Abstract:
A tool for installing a cable tie, said cable tie having a head portion and an elongate tail portion extending therefrom, said tool comprising a housing having a distal end and a proximate end, a tensioning mechanism for tensioning said cable tie to a predetermined tension setting, said tensioning mechanism operatively supported by said housing, a cutting mechanism for severing an excess portion of said tail from said tensioned cable tie, said cutting mechanism operatively supported by said housing, a manually actuable external power delivery system for actuating said tensioning and cutting mechanisms, said power delivery system for delivering power generally in line with said tensioning mechanism, and a restraint mechanism for providing said predetermined tension setting wherein said restraint mechanism provides said predetermined tension generally in line with said tensioning mechanism and said power delivery system.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to hand-held cable tie tensioning and severing tools, and more particularly, to an improved tool for reliably installing or applying high tension to flexible cable ties and severing the ends thereof without over-tensioning the cable ties.  
           [0002]    As is well known to those skilled in the art, cables ties are typically used to bundle or secure a group of elongated articles, such as electrical wires and cables. Cable ties of conventional construction include a cable tie head and an elongated tail extending therefrom. The tail is wrapped around a bundle of articles and thereafter inserted through a passage in the head. The head of the cable tie typically supports a locking element that extends into the head passage and engages the tail to secure the tail to the head, or at least prevent rearward travel of the tail back through the passage so as to disengage the head.  
           [0003]    In practice, the installer manually places the tie about the articles to be bundled, inserts the tail through the head passage and then manually tightens the tie about the bundle. At this point, a cable tie installation tool may be used to tension the cable tie to a predetermined tension about the bundle. With manually powered tools, one or more grip strokes may be needed to sufficiently tension the tie, depending upon, among other things, how much tension is desired. Once the strap tension approaches the desired level of tension, as predetermined and reflected in the tension setting level of the tool, the tool severs the excess tail portion from the tie, i.e., that portion of the tail which extends beyond the head of the cable tie.  
           [0004]    With pneumatic tools, a single depression of a button or the like is typically used to activate pneumatic pressure to tension the cable tie to the predetermined tension. Similar to the manually powered tool, once the predetermined tension setting level is reached on a pneumatic tool, the tool severs the excess tail portion from the tie.  
           [0005]    Most prior tools, though capable of tensioning and thereafter severing the excess tail portion of the cable tie, have several disadvantages associated therewith which, either singularly or plurally, increase the frequency of operator injuries, and increase the frequency and magnitude of tool degradation and failure. For example, the cast metal body tool disclosed in U.S. Pat. No. 3,661,187 to Caveney, et al., represents what is now a conventional linkage style tensioning and severing assembly. Relative to more recent designs, the tool housing shown in the &#39;187 patent is not very ergonomic, though the linkage design is extremely durable. The cast metal body provides apertures in which pins or shafts are secured to mount and provide pivot points for the many linkage arms. Since the linkage assembly style of tensioning and severing generates such high forces at the pin locations and cantilevered loads on the linkages, the durable cast metal body becomes a necessity for reliable operation and to keep the pins from distorting the housing and deleteriously migrating. Using the stored energy principle of a partially compressed spring, accurate and predictable severance breakaway is achieved when the pins cannot move and the arms move through their intended movements. A disadvantage of the cast metal body, however, is that it requires a significant number of manufacturing steps, driving the cost higher.  
           [0006]    Other prior art examples include U.S. Pat. Nos. 4,793,385, 4,997,011, and 5,492,156, all to Dyer, et al., which disclose an ergonomically motivated plastic bodied tool. A conventional linkage style arrangement similar to that disclosed in Caveney, et al., is used, but the tension adjustment assembly has been moved to the top of the tool. In this location, the operator can more easily see and manipulate the tension adjustment knobs. Additionally, a more deeply curved handle is shown, though in practice the foam handle cover used therewith yields a result which is not very ergonomic. The major disadvantage of this tool is the combination of a high angular force linkage design and a plastic body. Due to this combination, the tool is not nearly as durable as some previous designs. The high off-center loading forces of the linkage design are exerted on the pins mounted in the plastic body. As the number of cycles of the tool increases, the pin holes become elongated and allow the pins to migrate or wobble. Consequently, the uniform severance point that is normally achieved with the linkage style design becomes unpredictable, and accurate and consistent tensioning is not possible. Ultimately such a tool will fail to produce reasonably repeatable results, after which the tool must be discarded.  
           [0007]    Another prior art tool is described in U.S. Pat. No. 5,915,425 to Nisson, et al. It proposes to solve several ergonomic disadvantages of prior tools by providing an adjustable grip size, a rotatable nose, and reduced recoil shock/vibration. While attempting to overcome these disadvantages, the plastic bodied tool disclosed in the &#39;425 patent incorporates a more variable tensioning and severing assemblies than those previously disclosed. In practice, the design has resulted in a poorly performing tool that is not durable, is subject to tensioning inconsistences between tools, fails to provide a distinct and uniform severance point, is unable to accurately calibrate its tension setting, and includes a fragile tension setting device.  
           [0008]    Yet another tool is described in U.S. Pat. No. 6,206,053 to Hillegonds. The manually activated and manually powered cable tie tensioning and severing tool described therein provides numerous advantages over prior designs and permits users to quickly and economically apply successive ties under uniform predetermined tensions, resulting in consistent cut-off heights. Additionally, the design includes a tension rod and generally aligned cutting mechanism sleeve, and a concentrically/coaxially mounted restraining means that reduces off-center loads and thereby increases the cycle life of the tool. Despite its advantages over many prior designs, however, the tool still requires manual power to tension the cable ties. Additionally, this prior design utilizes many parts and thus has a somewhat higher manufacturing cost than other designs, particularly those using external power. As the tool embodiments shown and described in U.S. Pat. No. 6,206,053 include some structures and/or assemblies that are similar or identical to specific structures and/or assemblies of the tools described herein, the entire disclosure of the &#39;053 patent is incorporated herein by reference.  
           [0009]    There is therefore a need in the art for a cable tie installation tool which is ergonomic, reliable, durable, consistent, lightweight, cost-efficient and externally powered.  
         SUMMARY OF THE INVENTION  
         [0010]    To address the above-described need, there is provided, described, and claimed herein a cable tie installation tool that is not human-powered and includes in-line power delivery from a source external to the tool.  
           [0011]    In one embodiment of the invention, there is provided a tool for installing a cable tie, the cable tie having a head portion and an elongate tail portion extending therefrom. The tool includes a housing having a distal end and a proximate end, a tensioning mechanism for tensioning the cable tie to a predetermined tension setting, the tensioning mechanism operatively supported by the housing, a cutting mechanism for severing an excess portion of the tail from the tensioned cable tie, the cutting mechanism operatively supported by the housing, an external power delivery system for actuating the tensioning and cutting mechanisms, the power delivery system for delivering power generally in line with the tensioning mechanism, and a restraint mechanism for providing the predetermined tension setting wherein the restraint mechanism provides the predetermined tension generally in line with the tensioning mechanism.  
           [0012]    In another embodiment of the invention, there is provided a tool for installing a cable tie, the cable tie having a head portion and an elongate tail portion extending therefrom. The tool includes a housing, a tensioning mechanism for tensioning the cable tie to a predetermined tension setting, the tensioning mechanism operatively supported by the housing, the tensioning mechanism including a linearly reciprocating tension rod and a reverse single acting cylinder, a cutting mechanism for severing an excess portion of the tail from the tensioned cable tie, the cutting mechanism operatively supported by the housing, a restraining mechanism including a ball detent assembly, the restraining mechanism being in communication with the reverse single acting cylinder and being generally axially aligned with the linearly reciprocating tension rod and the reverse single acting cylinder, the restraining mechanism for effecting a predetermined tension setting on the reverse single acting cylinder, and a manually actuable external power delivery system for actuating the tensioning and cutting mechanisms, the power delivery system including a pneumatic power source, a trigger, and a three-way pneumatic valve, whereby when the trigger is manually actuated, pneumatic pressure forces the reverse single acting cylinder to rearwardly pull the linearly reciprocating tension rod, thereby simultaneously restraining movement of the cutting mechanism and tensioning the cable tie until the predetermined tension setting effected by the restraining mechanism is reached in the cable tie, after which the reverse single acting cylinder is released from the pneumatic pressure such that the reverse single acting cylinder is thrust forwardly to activate the cutting mechanism such that it severs the cable tie.  
       
    
    
     BRIEF DESCRIPTION OF FIGURES  
       [0013]    [0013]FIG. 1 is a left side front upper perspective view of a tool embodying the present invention;  
         [0014]    [0014]FIG. 2 is a right side upper rear perspective view of the tool of FIG. 1;  
         [0015]    [0015]FIG. 3 is a top plan view of the tool of FIG. 1;  
         [0016]    [0016]FIG. 4 is a side elevation view of the tool of FIG. 1 with the left hand side body housing removed to permit interior parts to be viewed;  
         [0017]    [0017]FIG. 5 is a left side front upper perspective view of the tool of FIG. 1 with the left hand side body housing removed to permit interior parts to be viewed;  
         [0018]    [0018]FIG. 6 is an exploded left side front upper perspective view of the tool of FIG. 1;  
         [0019]    [0019]FIG. 7 is a fragmentary cross-sectional view taken through the tool substantially along the line  7 - 7  in FIG. 3, wherein the tool is shown prior to tensioning the cable tie;  
         [0020]    [0020]FIG. 8 is an enlarged view of a portion of FIG. 7;  
         [0021]    [0021]FIG. 9 is a fragmentary cross-sectional view of the tool of FIG. 1 taken substantially along the line  9 - 9  in FIG. 4;  
         [0022]    [0022]FIG. 10 is a fragmentary cross-sectional view of the tool of FIG. 1 taken substantially along the line  10 - 10  in FIG. 4;  
         [0023]    [0023]FIG. 11 is a fragmentary cross-sectional view of the tool of FIG. 1 taken substantially along the line  11 - 11  in FIG. 4;  
         [0024]    [0024]FIG. 12 is a fragmentary cross-sectional view of the tool of FIG. 1 taken substantially along the line  12 - 12  in FIG. 4;  
         [0025]    [0025]FIG. 13 is a fragmentary cross-sectional view of the tool of FIG. 1 taken substantially along the line  13 - 13  in FIG. 4;  
         [0026]    [0026]FIG. 14 is a fragmentary cross-sectional view of the tool of FIG. 1 wherein the cable tie has not yet been engaged by the tool;  
         [0027]    [0027]FIG. 15 is a view akin to that of FIG. 7 wherein the tool is in an intermediate stage of tensioning the cable tie;  
         [0028]    [0028]FIG. 16 is a view akin to that of FIG. 7 wherein the tool has fully tensioned and cut the cable tie;  
         [0029]    [0029]FIG. 17 is an enlarged view of a portion of FIG. 16. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]    A tool for installing a cable tie embodying the present invention is designated generally by the reference numeral  20  in the accompanying drawings. As shown in FIGS.  1 - 3 , the hand-held tool  20  has a housing  30  having a handle portion  32  and a barrel portion  50 . The housing  30  includes two separate complimentary sidewall portions  90  (left) and  92  (right) that are secured together to define the handle portion  32  and the barrel portion  50 . The handle portion  32  has a front  34 , a back  36 , opposite sides  38  and  39 , and a bottom  40 . In the illustrated embodiment, the sides  38  (left) and  39  (right) are generally arcuately shaped for ergonomic reasons and are substantially mirror images of one another. The back  36  is also correspondingly arcuately-shaped, including a deeply recessed portion  37  which enhances the ergonomics of the tool  20 . The front  34  is also arcuately-shaped, however, less dramatically so than the back  36 . The bottom  40  has a curvilinear surface joining the sides  38  and  39 , and the front  34  and back  36  together at a common point on the lower extension of the handle.  
         [0031]    The barrel portion  50  has a top  52 , a bottom  56 , and opposite sides  60  (left) and  62  (right). In the illustrated embodiment, the top  52  is generally characterized as having a rounder portion  51  nearer the handle portion  32  and a more planar top portion  53  formed near the distal end  22  of the tool. The bottom  56  is substantially planar in configuration and is generally parallel to the planar top portion  53 . As seen in FIGS. 4 and 5, a substantially rectangular aperture  58  is provided in the bottom  56  in order to accommodate the cutting mechanism.  
         [0032]    In FIGS.  4 - 7 , one side wall  90  of housing  30  has been cut away or removed to show the other housing sidewall  92  interior and the internal parts and assemblies. The housing  30  generally contains a reciprocating tensioning mechanism  120 , formed by a preferably cylindrically shaped tension rod  122  and a gripper assembly  132  disposed at the distal end of the tension rod  122  for gripping the tie tail  12  of cable tie  10 . The tension rod  122  extends generally parallel to the planar portion  53  of the top  52  of the barrel portion  50 . The tensioning mechanism  120  is operatively associated with an actuating mechanism  170  and is also operatively connected to a restraining mechanism  230 , and to a tie cutting mechanism  330 .  
         [0033]    The tool  10  includes a blade guard  70  at the distal end  22  of the tool. In a preferred embodiment, the blade guard  70  is made of metal. The blade guard  70  is preferably manufactured by a metal injection process for providing strength at a lower cost. The blade guard  70  preferably includes a forward planar surface  71  facing away from the tool barrel  50 . Formed thereon is an arcuately-shaped recessed element  72  for receiving a variety of differently sized cable tie heads of various different curvilinear shapes. The blade guard  70  also includes a tie slot  73  through the forward planar surface  71 , through which the tool operator passes a cable tie tail  12  after the tail has been first wrapped around a bundle of wires  13  and threaded through a passage in the cable tie head  11 .  
         [0034]    The gripper assembly  132  is preferably identical or nearly identical in structure and function to the gripper assembly described in the &#39;053 patent, greater detail of a preferred embodiment being shown therein. The gripper housing  134  is secured to the distal end of the tension rod  122  by a nut which engages a set of threads disposed at the distal end of the tension rod  122  after the tension rod has been inserted through an aperture in the end plate thereof. Prior to the nut being secured to the distal end of the tension rod  122 , a cover, having an aperture disposed on the end panel thereof, is mounted over the distal end of the tension rod  122 . The tie tail  12  is engaged by the pawl  150 , which has a plurality of tie tail gripping teeth. The pawl extends out of the gripper housing  134  through a generally rectangular aperture disposed below a cable tie pressure plate. The aperture extends between the distal end of the cover and the distal end of the gripper housing. The gripping teeth are spaced apart and angled upwardly from the pawl, and have a depth and sharpness sufficient to enable the gripper to grasp either a flat or serrated cable tie tail. The pawl  150  is biased for forward rotation toward the distal end  22  of the tool  20  about a shaft by a gripper spring  136  which engages the shaft and the pawl. The pawl applies the grasping pressure on the cable tie tail  12  being held in the tie passageway between the tie pressure plate and the pawl.  
         [0035]    With particular reference to FIGS. 7 and 8, the actuating mechanism  170  includes a piston-like reverse single acting cylinder  410 . After threading a cable tie tail  12  through the tie slot  73  such that it is disposed within the gripper assembly, the user, preferably holding the tool like a pistol, uses his finger to depress the trigger  412  against the resistance of an internal spring  414  to activate a three-way pneumatic valve  416  to permit pneumatic pressure to be transmitted from an external pneumatic power supply  418  and pneumatic inlet tube  420  into the pneumatic outlet tube  422  and ultimately into the reverse single acting cylinder  410 . The application of pneumatic pressure to its distal side pushes the piston  424  and the attached tension rod  122  toward the proximate end  24  of the tool  20 , thereby drawing the gripped tie tail  12  back toward the proximate end and simultaneously tensioning the cable tie  10  around the bundle of wires  13 .  
         [0036]    When the tool  20  is in its initial position (FIG. 7), the tensioning mechanism  120  is biased into its forwardmost extent within the tool barrel  50  by a return spring  426  located in the reverse single acting cylinder  410 . In this position, the piston  424  is just short of abutting wall  428  due to pre-load bias in the system. As pneumatic pressure fills the annular space  427  within the reverse single acting cylinder  410  on the distal side of the piston  424  and surrounded by wall  428  and the small space between wall  428  and the piston, the piston is forced proximately against the bias of a restraining mechanism  230 , which is set to a predetermined tension level, as discussed in further detail below. When the reverse single acting cylinder, via the proximate piston thrust, exerts a force on the restraining means just beyond the predetermined tension setting, the reverse single acting cylinder  410  is rapidly thrust forwardly (distally). When the reverse single acting cylinder  410  is thrust forwardly, the cam  411  on the distal end thereof activates the cutting mechanism  330 , and the cable tie tail is severed by the cutting mechanism in the same manner as is discussed in the &#39;053 patent.  
         [0037]    The restraining mechanism  230 , as shown in FIGS.  8 - 11  and other figures, includes a ball detent assembly  232  and a tension adjustment assembly  270 . Identically to the embodiment shown in the &#39;053 patent, the ball detent assembly is generally comprised of a housing which is substantially cup-shaped and has a flange portion which radially extends from the cup-shaped bottom thereof and preferably has an annular configuration. An aperture is formed in the bottom of the cup which is generally appropriately configured to accept only a proximate surface of the detent sleeve  333  therethrough, but retain other elements of the assembly. The flange portion is positively secured to each housing sidewall  90  and  92  when inserted into a complimentary-shaped semi-circular slot formed in each housing sidewall which circumferentially retains the annularly-shaped flange portion to prevent any longitudinal movement thereof. Preferably, rotational movement is also controlled, though this is not critical. Disposed within the housing of the ball detent assembly are a number of ball bearings that are captured between the bottom of the housing and the seat for securing the sleeve in position during tensioning of the tie tail  12  until the level of predetermined tension setting in the tension adjustment assembly  270  is attained. A detailed description of this operation is provided below.  
         [0038]    The seat has a preferably planar, annularly-shaped proximate face. An aperture is disposed therethrough and extends distally through the seat with an increasing diameter so that, at its final distal extent, it nearly equals the outside diameter of the seat. The rate of diameter increase may change the force which is imparted to the sleeve relative to the force stored in the tension adjustment assembly  270 . Consequently, a circumferential restraining force is created when an angled or conical face of the seat contacts the ball bearings to impart the stored force to the sleeve.  
         [0039]    In a preferred embodiment of the invention, the restraint mechanism  230 , which may or may not be a ball detent assembly such as the one previously described, is axially aligned with the tensioning mechanism, and even more preferably also with the power delivery system, to minimize the number and degree of off-center loads in the tool, and to thereby increase the life of the tool and provide greater ease of use to the tool operator.  
         [0040]    As seen in FIGS. 8, 9, and  17 , The tension adjustment assembly  270  is operatively connected to the ball detent assembly  232  by force transfer assembly  250 , which includes a pair of reversing links pivotally mounted between the ball detent assembly  232  and tension adjustment assembly  270 . At a desired position a pivot pin  262  is disposed in apertures formed substantially in the central region of each link. The pivot pin is disposed in mounting bosses of tool housing sidewalls  90  and  92 . Thus, the reversing links are positively mounted, but free to pivotally rotate. One who is skilled in the art will recognize the balanced load carried by the pivot pin, resulting in less off center or cantilevered load transfer to the sidewalls  90  and  92 .  
         [0041]    Another shaft disposed in two apertures at the upper end of each reversing link operatively connects the force transfer assembly  250  to the tension adjustment assembly  270 . Guide projections are disposed on each housing sidewall  90  and  92  along the travel path of the shaft in order to maintain proper alignment of the reversing links and prevent rotation of the tension adjustment assembly  270 . Preferably, a light application of grease is applied to each guide projection to ensure smooth tool operation.  
         [0042]    [0042]FIGS. 8 and 9 show a preferred embodiment of the selective tension adjustment assembly  270  which includes a tension spring  272  held between two arms  275  of the yoke  274 . The spring  272  encircles a tension shaft  282  axially disposed within the yoke arms  275 . The tension shaft has a threaded portion at its distal end which threadedly engages a threaded tension nut. The tension nut has opposite slots formed on the lateral edges thereof which capture and ride along the yoke arms, and which prevent rotation of the tension nut relative to the yoke arms  275 . In the initial tool position (FIG. 7), the tension spring  272  is subjected to a slight preload or compression due to its placement between the tension nut and the yoke end plate. It will be seen that any rearward movement of the tension nut on the tension shaft  282  will increase the tension on the spring  272 , and increase the reactive force that the spring  272  exerts upon force transfer assembly  250 , and ultimately the cutting mechanism  330  via the ball detent assembly  232 , and reverse single acting cylinder  410 .  
         [0043]    Preferably, substantially disposed in the generally central portion of the tension shaft  282  is a hexagonally-shaped section  285 . As is obvious to those of ordinary skill in the art, this section  285  of the tension shaft  282  may have any number of flat portions as desired. Mounted on section  285  is a fine adjustment knob  290  having a generally circular outer diameter configuration and an aperture extending therethrough disposed about its center and shaped complimentary to the hexagonal section  285 . Preferably, a cam  294  is provided which is generally cylindrical in shape having a variety of pairs of cam surfaces disposed at different desired heights defining the top or proximate end of the cam. These various pairs of cam surfaces enable coarse tension adjustment of the tool  20  when used in cooperation with the coarse tension adjustment knob  310 .  
         [0044]    The cam  294  preferably further includes at least one projection extending a desired distance radially inward and at least one slot extending radially outward into a wall of the cam disposed adjacent the distal end thereof, the projection and slot extending radially outward into a wall of the cam disposed adjacent the distal end thereof. The projection and slot preferably engage a complimentary slot and projection, respectively, on the tool housing to positively secure the cam in position and prevent any rotation or movement thereof, as explained in greater detail in the &#39;053 patent. The tension shaft  282  also has a threaded portion at its proximate end which threadedly engages a threaded calibration nut for positively securing the coarse tension adjustment knob  310  to the tool and permitting the operator to establish a baseline tension setting, thereby accommodating various production tolerances. A washer is preferably provided, disposed between the head of the calibration nut and a generally segmented disk-shaped flange disposed interiorly of the proximate end of the coarse tension adjustment knob  310 . Preferably, a cam follower extends from each segmented disk flange portion, which cooperate with the various pairs of cam surfaces to provide desired tension settings. A cover is preferably provided to enclose the proximate end of the coarse tension adjustment knob  310  to prevent dirt and other contaminants from reaching the calibration nut and other internal parts and mechanisms.  
         [0045]    Compression of the tension spring  272  is selectively increased by the operator rotating the coarse tension adjustment knob  310  which consequently rotates the cam followers. In the low tension setting, the cam followers engage a first or low tension cam surface pair to establish a preselected compression or preload of the tension spring  272 . When the cam followers engage the first cam surface pair, the distance between the tension nut proximate face and the yoke endplate is substantially at a maximum and thus the compression exerted on the tension spring  272  is at a minimum setting. Because the cam  294  is positively secured to the housing, when the coarse tension adjustment knob  310  is rotated from the low tension setting position to the medium tension position, the tension nut is drawn proximately toward the yoke endplate (which is fixed in its location) a distance corresponding to the difference in height of the first pair of cam surfaces relative to the second pair of cam surfaces. As is obvious to one having ordinary skill in the art, the coarse tension adjustment knob  310  does not rotate the tension shaft  282  in order to move the tension nut. Rather the coarse knob  310  pulls the tension shaft  282  and nut toward the yoke endplate. Turning the coarse tension adjustment knob  310  to the medium tension setting brings the cam followers into engagement with the second pair or medium tension cam surfaces which increases the compression on the tension spring  272  (and decreases the distance between the tension nut and yoke endplate) by an amount equal to the difference in heights of the first and second cam pair surfaces. As one of skill in the art will recognize, similar and further rotation of the coarse tension adjustment knob  310  to the high tension setting results in engagement of the third cam pair surfaces by the cam followers, further increasing the compression of the tension spring  272  and further decreasing the distance between the tension nut and yoke endplate. Increasing the compression in the tension spring  272  in this manner increases the circumferential restraining force applied to the ball detent assembly  232  via the force transfer assembly  250  and ultimately the tension in the tie tail  12 .  
         [0046]    The fine tension adjustment knob  290  is provided so that the operator has a means for finely adjusting or “fine tuning” the tension values chosen by rotation of the coarse tension adjustment knob  310 . As discussed above, the fine tension adjustment knob  290  includes an aperture extending axially therethrough which has a shape that is complimentary to the central portion  285  of the tension shaft  282 , preferably hexagonal as in this preferred embodiment. Consequently, the fine tension knob  290  is fixedly attached to the tension shaft central portion  285  so that the shaft  282  and fine tension knob  290  are co-rotatable. Thus, rotation of the tension shaft  282  moves the helically threaded tension nut a slight distance proximally or distally on the distal threaded shaft portion, depending on the direction of rotation of the fine tension knob  290 . The tension shaft  282  extends axially through coaxial bore opening and in the cam  294  and coarse tension adjustment knob  310 , respectively, such that when the shaft  282  is rotated by turning the fine tension adjustment knob  290 , the shaft  282  does not rotatably engage the coarse tension adjustment knob  310  or cam  294 . The proximate threaded portion of the tension shaft  282  merely threads in or out of the detent nut freely, without rotating the coarse tension adjustment knob  310 . The distal end of the tension shaft  282  is threaded for a distance limited by a stop. The stop limits the extent of travel of the tension nut on the distal end of the tension shaft  282 , and correspondingly limits the amount of fine tension adjustment in the compression of the tension spring  272 . By turning the fine tension adjustment knob  290 , the operator can slightly increase or decrease the spring length between the tension nut and the yoke endplate.  
         [0047]    As discussed above, in a preferred embodiment, the inventive cable tie installation tool is pneumatically powered, and the actuating mechanism  170  includes a piston-like reverse single acting cylinder  410 . Depression of the trigger  412  activates the three-way pneumatic valve  416  to permit pneumatic pressure to be transmitted from an external pneumatic power supply  418  ultimately into the reverse single acting cylinder  410 . The application of pneumatic pressure pushes a piston  424  disposed within the cylinder  410  toward the proximate end of the tool. The tension rod  122 , being integrally or otherwise attached to the piston  424 , moves with the piston to activate the gripper assembly  132  and tension the tie.  
         [0048]    [0048]FIG. 7 shows a preferred embodiment of the cutting mechanism  330 , some parts of which are more easily viewed in exploded FIG. 6. The cutting mechanism includes a lever arm  350 , a spring  358 , a severing blade  360 , and a blade guard  70 .  
         [0049]    The ball detent assembly  232  supports, guides and controls movement of a detent sleeve  333  that is threadedly received into the proximate end of the single reverse acting cylinder. The detent housing  234  provides a bearing element at the distal or bottom of the cup for the smooth cylindrical portion of the proximate bearing surface. The ball bearings  240  of the ball detent assembly  232  are circumferentially forced into a groove and oppose the constant force applied by the reversing links and prevent actuation of the cutting mechanism  330  until the desired predetermined tension setting is achieved. Further discussion of this operation is included below.  
         [0050]    The cutting mechanism lever arm  350  proximate end  352  has a generally arcuately or rounded shape protrusion formed thereon. Preferably, a slight amount of grease provided thereon will allow smooth pivotal actuation of the lever arm  350  by the conically shaped cam  411  at the distal end of the single reverse acting cylinder  410 . As the force applied to the tension rod  122  readies the desired tension setting, the ball bearings  240  of the ball detent assembly  232  are forced radially outward away from the groove, pushing the seat proximately, thus overcoming the stored force in the tension adjustment assembly  270 , the detent sleeve  332  may then be further urged distally and the proximate end  352  of the lever arm  350  will be forced toward the bottom  56  of the barrel  50 . A laterally extending aperture is provided at a desired position in a central portion of the lever arm  350  for receiving a pivot pin  357  therethrough, the pin  357  being complementarily sized to engage a pin boss formed in each housing sidewall  90  and  92 . The distal end  354  of the lever arm  350  includes a stepped or raised surface. The stepped surface engages a slot disposed on a lower end of the severing blade  360 . The severing blade  360  remains in position, captured between the guide boss and the blade guard  70 , during movement of the lever arm  350 . The blade  360  cuts through a portion of the thickness of the cable tie tail  12 , typically about ½ or ⅔ of the thickness, before returning toward its initial position—preferably the blade does not contact the anvil. The tension stored in the tie tail during the cutting step serves to propagate the cut and complete the severance of the tail  12  after the blade cuts through a portion thereof.  
         [0051]    As shown in detail in the &#39;053 patent, the depicted embodiment includes a means for visually indicating the tension level setting. A window is provided in the top raised surface of the tool housing  30  adjacent the tension adjustment assembly  270 . Guide tracks are formed in the housing sidewalls  90  and  92  and support a display plate which is slidable in the tracks. The sliding display plate is preferably generally flat and has means for engaging the tension adjustment assembly in the form of a notch defined by a pair of parallel depending projections. The notch engages an upper extension of the tension nut and correspondingly moves therewith.  
         [0052]    Also like the embodiment(s) shown described and shown in the &#39;053 patent, the present tool further includes a retractable bail disposed to extend out of and retract into the bottom  40  of the handle portion  32 .  
         [0053]    In operation, as shown in FIGS.  7 - 8  and  14 - 17 , a cable tie tail  12 , after having been wrapped around a bundle of wires or cables  13  and inserted through the cable tie head  11 , is inserted into the tie slot  73  with the tool  20  at its normal, initial at-rest position, with the tie head  11  positioned adjacent the tie slot  73 , and received within the recessed portion  72  thereof. As the trigger  412  is depressed by the operator, the three-way pneumatic valve  416  is actuated to permit pneumatic pressure to be transmitted from the external pneumatic power supply into the reverse single acting cylinder  410  on the distal side of the piston  424 . The pressure pushes the cylinder  410  proximately so that the gripper assembly  132  is camingly actuated by the cam  411  to grip the tail tie  12 . As the gripper assembly  132  is drawn away from the guide boss, the pawl  150  is rotated counterclockwise by the gripper spring  136  to capture the tie tail  12  between the pawl  150  and the pressure plate.  
         [0054]    Thus, as the tie is tensioned around the bundle, and pneumatic pressure simultaneously pushes the piston proximately, the tension rod  122  is placed in tension, which through the single reverse acting cylinder  411 , and the integrally attached detent sleeve  333 , applies a force to the force transfer assembly  250 . The detent sleeve  333  is held stationary during tensioning by the restraining mechanism  230 . The detent sleeve  333  remains stationary in its initial position with the ball bearings  240  engaging the groove and exerting a circumferential force thereon equal to the force stored in the tension adjustment assembly  270  as long as the force imparted to the detent sleeve  333  is less than the force stored in the tension adjustment assembly  270 . When the desired predetermined tension setting is achieved in the cable tie  10  or, a more accurately when the force imparted to the sleeve  333  in the distal direction, exceeds the force stored in the tension adjustment assembly  270 , the ball bearings  240  are forced out of the groove in the detent sleeve  333 . The force stored in the tension adjustment assembly  270  is overcome when the ball bearings  240  are forced out of the groove and push the seat proximately back slightly, which causes the force transfer assembly  250  to temporarily further compress the tension spring  272 . The detent sleeve  333 , along with the rigidly attached reverse single acting cylinder, are thus thrust distally forward causing the cam  411  on the distal end thereof to impart a force on the lever arm  350 . The lever arm pivots about its pivot pin  357 , thereby raising the stepped surface and the severing blade  360  upwards to partially cut the cable tie  10 . The tension stored in the tie propagates the partial cut to severance, and tool  20  resets to its normal initial position through the biasing action of the lever arm spring  358  and the return spring  426  within the cylinder  410 .  
         [0055]    While the preferred embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims.