Abstract:
A torque-limiting mechanism is provided for use in a variety of torque-applying tools. The mechanism includes a handle defining a housing in which are disposed a slip gear and a fixed gear. The fixed gear is attached to the housing while the slip gear is attached to drive body extending outwardly from the housing and engageable with an item to be turned utilizing the tool. The slip gear and the fixed gear are connected by teeth disposed on each gear and by ball bearings disposed within recesses located on each gear that are pressed into the recesses by a force exerted on the gears by a number of spring members disposed between an enclosed end of the housing and the fixed gear. The amount of force exerted by the springs on the gears can be varied as necessary, thereby allowing the amount of torque required to enable the slip gear to move with respect to the fixed gear to be set where desired. The use of the ball bearings as the engagement members between the fixed gear and the slip gear provides a smooth transition between positions when the slip gear rotates with respect to the fixed gear, and greatly reduces the amount of friction forces acting on the torque-limiting mechanism, such that the force controlling the operation of the mechanism is solely provided by the springs and easily predictable and controllable. Further, the teeth, due to the angled locking surfaces formed in the teeth, enable the gears to only rotate with respect to one another in one direction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. application Ser. No. 11/153,286 filed on Jun. 15, 2005, which claims priority from U.S. provisional application Ser. No. 60/580,160 filed on Jun. 16, 2004, and each is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to tools used to rotate and/or drive fasteners, and more specifically to a torque-limiting mechanism for use with these types of tools.  
       BACKGROUND OF THE INVENTION  
       [0003]     With regard to hard-held and powered tools used to drive features into or out of an item, especially those used in medical applications, there are several common problems associated with tools incorporating existing torque-limiting devices. These problems include loss of consistent torque value after repeated autoclave sterilization cycles, internal components breaking due to high forces and loads on internal cams and gears, inconsistent torque values due to wear on internal components, a strong recoil or snap when set at higher torque values, and difficulty in servicing the mechanism.  
         [0004]     More particularly, as shown in  FIGS. 20 and 21 , in prior art torque-limiting devices, the devices include gears  100 ,  101  including a number of generally angular teeth  102  disposed along one side of the gears  100 ,  101 . Each tooth  102  includes an angled sliding surface  104  and a flat, vertical locking surface  106  located between the sliding surfaces  104  of adjacent teeth  102 . These gears  100 ,  101  are positioned in the mechanism with the teeth  102  facing one another in a manner where one of the gears  100  can rotate with respect to the other gear  101 . This is due to the construction of the mechanism in which one gear  100  is fixed to mechanism and the other gear  101  can move with a drive body (not shown) for the tool to provide the torque-limiting function. When the tool incorporating the gears  100 ,  101  is subjected to a torquing force greater than a preset maximum, the moveable gear  101  rotates with respect to the fixed gear  100 , such that the sliding surfaces  104  of the opposed teeth  102  slide against one another and urge the fixed gear  100  against a spring member (not shown) that biases the gears  100 ,  101  towards one another. The movable gear  101  can continue to rotate in response to the excessive torque until the flat locking surface  106  on the opposed teeth  102  are moved past the edges  105  of the sliding surfaces  104 . In this position the gears  100 ,  101  move or snap back towards one another due to the bias of the spring member, and the respective flat surfaces  106  come into contact with one another to secure the gears  100 ,  101  in a camming position.  
         [0005]     In order to enable the prior art mechanism to provide a closely controllable amount of torque resistance, the mechanism requires that the forces biasing the gears  100 ,  101  towards one another from: 1) the spring member; 2) the surface friction provided by the contact of the angled surfaces  104  on the opposed teeth  102  sliding with respect to one another; and 3) the drag of the gears  100 ,  101  on a housing (not shown) for the mechanism all be known and properly maintained. To enable the surface friction and drag to be controlled, a proper amount of lubrication is required to be present both on the teeth  102  and on the back of the rotatable gear  101  in contact with the housing in order to maintain the constant drag forces on the angled surfaces  104  and the movable gear  101 . However, due to the cleaning and/or sterilization of tools including devices of this type, each sterilization cycle causes an inherent loss of the lubrication in the mechanism. As a result, the amount of surface friction and drag between the gears  100 ,  101  changes over time. This in turn drives the torque values up such that a consistent amount of torque resistance is not provided by the device.  
         [0006]     Further, as a result of the particular shape of the teeth  102  on each gear  100 ,  101  the rotation of the gear  101  results in the locking surfaces  106  on each gears  100 ,  101  “snapping” into engagement with one another in both the axial and circumferential directions after passing one another. This movement of the locking surfaces  106  into engagement with one another necessarily creates vibrations in the mechanism which are transmitted through the mechanism and the tool incorporating the mechanism to the fastener and/or the person on which the device is being utilized. In many situations, these vibrations are highly undesirable. Also, the stress exerted on the surfaces  106  as they strike one another also leads to fracturing or chipping of the teeth  102 , lessening the useful life of the mechanism. When the teeth  102  are chipped, this additional material can also collect on the sliding surfaces  104  of the teeth  102 , thereby causing even more inconsistent torque values for the mechanism.  
         [0007]     In addition, prior art torque limiting devices include one piece calibration nuts (not shown) that engage the spring members of the mechanism to calibrate or set the amount of torque necessary to rotate the gears  100 ,  101  with respect to one another. The calibration nut is normally secured to the mechanism by adhesives, by pairs of jam or locking nuts to reduce space and/or a mechanical interruption of threads to which the calibration nut is mounted. The design of each of these prior art calibration nut assemblies increases the complexity of the overall mechanism, and provides an additional manner in which the mechanism can break down.  
         [0008]     Due to the multitude of problems associated with prior art torque limiting devices, it is desirable to develop or design a torque-limiting device which greatly reduces each of the problems associated with prior art devices at this time.  
       SUMMARY OF THE INVENTION  
       [0009]     According to a primary aspect of the present invention, a torque-limiting device for use in hand-held and power tools is provided in which the torque-limiting device includes a number of rolling ball bearings disposed partially within opposed pairs of recesses located in a pair of opposed gears that, in conjunction with springs acting on the gears and ball bearings, are utilized to control the movement and resistance to movement of the mechanism. The recesses in one of the gears are connected by a raceway along which the bearings can move between recesses when the mechanism is in operation. The use of the ball bearings and a raceway on one of the gears that the ball bearings can move along between the recesses enables the mechanism to be operated in a manner that greatly reduces the amount of variation over time of the preset torque values for the mechanism by reducing the wear experienced by the internal components controlling the actuating of the mechanism, and by avoiding the significant recoil or snap experienced by prior art mechanisms. This construction also greatly reduces the effects of varying levels of friction present in prior art mechanism by using ball bearings as the main friction generating members in the mechanism. The shape of the bearings creates much less overall friction, as well as a relatively constant amount of friction over extended periods of use of the mechanism, without the need for significant amounts of lubricants within the mechanism.  
         [0010]     According to another aspect of the present invention, the ability of the mechanism to provide consistent torque values is also enhanced by the use of a split locking calibration nut that is securable to the mechanism in a simple manner, thereby avoiding the previous issues concerning the shifting of the nut and the consequent variation of the torque value applied by the mechanism. The calibration nut is threadedly engaged with a housing for the tool and with single locking nut that selectively positions the calibration nut within the housing to provide the desired amount of force against the springs that are used to determine the maximum torque level at which the mechanism will operate. By varying the position of the calibration nut, the amount of torque at which the mechanism slips can be set as desired, while the locking nut can maintain position of the calibration nut at this desired value. In addition to using a locking nut to hold the calibration nut in position, the calibration nut itself may include protrusions that are urged outwardly into engagement with the housing for the mechanism when the locking nut is engaged within the calibration nut. Thus, the calibration nut can be easily adjusted or removed in order to service the mechanism, without the need for disengaging any additional securing means, such as adhesive, or additional lock nuts as used in prior art mechanism.  
         [0011]     According to still a further object of the present invention, a mechanism is enclosed within housing having a cover secured to the housing in an easily removable manner. The cover also includes an access cap that can be removed from the cover to enable the mechanism to be serviced without having to completely disassemble the mechanism. Further, the access cap engages the cover in a manner that prevents the cover from being inadvertently disengaged from the housing while the tool including the mechanism is in use.  
         [0012]     According to still another aspect of the present invention, the gears can be formed with a number of inter-engaging locking surfaces that assist in enabling the gears to engage one another and provide the resistance to a movement of the mechanism. Each of the gears is formed with relatively shallow, sloped teeth around the periphery of the gear that are capable of mating with the similarly shaped teeth formed on the opposite gear to assist in preventing the rotation of the gears with respect to each other in one direction. However, the depth and slope of the teeth on each of the gears is shallow enough to prevent the “snapping” and vibration problems associated with prior art toothed engaging gears, as discussed previously.  
         [0013]     Numerous other advantages, features, and objects of the present invention will remain apparent from the following detailed description taken together with the drawing figures.  
     
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0014]     In the drawings:  
         [0015]     The drawings illustrate the best mode currently contemplated of practicing the present invention.  
         [0016]      FIG. 1  is a side plan view of a tool including the torque-limiting mechanism constructed according to the present invention;  
         [0017]      FIG. 2  is an end plan view of the device of  FIG. 1 ;  
         [0018]      FIG. 3  is a cross-sectional view along line  3 - 3  of  FIG. 2 ;  
         [0019]      FIG. 4  is an exploded, cross-sectional view of the device of  FIG. 1 ;  
         [0020]      FIG. 5  is an exploded, isometric view of the mechanism of  FIG. 1 ;  
         [0021]      FIG. 6  is a partially broken away, exploded view along line  6 - 6  of  FIG. 5 ;  
         [0022]      FIG. 7  is an exploded, isometric view of the mechanism of  FIG. 5  in a direction opposite  FIG. 5 ;  
         [0023]      FIG. 8  is a partially broken away, exploded view of the mechanism along line  8 - 8  of  FIG. 7 ;  
         [0024]      FIG. 9  is an isometric view of a second embodiment of the fixed gear of the mechanism of  FIG. 1 ;  
         [0025]      FIG. 10  is a top plan view of the fixed gear of  FIG. 9 ;  
         [0026]      FIG. 11  is a side plan view of the fixed gear of  FIG. 9 ;  
         [0027]      FIG. 12  is a bottom plan view of the fixed gear of  FIG. 9 ;  
         [0028]      FIG. 13  is a cross-sectional view along line  13 - 13  of  FIG. 12 ;  
         [0029]      FIG. 14  is an isometric view of the slip gear of the device of  FIG. 1 ;  
         [0030]      FIG. 15  is a bottom plan view of the slip gear of  FIG. 14 ;  
         [0031]      FIG. 16  is a side plan view of the slip gear of  FIG. 14 ;  
         [0032]      FIG. 17  is a top plan view of the slip gear of  FIG. 14 ;  
         [0033]      FIG. 18  is a cross-sectional view along line  18 - 18  of  FIG. 17 ;  
         [0034]      FIG. 19  is a cross-sectional view along line  19 - 19  of  FIG. 17 ;  
         [0035]      FIG. 20  is an isometric view of a fixed gear used in a prior art torque-limiting mechanism;  
         [0036]      FIG. 21  is an isometric view of a slip gear used with the prior art fixed gear of  FIG. 20 ;  
         [0037]      FIG. 22  is an isometric, exploded view of a second embodiment of the torque-limiting mechanism of the present invention;  
         [0038]      FIG. 23  is a side plan view of the mechanism of  FIG. 22 ;  
         [0039]      FIG. 24  is a cross-sectional view along line  24 - 24  of  FIG. 23 ;  
         [0040]      FIG. 25  is an isometric front view of a fixed gear of the mechanism of  FIG. 22 ;  
         [0041]      FIG. 26  is an isometric rear view of the fixed gear of  FIG. 25 ;  
         [0042]      FIG. 27  is a top plan view of the fixed gear of  FIG. 25 ;  
         [0043]      FIG. 28  is a cross-sectional view along line  28 - 28  of  FIG. 27 ;  
         [0044]      FIG. 29  is a side plan view of fixed gear of  FIG. 25 ;  
         [0045]      FIG. 30  is a partially broken away side plan view of a tooth of the fixed gear of  FIG. 29 ;  
         [0046]      FIG. 31  is an isometric front view of a slip gear of the mechanism of  FIG. 22 ;  
         [0047]      FIG. 32  is an isometric rear view of the slip gear of  FIG. 31   
         [0048]      FIG. 33  is a top plan view of the slip gear of  FIG. 31 ;  
         [0049]      FIG. 34  is a cross-sectional view along line  34 - 34  of  FIG. 33 ;  
         [0050]      FIG. 35  is a cross-sectional view along line  35 - 35  of  FIG. 33 ;  
         [0051]      FIG. 36  is a side plan view of the slip gear of  FIG. 31 ; and  
         [0052]      FIG. 37  is a partially broken away side plan view of a tooth on the slip gear of  FIG. 36 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0053]     With reference now to the drawing figures in which like reference numerals designate like parts throughout the disclosure, a tool including a torque-limiting mechanism constructed according to the present invention is indicated generally at  200  in  FIGS. 1-4 . The tool  200  can be virtually any type of hand-held or power-driven tool that is used to apply torque to a driven member, e.g., a fastener, but in a preferred embodiment, is a hand-held torque wrench that includes a handle  202  with a gripping part  201  operatively connected to a drive body  204  extending outwardly from the handle  202  by the torque-limiting mechanism  206 . The handle  202  is preferably formed of a suitably rigid, but relatively lightweight material, such as a light metal or plastic, to reduce the weight of the tool  200 . Also, the handle  202  can be formed to have any desired configuration, and may include on the gripping part  201  an inner portion  203   a  formed of a more rigid material, and an outer portion  203   b  of a more flexible material to increase the ease of use of the tool  200 .  
         [0054]     The drive body  204  is preferably an elongate member that is used to transfer the torque applied to the tool  200  via the handle  202 , or motor (not shown) in power-driven tool embodiments, to the fastener to be rotated, such as a screw, engaged by the drive body  204  opposite the handle  202 . The drive body  204  is formed of a generally rigid material, such as a metal or hard plastic, and is preferably circular in cross-section, but can be formed to have other cross-sectional configurations as desired. Opposite the mechanism  206 , the drive body  204  supports a connector  208 . The connector  208  can have any desired configuration for releasably retaining thereon a suitable fastener-engaging implement (not shown), but in one embodiment best shown in  FIGS. 3 and 4 , includes a locking collar  210  slidably secured to the exterior of the connector  208  by a spring  212  and retaining ring  214 . When the collar  208  is urged against the bias of the spring  212  towards the drive body  204 , a retaining ball  216  on the connector  208  is moved out of the interior of the connector  208 . This enables the implement to be inserted into the interior of the connector  208  without interference from the retaining ball  216 . When the collar  210  is released, allowing the collar  210  on the connector  208  to return to its original position due to the bias of the spring  212 , the retaining ball  216  is urged by the collar  210  back into the interior of the connector  208  into engagement with an aligned recess (not shown) in the implement, thereby securing the implement within connector  208 .  
         [0055]     Referring now to  FIGS. 3-19 , the torque-limiting mechanism  206  includes a pair of gears  218 ,  220  formed of a rigid material, such as a metal, or hard plastic that are positioned generally opposite one another within the mechanism  206 . The gear  218 , best shown in  FIGS. 5-8  is a fixed gear secured within a generally cylindrical housing  234  attached to or integrally formed with one end of the handle  202  opposite the gripping part  201 . The fixed gear  218  is preferably secured within the housing  234  by a pair of locking pins  222  that extend through the housing  234  into connection with the gear  218 . The pins  222  extend through bores  223  in the housing  234  into slots  224  formed on opposite sides of the gear  218  to prevent rotation of the gear  218  within the housing  234 . In an alternative embodiment, best shown in  FIGS. 9-13 , the fixed gear  218  can be formed with a pair of flats  252  on opposite sides of the gear  218  that are engaged with similarly shaped flat surfaces (not shown) located on the interior surface of the housing  234 . The flats  252  take the place of the pins  222  and slots  224  to hold the fixed gear  218  in position within the housing  234  to enable the transfer of torque from the handle  202  to the fixed gear  218 .  
         [0056]     The fixed gear  218  also includes a number of dimples  225  spaced around a central opening  227  in the gear  218  on one surface of the fixed gear  218 . The opening  227  can be cylindrical or can define an annular shoulder  327  therein to assist in the formation of the dimples  225 . A number of generally spherical ball bearings  226  are disposed partially within the dimples  225  and are able to rotate therein. The depth of the dimples  225  in the gear  218  is preferably sufficient to receive approximately one half of the volume of each bearing  226 , such that while the bearings  226  can rotate within the dimples  225 , the bearings  226  are each maintained within the dimples  225 . In a particularly preferred embodiment, the bearings  226 , which are formed of a rigid and smooth material, such as a metal, are formed to have a diameter slightly less than the diameter of the dimples  225 . This allows the bearings  226  to rotate more freely within the dimples  225  when the tool  200  and mechanism  206  are in use and also enables the mechanism  206  to be assembled more easily.  
         [0057]     The gear  220 , i.e., the rotatable or slip gear, is also positioned within the housing  234  immediately adjacent the fixed gear  218  between the fixed gear  218  and the gripping part  201  of the handle  202 . The slip gear  220 , best shown in  FIGS. 5-8  and  14 - 19 , is formed similarly in shape and material to the fixed gear  218 , with a central opening  227  and a number of dimples  228  spaced around the opening  227  on one side of the gear  220  that is positioned to face the dimples  225  in the fixed gear  218 . The dimples  228  receive the end of each of the bearings  226  extending outwardly from dimples  225  in fixed gear  218 , but are less deep than dimples  225  in the fixed gear  218 . The slip gear  220  also includes an arcuate raceway  230  extending around the surface of the gear  220  along a circular centerline between the dimples  228 . During operation of the mechanism  206 , the bearings  226 , while retained in dimples  225  on the fixed gear  218 , can move along the raceway  230  in order to displace the bearings  226  between the respective dimples  228  as the slip gear  220  rotates with respect to the fixed gear  218  when a torque level above a pre-selected maximum is applied to the tool  200 .  
         [0058]     Additionally, the slip gear  220  includes a cross pin opening  221  that extends across and through the slip gear  220  generally perpendicular to the central opening  227 . The opening  221  is positionable in alignment with a bore  229  formed in the drive body  204  in order to enable a cross pin  329  to be inserted through the opening  221  and bore  229  to secure the slip gear  220  to the drive body  204 . Further, while the diameter of the bore  229  and opening  221  within which the pin  329  is received can be formed to closely conform to the outer diameter of the pin  329 , in a preferred embodiment, the diameter of the opening  221  and bore  229  are formed to be greater than required for insertion of the pin  329 . This gap created between the pin  329  and the opening  221  and bore  229  enables a certain amount of play between the drive body  204  and the slip gear  220 , thereby providing a smoother feel to the mechanism  206 . Additionally, in an attempt to further enhance the feel of the mechanism  206  and reduce the potential for unwanted drag or friction acting on the mechanism  206 , in a preferred embodiment, the outer diameter of the slip gear  220  is selected to allow for a space between the outer periphery of the slip gear  220  and the interior surface of the housing  234 , allowing the slip gear  220  to “float” within the housing  234 , and not rub against the sides of the housing  234 .  
         [0059]     Referring now to  FIGS. 3-8 , to provide the torque level control for the mechanism  206 , the fixed gear  218  and slip gear  220  are biased into engagement with the bearings  226  and one another by a number of biasing members or springs  232 . The springs  232  can each be formed from any suitable biasing member or material, but are preferably formed as Belleville washers and are disposed within the housing  234 . Each spring  232  is generally circular in shape with a central opening  235  through which the drive body  204  can extend and are disposed within the housing  234  against the fixed gear  218  opposite the slip gear  220 . The springs  232  can be selectively compressed into engagement with one another and with the fixed gear  218  in order to provide the desired amount of force resisting the rotation of the gears  218 ,  220  and the bearings  226  with respect to one another during use of the tool  200 .  
         [0060]     In order to enable the force applied to the gears  218 ,  220  by the springs  232  to be varied as desired, an open end  235  of the housing  234  opposite the gripping portion  201  of the handle  202  is covered by a generally circular calibration nut  236  disposed around the drive body  204  in engagement with the springs  232  opposite the fixed gear  218 . The calibration nut  236  preferably includes an expansion slot  237  that extends across the nut  236  and separates opposed portions  239  of the nut  236 . The opposed portions  239  can be deflected away from one another and into engagement with the interior of the housing  234  to secure the nut  236  within the housing  234  and provide the desired force on the gears  218 ,  220  from the springs  232  by a tapered lock nut  238  also positioned around the drive body  204  and engaged between the body  204  and nut  236 . To enable calibration nut  236  to be deflected, the nut  236 , as well as the locking nut  238 , is formed of a somewhat rigid material, such as a metal or hard plastic.  
         [0061]     To utilize the calibration nut  236 , the nut  236  is advanced into engagement with the springs  232  within the housing  234  until the desired spring force is exerted by the springs  232  against the gears  218 ,  220 . In a preferred embodiment, the calibration nut  236  is advanced into the housing  234  by the engagement of exterior threads (not shown) on the nut  236  with interior threads (not shown) disposed on the interior of the housing  234 . When the calibration nut  236  is positioned against the springs  232  at a location which provides the desired spring force to the gears  218 ,  220 , the tapered lock nut  238  is engaged within the calibration nut  236  to urge the portions  239  of the nut  236  on opposite sides of the expansion slot  237  outwardly against the interior of the housing  234  and hold the calibration nut  236  in position. To further enhance the engagement of the calibration nut  236  with the housing  234 , the nut  236  can include a number of a outwardly extending drive tangs (not shown) disposed on the exterior of the calibration nut  236  that engage the threads on the interior of the housing  234  in a manner to further prevent movement of the nut  236  with respect to the housing  234 .  
         [0062]     Looking now at  FIGS. 5-8 , to reduce any drag exerted by the inner housing  234  on the rotation of the slip gear  220 , and to ensure that the force acting on the gears  218 ,  220  is limited as much as possible to only the force of the springs  232 , the slip gear  220  is isolated from the inner end of the housing  234  by a hardened washer  241  and thrust bearing  240 . The thrust bearing  240  includes roller bearings  242  therein that rotate within the thrust bearing  240  and contact the slip gear  220  to enable the slip gear  220  to rotate easily within the housing  234 . A hardened washer  243  is also positioned between the springs  232  and the fixed gear  218  to enhance the frictional contact between the fixed gear  218  and the springs  232 .  
         [0063]     Look now at  FIGS. 3-5  and  7 , the interior components of the mechanism  206  described previously are enclosed within the housing  234  of the tool  200  by a generally cylindrical cover  244  that is releasably engaged with the exterior of the housing  234 , such as by mating threads  344  on the exterior of the housing  234  and the interior of the cap  244 . The cap  244  can be quickly and easily removed from the handle  202  in order to expose the mechanism  206  and enable the easy adjustment, service and/or replacement of any parts of the mechanism  206 . The cover  244  defines a central opening  245  at an outer end thereof that receives an access cap  246  releasably secured to the cover  244  within the opening  245  around the drive body  204 . The access cap  246  is fixed to the cover  244  by any suitable means in order to prevent the rotation of the cover  244  with respect to the housing  234 , thereby preventing the inadvertent detachment of the cover  244  from the handle  202 , such as during use of the tool  200 . Preferably a number of fasteners (not shown) are engaged within bores  247  in the cap  246  to deflect the cap  246  into engagement with the cover  244  around the opening  245 . The access cap  246  includes an O-ring  248  disposed around an inner opening  249  of the cap  246  that sealingly engages, but does not impede the rotation of the drive body  204  within the cap  246 , in order to seal off the interior of the cover  244  and prevent the mechanism  206  from encountering any water, dust or other debris which can negatively affect the operation of the mechanism  206 . A similar O-ring  250  can be disposed on the inner end of the drive body  204  located within the handle  202  to effectively seal the interior of the tool  200  to protect the components of the mechanism  206 .  
         [0064]     Other alternatives to the preferred embodiment described previously can be formed by changing the orientation of the fixed gear  218 , slip gear  220  and springs  232  from the order of these components shown in the drawing Figs. Also, the location of the calibration nut  236  can also be altered depending upon the location of the springs  232 , or can be positioned to engage the gears  218 ,  220  instead of the springs  232 . Further, the bearing members  226  can be other than ball bearings, such as pin bearings, with corresponding changes to the shape of the dimples  225 ,  228  in the respective gears  218 ,  220 . Additionally, the housing  234  can be formed separately from the handle  202  while the cover  244  can be formed as part of the handle  202 .  
         [0065]     In addition, in order to further provide a tool  200  with the ability to control the torque applied using the tool  200 , a second embodiment of the torque-limiting mechanism  306  for use in a tool  200  is illustrated in  FIGS. 22-35 . In this mechanism  306 , a fixed gear  318  and a slip gear  320  that provide the torque-limiting function to the mechanism  306  are formed of a rigid material and positioned adjacent to one another as described previously with regard to mechanism  206 . The fixed gear  318  includes a number of dimples  325  spaced around a central opening  327  in the gear  318  on one surface of the fixed gear  318 . The opening  327  can be cylindrical or can define an annular shoulder  327 ′ therein to assist in the formation of the dimples  325 . A number of spherical ball bearings  326  are disposed within the dimples  325  and are able to rotate therein. The depth of the dimples  325  in the gear  318  are preferably sufficient to receive approximately one-half of the volume of each bearing  326  such that while the bearings  326  can rotate within the dimples  325 , the bearings  326  are each maintained within the dimples  325 . In a particularly preferred embodiment, the bearings  326 , which are formed of a rigid and smooth material, such as a metal, formed to have a diameter slightly less than the diameter of the dimples  325 . This allows the bearing  326  to rotate more freely within the dimples  325  when the mechanism  306  is in use. The gear  318  also preferably includes a pair of flats  352  formed on opposite sides of the gear  318  that are engageable with the tool housing  234  to maintain the position of the gear  318  within the housing.  
         [0066]     The rotatable or slip gear  320  is formed similarly to the fixed gear  318  with a central opening  327  and a number of dimples  328  spaced around the opening  327  on one side of the gear  320  that are positioned to face the dimples  325  in the fixed gear  318 . The dimples  328  receive the end of each of the bearings  326  extending outwardly from the dimples  325  in the fixed gear  318 , but are less deep than the dimples  325  in the fixed gear  318 . The slip gear  320  also includes an arcuate raceway  330  extending around the surface of the gear  320  along a circular centerline between the dimples  328 . During operation of the mechanism  306 , the bearings  326 , while retained in dimples  325  on the fixed gear  318 , can move along the raceway  330  in order to displace the bearings  326  between the respective dimples  328  on the slip gear  320  as the slip gear  320  rotates with respect to the fixed gear  318  when a torque level above a pre-selected maximum as applied to the tool  200 .  
         [0067]     In order to provide additional resistance control to the movement of the slip gear  320  with regard to the fixed gear  318 , each of the fixed gear  318  and the slip gear  320  includes teeth  340  positioned on the outer periphery of the gears  318  and  320 . The teeth  340  are spaced equidistant from one another around the periphery of each gear  318  and  320  in a form so as to be positioned in a locking engagement when the gears  318  and  320  are assembled, as best shown in  FIG. 23 . In this configuration, the teeth  340 , which each include a sloped friction surface  342  and a locking surface  344 , oppose the rotation of the slip gear  320  with regard to the fixed gear  318  by the frictional engagement of the sloped surfaces  342  and vertical surfaces  344  of each of the teeth  340 . However, as opposed to prior art gears  100 ,  101 , the locking surfaces  344  of the teeth  340  are formed to be inclined from the vertical at an angle of between ten degrees (10°) to twenty-five degrees (25°), and preferably around fifteen degrees (15°), similar to the angle for the friction surfaces  342  from the horizontal. The angle of the locking surfaces  344  allow the teeth  340  to slip more easily with regard to one another and prevent the snapping and vibrations caused by the shape of the teeth  102  in prior art gears  100 ,  101 .  
         [0068]     Additionally, the formation of the teeth  340  including the locking surface  344  on each of the gears  318  and  320  provides a one-way rotational or ratcheting function for the mechanism  306 . In other words, due to the positioning of the locking surfaces  344  on each gear  318  and  320 , when the slip gear  320  is rotated in a direction which contacts locking surfaces  344  of teeth  340  on each gear  318  and  320  with one another, the contact between the locking surfaces  344  prevents any further rotation of the slip gear  320  in this direction. However, rotation in the direction moving the locking surfaces  344  away from one another is permitted by the construction of the mechanism  306 .  
         [0069]     In an additional variation to the construction of the gears  318  and  320 , it is possible to vary depth of dimples  325  and/or  328  to vary the amount of torque provided by the friction generated between the gears  318  and  320  and the bearings  326  without changing biasing or spring pressure provided by the particular springs  232  being utilized in the tool  200 .  
         [0070]     Further, as an alternative to the lock nut  238 , it is possible to drill a hole (not shown) into the side of the housing  234  and insert therein a pin (not shown) through the side of the housing  234  to engage the calibration nut  236 .  
         [0071]     Various additional alternatives are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.