WO1987002611A1

WO1987002611A1 - An impact tool

Info

Publication number: WO1987002611A1
Application number: PCT/GB1985/000492
Authority: WO
Inventors: James D. Cunningham
Original assignee: Cunningham James D
Priority date: 1985-10-29
Filing date: 1985-10-29
Publication date: 1987-05-07
Also published as: EP0252904A1

Abstract

An impact tool comprises two flywheels (F, F') disposed on opposite sides of a ram (R) and rotatable in opposite directions to drive the ram when the flywheels are moved into peripheral engagement with the ram. The flywheels are driven by a single motor (54) through pairs of pulleys (62, 21; 62', 21') interconnected by drive belts (65, 65'). Movement of the flywheels towards the ram disengage the drive by slacking the belts so that the flywheels are rotating under their own inertia when they engage the ram.

Description

AN- IMPACT TOOL

The invention relates to impact tools.

It is known from U.S. Patent No.4 ,042,036 to provide an impact tool comprising two flywheels mounted within a housing for rotation in opposite directions, a ram disposed between the flywheels, means for causing the periphery of the flywheels to engage the ram, the ram being movable longitudinally by engagement with the rotating flywheels, a drive assembly, and a drive coupling for connecting the drive assembly to drive the flywheels.

In U.S. Patent No. ,042,036 , the impact tool, which is particularly adapted for driving nails, utilizes one stationarily mounted and one pivotally mounted motor and rotating flywheel assembly, with the pivotally mounted flywheel being moved toward a ram and pushing the ram against the stationarily mounted flywheel. The flywheels are rotated in opposite directions, such that engagement of each with the ram will drive the ram in the desired direction.

U.S. Patent No. , 323, 127 also discloses an impact tool in which a pair of pivotally mounted, motor driven flywheels are moved essentially simultaneously into engagement with a ram disposed between them.

Although the impact devices disclosed by these Patents may be highly effective, the weight of the two motors, in a hand held tool particularly adapted to drive nails and the like, leaves room for improvement. In addition, a direct drive between a motor and flywheel causes the motor to reduce speed when the flywheel is reduced in speed, due to loss of inertia through transmission of a driving force to the ram. The necessary capacity for acceleration of the motor, to bring the flywheel up to the desired speed for the next operation, has resulted in an undue expense for a tool which is to be marketed in large quantities.

According to the present invention there is provided a drive assembly comprising a single motor arranged to drive both flywheels through said drive coupling, and said drive coupling can be disconnected from the flywheels to permit the flywheels to rotate .under .their own inertia before they engage the ram.

The weight of the tool is reduced by employing a single motor and transferring rotation to a pair of rotating flywheels, individually pivotally mounted on opposite sides of a ram to be driven. The ram can carry a blade or the like for impacting a desired object, such as a nail. The preferred drive arrangement includes a gear driven by the motor and engaging two gears from which one of the flywheels, is rotated, the first gear in turn engaging a second gear of the same pitch diameter or number of teeth, with the second flywheel being driven from this second gear. In order to permit the first and second gears to be mounted in a stationary position and the flywheels to pivot, the drive from the respective first and second gears may be through a separate belt and pulley mounted for driving the respective flywheel. In order to prevent the speed of the motor or drive means from being reduced in proportion to the speed of rotation of the flywheels, as they are slowed down due to the reduction of inertia through the transfer of a driving force to the ram, each flywheel may be pivotal about a suitable axis in a direction which causes the distance between a separate pulley driven by the respective first and second gears and separate pulleys attached to the drives of the respective flywheels to be reduced. In effect, the belt connecting the respective first and second pulley with the respective flywheel pulley will tend to slip on the latter, in the sense that the engagement of the belt with the respective flywheel pulley will be reduced, i.e. the tension of the belt on the respective pulley will decrease. A preferred construction of the flywheel pulleys is a V-shaped groove which is adapted essentially to securely engage the flywheel pulley when the flywheel is away from the ram, toge±h.er- with parallel side walls which will guide the pulXey into the groove when full tension again occurs, but wilT, aeLlso- maintain the belt in alignment with the pulley but without engagement with the inner groove. A further improvement is the use of a hollow housing which may be made of lighter and less strong material, such as plastic, attached to an end plate, with a pair of end plates attached thereto and formed of a material having a greater strength, such as steel. Such a plate may carry a pair of sockets or the like for receiving the pivot pins for the respective flywheels, with these sockets being connected by a bar which is integral with the corresponding end plate. These bars not only withstand the stress of opposing precession forces, produced in opposite directions by the oppositely rotating flywheels, but more significantly, the opposing tensile forces produced by the reaction of the compression forces between the opposed flywheels and the sides of the ram. A further feature is a spring which returns each flywheel to its initial position away from the ram and a pivotal connection between a cup which receives one end of the spring and a special housing for the corresponding flywheel, particularly when the flywheels are moved into engagement with the ram through a system actuated by a rod which engages the work and thereby is adapted to actuate the tool when it is placed against a workpiece for driving a nail therein.

An additional significant feature is the preferred material of which the friction surface engageable by the respective flywheel is formed. A substantial number of tests have indicated that a sufficiently high coefficient of friction accompanied by a sufficient resistance to wear is produced, particularly when the periphery of the flywheels is polished steel, when the side surfaces of the ram are formed by a fabric layer of natural fiber, preferably long fiber cotton cloth, impregnated by and molded in a suitable plastic, preferably polyurethane. The entire body of the ram may be formed of such fabric layers and plastic. In this event, a blade or similar tool may be provided with a stem or rod which extends from the lower to the upper end of the ram, being attached to the blade at the lower end and attached to the body at the upper end of the ram. Each side surface of an alternative ram is formed of a natural fiber embedded and molded in a suitable plastic, but the central portion of the ram may comprise an insert of material of a higher strength, such as metal, having attachment means for the blade, such as a threaded socket at the lower end and a series of spaced fingers extending upwardly within the molded plastic.

A special bu ber having a corresponding shaped socket, may be provided for the upper end of the ram when the latter is pyramidal in shape. Also, a bumper for the lower end of the ram, which is impacted by the ram only if the ram is moved slightly further than normal, may be attached to the upper end of a conventional nose piece.

The ram, an elastic cord and a plate to which the cord is attached and through which the ram may move to engage the upper bumper, may form a readily replaceable unit or sub- assembly for cord or ram replacement, when access thereto is readily provided, such as when the upper bumper is readily removable.

The invention will now be particularly described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a perspective view, on a reduced scale, of an impact device of this invention, particularly adapted for driving nails;

Figure 2 is a transverse longitudinal section, on an enlarged scale, through the device of Fig.1;

Figure, 3 is an offset longitudinal section taken along line- 3-3 of Fig.2, the left portion of the view being broken away to the longitudinal center of Fig. 2 to show a dual drive arrangement;

Figure 4 is an elevation, from the inside, of a front cover plate of the device;

Figure 5 is a central longitudinal section of the cover plate, taken along line 5-5 of Fig. ;

Figure 6 is a fragmentary section, taken along line 6-6 of Fig. 3 and showing a drive arrangement for a pair of flywheels or rotors which are rotated in opposite directions;

Figure 7 is a fragmentary section, taken along line 7-7 of Fig.3, showing the dual drive arrangement thereof;

Figure 8 is a side elevation of a pulley of Fig. 6 and an integral shaft therefor;

Figure 9 is fragmentary portion of a pulley of Fig.3_> on an enlarged scale;

Figure 10 is a fragmentary portion of another pulley of Fig. 3_» also on an enlarged scale;

Figure 11 is an offset section, taken along line 11-11 of Fig.13, of a drive ram which is engaged at selected times, by a pair of rotors or flywheels of Figs. 2 and 3;

Figure 12 is an end elevation of the drive ram of Fig.11;

Figure 13 is a bottom plan view of the drive ram of Figs. 11 and 12;

Figure 14 is a side elevation of an alternative drive ram, partially broken away to show the interior construction and also showing a drive blade for nails in dotted line;

Figure 15 is an end elevation of the alternative drive ram of Fig.14, also partially broken away to show the interior construction; Figure 16 is a bottom plan view of a housing cap of Figs. 2 and 3;

Figure 17 is a longitudinal section thereof, taken along line-17-17 of Fig.16;

Figure 18 is a lateral section thereof, taken along line 18-18 of Fig.16;

Figure 19 is a bottom plan view of a plate to which are attached the upper ends of a resilient cord for returning the drive ram; and

Figure 20 is a vertical longitudinal section of a bumper installation.

A single motor impact device, such as for driving nails and the like, constructed in accordance with this invention, as illustrated in Fig. 1 , may include a housing H in which is installed a reciprocating ram R of Fig. 2 adapted to move a conventional blade B' of Figs. 14 and 15 or B of Fig.11 into engagement with the head of a nail fed from a conventional nail feeding magazine M into a nose piece N of a suitable nature. An auxiliary housing A, which serves as a combined gear and motor box, extends rearwardly from housing H to a handle 10, which in turn extends rearwardly from the gear and motor box and is provided with an electrical switch 11, to which an electrical cord 12 leads. As shown in Fig. 2, the reciprocabie ram R may be disposed centrally of the housing; H: and the opposite sides of which are engageable by a pai__r of flywheels F and F¹ , which are rotated in opposite directions and each of which is moved toward the ram by pivotal movement of a pivotal, hollow mount 13 or 13', each pivoted on a pin 14. Each flywheel is rotated in the direction of the arrow shown and is conveniently moved upwardly for engagement with the sides of the ram R by a lift pin 15. Each lift pin engages a socket 16 on the underside of the respective mount, while each flywheel is mounted on a shaft 17. Each flywheel shaft, as in Fig. 3, extends through a pair of bearings 18, and is in turn supported by the side walls of mount 13. A lock ring 19, inserted in a slot in each shaft 17, prevents axial movement of the shaft in one direction, at the rear bearing 18, while an enlargement 20 of the shaft, at the front bearing 18, prevents axial movement in the opposite direction. A pulley 21, by which the flywheel is rotated in a manner described later, is mounted on and keyed to enlargement 20. Each flywheel may comprise a hub 22, which is keyed to shaft 17, and a rim 23, with each of the hub and rim being provided with a central radial flange which is slotted for connection of the housing and rim by rivets 24 at spaced positions circumferentially of the hub.

As in Figs. 2 and 3, each lift pin 15 is moved upwardly, or permitted to move downwardly, by a pivot arm 25 with the lower end of each lift pin 15 engaging a socket 26 on the respective pivot arm and the rear end of the latter being pivoted on a pin 27. The pivot arms 25 are connected together at the front by a cross bar 28, shown also in dotted lines in Fig. 2, so as to form a forked

_* structure, with each pivot arm extending through a hole 29 in the housing H. Cross bar 28 , at the center , is prov ided with a reinforcement 30 for a tapped hole (not shown) for attachment of the upper end of a conv entional rod 31 , the lower end of which engage s the work piece when a nail is to be driven, thereby causing the flywheel s F and F' to pivot upwardly f or engagement with the si de s of ram R, to mov e the ram R downwardly, so that bl ade B or B ' of Figs. 14 , 15 or 1 1 w ill impact the na il to driv e i t . The length of rod 31 is conv entionally proportioned so that the lower end of the rod w ill engage the work piece suff iciently before the nosepiece N that the ram R will begin to be moved downwardly a s the lower end of the nosepiece N reaches the workpiece.

An upper pin 32 extends into a well 33 in the top of each mount 13_» as in Fig. 2, and is provided with an attached or integral cup 34 engaged by the lower end of a compression, snubbing spring 35 while the rounded lower surface of cup 34 pivots on the edge of well 33 as mount 13 or 13' moves upwardly or downwardly. Pin 32 and spring 35 extend upwardly within a sleeve 36, with snubbing spring 35 extending beyond the pin and its upper end engaging a disc 37, held in position by a set screw 38 threaded into the upper end of the sleeve. As will be evident, when the nail is driven and the device lifted to drive another nail at a different position, the upward pressure on cross bar 28 and pivot arms 25 will be released, enabling each snubbing spring 35 to return the corresponding flywheel to its initial position.

The housing H includes a central portion having side walls 40 and 40', each of which is.provided with a laterally extending wing 41, together with an upper block 42 and a lower block 43. The upper and lower portions of the side walls are reinforced by pairs of upper and lower transverse bolts 44 which resist a portion of the stresses caused by movement of the ram and the reactions at the ends of pins 14, since precession forces produced by flywheel F ill be counteracted by flywheel F' , but are transmitted through the housing H. Also, compression forces produced by the thrust of the respective flywheels against the ram will also not counteract each other but will, produce tension forces, as large as 1,000 to 3,000 lbs., again transmitted through the housing H. The front and the rear of the housing may be closed by a front plate P and a rear plate P' , respectively, with the front plate P, as in Figs. 4 and 5, being provided with a wing 45 at each side, corresponding to the configuration of wings 41 of the central portion of housing H. Inwardly extending, integral blocks 46 have sockets 47 for receiving the corresponding end of a pivot pin 14.

A reinforcing bar 48 extends laterally between the blocks 46, as in Fig. 4, and is integral with the front plate P, as in Fig. 5, to withstand the stress imposed by the forces produced by the oppositely rotating flywheels and transmitted through the respective mounts 13 and pivot pins 14, to the housing, but cancelled at the front through the reinforcing bar 48. Plate P¹ is also provided with inside blocks and sockets corresponding to blocks 46 and sockets 47, as well as with a reinforcing bar 48' of Fig. 3 but on the outside of the plate, as shown, opposite the pulleys 21, merging to the inside of the position of blocks 46. There are several advantages to the integral reinforcing bars 48 and 48', including the lack of necessity for installing a separate bar, such as a bolt or the like. Another advantage is that integral bars 48 and 48' are connected directly to sockets 47, to which the forces are transmitted directly from the flywheel mounts. A further advantage is that the housing H may be formed of plastic or other material less expensive and less resistant to stress, while the plates P and P* may be formed of steel. Each plate, as shown in Fig. 4 for front plate P, may be provided with a narrower upper section 49 which abuts a housing cap C of Figs. 2 and 3, while each upper section 49 may be provided with holes 50 through which bolts 51 of Fig. 3 extend, as well as through a corresponding upper section of rear plate P', for securing a cap C in place. Additional holes 52, at each lower corner of front plate P, and holes 52', as in reinforcing blocks 46, permit the front plate to be attached to the center section of the housing, by cap screws engaging tapped holes in the center section of the housing.

The flywheels F and F¹ are rotated in opposite directions by a single motor 54 which is installed in auxiliary housing A, a portion of which is shown in Fig. 3. Motor 54 may have an integral speed reduction unit or an attached speed reduction unit, connected to a shaft 55 on which a drive gear 56 is keyed, with shaft 55 extending through a bearing 57 mounted within the auxiliary housing A. Motor 54 may be a universal type having an idle speed in the neighbourhood of 26,000 r.p.m. with the gearing having a* reduction ratio of between 2 to 1 and 4 to 1 , such as 2.5 to 1. As in Fig. 7, drive gear 56 engages a larger gear 58, which in turn engages a second gear 59 of the same pitch diameter so that gear 58 will drive gear 59 at the same speed but in the reverse direction, drive gear 56 and gears 58 and 59 being represented in Fig. 7 by dotted circles corresponding to the respective pitch diameters. As shown, drive shaft 55 is offset slightly from the vertical plane of the engaging pitch circles of gears 58 and 59 so that drive gear 56 will engage larger gear 58 only. Gear 58 is keyed to a shaft 60, as in Fig. 3, at a keyway 51 of Fig. 8, while shaft 60 is integral with a pulley 62 having a V-notch 63. Shaft 60 is supported by bearings 64 mounted in housing A, while similar bearings support a shaft 60', of Fig.7, to which gear 59 is keyed and which is integral, in a manner similar to shaft 60, with a pulley 62' of Fig. 6. A V- belt 65 connects pulley 62 with pulley 21, engaging the notch 63 of pulley 62 and a notch 66 of pulley 21 , for rotating flywheel F. A similar belt 65' connects pulley 62' with a pulley 21' for rotating flywheel F' . It will be evident from the construction thus described that the flywheels may be rotated in opposite directions from a single motor, indicated by the arrows of Fig. 6, and will be rotated at the same speed due to the identical diametric pitch of gears 58 and 59.

The V-notch 63 of pulley 62, as in Fig. 9, is conventional, but notch 66 of pulley 21, as in Fig. 10, has a similar angularity at the inside to the notch of pulley 62, but outwardly therefrom parallel side walls 67 which are spaced apart a distance slightly greater than the width of the belt. The pulleys 62' and 21' for rotating the flywheel F' may be identical in construction with pulleys 62 and 21 , respectively, for rotating the flywheel F. The effect of this variation in the notch 66, as illustrated on an enlarged scale in Figs. 9 and 10, is to permit the V-belt 65 or 65' of Fig. 6 to move downwardly between side walls 67 and the belts to slip slightly on the respective pulleys 21 and 21', when the flywheels are moved upwardly and into engagement with the respective sides of ram R, since the distance between the centers of pulleys 62 and 21 driving flywheel F, as well as between the centers of pulleys 62' and 21* driving flywheel F' , will decrease. Thus, when the flywheels tend to slow down through engagement with the sides of the ram, the speed of the motor will not be similarly reduced due to belt slippage but, after the flywheels are returned to their initial position, the belts will again tighten into the V-notches 66 of the flywheel pulleys and the motor will be able to accelerate the flywheels up to the previous speed more quickly. Such ability to accelerate the flywheels enables a greater number of nails, for instance, to be driven within a given period of time. In fact, with such a construction, the device of this invention has been used to drive a series of two inch (5cm) nails in succession by manual movement of the device from the position of one nail to the position of the next nail sufficiently quickly that one nail could be driven every 333 milliseconds, but the motor was able to accelerate the flywheels up to the desired speed as soon as the next nail position was reached. For 3.5 inch (9cm) nails one nail could be driven between every 400 milliseconds and each second, depending on the type of wood or .other material into which the nails were being driven.

The auxiliary housing A may include a casting 70, of Figs. 3 and 7, which abuts against a rear plate P' and conveniently interfits with integral tension bar 48', being attached to plate P' by cap screws (not shown) extending through slotted ears 71 of Fig.7 for locking the auxiliary housing in an adjusted position. Casting 70 has a bottom wall 72 and in interior partition 73 which provides an appropriate configuration to receive the gears 56, 58 and 59, bearings 57 for shaft 56 and bearings 64 for shaft 60 to which gear 58 is keyed and which, in turn, is integral with pulley 62, as well as corresponding bearings for shaft 60' to which gear 59 is keyed and which, in turn, is integral with pulley 62'. Bearings 57, 64 and the bearings for the shaft 62* may be held in place by a rear plate 74 attached to casting 70 by conventional cap screws (not shown), while the space above gears 58 and 59 may be closed by a top plate 75. Lower wall 72, as in Fig. 3, may be provided with a depending boss 76 which is threaded as shown, to receive an adjusting bolt 77, the head 78 of which may engage a slot 79 in an ear 80, integral with rear housing plate P' on the rear side thereof. The head of bolt 78 may be placed in slot 79 by slipping the stem of the bolt, adjacent the head, into an upright slot 81 in ear 80, centered above transverse slot 79. Bolt 77 may be locked in position by a set screw 82 extending into a tapped hole in boss 76.

The sides 83 and 83' of ram R, shown in Figs. 2 and 11-13, may be provided with a friction surface, as of the type described later, while the lower ends of the ram sides, for initial engagement by the flywheels F and F' , are also provided with a taper or bevel 84. The top of the ram, as in Figs. 11 and 12, may be provided with a pyramidal configuration 85, for a purpose described later, while each end edge may be provided with a groove 86 for reception of an elastic cord 87 of Fig. 2. Cord 87 may be of the bungee type for returning the ram to the position of Fig. 2 after a nail has been driven and extends from a plate 88, shown in greater detail in Fig. 19 and described later, but mounted just below cap C, as in Fig. 2. Cord ,87 extends from plate 88 downwardly along one groove 86, then through a transverse hole 89 of Figs. 11 and 12, adjacent the lower end of the ram, across an oval axial hole 90 at the lower end of the ram, through the opposite hole 89 and upwardly along opposite groove 86 to plate 88. A blade B, shown partially in Fig. 11 and the lower end of which is similar to modified blade B' shown in dotted line outline in Figs. 14 and 15 in connection with an alternative ram R' , has a cylindrical^' head 91 which fits within oval hole 90 and a conventional lower portion 92, shown in Figs. 14 and 15, which is slightly arcuate in cross-section and is adapted to engage the head of a nail for driving purposes while avoiding the head of the next nail carried by the feeding mechanism M of Fig. 1, thereby being concave on the side facing the next nail. Cord 87 may pass around the head 91 of blade B, within oval hole 90 when extending through transverse holes 89. An upper rod 93 may be attached, as by welding, or may be integral with head 91 and extend upwardly through a central longitudinal hole 94 in the ram to an upper socket 95 of Fig. 11. Socket 95 receives a nut 96 or similar fastening device, which engages the upper end of the rod, such as threaded, and thereby locks the rod and blade to the ram. The grooves 86 conveniently extend to the lower end of the ram, as in Figs. 12 and 13, even though the cord extends through transverse holes 89 above the lower end.

The ram R of Figs. 11-13 is formed of suitable fabric layers 97 of natural fiber, preferably long fiber cotton cloth, impregnated and molded in a suitable plastic 98, preferably polyurethane. This combination appears to have a high resistance to wear, to provide a high coefficient of friction and to resist cracking or breakage, particularly when used in conjunction with flywheels whose rims 23 are formed of steel which is highly polished on the periphery.

Ram R may be produced by molding with tapers 84 and pyramid 85 produced during molding, while any of grooves 86, holes 89 and 90, hole 94 and socket 95 may be produced during molding or afterward, such as holes 89 and 94 drilled after molding and the remainder produced during molding.

A further preferred construction of the ram is the ram R¹ of Figs. 14 and 15, which comprises a metal insert 104 molded into a plastic section 105 which forms the periphery of the ram and surrounds the insert 104. Metal insert 104 is provided with a threaded socket 106 for receiving the threaded upper end of blade B*. Section 105 is formed of a suitable plastic, such as polyurethane, along each side of which may be embedded layers 97 of suitable fabric, such as cloth of long fiber cotton, to provide a friction layer at each side which resists the wear of the flywheels F and F' . Although only one layer of fabric 97 is shown at each side of ram R' , it will be evident that more than one layer is preferably provided. Molded plastic section 105 has a pyramidal top 85, end slots 86 f r a return cord and the outer portion of transverse holes 89, while metal insert 104 is provided with the remainder of transverse holes 89 and an axial oval hole 90, similar to ram R. The bond between the plastic section 105 and the metal insert 104 is enhanced by the presence of a series of integral, upright, metal fingers 107, around each of which the plastic flows, as during molding. Attempts to provide a friction layer on the outside of a lower metal portion by plastic which also formed an upper portion of the ram, produced unsatisfactory results when the metal insert had merely a rectangular cross section. Also, a single small stem, projecting upwardly from the insert, did not provide a sufficient bond between the plastic and the metal of the insert to prevent breakage of the plastic within a short time after the beginning of use. If desired, the fingers 107 of the ram R' of Figs^*. 14 and 15, may be provided with lateral holes, through which the plastic matrix may extend, as during molding.

Cap C of Figs. 16-18, which is mounted at the upper end of housing H, as in Figs. 2 and 3, may comprise a body 110 formed of a suitable rubber or synthetic rubber, such as polyurethane, and may include a pyramidal socket 111 which corresponds- in shape to the pyramid 85 at the top of ram R or R' , to receive and guide the upper end of the ram when the elastic cord 87 returns the ram. The cap is provided with a slot 112 at each end of socket 111, which accommodates the upper ends of cords 87, as described later. Cap C may be provided with a lip 113 at each side which fits over opposite sides of the top block 42 of the housing H, as in Fig. 2, as well as three lateral holes 114 and 118, as in Figs 2 and 13 to receive bolts 51 of Fig- 3.

As: indicated previously, the cord plate 88 is positioned below cap C within a notch provided for the purpose in the top block 42, as in Fig. 2. Plate 88, as in Fig. 19, is provided with a central rectangular opening 116 through which the upper end of the ram moves, with a small groove 117 at each end of the opening, corresponding to the position of slots 112 of the cap C, to accommodate cord 87 as it extends into grooves 86 in the ends of the ram. Thus, slots 112 and grooves 117 complement grooves 86 of the ram and provide clearance for the cord. A pair of tapered holes 118 permit the opposite ends of the cord to be extended downwardly therethrough and a knot tied in the cord or a hog ring attached thereto, to wedge the respective end of the cord within a tapered sleeve 119 of Fig. 2, which engages the respective hole 118 of Fig. 19 to secure each end of the cord to the plate. The upper surface of top block 42 of the housing may be provided with wells at the position of holes 118, to receive the sleeves 119. In the event that the sides of ram R wear 24

due to continued use, such as after driving many thousand of nails, or for some other reason, ram R or cords 87 require replacement, a ram assembly may be formed of ra R, cords 87 and plate 88, with a knot or hog ring in eac end of cords 87 after passage through the ram and holes 118 in plate 88, as well as tapered sleeves 119 installed. Cap C may be readily removed by removing bolts 51 so that the previous ram assembly may be removed and replaced by a new one, after which cap C may be replaced. As will be evident, such replacement of a ram assembly may be accomplished in a very short time.

A bumper 122, illustrated in Fig. 20, may be positioned in the upper end of nose piece N and is engaged by the lower end of the ram, if the ram should accidentally be propelled a distance greater than that normally utilized to drive a nail. Bumper 122 may be formed of a suitable resilient material, such as polyurethane, and has a central hole 123 which is smaller than the bottom of the ram, but will easily permit blade B to pass through. From the bottom of hole 123, a downwardly inclined flare 124 extends outwardly, while the remainder of the underside of the bumper may be provided with an inwardly and downwardly extending taper 125, to engage corresponding contours of a lower clamp 126, as of metal, to prevent the material of the bumper from being driven inwardly and thereby tend to close hole 123, in the event of repeated impacts by the ram. Lower clamp 126 is provided with a central hole 127, corresponding to hole 123, while an upper clamp 128 may be provided with an annular, upper rim 129 which provides adequate clearance for the lower end of the ram. The.* upper and lower clamps may be attached together and installed in the upper end of nose piece N in a conventional manner.

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Claims

1. An impact tool comprising two flywheels (F,F') mounted within a housing (H) for rotation in opposite directions, a ram (R) disposed between the flywheels, means for causing the periphery of the flywheels to engage the ram, the ram being movable longitudinally by engagement with the rotating flywheels, a drive assembly (54-59), and a drive coupling (62,65,21 ,62'65' ,21 ^♦) for connecting the drive assembly to drive the flywheels characterised in that the drive assembly comprises a si _*ngle motor (54) arranged to drive both flywheels (F,F') through said drive coupling, and said drive coupling can be disconnected from the flywheels to permit the flywheels to rotate under their own inertia before they engage the ram (R) .

2. An impact tool according to claim 1, characterised in that said drive coupling comprises first pulleys (62,62') each associated with a separate one - of the flywheels (F,F') and rotatably mounted on the housing, second pulleys (21,21') each secured to a separate one of the flywheels for rotation therewith, and two V-shaped belts (65,65') each connecting one of said first pulleys (62,62') to the associated one of said second pulleys (21,21'), each of said second pulleys having a compound groove for accommodating the belt, the compound groove comprising an inner V-shaped portion (66) for close engagement with said belt when the latter is tight, and a second portion having side walls (67) which are spaced apart far enough to retain the belt within the groove but without transmitting drive to the pulley when the belt is slack, the flywheels being mounted on supports (13,13') mounted on the housing and movable to bring the flywheels into and out of engagement with the ram (R) and simultaneously to move the second pulleys (21,21') to release the drive coupling by slackening the belts, the means for disconnecting the drive coupling comprising rods (15) connected to the respective supports (13,13') and movable by engagement of the tool with a workpiece to move the supports (13,13') against return springs (35) in a sense to slacken the belts (65,65').

3. An impact tool according to claim 1 or claim 2, characterised in that the sides of the ram engageable with the flywheels are provided with a surface formed by a natural fiber embedded in a plastic or rubber.

4. An impact tool according to any preceding claim characterised in that the means for returning the ram 28

after an impact comprises a resilient cord (87) connected between the housing (H) and the ram (R) and extending within a longitudinal groove (86) in the ram.

5. An impact tool according to claim 4, characterised in that the-, ram is provided with a pyramidal rearward end (85), a soxxket shaped to receive said pyramidal end of the ram is located at the end of the return stroke of the ram, and a bumper (122) fprmed of a resilient material is located at the end of the forward stroke of the ram.

6. An impact tool according to claim 4, characterised by a cap mounted on the housing for securing the cord to the housing but removable from the housing to permit the cord and the ram to be removed as a unit when replacement of the ram or cord is desired.

7. An impact tool according to claim 5 or claim 6, characterised by a plate having an aperture through which the rearward end of the ram can move for engagement with the bumper, - the plate forming an anchorage for the end of the resilient cord.

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