US3020789A - Predetermined torque release hand tool - Google Patents

Description

Feb. 13, 1962 E. F. ETzKoRN 3,020,789

PREDETERMINED TORQUE RELEASE HAND TOOL Filed April l1, 1960 3 Shee'bS-Sheet 1 Feb. 13, 1962 E. F. ETzKoRN 3,020,789

PREDETERMINED ToRQuE RELEASE HAND Toor.

Filed April 11, 1960 s sheets-sheet 2 Feb. 13, 1962 E. F. ETzKoRN PREDETEIRMINED TORQUE RELEASE HAND TOOL 3 Sheets-Sheet 3 Filed April l1, 1960 E BY United States Patent() 3,020,789 PREDETERMINED TORQUE RELEASE HAND TOOL Elmer F. Etzkorn, Park Ridge, lll., assignor to Skil Corporation, Chicago, Ill., a corporation of Delaware Filed Apr. 11, 1960, Ser. No. 21,269 11 Claims. (Cl. 81-52.4)

This invention relates to innovations and improvements in tool attachments which upon being attached to a suitable power tool can be used for driving screws, running nuts, etc.

Tool attachments of this type are known and cornmerically available. In general, they have a sleeve-like or tubular casing or housing with the rear end adapted to be screwed on or otherwise attached to the forward end of a power tool such as an electric drill and with the front end arranged to receive a tool bit for driving or tightening a fastener element. When used for driving screws, a screw driver bit is used and when used for running nuts, a suitable socket bit is used.

Usually, these tool attachments are arranged to be driven from the rear, as by means of a shaft projecting therein from the power tool. There is suitable mechanism on the interior of the casing including a spindle, clutches, latching means, springs, etc., so that when the tool is applied to drive a fastener element, such as a screw, as soon as the driver has engaged the head of the fastener and pressure or a thrust is applied, the clutches engage and power is supplied to drive the driver. Driving continues until the screw or nut is tightened to a predetermined torque. When this predetermined torque is reached and exceeded, then the interior mechanism kicks out so that driving torque is no longer applied to the tool bit and the mechanism runs in a free wheeling or unclutched manner until such time as pressure or thrust on the fastener is released, whereupon the mechanism recycles. It is known to make such tool attachments so that they are non-ratcheting whereby when the predetermined torque has been applied and exceeded and the tool kicks out the mechanism runs completely free with not even a slight dragging torque being applied to the driver bit or other tool.

The object of the present invention, generally stated, is to provide tool attachments of the foregoing type, which are competitive or lower in price than the presently available devices, and which embody several improvements which enhance their utility and eiciency.

More specifically, the object of the present invention is the provision of new and improved tool attachments of the foregoing type characterized by improvements and innovations in the following respects and features: each has a hollow spindle which shifts co-axially in certain phases of operation; there is shifting or co-axial movement within the casing of both the tool bit and also the spindle; the only moving parts in the idling condition are the torque clutch elements; the latching mechanisms for the anti-ratcheting feature includes a spool member which is slidable within the hollow spindle and acted upon from opposite ends by separate springs; the torque clutch includes camming means tending to separate the clutch elements which are in the form of balls permanently retained in sockets in oneclutch member and projecting into slanting holes or pockets in the opposite clutch member whereby the balls tend to cam out of such holes with less torque in the driving direction than in the back-olf direction; and, the torque adjustment for loading the main torque spring or the torque control spring is of simplified and improved construction.

Certain other objects of the invention will, in part, be obvious and will in part appear hereinafter.

For a more complete understanding of the nature and ice scope of the invention reference may now be had to the following detailed description thereof, taken in connection with the accompanying drawings, wherein:

' FIG. 1 is a side elevational view showing a known type of power tool with a pistol grip, and having a tool attachment constituting one embodiment of the present invention screwed to the front end thereof;

FIG. 2 is a longitudinal sectional view on enlarged scale, certain parts being shown in elevation, through the tool attachment element shown in FIG. v1, the parts being shown in their condition when the tool attachment is idling and the tool bit is not in the engaged or driving condition;

FIG. 3 corresponds to FIG. 2 but shows the relationship of the parts when the driver bit is engaged with a screw and the bit is being driven by the tool attachment;

FIG. 4 corresponds to FIG. 2 but shows the conditions of the parts the instant the predetermined torque has been exceeded and the device kicks out;

FIG. 5 corresponds to FIG. 2 but shows the conditions of the parts when they are latched in the free wheeling, non-ratcheting condition but with the tool bit still engaging a screw; v

FIG. 6 is a view on line 6-6 of FIG. 2;

FIG. 7 is a view on line 7-7 of FIG. 2;

FIG. 8 is a detailedv section on line 8-8 of FIG. 7;

FIG. 9 is a detail section on line 9--9 of FIG. 7;

FIG. 10 is a view on line 10-10 of FIG. 2; and

FIG. 1l is a view on line 11-11 of FIG. 3.

Referring to FIG. l of the drawings, a tool attachment representing one embodiment of the invention is designated generally at 5 in its attached condition to the power take-off connection of a power tool indicated generally at 6. The power tool 6 is of known type and does not itself form a part of the present invention. The power tool 6 has an electric motor within a housing which includes a pistol grip handle 7, and a trigger control switch member 8. An electric conductor cord by which the motor is connected to a source of electric power is designated at 9 entering the underside of the handle 7.

The forward end of the power tool 6 has an interiorly threaded power take-off opening 10 (FIG. 2) into which an adapter 11 is screwed. The interially threaded rear end cup portion 12 of the tool attachment 5 is screwed onto the adapter 11 as shown in FIG. 2. A drive shaft 13 projects from the front end of the tool 6 into the rear end of the tool attachment 5 and serves to drive this attachment in a manner to -be described in detail in connection with FIGS. 2-5.

Referring to FIG. 2, the tool attachment S has a sleevelike or tubular casing or housing 14 which includes the rear end attaching cup portion 12. Desirably, the exterior of the rear end cup portion 12 is provided with a band of knurling as indicated in FIG. 1 to facilitate attachment and removal by hand. At the front end, the casing 14 is deformed so as to provide an inturned flange 15 which serves to provide an inner shoulder or abutment face and an exterior shoulder and abutment face.

A key component of the tool attachment 5 is a hollow spindle 16. The spindle 16 is co-axially supported within the casing 14 and is co-axially shiftable in the operation of the tool attachment 5 as will be described. The spindle 16 is slidably journalled for rotation and co-axial movement at its front end in a bearing 17 in the form of an inturned ange on the inner end of a hollow or tubular threaded member 18 which also constitutes a component of the front end assembly means for adjusting the compression on a torque control spring 20.

At its rear end the hollow axle 16 is journalled for rotation and longitudinal movement in the rear member 21 of a torque control clutch designated generally at 22. The rear member 21 constitutes the power receiving member of this clutch and the front clutch member 23 constitutes the driven member. Both clutch members 21 and 23 are provided with co-axial bores which accurately fit the rear end of the spindle 16.

The forward end of the power tool shaft 13 is journalled in the inner race of a ball bearing 24 the outer race of which fits within a counter-bore in the adapter 11 and against an inner retainer ring nut 25 which is screwed into the casing end 12. The torque control clutch 22 is suspended between a rear ball bearing ring 26 and a front ball bearing ring 27. Both clutch members 21 and 23 are continually biased or urged toward the rear of the casing by the torque control spring 20, thereby maintaining the suspension of the clutch 22 between the ball bearing races 26 and 27.

The torque control spring 20 is under compression and is stationary within the casing 14. At the rear end it bears against a at ring member 28 which presses against the bearing race 27. At the front end, the spring 20 bears against a pressure adjusting nut 30 which is threaded on the inner end of the hollow screw member 18 and which is dimensioned to fit slidably within the casing 14. This nut 30 is provided with at least one longitudinal groove 31 in the outer surface which receives a detented portion 32 of the casing 14. This arrangement prevents the nut 30 from turning but allows it to move longitudinally within the casing. It will be seen that by turning the hollow screw member 18 it is possible to longitudinally adjust the position of the nut 30 and thereby adjust the degree of compression on the torque control spring 20.

The hollow screw member 18 has a circumferential ange or shoulder 33 which serves as a shoulder for bearing against the inner face of the front casing flange 15. The forward end 34 of the sleeve member 18 is provided with at least two opposed at surfaces for purposes of receiving a wrench to turn the member 18. Adjustment in any particular position is maintained by means of a jam nut 35 which fits over the outside of the member 18 and screws up against the front end of the casing as shown. It will be seen that by loosening the jam nut 35, rotation of the sleeve member 18 will produce shifting of the inner nut 30 either forwardly or rearwardly. After adjustment has been made the jam nut 35 is then tightened. The compression spring 20 Vserves to maintain the front end assembly in the relationship shown with the circumferential ange 33 pressing against the inturned flange 15 on the casing.

Returning to the torque control clutch 22 (FIG. 2), cam means are provided for drivingly interconnecting the power-receiving clutch member 21 with the driven clutch member 23. The preferred Iform of this cam or camming means comprises three bearing balls 36-36 disposed between the opposing faces of the clutch members. The balls 36 are set more than half way in their equispaced recesses 37-37 provided therefor as shown in FIG. 2. Normally the driven clutch member 23 is in the closed position and juxtaposed to clutch member 21. In`

the rear face of the driven clutch member 23 there are six equi-spaced dimples or pockets 38 (FIG. 7), these being shallower than the pockets 37. It will be seen that when torque is applied between the clutch members- 21 and 23 there will be a tendency for the balls 36 to cam out of the recesses 38 since they are shallower than the recesses 37. The greater the torque, the greater this camming tendency.

While there are two sets of the shallow recesses 38 each of which will mate with the deep recesses 37, preferably, the pockets or recesses 38 are not co-axially aligned with the straight recesses 37. On the contrary, the recesses 38 are preferably drilled on a slant or angle as shown in FIG. 8 using a cutting tool having a frustoconical shape and held so that one Side 419i each recess 38 is vertical with respect to the face of the clutch member 23 and the opposite side 40 is slanted. This means that with the tool attachment 5 designed to drive screws or tighten nuts having right-hand threads so that the moving parts including the spindle 16 turn in a clockwise direction when viewed from the rear, the pockets 38 are so inclined that the clockwise driving walls 40 thereof are outwardly slanted from the vertical thereby facilitating the ease with which the balls 36 can be cammed out or rolled out of the shallow pockets 38.

Since, the opposite driving walls 41 of the recesses 38 are straight or vertical, a greater force or torque is required to cam the balls 36 out of the pockets 38 in the counterclockwise direction than in the driving or clockwise direction. This arrangement of the opposite driving walls of the pockets 38 is of considerable practical importance in that after a fastening element, such as a screw or nut has been driven to a predetermined torque, it is not infrequent that the fastening element has to be removed or backed oit. Normally, it requires greater baclooi or reverse torque to remove a fastening element than the torque to which it was driven. Accordingly, by having the respective driving walls 40 and 41 of the pockets 38 slanted in the manner described, the torque control clutch 22 automatically supplies a greater removing torque in the counter-clockwise direction than driving torque in the clockwise direction. Accordingly, it is merely necessary to reverse the motor in the power tool to remove a fastening element after it has been driven and no readjustment in torque has to be made.

ln addition to torque control clutch 22, the tool attachment 5 also incorporates a positive clutch indicated generally at 42. The positive clutch 42 is so-named since it is engaged in a positive manner in contradistinction to the torque control clutch 22 which is normally engaged except when a predetermined torque is exceeded whereupon it becomes temporarily disengaged. The clutch 42 comprises a collar-like member 43 which accurately ts the mid-portion of the spindle 16 and is longitudinally slidable thereon, and which has three equi-spaced clutch teeth 44 projecting from the rear end thereof. The teeth 44 are for mating or meshing engagement with three equi-spaced teeth 4S carried on the front side of the driven clutch member 23. The sets of clutch teeth 44-44 and 45-45 are shown in driving engagement in FIG. 1l.

The collar like clutch member 43 in addition to carrying the teeth 44 also serves as the means for transmitting driving torque from the torque control clutch 22 to the spindle 16. This is accomplished by having the member 43 provided on its interior with three equi-spaced longitudinal grooves 46 (FIG. 10) which receive the outer halves of sets of balls 47-47. The inner halves of the balls are retained in three grooves 48 which extend longitudinally on the outer surface of the spindle 16. It will be seen that this ball-groove arrangement is the equivalent of a plurality of splines between the collar-like member 43 and the spindle 16. Accordingly, whenever the collarlike member 43 is rotated it carries the spindle 16 with it. However, the ball-groove arrangement permits free and easy sliding movement between the spindle 16 and the member 43.

In addition to the three equi-spaced grooves 46, the interior of the collar-like member 43 is provided at the rear or right side with a counter-bore or relief 50 (FIG. 3) which in operation of the tool attachment 5 4are periodically engaged by three latching balls 51.

The collar-like clutch member 43 is continually urged to the rear toward a closed or engaging direction, by means of a spring 52 which surrounds the spindle 16 and is maintained under compression between the front side (left end) of the collar member 43 and the rear side of a circumferential flange or shoulder 53 on the spindle 16. It will be seen that when the inner (left) ends of the grooves 46 engage the front or left-hand ball 47 therein, and the right-hand or rear ball engages the rear or right end of a groove 48, the collar 43 is not permitted to move further to the rear or right relative to spindle 16 under the inuence of the spring 52. In this manner the clutch member 43 is maintained out of engagement with the clutch teeth 45 formed on the fron-t side of the driven clutch member 23 when the spindle 16 is in its forward or left-most position;

The front or left-hand end of the spindle 16 constitutes the tool bit holder. Thus, this end may be hexshaped on the interior to provide a socket for receiving the hex-shaped end 54 of a screw driven bit, indicated generally at 55. Since the hex-shaped inner end S4 lits slidably within the hex-shaped hollow end 56 of the spindle 16, rotation of the spindle produces rotation of the tool bit 55. The inner telescoping movement of the tool bit 55 in the spindle 16 is limited by means of the front or left-hand edge of an inner shoulder 57 formed on the interior of the spindle 16. That is, when the rear end of the tool bit 55 engages the forward edge of the shoulder 57 the tool bit cannot be shoved or slid further into the spindle and any additional movement of the tool bit 55 to the rear will have to carry the spindle 16 with it.

The tool bit 55 is temporarily retained in the forward end of the spindle 16 against accidental removal by means of a detent ball 58 which tits in a necked portion 60 of the tool bit. The ball 58 fits through an opening 61 in the end of the spindle 16 which is covered by a garter-like spring or clip 62 retained in a groove 63. This arrangement for retaining the tool bit 55 in place against accidental removal, but in a way which permits its intentional removal, may be replaced by other known retention arrangements.

Preferably the forward end of the Itool bit 55 is sheathed within a finder device of known type including a sheath 64 which is slidable within the outer end of the hollow threaded member 18. The forward end of the sheath 64 is provided with an outwardly flared opening 65 which serves as a guide for placement over a fastener such as a screw head. The sheath 64 is telescopically retained in the member 18 by means of a detent 66 which projects through an opening in the side of a member 18 and extends downwardly into a groove 67 in the outer wall of -the sheath 64. The detent 66 is continually pressed inwardly under the force and urging of a garter spring or clip 68 retained in a groove 70. The sheath 64 is continually urged to its outer position by means of a compression spring 71 which is retained between the forward face of the bearing shoulder 17 and the rear end of the sheath 64. The right-hand or inner end of the slot 67 constitutes a stop which prevents the spring 71 from pushing the sheath 64 completely out of the end of the member 18.

The hollow spindle 16 contains mechanism on the interior for the purpose of actuating the latching balls 51 into the latching recess 50 in the collar-like clutch member 43. This mechanism comprises a plunger 72 which has a shoulder 73 on its inner or right end which ts the inner bore of the spindle 16 and which engages tne inner side of the shoulder 57 so as to stop the outer or forward movement of the plunger 72.

On its inner or right-hand end the plunger 72 carries a plunger rod 74 on which slidably its a spool member 75 the right-hand end of which is reduced in diameter so as to provide a truste-conical cam surface 76 intermediate the reduced end portion and the full diameter portion which is sized to slide within the bore of the spindle 16. At the inner or right-hand end the rod 74 slidably projects through a washer member 77 which lits against the inner counter-bored rear end of the spindle 16. The collar 77 is held in place by means of a compression spring 78 into the outer end of which is inserted the stem portion of a button. The outer rounded surface of the button 80 is engaged by the inner end of the power shaft 13 as shown. The spring 78 also serves the purpose of biasing the 6 spindle 16 to the front or left so as to normally hold the shoulder 53 on the front end in engagement with the bearing shoulder 17 of the member 18. The tip end of the rod 74 is provided with a small garter spring 81 which holds the washer 77, spring 83, spool 75 and spring 82 in place on the rod 74.

The spool member 75 is engaged from both ends by compression springs. From its front or left-hand end it is engaged by one end of a compression spring 82 which lits over the rod 74 with its opposite end engaging the rear or right-hand side of the plunger shoulder 73. The rear or right-hand end of the spool member 75 is engaged by one end of a compression spring 83 which lits over the rod 74 and which is compressed from its opposite end by means of the washer 77. The spring 82 is under greater compression than the spring 83 when the parts are in the relative positions shown in FIGS. 3-5 so that the spool member 75 is biased or resiliently pushed to the rear or right.

'In use, the tool attachment \5 operates as follows: Assuming that the tool attachment is in place on a power tool 6 as shown in FIG. 1, the trigger 8 is pressed so as to energize the motor and thereupon the power shaft 13 is driven in a right-hand direction so that the powerreceiving clutch member 21 is driven in a clockwise direction as viewed from the rear, i.e. looking toward the left as shown in FIG. 2. The driven clutch member 23 is also rotated with member 21 through the camming balls 36 but otherwise the mechanism on the interior of the housing or casing 14 is all stationary. This is important in that it keeps wear to a minimum, and also minimizes the drag placed on the power tool.

The tool is now manipulated so that the finder 64 approaches the head of a screw for telescopic movement over it. Upon pressing of the tool attachment against the screw, the head enters the opening 65 and centers therein with a result that further pressure causes the nder sheath 64 to move to the rear against the force of the compression spring 71 to the position shown in FIG. 3. When the tip of the driven bit 55 engages the screw slot, additional pressure causes the tool bit 55 to move rearwardly with the sheath 64 with the result that the rear end 54 of the tool bit engages and depresses the plunger 72, thereby unseating it and moving it rearwardly within the hollow spindle 16.

Up to this point the torque control clutch 22 has been rotating but other parts of the mechanism remain stationary. However, when the inner end 54 of the tool bit engages the shoulder 57 further pressure on the screw causes the spindle 16 itself -to shift rearwardly to the right against the force of the compression spring 78. As this shifting of the spindle 16 occurs it permits each set of balls 47-47 to follow the shifting movement, and the compression spring 52 forces the positive collar-like clutch member 43 to also shift to the rear.l Upon sufcient shifting movement it will be seen that the teeth 44 on the collar-like member 43 engage the teeth 45 on the driven clutch member 23 which is rotating. Preferably the driving faces of the clutch teeth on the positive clutch 42 are so slanted that once there is engagement the teeth tend to cling together rather than to separate. After the teeth 44 bottom with the front face of the driven mem- Iber 23 the spindle 16 is still permitted to move somewhat to the rear or right if continued pressure is exerted.

Since the spool member 75 cannot move to the right because it is restrained by the balls 51, the rearward movement of the plunger 72-serves to compress the spring 82 to the condition shown in FIG. 3 and spring 78 is also compressed.

Withthe positive clutch 42 engaged it will be seen that the spindle 16 is now driven and in turn this drives the driver bit 55 and the screw or other fastener. The driving continues until such time as the fastener is driven to the point where the torque exceeds the predetermined torque for which the clutch 22 is set by means of adjusting the compression or pressure on the torque control spring 20. When this torque is exceeded the balls 36 cam out of the set of shallow recesses 38 in which they happen to be in by rolling out over the forwardly inclined sides 40 (FIG. 8). The position of the parts when this camming out occurs is illustrated in FIG. 4. The main result of the camming out is the movement of the driven clutch member 23 to the front or left against the force of the spring 20. This shifting movement also causes the collar-like positive clutch member 43 to shift to the front or left, the distance of movement being sufficient to bring the latch recesses 50 over the latch balls 51 which move into the recesses 50 as shown in FIG. 4. The balls 51 are snapped out when the latch recess 50 permits it to be, by reason of the camming surface 76 on the spool member 75 which is being urged to the rear by the compressed spring 82.

The parts assume the condition illustrated in FIG. 4 in an instant and remain in this condition only an instant.

As soon as the balls 36 are rotated to bring them into mating engagement with the next set of shallow recesses 38 in the now stationary driven clutch member 23, the driven clutch member immediately snaps closed with the clutch member 21 and is again driven with it. The condition of the parts when the driven clutch member 23 closes with the power-receiving clutch member 21 while the positive clutch member 43 is retained in its caught or inoperative position is illlustrated in FIG. 5. It should be noted that the distance which the driven clutch member 23 and the collar-like clutch member 43 shift when the balls 36 cam out of the pockets 38 is greater than the length of the clutch teeth 44 with the result that the clutch teeth 44-44 and 45-45 are completely separated when the member 23 resumes its engaged position. Hence there is no dragging movement whatever placed on the spindle 16. As long as pressure is maintained on the tool attachment and against the screw head the parts will stay in the position shown in FIG. wherein only the torque control clutch 22 is operating and all of the other parts are stationary. Thus there is no ratcheting action of the tool once it has kicked out after the predetermined torque has been exceeded.

Upon release of the pressure against the fastener head the springs cause the parts to resume the positions shown in FIG. 2. Thus, as soon as the plunger 72 is permitted to recede by moving forward on the spindle 16, and when the spindle itself moves to the front to its normal position, the spool member 75 will be no longer retained in the position shown, and each latch ball 51 will be forced into its normal inner position by the collar 43 releasing the collar-like clutch member 43 so that it is only retained from closing by means of the sets of balls 47.

It will be appreciated that certain changes may be made in the embodiment of the invention above-described and shown in the drawings, and that other embodiments of the invention may be made, Without departing from the spirit and scope of the invention as reflected in the appended claims.

I claim:

1. In a tool attachment of the class described for driving and tightening rotary fastener elements, in combination: a sleevelike casing; a hollow spindle the front end of which constitutes a tool holder; front bearing means in said casing for supporting the front end of said spindle for rotation and co-axial sliding movement within said casing; a main torque clutch in the rear portion of said casing comprising a power-receiving clutch member, a driven clutch member, and completely disengageable camming means normally directly interconnecting said clutch members and tending to separate said driven clutch member from said power-receiving clutch member, said clutch members having co-axial spindle-receiving openings therein with the rear end of said spindle being slidable and rotatable therein; spring means within said casing resiliently urging said driven clutch member into 8 driving engagement Vand resisting separation by said cai-nf ming means until a predetermined torque value is exceeded; and, secondary clutch means for drivingly connecting said power-receiving clutch member with said hollow spindle when said tool is driving a fastener element.

2. The combination called for in claim 1, wherein said camming means comprises ball members rotatably disposed in relatively deep individual pockets in the clutch face of one of said members and rotatable in individual shallower mating recesses in the other of said members.

3. The combination called for in claim 1 wherein said spring means comprises a compression spring compressed between stationary parts, and a ball bearing ring is interposed between the front face of said driven clutch member and the stationary part adjacent thereto.

4. A tool attachment of the class described for driving and tightening rotary fastener elements, comprising: a sleeve-like casing; a hollow spindle the front end of which constitutes a tool holder; front bearing means in said casing for supporting the front end of said spindle, for rotation and co-axial sliding movement within said casing; a torque clutch in the rear portion of said casing comprising, a power-receiving clutch member, a driven clutch member in front of said rst clutch member, and camming means normally interconnecting said clutch members in driving relationship and tending to separate said driven clutch member from said power-receiving clutch member, said clutch members having spindle-receiving co-axial openings therein with the rear end of said spindle being rotatable and slidable therein; first spring means within said casing resiliently urging said driven clutch member into driving engagement and resisting separation and disengagement by said camming means until a predetermined torque value is exceeded; a positive clutch for driving said spindle, comprising iirst engaging means on the front side of said driven clutch member and a collar-like clutch member slidably mounted on said spinde in front of said driven clutch member and having second engaging means on the rear thereof for interengaging said rst engaging means; coupling means interconnecting said spindle in driven relationship with said collar-like clutch member; second spring means resiliently urging said collar-like clutch member into driven re'ationship with said driven clutch member; and latch means for holding said collar-like clutch member temporarily out of engagement with said driven clutch member against the force of said second spring means, said latch means being actuated by tool pressure and being tripped on release of tool pressure.

5. A tool attachment of the class described for driving and tightening rotary fastener elements, comprising: a sleeve-like casing; a torque control spring in the forward portion of said casing; means for adjusting the compression on said torque control spring comprising a longitudinally movable nut, means preventing turning of said nut, a hollow screw member threadedly engaging said nut and having a portion projecting from the front end of said casing for manual adjustment; a torque clutch disposed in the rear portion of said casing comprising, a power-receiving clutch member, a driven clutch member in front of said first clutch member, and cam means normally interconnecting said clutch members in driving relationship and tending to separate said driven clutch member from said power-receiving clutch member, said clutch members having center bores co-axial with said casing; a hollow spindle, the front end of which constitutes a tool holder and is journalled and longitudinally shiftable in said hollow screw member and the rear end of which is journalled and longitudinally shiftabfe in said bore in said power-receiving clutch member with said driven clutch member being slidable and rotatable thereon; said torque control spring compressed between said nut and said driven clutch member resiliently holding the latter in driven engagement with said power-receiving clutch member until a predetermined torque value is exceeded; a positive clutch for driving said spindle comprising, first engaging means on the front face of said driven clutch member, and a collarlike clutch member slidably mounted on said spindle in front of said driven clutch member and having second engaging means on the rear face thereof for interengaging said first engaging means; coupling means interconnecting said spindle in driven relationship with said collar-like clutch member and allowing co-axial movement therebetween; second spring means surrounding said spindle and compressed between the front side of said collar-like clutch member and stop means on said spindle for resiliently urging said collar-like clutch member into driven relationship with said driven clutch member; third spring means resiliently urging said spindle in its forward position; and, latching means for holding said collar-like clutch member temporarily out of engagement with said driven clutch member against the force of said second spring means comprising, a spool member co-aXially slidable within the mid-portion of said spindle and having a cam surface at the rear end thereof, a plunger member in the front end of said spindle and engageable by the rear end of a tool held therein, fourth spring means compressed between said spool member and said plunger urging said spool member to the rear and said plunger to the front, and at least one cammed latch member retained in a window in said spindle member covered by said collarlike clutch member with a latching recess in alignment therewith, said latch member being urged out through said window when said plunger is pressed in by the tool and moving out to its latching position when said collarlike clutch member moves suiiiciently toward the front for said latching recess to pass over said window, and said latch member remaining in the latching position until tool pressure on said plunger is released.

6. The tool attachment of claim wherein said means for preventing turning of said longitudinally movable nut comprises a detent in said casing and a detent-receiving slot in the surface of said nut aligned with the axis of said casing.

7. The tool attachment of claim 5 wherein said cam means drivingly interconnecting said torque control clutch members comprises a plurality of bearing balls retained for rotation in relatively deep sockets in the face of one of said clutch members with the projecting portions of said balls received in relatively shallow mating sockets in the face of the other clutch member, the side Walls of said shallow recesses being inclined in the direction of driving rotation to facilitate camming out of said balls and the opposite side walls being approximately straight.

8. The tool attachment of claim 5 wherein said coupling means between said collar-like positive clutch member and said spindle comprises a plurality of splining balls retained partly in grooves in the surface of said spindle and partly in grooves in said collar all of said grooves being aligned with said spindle, said grooves having end walls allowing limited relative co-axial movement of said collar-like clutch member and said spindle.

9. The tool attachment of claim 5 wherein said third spring means comprises a compression spring disposed within a counterbore in the rear end of said spindle and a button seated in the rear end of said spring for engagement by the end of a drive shaft projecting into said powerreceiving clutch member.

10. The tool attachment of claim 5 wherein said plunger member has a rod projecting rearwardly on which said spool member is slidable, and there is a lifth spring cornpressed between the rear end of said spool member and a backing member on the rear end of said spindle.

11. In a tool attachment of the class described for driving and tightening rotary fastener elements and the like, clutch means comprising a power-receiving clutch member, a driven clutch member, means supporting said clutch members for co-axial rotation with at least one being co-aXially shiftable relative to the other, the opposing face of one of said clutch members having a plurality of relatively deep sockets therein for receiving bearing balls so that less than half the surfaces of said balls project therefrom, the opposing face of the other of said clutch members having a plurality of relatively shallow sockets therein for receiving said balls so that more than half the surfaces of said balls projected therefrom, a plurality of balls retained in said relatively deep sockets, and spring means urging said clutch members toward each other, the driving side walls of said shallow recesses being outwardly inclined in one direction of rotation of said clutch and being overhung in the opposite direction of rotation.

References Cited in the le of this patent UNITED STATES PATENTS 1,855,456 Miller Apr. 26, 1932 1,881,633 Johnson Oct. 11, 1932 2,263,709 Van Sittert Nov. 25, 1941 2,743,636 Shal May 1, 1956 2,857,997 Traybill Oct. 28, 1958 2,886,075 Skoog May 12, 1959 2,923,191 Fulop Feb. 2, 1960 2,948,173 Herrmann Aug. 9, 1960

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