided in the walls of the bore PQ tion 10? to engage with the side Walls O tubular an in he e Pre ing he escap o ubricant via the central bore in the neck. structure 106.

My oposa to et ect selective. d senga m o the .0 bi fro the insec deli e m a side in a structu al a rangements: ma ntain ng he o t in n axially dis laced p sit n has a d c ea Q t e nflu c 'q hamm r a m 68., this end the neck st ucture 10.6

is with; 9- unaost a. air-eel lat h. member 115. formed with forked bell crank arm portions 116 which are pivoted intermediate their ends on an axle member 117 carried by the neck structure. A spring member 118 is mounted about the axle 117 and has one end 119 thereof in engagement with the body of the neck structure 106 and its other end 120 bearing against the latch member 115. Such spring normally biases the latch member clockwise, as viewed in Figure 3. An end surface 121 is formed on the latch member for engaging the back side of the collar 110 formed on the tool bit. This is accomplished by virtue of an enlarged opening 122 formed through the side of the neck structure 106 such that the biasing action of the spring member 118 maintains the latch sub. stantially against the side of a tool bit inserted within the axial bore of the neck structure.

The neck 106 also carries a standard chisel or tool bit retainer member 125 located adjacent its outer end and on the opposite side thereof from that which mounts the latch member 120. Such retainer 125 is pivotal about axle 126 and it is formed with a collar engaging projec-v tion or surface 127. A compression spring and plug means 1.28 is utilized between the retainerand'neck structure to normally bias the retainer 125 toward the axis of the chisel, such spring and plug being retained or held in the neck portion 106 of the hammer housing. The retainer 125 is designed to normally engage the lower end or face of collar 110 on the chisel to prevent free axial removal of the same from the neck portion 106. However, it will be appreciated and understood that by swinging retainer 125 counterclockwise a suflicient dis tance the retention projection 127 thereon will clear collar 110 and allow removal of the tool bit as desired.

From the above description it will be appreciated that the tool bit or chisel is arranged to be axially displaced sulficiently away from hammer arm 68 (as shown by dotted lines in Figure 3) so that collar 110 thereon is located between surface 121 of the latch member 120 and the catch projection 127 of the chisel retainer. In such a condition the tool bit is locked out of its normal engaging position with striker 82 so that spring 86 can pull the striker out of engagement with the cam projection '71 of the hammer arm 68. The demolition device may then be rested on the point of the tool bit and the impact delivery or hammer mechanism and motor allowed to run free without imparting blows to the tool.

The cam projection 71 of the hammer arm will not then again engage the striker 82 to deliver a blow to the chisel until latch 120 is raised to release collar 121 of the tool bit. Such releasing of the latch 120 permits the tool bit and cap 112 to move into their normal operating positions. Such releasing action 'is accomplished by squeezing a release lever 130 located adjacen'tly beneath one of the operating handles 47 at the upper end of the demolition device (see Figures 5 and 6). Lever 130 in turn serves to actuate a link 131 which connects by pivot pin 132 to the outer or free ends of the bell crank arms 116 associated with latch member 120. Therefore, when lever 130 is raised the latch 120 will swing away from the tool bit or chisel, releasing collar 110 and allowing the chisel to return to a socketed position within cap 112. The entire weight of the demolition hammer then tensions spring 86 and return striker 82 into a position for engagement by the cam projection 71 of the hammer arm. Thusly the hammer is returned to a position or condition to perform work.

Operation The basic operation and various. mechanical movements embodied in the hammer device of my invention may best be understood by examining Figure 2,. It, will be recognized that rotation of the motofs armature shaft 22 according to arrow A, serves to rotate worm member 35 in a like direction. The rotation of the armature shaft and worm is carried forth at a rather high R. P. M., but such is reduced through worm gear 41 which is attached to and thus drives the shaft member 38 according to the direction of arrow B in Figure 2. The J-belts 77 transmit driving power from pulley wheels 40, 40 to the two combination sheave and fiy wheel members 76, 76. Rotation of the fly wheel members, of course, rotates the hammer unit 65 within its chamber formed between the Walls of the drive and driver unit housings i5 and 55. The hammer body 66 then rotates with the fly wheels 76 and at the same R. P. M. thereas. The hammer arm member 68, secured pivota'lly to the hammer body 66 on axle 69, will swing outwardly and move along a circular path with the hammer body until. the cam pro-- jection 71 thereof engages the leading striker appendage 83 of the striker member 82. Such engagement of the cam projection andstriker appendage serves to deliver a hammer blow through the striker member to the shank end 90 of the chisel or to cap 112 in the alter .te structure of Figures 36. It will be noted that tension spring 86 maintains striker member 82 tightly against the adjacent end of the chisel or cap member so that on impact thereof with the hammer arm, the full force of the blow is transmitted directly to the chisel with minimum vibration, loss of power and reverberation effect, between the striker and the chisel. The delivery of an impact or power blow to the striker member by the projecting cam of the hammer arm is accomplished during each revolution of 360 of the hammer body; such rotational motion of the hammer permitting its arm member to swing outwardly into an interfering or engaging arc with appendage 83 of the striker as noted by dotted circle C. Urging the hammer arm into such interfering position is the functioning of compression spring 73 which also serves to absorb the repercussive effects transmitted to the hammer arm on impact with the striker; the same spring thereafter redirecting the repercussive forces to the hammer arm for reinforcing its impact delivery to the striker. This repercussion or absorbing function of spring member 73 does much in the way of reducing vibrational effects on the hammer unit and likewise the transmission of vibrations to the drive unit and operator.

It will thus be recognized that by providing the compression spring means 73 intermediate the arm 68 and hammer body 66 and by tensioning spring 86 so that the striker member 82 is in constant contact with the adjacent end of the chisel or cap member, vibrational repercussion on the drive unit at the delivery of a blow to the chisel member is reduced to a minimum. At the same time, power loss due to vibration or chattering of the striker on the chisel or cap member is eliminated.

Additional minimizing of vibration between the driver unit and the drive unit is accomplished in an efficient manner by use of the V-belt drive means; such being resilient by nature and capable of absorbing shocks produced in the driver unit without transmitting the same to the drive unit. Additionally the insulation around the operating handle members 47 as provided by mounting means 45 and handle grips 43, advances the safety and security of the operator and insulates him from whatever vibrational shocks are transmitted to the drive unit.

A further advantage is found in the modified structure shown in Figures 3-6 where a latch mechanism is provided for selectively interrupting operation of the chisel tool bit by eifectively holding the same out of driving engagement with the impact delivering hammer mechanism. This feature permits stopping the operation of the hammer without the need for deenergizing the electric motor.

Recognizing the above features and advantages of my invention, it will be readily understood that i. do not wish to be limited to the particular features of construction and arrangements of elements as have been described herein and illustrated in the accompanying drawings since obviously modifications changes and substitutions of equivalents may be carried forth in my hammer without departing from the spirit and scope of its inventive concepts. As a consequence it is my desire and wish that 8 I be limited in my invention only as may appear the following appended claims. 6 d

I claim:

1. A percussive device of the class described, .co prising in combination, an elongated housing, an electrical motor mounted within said housing and adjacent one end thereof, a hammermass mounted for rotation within said housing and adjacent the opposite end thereof, worm and worm gear means driven by said motor, a shaft means paralleling the axis of -rotation for said hammer mass and arranged to be driven by said worm and worm gear means, pulley wheel means mounted atopposite ends of said shaft means and outwardly of said housing, a pair of sheave wheel members mounted coaxially with said mass and rotatable therewith outwardly of said housing, belt means interconnecting each of said pulleywheels with one of said sheave wheel members to drive said rotating hammer mass, a hammer arm member pivotally connected to said mass for free arcuate movement between limits and radially of-said mass about an axis located inwardly of the periphery of said mass, a cam projection formed on the outer periphery of said arm member, a striker pivotally carried by said housing adjacent said arm member for movement about an axis paralleling the axis of pivotal movement for said arm member, an appendage formed on said strikerand arranged to be engaged by said cam projection when said arm is swung centrifugally to its radial-1y outermost position, during rotation of said mass; said arm after engaging said appendage swinging inwardly toward said mass to bypass said striker, shock absorbing means mounted between said arm and mass for absorbing repercussion of said arm after engaging said striker and for reversing the directional movement of said hammerarni to bolster its delivery of a succeeding blow to the striker, an impact tool mounted for rectilinear movement c-oaxially of said housing and extending outwardly of its said opposite end, said impact tool means having a shank portion disposed adjacent said striker for receiving percussive blows therefrom, and spring means mounting between said striker and housing for maintaining said striker and the said adjacent end of said tool means in constant contact throughout the rotational cycle of said mass.

2. A percussive device of the 'class described, comprising in combination, a first housing, the side walls of said housing being formed with registeringly aligned semicircular cut-out portions at their-ends, an electrical motor mounted within said housing and having an armature shaft extending coaxially therewith, a shaft means disposed transversely of said housing and armature shaft and extending outwardly of the said housings sidewalls, a worm gear mounted on said shaft means, a worm means mounted on said armature shaft in engagement with said worm gear for rotating said shaft means, pulley wheel means mounted at the ends of said shaft means for rotation therewith outwardly of said housing, a second housing attachable to said first housing and having side wall portions with semi-circular cut-ou-t portions mating with said cut-out portions of said first housing, coaxially aligned bearing means carried in resilient cushions between said two housings in said cut-out portions thereof, a hammer body means mounted intermediate the side walls of said two housings and having stub-shaft portions extending outwardly and supported in said bearing means, a combined sheave and fiy wheel member mounted on each of said stub-shaft portions outwardly of the side walls of said two housings and in coplanar alignment with said pulley wheels, flexible belt means interconnecting said pulley wheels and fly wheels, said hammer body being rotatable with said fly wheels and having a substantially arcuate cut-out portion intermediate its ends, an arm member comprising substantially the cut-out portion of said hammer body, mounted for pivotal movement about one end and radially with respect to the rotational axis of said mass, said arm being rotatable with said mass and arranged to swing arcuately therefrom under centrifarrests 'ugal force; shock absorbing means inner-mediate, the free end of, said arm and said mass, a pr jection formed at the outer end of said arm, a striker inember pivotally mounted adjacent said arm for engagement by said cam projection on the latter as the same moves to its radially outermost position during rotation of said hammer body, an impact tool having a shank portion adjacent said striker for receiving a percussive blow therefrom, and tension spring means between the free end of said striker and said housing for holding said striker in contact with the said impact tool throughout the rotational cycle of said hammer body thereby to substantially eliminate vibration and repercussive impact between said striker and impact tool during the delivery of a blow thereto from said striker means.

3. A device of the class described comprising, a housing, an electrically powered motor mounted within said housing, shaft means rotatable transversely of said housing adjacent the armature shaft of said motor, worm and worm gear means coupling said shaft means in driving relation with the armature shaft of said motor, a pair of pulley wheels, one mounted at each end of said shaft means, a pair of coaxially aligned combined sheave and fly wheels mounted in spaced coplanar relation with said pulley wheels, belt means interconnecting each of said pulley wheels with one of said sheave wheels, a substantially cylindrical hammer body mounted within said housing and between said sheave wheels, said ihammer body having connection with said sheave wheels for coaxial rotation therewith, a hammer arm pivotally carried by said hammer body and moveable radially relative thereto, projection means on said arm and hammer body for limiting the outward arcuate swing of said arm from said hammer body, shock absorbing means mounted between the free end of said hammer arm and said hammer body for resisting movement of said arm toward said hammer body and urging the same toward its outward radial limit, a cam projection formed at the outer free end of said hammer arm, a pivotally moveable striker member mounted adjacent said arm for engagement with said projection thereon when said arm is at its radially outermost limit, an impact tool mounted for rectilinear reciprocation within the lower end of said housing and having its shank end adjacent said striker, said hammer arm after delivering a blow to said striker member retracting radially inward of said hammer body to compress said shock absorbing means and bypass said striker arm, and spring means maintaining said striker in constant contact with the adjacent end of said impact tool.

4. In a demolition hammer of the class described, the combination comprising, a housing, operating handle means mounted in resilient electrical insulating material at one end of said housing, an electrical motor mounted within said housing adjacent said one end thereof, a substantially cylindrical hammer body mounted below said motor for rotation about an axis substantially transverse of the longitudinal axis of said housing, combined sheave and fly wheel members connected to opposite ends of said hammer body for rotation therewith, drive means, including flexible belt means, interconnecting said sheave wheel members with said motor for the rotational driving of said hammer body, an arcuately moveable hammer arm pivoted at one end on said hammer body and rotatable therewith, shock absorbing means normal-1y urging said hammer arm outwardly of the external periphery of said hammer body, a pivotally mounted striker member located adjacent said hammer body for engagement with said hammer arm when the latter is swung to its radially outermost position, means formed on said hammer arm for engaging said hammer body to limit the outward radial swing thereof, chisel means mounted for rectilinear sliding movement at the other end of said housing and substantially ooaxially of the longitudinal axis thereof, spring means for holding said striker means in contacting engagement with said chisel means, and means selectively operative at said handle means "to hold said chisel means away from said striker member thereby permitting the latter to maintain a noninterfering posi- 'tion with respect to said hammer arm such that operation of the device, wherein impact blows are delivered to said chisel member, may be interrupted as desired without deenergizing said motor.

5. In a device of the class described, the combination comprising, a housing having resiliently mounted operating handles at its one end, an electrical motor mounted within said housing, a rotatably mounted mass disposed within said housing adjacent said motor, combination sheave and flywheel members mounted for rotation with said mass, drive means interconnecting said sheave wheels with said motor whereby said mass is rotatably driven by said motor, a pivotal hammer arm mounted on said mass for swinging movement about one end, the axis to the rotational axis of the latter, means limiting the outward arcuate swing of said hammer arm, spring means intermediate the free end of said hammer arm and said mass for normally urging said arm toward its outermost radial limit, a cam projection formed on the outer periphery of said arm, a striker member pivotal about one end and located adjacent said hammer arm for periodic engagement therewith, said striker member having an extending appendage thereon which is periodically engaged by said projection in response to rotational driving of said mass which causes said hammer arm to swing to its outermost limit under centrifugal action, said spring means serving to cushion the impact eiiect at the engagement of said projection with said appendage and further to harness vibrational repercussions of said arm for imparting the force of its repercussion to said striker, additional spring means tensioning said striker away from said mass and arm, chisel means disposed substantially axially of said housing for rectilinear reciprocation relative to said striker, said chisel means being in position for receiving impact blows from said striker with said additional spring means normally urging said chisel and striker into contacting engagement, a collar member formed about said chisel intermediate its ends, a chisel retainer pivotal on said housing and arranged to engage: one side of said chisels collar, a spring biased latch means located in axially spaced relation with said retainer for engaging the opposite side of said collar, said latch means having bell crank arms, linkage means connected to one end of said crank arms, and a release latch operable adjacent said operating handles for actuating, said linkage means to swing said latch means outwardly from said chisel, the arrangement being such that the normal operating position of said chisel disposes the collar thereon between said striker and latch means whereat said chisel is disposed for receiving periodic impact from said striker, axial displacement of said chisel away from said striker so as to dispose the collar thereof intermediate said latch means and retainer serving to lock said chisel out of engagement with said striker and hammer arm to halt impact delivery to said chisel means.

References Cited in the file of this patent UNITED STATES PATENTS 1,725,212 Schneider Aug. 20, 1929 1,887,980 Martin Nov. 15, 1932 1,898,069 Tschudi Feb. 21, 1933- l,9l5,07l OGorman June 20, 1933 (Other references on following page),

11 UNITED STATES PATENTS Rasch Nov. 5, 1935 Byford "Jan. 19, 1937 Pinazza Dec. 21, 1937 Smith Sept. 17, 1940 Woodin May 26, 1942 Worth Aug. 24, 1948 12 Sparano May 19, 1953 Van Russum Oct. 20, 1953 FOREIGN PATENTS Sweden Aug. 14, 1928 France July 26, 1927 France Oct. 7, 1935

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