Abstract:
A power tool comprising: a housing; a cable outlet with a central axis; an motor; a flexible electrical supply cable; a cable sheath for protecting supply cable projected through the cable outlet and for directing unprotected supply cable away from the central axis wherein the sheath is rotatable to change direction of unprotected supply cable; and locking means for locking the sheath in one of a plurality of rotational orientations. The locking means comprises: a receiving member connected to one of the sheath or the cable outlet; an engaging member connected to the other of the sheath or the cable outlet; and a biasing means for biasing the engaging and receiving members into engagement to lock the sheath in a rotational orientation, wherein movement of the sheath against the biasing means disengages the engaging and receiving members and unlocks the sheath for rotation.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an electric supply cable sheath for a power tool. 
       BACKGROUND OF THE INVENTION 
       [0002]    Power tools are commonly operated by an electric motor for driving a work tool to perform a machining operation on a work-piece. The motor requires electric power which is usually delivered by an electric supply cable. The supply cable couples the motor to an external electric power source such a mains electric power socket or a portable electric power generator. The electric supply cable is typically made of flexible material so that it may be connected to the electric power source without limiting movement of the power tool. Over time, repetitive flexing of the electric supply cable may cause damage, especially at locations where it comes into contact with other bodies. One such location, where the electric supply cable is particularly vulnerable, is a cable outlet from the power tool&#39;s housing in which the motor is located. Sideward movement contorts the electric supply cable against the cable outlet. To mitigate the detrimental effect of this contortion, a protective cable sheath is clad around a portion of the electric supply cable where it projects through the cable outlet. The protective sheath stiffens the electric supply cable and provides an additional layer to protect against wear cause by friction. The sheath noticeably reduces maneuverability of the power tool unless some degree of movement between the sheath and the cable outlet is provided. 
         [0003]    Patent publication number DE 43 44 635 discloses a power tool with an electric motor coupled to an external electric power source by an electric supply cable. The electric supply cable is projected though the power tool&#39;s housing via a cable outlet. A protective sheath is clad around a portion of the electric supply cable projected through the cable outlet. One end of the sheath has a ball supported for rotation by a spherical socket in the housing. A spring-loaded detent engages indentations in the ball. 
         [0004]    Patent publication number DE 199 52 643 discloses a housing for a power tool with an electric motor coupled to an external electric power source by an electric supply cable. The electric supply cable is projected though a cable outlet with a rotatable element surrounding a portion of the electric supply cable. A resilient detent engages notches in the rotatable element. 
         [0005]    A drawback of the arrangements disclosed by DE 43 44 635 and DE 199 52 643 is that the electric supply cable, and its protective sheath, may be misaligned when unintentionally knocked or when the power tool is re-orientated between machining operations. The user must take the trouble to re-align the sheath to its proper position or, alternatively, tolerate a misaligned electric supply cable until re-alignment of the sheath is possible. It is an object of the present invention to provide a power tool with improved control over movement between the protective sheath and the cable outlet. 
       SUMMARY OF THE INVENTION 
       [0006]    Accordingly, in a first aspect, the present invention provides a power tool comprising: a housing; a cable outlet through the housing wherein the cable outlet has a longitudinal central axis; an electric motor for driving a work tool to perform a machining operation on a work-piece wherein the motor is located in the housing; a flexible electric supply cable for supplying electric current to the motor; a tubular sheath for protecting supply cable projected through the cable outlet and for directing unprotected supply cable at an inclined angle away from the cable outlet central axis wherein the sheath is rotatable in relation to the cable outlet to change direction of unprotected supply cable in relation to the cable outlet; and a locking means for locking the sheath in a plurality of rotational orientations in relation to the cable outlet, wherein the locking means comprises: a receiving member connected to one of the sheath or the cable outlet; an engaging member connected to the other of the sheath or the cable outlet; and a biasing means for biasing the engaging member into engagement with the receiving member to lock the sheath in one of the plurality of rotational orientations, wherein movement of the sheath against the biasing means causes disengagement of the engaging member from the receiving member and unlocks the sheath for rotation in relation to the cable outlet. With the present invention unintentional rotational force applied to the cable sheath is blocked by the locking means. The sheath may be rotated in relation to the cable outlet, but not before the locking means has been unlocked by a deliberate application of force from the sheath against the biasing means. This has the added advantage of providing the user with tactile and positive feedback of locking means operation. 
         [0007]    Preferably, movement of the sheath against the biasing means is along the cable outlet central axis. The user may easily manoeuvre the sheath to push, or pull, it along the cable outlet axis to firstly unlock the locking means by axial movement and then secondly apply rotational movement to the sheath. 
         [0008]    Preferably, the cable outlet comprises a hollow substantially cylindrical cable outlet collar to support movement of the sheath along the cable outlet central axis. The cylindrical cable outlet collar provides directional support for the sheath as it slides inside. 
         [0009]    Preferably, the cable outlet collar comprises an annular bearing through which projects the sheath and wherein the annular bearing supports the biasing means against the sheath. The bearing provides additional directional support for the sheath as slides inside the cylindrical outlet collar as well as supporting the biasing means. 
         [0010]    Preferably, the sheath comprises an annular flange fixed around the sheath and wherein an interior surface of the outlet collar supports movement of the annular flange with respect to the cable outlet. The interior surface provides additional directional support for the sheath as slides inside the cylindrical cable outlet collar. 
         [0011]    Preferably, the biasing means is held in compression between the bearing, the annular flange and the interior surface of the cable outlet collar. Any tendency of the biasing means to bulge outwardly when under compression is contained by this arrangement. The annular flange distributes the axial force of the biasing means evenly around the sheath. 
         [0012]    Preferably, the biasing means comprises a helical spring coiled around the sheath. The helical spring fits neatly in an annular chamber enclosed between the sheath and the interior surface of the cable outlet collar. 
         [0013]    Preferably, the receiving member comprises a ring with a plurality of grooves facing the engaging member, wherein the grooves are arranged at angular intervals about the cable outlet central axis and wherein each groove corresponds to one of the plurality of rotational orientations of the sheath in relation to the cable outlet. The grooves may be easily arranged to suit different configurations of rotational orientations. 
         [0014]    Preferably, the engaging member comprises at least one tongue protruding radially outward from the sheath and wherein the ring comprises a cable outlet ring fixed to the cable outlet collar. The tongue and groove arrangement provides reliable and compact locking means. 
         [0015]    Preferably, the at least one tongue is connected to a side of the annular flange facing the plurality of grooves. The annular flange may support and strengthen the at least one tongue in an axial direction and in a rotational direction. 
         [0016]    Preferably, the annular flange abuts the cable outlet ring upon engagement of the engaging and receiving members. The annular flange transfers the majority of the axial force applied by the biasing means to the cable outlet ring. This protects the at least one tongue from fatigue caused by repetitive application of axial forces. 
         [0017]    Preferably, sides of the at least one tongue and the grooves are substantially parallel with the cable outlet central axis. This arrangement provides a more positive engagement between the engaging and receiving members and a more tactile feedback of engagement to the user. 
         [0018]    Preferably, the sheath is kinked to direct unprotected electric supply cable at an inclined angle of substantially forty five degrees from the cable outlet central axis and wherein two of the plurality of rotational orientations of the sheath are diametrically opposed. Rotation of the sheath from one diametrically opposed orientation to the other re-directs the unprotected electric supply cable to a new direction perpendicular to the original direction. 
         [0019]    Preferably, the plurality of rotational orientations of the sheath comprises two rotational orientations. This avoids over-crowding the receiving member. 
         [0020]    Preferably, the sheath is fixed to the electric supply cable and/or the sheath is formed of rigid rubber material. Fixation of the sheath to the electric supply cable simplifies assembly of the power tool by unifying these to two parts. Rigid rubber material is easily moulded around, and adhered to, insulation material clad around the electric supply cable. The resilience of rubber material makes it suitable for protecting the electric supply cable from physical shocks. 
         [0021]    Preferably, the power tool comprises a circular saw with a base plate, wherein the work tool comprises a circular saw blade with a central axis and wherein the height and/or the angle of inclination of the circular saw blade central axis in relation to the base plate are/is adjustable. The configuration of a circular saw may be altered to different depth, or angle, of cut and it is advantageous to change the orientation of the sheath to suit the preferences of the user who may be left or right handed or who may be constrained to perform a machining operation in a tight space. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Further features and advantages of the present invention will be better understood by reference to the following description, which is given by way of example and in association with the accompanying drawings, in which: 
           [0023]      FIG. 1  shows a side elevation view of a hand-holdable circular saw with a circular saw blade; 
           [0024]      FIG. 2  shows a plan view of the circular saw of  FIG. 1  with a protective electric cable sheath in a rearward orientation parallel to the saw blade; 
           [0025]      FIG. 3  shows a plan view of the circular saw of  FIG. 1  with the sheath in a sideward orientation perpendicular to the saw blade; 
           [0026]      FIG. 4  shows a perspective view of the sheath; 
           [0027]      FIG. 5A  shows a horizontal cross-section V-V through a cable outlet of the circular saw and the sheath in the rearward orientation; 
           [0028]      FIG. 5B  shows the horizontal cross-section V-V with the sheath in the sideward orientation; 
           [0029]      FIG. 6A  shows a vertical cross-section VI-VI through the cable outlet of the circular saw and the sheath in the rearward orientation; 
           [0030]      FIG. 6B  shows the vertical cross-section VI-VI with the sheath in the sideward orientation; 
           [0031]      FIG. 7  a cable outlet collar of the cable outlet. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Referring to  FIGS. 1 to 3 , there is shown a hand-holdable circular saw  10  comprising a main housing  20 , an electric motor  40  within a side of the main housing, a circular saw blade  50  driven by the motor via a gear box (not show) and a generally rectangular base plate  60  pivotally connected to the main housing about two axes. 
         [0033]    The main housing  20  is formed by two opposing claim shells  20   a , 20   b  connected together by fasteners  22 . A join line between the clamshells is parallel to the saw blade  50  and defines a central longitudinal plane  23  of the circular saw  10 . The main housing comprises a front handle  24  and a rear handle  26 . Both the front  24  and the rear  26  handles are grasped by a user when the circular saw is being used to cut a work-piece W. A fixed blade guard  28  is fixed to a side of the main housing. A pivotable blade guard  30  is pivotally coupled to the main housing to rotate about a central axis  52  of the saw blade  50 . The fixed blade guard covers the upper portion of the saw blade  50 . The pivotable blade guard  30  is biased by a spring (not shown) to cover the bottom of the saw blade  50 . The pivotable blade guard rotates about the blade central axis  52  and progressively retracts within the fixed blade guard when it encounters a work-piece W being cut by the circular saw  10 . 
         [0034]    The motor  40  is electrically coupled to a flexible mains electric supply cable  42  via an on/off trigger switch  44 . The on/off switch projects from inside the main handle  26  for manual operation by the user. 
         [0035]    The saw blade  50  rotates when the motor  40  is energised by the electric supply. The saw blade protrudes through a slot  62  in the base plate. 
         [0036]    The base plate  60  provides the circular saw  10  with sliding support upon a work-piece W. The base plate comprises a pair of lateral pivot brackets  64   a , 64   b  located near opposite ends of the base plate and a longitudinal pivot bracket  72 . 
         [0037]    The main housing  20  is pivotable with respect to the base plate  60  in a lateral direction indicated by double-headed arrows LT about a lateral pivot axis  66  of the lateral pivot brackets  64   a , 64   b . The lateral pivot axis is parallel to the circular saw blade  50  and to the longitudinal plane  23  of the circular saw  10 . Lock nut  68  releasably secures the main housing against lateral movement with respect to the base plate  60 . 
         [0038]    The main housing  20  is pivotable with respect to the base plate  60  in a longitudinal direction indicated by double-headed arrow LG about a longitudinal pivot axis  74  of the longitudinal pivot bracket  72 . The longitudinal pivot axis is perpendicular to the longitudinal plane  23  of the circular saw  10 . Lock nut  76  releasably secures the main housing against longitudinal movement with respect to the base plate  60 . The saw blade  50  pivots with the main body  20 . Pivotal adjustment of the main housing in the direction of arrow LT allows the user to select angled mitre cuts in the work-piece within a range of zero degrees (saw blade perpendicular to the base plate) to 45 degrees (maximum mitre cut angle). The mitre cut angle is indicated on a scale  70  adjacent the lateral pivot bracket  64   a . Pivotal adjustment of the main housing in the direction of arrow LG allows the user to select a depth of cut in the work-piece. The depth of cut is indicated on a scale  78  marked on the blade guard  28 . 
         [0039]    The clamshell  20   a  has a cable outlet  21   a  located under the rear handle  26 . A generally cylindrical cable outlet collar  80  is attached around the cable outlet. A longitudinal central axis  82  of the cable outlet and cable outlet collar is inclined by an angle α with respect to the longitudinal plane of the circular saw  10 . The angle α is approximately 45 degrees. The electric supply cable  42  projects through the cable outlet and the cable outlet collar. An exit point from a power tool, such as the cable outlet collar  80 , is where an electric cable is mostly prone to damage caused over time by pinching, chafing, bending and other general wear. To help protect against such damage, and in doing so extend the life of the electric supply cable, a portion of the electric supply cable projecting through the cable outlet collar is clad with a tubular cable sheath  84 . 
         [0040]    Referring to  FIGS. 4 to 7 , there is shown more detail on the cable outlet  21  a from the clamshell  20   a , the cable outlet collar  80  and the sheath  84 . The sheath is made of rigid rubber material, although it may be made of any plastics material, or other material, which provides the sheath with sufficient flexibility, resilience and durability. The sheath comprises an inner portion  86  and an outer portion  88  joined by a curved portion  90  which kinks the inner and outer portions in different directions. The outer portion has a central longitudinal axis  92  which is inclined by an angle β with respect to a longitudinal central axis  94  through the inner portion. The angle β is approximately 45 degrees. The cable outlet collar surrounds the inner portion of the sheath. The inner portion central axis  94  is coaxial with the cable outlet central axis  82 . The inner portion is circumscribed by an annular flange  96  with a tongue  98  facing axially towards the curved portion  90 . The annular flange  96  and the tongue  98  are integral with the inner portion, although they could, optionally, be press fitted or adhered to the inner portion. Electric supply cable  42  protected by the sheath also curves at the curved portion by 45 degrees. 
         [0041]    The cable outlet collar  80  comprises a cable outlet ring  100  at an opposite end to the clamshell  20   a . The cable outlet ring is moulded as one piece with the cable outlet collar, although optionally the cable outlet ring may be a separate part fixed to the cable outlet collar. The cable outlet ring surrounds the inner portion  86  of the sheath  84  near a transition  102  between inner portion and curved portion  90  of the sheath. The interior of the cable outlet ring comprises a pair of diametrically opposed grooves  104   a , 104   b  facing axially towards the tongue  98  on the annular flange  96 . Each groove is sized to accommodate the tongue with a small amount of additional space. This additional space is to allow for a small degree of play between walls of the tongue and grooves when engaged. The walls of the tongue and grooves are substantially parallel to the cable outlet central axis  82 . 
         [0042]    The cable outlet collar  80  comprises an annular bearing  106  fixed to an opposite end of the cable outlet collar with respect to the cable outlet ring  100 . The cable outlet collar  80 , the cable outlet ring  100  and annular bearing  106  are co-axial with each other and with the central axis  94  of the inner portion  86  of the sheath  84 . The annular bearing surrounds the inner portion  86  of the sheath  84  near an extreme end of the inner portion. The cable outlet collar comprises a helical spring  108  in abutment with the annular bearing and the annular flange  96  on an opposite side to the tongue  98 . The spring is held in compression between the annular bearing, the annular flange and an interior surface  110  of the cable outlet collar. The spring is coiled around the inner portion of the sheath  84  and biases the tongue  98  towards engagement with the grooves  104   a , 104   b  in the cable outlet ring  100 . This locks the electric supply cable and the sheath against rotation about the cable outlet central axis  82 . 
         [0043]    Manoeuvre from the rearward orientation to the sideward orientation, and vice versa, is quick and easy to perform. Initially, a user of the circular saw  10  can manually push the electric supply cable  42  and the sheath  84  inwardly in the direction of arrow A towards the main housing  20  and against the bias of the spring  106  to disengage the tongue  98  from one of the grooves  104   a , 104   b  in the outlet ring  100 . Next, the electric supply cable and the sheath may be rotated clockwise, or anti-clockwise, through 180 degrees about the central axis  94  of the sheath&#39;s inner portion  86  and released so as the tongue re-engages with the other of the grooves in the outlet ring. The small degree of play between walls of the tongue and grooves helps to avoid the tongue jamming in the groove during re-engagement. The parallel alignment of the walls of the tongue and grooves causes a step movement which provides the user with positive feedback of locking, or re-engagement, between tongue and groove. The central axis  92  of the sheath&#39;s outer portion  88  rotates with the sheath and, in doing so, is locked an orientation perpendicular to its position prior to its rotation through 180 degrees. 
         [0044]    Returning to  FIGS. 2 ,  5 A and  6 A, there is shown the electric supply cable  42  and the outer portion  88  of the sheath  84  orientated rearward with respect to the main housing  20  and generally parallel to the longitudinal plane  23  of the circular saw  10 . The tongue  98  is engaged with the groove  104   b.    
         [0045]    Returning to  FIGS. 3 ,  5 B and  6 B, the electric supply cable  42  and the outer portion  88  of the sheath  84  have been rotated from the rearward orientation to an alternative orientation where they are orientated sideward with respect to the main housing  20  and generally perpendicular to the longitudinal plane  23  of the circular saw  10 . The tongue  98  is engaged with the groove  104   a.    
         [0046]    The location of the work-piece W and the type of cut to be performed by the circular saw influences the user&#39;s choice of orientation of the sheath  84 . A cut beginning with limited clearance behind the circular saw  10  may necessitate sideward orientation of the sheath to avoid contortion and weakening of the sheath. A mitre cut with the circular saw tilted by 45 degrees about the lateral pivot axis  66  may necessitate rearward orientation of the sheath to avoid electric supply cable obstructing the user and the user&#39;s line of sight. Commonly, users store their electric power tools with the electric supply cable wrapped about the main body or bundled into a storage box. This applies equally to the circular saw  10 . The sheath  84  can be orientated to facilitate storage of the electric supply cable in a manner causing the minimum contortion and weakening of the sheath thereby prolonging its life. The skilled person will understand that other power tools may benefit from the advantages provided by the rotatable lockable electric supply cable sheath described herein.