Patent Publication Number: US-10786854-B2

Title: Table saw with electrically isolated arbor shaft

Description:
This application claims priority to U.S. Provisional Application Ser. No. 62/132,004 entitled “TABLE SAW WITH DROPPING BLADE”, filed Mar. 12, 2015, and U.S. Provisional Application Ser. No. 62/131,977 entitled “SYSTEM AND METHOD FOR CONTROL OF A DROP ARM IN A TABLE SAW”, filed Mar. 12, 2015, the disclosures of which are each incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The disclosure relates to power tools and more particularly to power tools with exposed shaping devices. 
     BACKGROUND 
     A number of power tools have been produced to facilitate forming a workpiece into a desired shape. One such power tool is a table saw. A wide range of table saws are available for a variety of uses. Some table saws such a cabinet table saws are very heavy and relatively immobile. Other table saws, sometimes referred to as jobsite table saws, are relatively light. Jobsite table saws are thus portable so that a worker can position the table saw at a job site. Some accuracy is typically sacrificed in making a table saw sufficiently light to be mobile. The convenience of locating a table saw at a job site, however, makes jobsite table saws very desirable in applications such as general construction projects. 
     All table saws, including cabinet table saws and jobsite table saws, present a safety concern because the saw blade of the table saw is typically very sharp and moving at a high rate of speed. Accordingly, severe injury such as severed digits and deep lacerations can occur almost instantaneously. A number of different safety systems have been developed for table saws in response to the dangers inherent in an exposed blade moving at high speed. One such safety system is a blade guard. Blade guards movably enclose the saw blade, thereby providing a physical barrier that must be moved before the rotating blade is exposed. While blade guards are effective to prevent some injuries, the blade guards can be removed by a user either for convenience of using the table saw or because the blade guard is not compatible for use with a particular shaping device. By way of example, a blade guard is typically not compatible with a dado blade and must typically be removed when performing non-through cuts. 
     Table saw safety systems have also been developed which are intended to brake the blade when a user&#39;s hand approaches or touches the blade. Various braking devices have been developed including braking devices which are physically inserted into the teeth of the blade. Upon actuation of this type of braking device, however, the blade is typically ruined because of the braking member. Additionally, the braking member is typically destroyed. Accordingly, each time the safety device is actuated significant resources must be expended to replace the blade and the braking member. Another shortcoming of this type of safety device is that the shaping device must be toothed. Moreover, if a spare blade and braking member are not on hand, a user must travel to a store to obtain replacements. Thus, this type of safety system can be expensive and inconvenient. 
     Another type of table saw uses a safety control system which, in response to a sensed unsafe condition, moves a blade beneath the level of the table. One such system is disclosed in U.S. Pat. No. 8,286,537 which issued on Oct. 16, 2012. The &#39;537 patent discloses a power tool including a workpiece support surface, a swing arm assembly movable along a swing path between a first swing arm position whereat a portion of a shaping device supported by the swing arm assembly extends above the workpiece support surface and a second swing arm position whereat the portion of the shaping device does not extend above the workpiece support surface, and a latch pin movable between a first position whereat the latch pin is engaged with the swing arm assembly and a second position whereat the latch is not engaged with the swing arm assembly. 
     In general, the power tool in the &#39;537 patent operates in a known manner until an unsafe condition is sensed by the safety control system. In response to the sensed unsafe condition, the safety control system controls a pressure operated actuator to force the latch pin from the first position to the second position and to force the swing arm assembly away from the first swing arm position and toward the second swing arm position. 
     In order to transfer power from a motor assembly to an arbor shaft in tools incorporating drop arm assemblies as a safety measure, a belt is used. The belt is typically required to exhibit increased strength in order to prevent stretching which adversely impacts operation of the tool. One common approach to providing the needed strength is to incorporate a metal or similar material into the belt. While providing the desired strength, such belts exhibit electrical conductivity. In some safety control systems, however, it is desirable to electrically isolate the arbor shaft from surrounding components and a conductive belt hampers such isolation. 
     In view of the foregoing, it would be advantageous to provide a power tool with a belt which is electrically isolated from an arbor shaft. It would be further advantageous if electrical isolation could be accomplished without sacrificing the strength of the belt. 
     SUMMARY 
     In one embodiment, a table saw assembly includes a motor assembly, an electrically conductive belt operably connected to the motor assembly, an arbor shaft operably connected to the belt, a drop arm assembly rotatably supporting the arbor shaft, and a first pulley rotatably supporting the belt, the first pulley including an inner bore and an outer surface, the first pulley configured to electrically isolate the inner bore from the outer surface. 
     In one or more embodiments, the inner bore is fixedly attached to the arbor shaft. 
     In one or more embodiments, a first pulley includes an inner component defining the inner bore, and an outer component defining the outer surface. 
     In one or more embodiments, the outer component is a plastic over-mold component. 
     In one or more embodiments, the inner component is formed from a conductive material, the outer component is formed from a conductive material, the first pulley further comprises an intermediate core positioned between the inner core and the outer core, and the intermediate core is formed from a non-conductive material. 
     In one or more embodiments, a table saw assembly includes a second pulley rotatably supporting the belt, the second pulley operably connected to the motor assembly such that rotation of the second pulley by the motor assembly causes the second pulley to rotate the belt. 
     In one or more embodiments, the second pulley includes an inner component formed from the conductive material, an outer component formed from the conductive material, and an intermediate core formed from the non-conductive material. 
     In one or more embodiments, the outer component and the inner component of the first pulley define a plurality of first dovetail connections therebetween, and/or the outer component and the inner component of the second pulley define a plurality of second dovetail connections therebetween. 
     In one or more embodiments, the first pulley is formed with a non-conductive material. 
     In one or more embodiments, the non-conductive material is anodized aluminum. 
     In one or more embodiments, a method of assembling a table saw assembly includes rotatably supporting an arbor shaft with a drop arm assembly, operably connecting the arbor shaft to an electrically conductive belt, operably connecting the electrically conductive belt to a motor assembly, and rotatably supporting the belt with a first pulley, the first pulley including an inner bore and an outer surface, the first pulley configured to electrically isolate the inner bore from the outer surface. 
     In one or more embodiments, operably connecting the arbor shaft to the electrically conductive belt includes fixedly attaching the inner bore to the arbor shaft. 
     In one or more embodiments, operably connecting the arbor shaft to the electrically conductive belt includes fixedly attaching an inner bore defined by an inner component of the first pulley to the arbor shaft, and rotatably supporting the belt with the first pulley includes rotatably supporting the belt with an outer component of the first pulley, the outer component defining the outer surface. 
     In one or more embodiments, rotatably supporting the belt with the first pulley comprises rotatably supporting the belt with a plastic over-mold component of the first pulley, the plastic over-mold component defining the outer surface the outer component. 
     In one or more embodiments, a method of assembling a table saw assembly includes using an inner component formed from a conductive material, using an outer component formed from a conductive material, and using an intermediate core positioned between the inner core and the outer core, the intermediate core formed from a non-conductive material. 
     In one or more embodiments, a method of assembling a table saw assembly includes rotatably supporting the belt with a second pulley, and operably connecting the second pulley to the motor assembly such that rotation of the second pulley by the motor assembly causes the second pulley to rotate the belt. 
     In one or more embodiments, a method of assembling a table saw assembly includes using a second pulley with an inner component formed from the conductive material, an outer component formed from the conductive material, and an intermediate core formed from the non-conductive material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate various embodiments of the disclosure and together with a description serve to explain the principles of the disclosure. 
         FIG. 1  depicts a top perspective view of a table saw mounted to a wheeled stand; 
         FIG. 2  depicts a side plan view of the right side of the table saw of  FIG. 1  with the housing, bevel plate, and workpiece support surface removed and the height adjust carriage at an upper position; 
         FIG. 3  depicts a side plan view of the left side of the table saw of  FIG. 1  with the housing, workpiece support surface, and bevel plate removed; 
         FIG. 4  depicts a top perspective view of the height adjust carriage, drop arm assembly, and motor assembly of the table saw of  FIG. 1 ; 
         FIG. 5  depicts a top perspective view of the height adjust carriage of  FIG. 4  along with rods and tubes used to guide movement of the height adjust carriage; 
         FIG. 6  depicts a side cross-sectional view of the motor assembly of  FIG. 4 ; 
         FIG. 7  depicts a plan view of the motor assembly of  FIG. 4  from the left side of the table saw; 
         FIG. 8  depicts a plan view of the motor assembly of  FIG. 4  from the left side of the table saw after the motor assembly has been rotated to provide a desired tension to the belt of  FIG. 4 ; 
         FIG. 9  depicts a side plan view of the orbit portion of the height adjust carriage of  FIG. 4 ; 
         FIG. 10  depicts an exploded view of the orbit portion of  FIG. 9 ; 
         FIG. 11  depicts a partially exploded view of the exemplary embodiment of an orbit portion; 
         FIG. 12  depicts a top perspective view of another exemplary embodiment of an orbit bracket; 
         FIG. 12A  depicts a top plan view of the orbit bracket of  FIG. 12 ; 
         FIG. 13  depicts cross-sectional view of the orbit assembly of  FIG. 10  supporting the drop arm assembly; 
         FIG. 14  depicts a bottom perspective cross-sectional view of the orbit assembly of  FIG. 13 ; 
         FIG. 15A  depicts an exploded view of the drop arm assembly of  FIG. 4 ; 
         FIG. 15B  depicts a side perspective view of the drop arm assembly of  FIG. 4 ; 
         FIG. 15C  depicts a side plan view of the drop arm assembly of  FIG. 4 ; 
         FIG. 16  depicts a side plan view of the right side of the table saw of  FIG. 1  with the housing and workpiece support surface removed; 
         FIG. 17  depicts a perspective view of the height adjust carriage of  FIG. 4  with the pyrotechnic assembly and latch assembly mounted to the height adjust carriage; 
         FIG. 18  depicts a perspective view of the cartridge of  FIG. 17 ; 
         FIGS. 19 and 20  depict perspective views of the pyrotechnic housing of  FIG. 17 ; 
         FIG. 21  depicts a partial top plan view of the table taw of  FIG. 1  with the throat plate removed; 
         FIG. 22  depicts a side cross-section view of the drop arm frame of  FIG. 4  showing a common point shared by the center of gravity and the locus of the ribs of the drop arm frame; 
         FIG. 23  depicts a side perspective view of the pyrotechnic housing mounted to the height adjust carriage; 
         FIG. 24  depicts an exploded view of the pyrotechnic assembly of  FIG. 17 ; 
         FIG. 25  depicts a top plan view of the active shot of  FIG. 17  with an electrical connector; 
         FIGS. 26-29  depict the active shot of  FIG. 17  moving the latch assembly of  FIG. 17  as the reaction plug of  FIG. 24  is threaded into the pyrotechnic housing; 
         FIGS. 30-31  depict the latch assembly of  FIG. 17  biasing the active shot outwardly from the pyrotechnic housing when the reaction plug is removed; 
         FIG. 32  depicts a side plan view of the drop arm assembly of  FIG. 4  indicating the axes of the various components; 
         FIG. 33  depicts a side plan view of the table saw of  FIG. 1  after the drop arm assembly has been dropped against a surface while the height adjust carriage is at an upper position; 
         FIG. 34  depicts a side plan view of the table saw of  FIG. 1  with the drop arm assembly latched and the height adjust carriage at a lower position; 
         FIG. 35  depicts a side plan view of the table saw of  FIG. 1  after the drop arm assembly has been dropped against a surface with the height adjust carriage at a lower position; 
         FIG. 36  depicts a top perspective view of the bounce back latch assembly mounted to the height adjust carriage; 
         FIGS. 37-39  depict left, top and right plan views of the height adjust carriage showing ribbing to provide increased strength; 
         FIGS. 40-41  depict perspective views of the bevel carriage showing ribbing to provide increased strength; 
         FIG. 42  depicts a saw control unit assembly mounted to the bevel carriage; 
         FIG. 43  depicts an exploded view of the saw control unit assembly of  FIG. 42  and the bevel carriage; 
         FIG. 44  depicts an exploded view of the saw control unit assembly of  FIG. 42 , the drop arm assembly, and the bevel carriage; 
         FIG. 45  depicts a side perspective view of the bevel carriage showing coaxial wiring used to provide communication with various components; 
         FIG. 46  depicts the shield and center conductor of the coaxial wiring used to provide electrical communication with various components; 
         FIG. 47  depicts a perspective view of the connection between the central conductor and the CCP; 
         FIG. 48  depicts a perspective view of the coaxial wiring offset from its normal position whereat it is connected to the bevel carriage with the protective covering removed to show the exposed shield which connects to the bevel carriage; 
         FIGS. 49-50  depict protective coverings used to cover stripped portions of the coaxial wire and also to provide communication between the coaxial wire and other components; 
         FIG. 51  depicts a side perspective view of the table saw of  FIG. 1  with the housing removed to show how components are in communication with the shield of the coaxial wiring; 
         FIG. 52  depicts an exploded view of the trunnions used to pivot the bevel carriage showing electrical isolation between the workpiece support surface and the bevel carriage; 
         FIG. 53  is a cross-sectional view of the arbor shaft showing electrical isolation of the arbor shaft from the rest of the drop arm assembly and the belt; 
         FIG. 54  is an exploded view of the pulley of  FIG. 53  which provides electrical isolation between the belt and the arbor shaft; 
         FIG. 54A  is a side plan view of the outer shell of  FIG. 54  showing dovetail splines; 
         FIG. 55  depicts a perspective view of the motor assembly showing radially directed vents which direct carbon dust away from one or more of the components; 
         FIG. 56  depicts a partial exploded view of the throat plate and workpiece support surface of  FIG. 1 ; 
         FIG. 57  depicts a perspective view of the throat plate engaged by a knob with the workpiece support surface removed; 
         FIG. 58  depicts a top perspective view of the knob of  FIG. 56 ; 
         FIG. 59  depicts a side plan view of the front of the throat plate; 
         FIG. 60  depicts a partial perspective view of the drop arm assembly with the arbor lock of  FIG. 15B  engaging the pyrotechnic housing to maintain the drop arm assembly in a latched condition; 
         FIG. 61  depicts a partial top perspective view of the table saw of  FIG. 1  with the throat plate removed to allow resetting of the drop arm assembly; 
         FIG. 62  depicts a side perspective view of the HMI unit of  FIG. 1 ; 
         FIG. 63  depicts an exploded view of the internal components of the HMI unit of  FIG. 62 ; 
         FIG. 64  depicts a rear plan view of the table saw of  FIG. 1  with the bevel carriage at zero degrees; 
         FIG. 65  depict a rear plan view of the table saw of  FIG. 1  with the bevel carriage at forty-five degrees of bevel such that a USB port of the saw control unit assembly is visible through a dust port access slot of the table saw housing; and 
         FIGS. 66-67  depict protective covers which can be used to protect the USB port of  FIG. 65  from undesired access. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Like reference characters indicate like parts throughout the several views. 
     DETAIL DESCRIPTION OF THE DISCLOSURE 
     While the power tools described herein are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the power tools to the particular forms disclosed. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims. 
     Referring to  FIG. 1 , a table saw assembly  100  is shown. The table saw assembly  100  includes a table saw  102  mounted to a wheeled stand  104  The table saw  102  includes a base housing  106  and a workpiece support surface  108 . Support surface extensions  110  and  112  are provided to assist in supporting larger workpieces. A fence  114  is provided to guide a workpiece along the workpiece support surface  108 . 
     A riving knife or splitter  116  is positioned adjacent to a blade  118  which extends from within the base housing  106  to above the workpiece support surface  108 . A blade guard  120  and kick-back pawls  117  may be attached to the splitter  116 . The blade  118  extends through a slot in a throat plate  122 . A human machine interface (HMI) unit  124  is provided at a front portion of the table saw  102 . 
     An angle indicator  130  located adjacent to the HMI unit  124  indicates the angle of the blade  118  with respect to the workpiece support surface  108 . A bevel adjust lock  132  may be used to establish the angle of the blade  118  with respect to the workpiece support surface  108  by pivoting a bevel carriage  134  (shown in  FIG. 2 ) within the base housing  106 . The bevel carriage  134  is then clamped between the bevel adjust lock  132  and a bevel clamp  133  (see  FIG. 3 ). As further depicted in  FIG. 3 , a height adjust wheel  136  is used to adjust the height of the blade  118  above the workpiece support surface  108  (not shown in  FIG. 3 ). Rotation of the height adjust wheel  136  rotates a bevel gear  138  which is engaged with a threaded rod  140 . The threaded rod  140  is thus forced to rotate either clockwise or counterclockwise, depending upon the direction in which the height adjust wheel  136  is rotated. 
     The threaded rod  140  threadedly engages a height adjust carriage  142 . In one embodiment, the threaded rod  140  engages a threaded bushing  152  of the height adjust carriage  142 . The height adjust carriage  142  is thus forced to move upwardly and downwardly as the threaded rod  140  rotates. Rotation of the height adjust carriage  142  is precluded by a height adjust rod  144  and a height adjust tube  146  which are fixedly attached to the bevel carriage  134 . The height adjust rod  144  and a height adjust tube  146  extend through openings  148  and  150 , respectively, in the height adjust carriage  142  which are shown in  FIG. 4 . 
     In order to reduce the weight of the table saw  102 , light-weight materials, e.g., aluminum, are used in the manufacture of the height adjust carriage  142 . While effective for reducing weight, aluminum is not typically strong enough to withstand the various forces (described more fully below) which are applied to the height adjust carriage  142  without deformation or damage. Accordingly, a powder metallurgy bushing  153  shown more clearly in  FIG. 5  is provided within the opening  150 . The bushing  153  distributes forces equally along the opening  150 , thereby reducing the possibility of damage particularly at the mouth of the opening  150  which could lead to undesired “looseness” between the height adjust carriage  142  and the height adjust tube  146 . 
     Similarly, a powder metallurgy slotted bushing  154  is provided at the upper mouth of the opening  148  to protect the opening  148  from damage from the height adjust rod  144 . In other embodiments, one or more of the bushings  153 / 154  are replaced with a linear bearing or split guide pads. In some embodiments, the bevel carriage  134  is protected by the incorporation of dampening bushings at the locations which support the height adjust rod  144  and/or the height adjust tube  146 . 
     Returning to  FIG. 4 , a motor assembly  160  is supported by the height adjust carriage  142 . The motor assembly  160  drives a belt  162 , which in one embodiment is made from a conductive material, through an offset drive shaft  164  and pulley  166  shown more clearly in  FIG. 6 . The offset drive shaft  164  is offset from a power shaft  168  by a gear  170 . The motor assembly  160  is attached to the height adjust carriage  142  in a manner which allows the belt  162  to be tensioned without the need of a linear tensioner as explained with reference to  FIG. 7 . 
     As shown in  FIG. 7 , the motor assembly  160  is attached to the height adjust carriage  142  with four screws  172  which are inserted through respective mounting slots  174  in a motor gear housing  176 . The mounting slots  174  are oriented to define a motor mounting axis of rotation  178  which is beneath the axis of rotation  180  of the power shaft  168  which is in turn below the offset shaft  164 . Accordingly, rotation in one direction of a jack screw  182  which is threadedly engaged with a plate  184  fixedly attached to the height adjust carriage  142  causes the jack screw  182  to push against a plate  186  attached to the motor gear housing  176 . In one embodiment, the plate  184  is either formed as a portion of the height adjust carriage  142  or integrated into the height adjust carriage  142  as a single unit. Thus, the jack screw  182  is threadedly engaged with the height adjust carriage  142  instead. Since the plate  186  which is impinged by the jack screw  182  is located above the motor mounting axis of rotation  178 , the motor assembly  160  rotates in the direction of the arrow  188  from the position of  FIG. 7  to the position of  FIG. 8 . 
     Returning to  FIG. 4 , the above described movement of the motor assembly  160  causes the pulley  166  which is attached to the offset drive shaft  164  to move in the direction of the arrow  190  away from a slave pulley  192  which is rotatably supported by a drop arm assembly  194 . Consequently, the belt  162  is placed into tension. Accordingly, the motor assembly  160  can be placed in the position of  FIG. 7  for initial assembly, and then pivoted toward the position depicted in  FIG. 8  to a location which provides the desired tension of the belt  162 . This configuration requires less linear travel than a linear adjustment mechanism to achieve the same tension within a constrained space. In other embodiments, a spring loaded actuator replaces the jack screw  182  to maintain belt tension over time. 
     Tension of the belt  162  is verified using a belt tension meter inserted through a belt tension access port  196  (see  FIG. 4 ) in an upper surface of a belt protective cover  198 . Positioning of the access port  196  on the upper surface of the belt protective cover  198  allows for access to the belt  162  from above the table saw  102 . This allows for easier access to setting the tension of the belt while maintaining structural requirements for the height adjustment carriage without flipping the saw upside down to gain access to the belt  162 . While depicted as a circular opening, the access port  196  in other embodiments is in a different geometry and in certain embodiments is provided with a removable plug or an access door. 
     Continuing with  FIG. 4 , the drop arm assembly  194  is movably connected to the height adjust carriage  142  by an orbit shaft  200  which defines a drop arm orbit axis  201 . The location of the drop arm orbit axis  201  is controlled to be located between the axis of rotation  202  of the offset drive shaft  164  (see  FIG. 6 ), which is also the axis of rotation of the pulley  166 , and an axis of rotation  183  of the slave pulley  192  using an orbit bracket  203  further described with reference to  FIGS. 9-10 . 
     The orbit bracket  203  includes an orbit shaft hole  204  through which the orbit shaft  200  is inserted. The orbit bracket  203  further includes an alignment bore  205  and an anti-rotation slot  206  which receive a locator pin  207  and anti-rotation pin  208 , respectively, which extend from the height adjust carriage  142 . The orbit bracket  203  is connected to the height adjust carriage  142  by two screws  210 . 
     The axis  211  of the anti-rotation slot  206  is aligned to intersect the central axis  212  of the alignment bore  205 . Accordingly, when the locator pin  207  and the anti-rotation pin  208  are positioned within the alignment bore  205  and the anti-rotation slot  206 , respectively, the anti-rotation pin  208  and the anti-rotation slot  206  provide an accurate angular position for aligning the drop arm orbit axis  201 . 
     The incorporation of the orbit bracket  203  with the anti-rotation slot  206  and the anti-rotation pin  208  enable the use of lightweight materials while providing increased accuracy in positioning the saw blade  118 . In some embodiments, accurate positioning of an orbit bracket is achieved using two shoulder screws  213  (see  FIG. 11 ), or alignment pins  214  ( FIG. 12 ) which are received within corresponding bores (not shown) on the height adjust carriage  142 . Alignment of the saw blade  118  is further provided by incorporating an inner face  228  of the orbit bracket  203  with an angle  230  of about 0.65° with respect to a plane parallel to the drop plane (see below and  FIG. 21 ). This angling of the inner face provides increased accuracy in positioning the saw blade  118  throughout various beveling angles even when the belt  162  is under increased tension. 
     Increased accuracy in positioning the blade  118  is further provided by the manner in which the drop arm assembly  194  is movably connected to the height adjust carriage  142 . Specifically, as shown in  FIG. 13 , the orbit shaft  200  is rotatably supported within a drop arm frame  242  of the drop arm assembly  194  by two bearings  215 . An orbit bolt  232  threadedly engages the orbit shaft  200  and compresses the bearings  215  against the inner bearing walls  234  of spaced apart brackets  236  of the drop arm frame  242 . 
     An orbit pin  216  extends through aligned bores  217 ,  218 , and  219 . The bore  218  extends through the orbit shaft  200 . The bore  217  extends through an upper portion of the orbit bracket  203  while the bore  219  extends through a lower portion of the orbit bracket  203 . The orbit shaft  200  is thus rotatably fixed with respect to the orbit bracket  203 . Two set screws  220  extend through bores  221  in the lower portion of the orbit bracket  203  and anchor the orbit shaft  200  against two shoulders  222  of the orbit shaft bore  204  which are depicted in  FIG. 14 . 
     The shoulders  222  are formed in the orbit shaft bore  204  by forming a lower circular portion  224  of the orbit shaft bore  204  and an upper circular portion  226  of the orbit shaft bore  204 . The lower circular portion  224  is substantially the same diameter as the diameter of the orbit shaft  200 . The upper circular portion  226  in different embodiments has the same or different diameter as the lower circular portion  224 . The origin of the upper circular portion  226 , however, is offset from the origin of the lower circular portion  224  in a direction opposite the location of the set screws  220 . 
     Accordingly, the upper circular portion  226  provides sufficient clearance for a slip fit between the orbit shaft  200  and the orbit shaft bore  204 . At the same time, the junction of the upper circular portion  226  and the lower circular portion  224  form the shoulders  222  which extend along the entire length of the orbit shaft bore  204 . Consequently, when the set screws  220  are installed, the set screws  220  force the orbit shaft  200  against the shoulders  222  forming a “three point” lock between each of the set screws and the shoulders. 
     In some embodiments, the shoulders are replaced by two ball bearings pressed into the drop arm frame  242  using the outer race of the bearing. The orbit shaft  200  is then inserted with one side of the orbit shaft engaging the inner race of one of the bearings. The orbit bolt  232  is then screwed inside the orbit shaft from the opposite direction of the orbit shaft engaging the inner race of the other bearing. The orbit shaft and bolt assembly move the inner races of the two bearings towards each other. With the outer races fixed in the drop arm, and the inner races pulled together, the internal clearances are minimized thus reducing or eliminating the side to side movement due to the internal clearances of the bearings. 
     Turning now to  FIGS. 15A-C , the drop arm assembly  194  is depicted in further detail. As noted above, the slave pulley  192  is engaged with the belt  162  and rotatably supported by the drop arm assembly  194 . More specifically, the slave pulley  192  is rotatably supported by an arbor shaft  240  which is configured to rotatably support the blade  118  (see  FIG. 1 ). The arbor shaft  240  is rotatably supported within a drop arm frame  242 . 
     The drop arm frame  242  further includes a spring well  244  ( FIG. 15B ) which houses a spring  246 . The spring  246  is operatively connected to a flange  248  of an arbor lock  250 . The arbor lock  250  includes an activation arm  252  positioned above the drop arm frame  242  and a locking ramp  254 . The arbor  240  extends through an arbor slot  256  and two shoulder screws  258  extend through guide slots  260  and threadedly engage the drop arm frame  242 . 
     The drop arm assembly  194  includes a capacitive coupling plate (CCP)  262  from which extends a connector tab  264 . The CCP is mounted to a CCP bracket  268  using screws, five screws either the same or different types of screws  266  are illustrated, which in turn is mounted to the drop arm frame  242  using three set screws  269 . The CCP bracket  268  includes a raised lip  270  configured to provide electrical isolation between CCP and the blade. While in the embodiment of  FIG. 15 a    a single piece CCP bracket  268  is depicted, the bracket in other embodiments is formed using multiple modules which in some embodiments are not connected to each other. 
     The CCP  262  is part of a capacitive sensing system (discussed in further detail below) and is made from electrically conductive material. As most clearly depicted in  FIG. 15C , the CCP  262  is not symmetrically shaped. Rather, the center of mass of the CCP  262  is shifted toward the orbiter  272  of the drop arm frame  242 . This shape provides sufficient capacitance while reducing the inertia of the drop arm assembly  194 . In one embodiment, a finish treatment for the CCP  262  is a non-conductive coating. Acceptable coatings include manganese phosphate for steel CCPs and anodizing for aluminum CCPs. Such thin non-conductive coverings provide isolation in case of accidental contact between the blade and a conductive portion of the CCP during heavy cuts due to blade deflection. 
     The CCP bracket  268  is made from a non-conductive material. In one embodiment, a plastic with a low di-electric constant which is not affected by water is used in order to minimize the capacitance variation in the system. The CCP bracket  268  is inserted into the drop arm and manually adjusted to the proper distance from the blade then locked in place by set screws  269  (see  FIG. 15A , only two are shown). 
     Specifically, the screws  266  are used to mount the CCP  262  to the CCP bracket  268  by threadedly engaging protuberances  271 . Optionally, a fastening element such as a nut (not shown) in addition to the screws  266  could be used to mount the CCP  262  to the CCP bracket  268 . In another embodiment, the CCP bracket  268  is overmolded to the CCP  262  as a single unit. Thus, any fastening element is no longer required. The protuberances  271  are then inserted into wells  273  formed in the drop arm frame and adjusted to set the CCP  262  at the desired location. Then, the set screws  269  are inserted through bores in the wells  273  to engage the protuberances  271 . 
     The protuberances  271  electrically isolate the screws  266  and the CCP  262  from the drop arm frame  242 . The raised lip  270  of the CCP bracket  268  wraps around the CCP  262  along the outside edge to protect the CCP  262  from incidental contact with the blade during heavy cutting. 
     Continuing with  FIG. 15C , the orbiter  272  includes rebound ledges  274 / 275  (see also  FIG. 15A ) and a pad  276  is mounted to a lower surface of the drop arm frame  242 . As best viewed in  FIG. 15B , the drop arm assembly  194  further includes two alignment pins  278 , a semi-spherical strike pin  280 , and a latch pin  282  supported by the drop arm frame  242 . 
     Referring now to  FIG. 16 , the drop arm assembly  194  is maintained in a latched position by a latch  300 . The latch  300  is movably connected to the pyrotechnic housing  322  by a pin  302 . The latch  300 , also shown in  FIG. 17 , includes a latch pin receiving area  304  which engages the latch pin  282  in the latched position. The latch  300  further includes two prongs  306 . The latch  300  is biased by a spring  308  such that the prongs  306  are biased into contact with a shot  310 . 
     The shot  310  is paired with another shot  312  by a cartridge  314  shown in  FIG. 18 . A bridge  320  joins the two shots  310 / 312  in the cartridge  314 . 
     The cartridge  314  is shown in  FIG. 17  mounted in a pyrotechnic housing  322 . The pyrotechnic housing  322 , also shown in  FIGS. 19-20 , includes an internally threaded chamber  324 , a mounting plate  326 , and a finger plate  328 . A locking ramp  364  is located at an upper portion of the finger plate  328 . A slit  330  extends along one side of the internally threaded chamber  324  and terminates at a rounded end portion  332 . This configuration allows for optimal positioning of the active shot as explained with further reference to  FIGS. 21 and 22 . 
       FIG. 21  depicts a partial top plan view of the table saw  102  with the throat plate  122  removed from a throat plate opening  334 . Visible through the throat plate opening  334  is an arbor nut  336  and the blade  118  mounted to the arbor shaft  240 . The drop arm  194  and a portion of the height adjust carriage  142  is also visible through the throat plate opening  334 . Also depicted in  FIG. 21  is a drop plane  338 . The drop plane  338  is a plane that is aligned with where the shot  310  interfaces with the drop arm assembly and along which the drop arm assembly moves in a substantially parallel manner when a saw control system is activated as discussed more fully below.  FIG. 22  depicts a cross-sectional view of the drop arm assembly  194  taken parallel to the drop plane  338  of  FIG. 21 . 
       FIGS. 21 and 22 , thus show that the drop arm assembly  194  is configured such that the center of gravity  340  of the drop arm assembly  194  lies on, in proximity to or adjacent to the drop plane  338  so that the transfer of force from the shot to the semi-spherical strike pin  280  occurs as close as practicable to the drop plane  338 . 
     Accordingly, the pyrotechnic housing  322  is configured to center the active shot substantially on the drop plane  338 . This results in reduced stress for the system and decreased drop time for the drop arm assembly  194 . Additionally, the inactive shot (shot  312  in the configuration of  FIG. 21 ) is positioned inwardly of the active shot while maintaining the cartridge  314  in a location which is easily accessible through the throat plate opening  334 . This configuration ensures that the inactive shot does not interfere with the movement of the drop arm assembly  194 . 
     To further improve the alignment of the active shot with the semi-spherical strike pin  280 , an alignment housing  342  is mounted to the pyrotechnic housing  322  as shown in  FIG. 17 . The alignment housing  342  receives the hardened steel alignment pins  278  ( FIG. 15B ) thereby reducing the blade deflection under load, as well as, ensuring proper alignment between the active shot and the semi-spherical strike pin  280 . Providing the pins  278  in the drop arm assembly  194  further provides enhanced stabilization of the drop arm frame  242  against side loading or torsional loading against the orbit shaft  200  ( FIG. 4 ). Using hardened steel pins as alignment pins extending from the aluminum drop arm frame  242  achieves this benefit while allowing for a light weight/low inertia drop arm frame  242 . 
     While two pins  278  are shown in  FIG. 15B , in other embodiments only one is used. Yet in another embodiment, one or more protrusion or surfaces is used in the system. Additionally, in some embodiments the alignment housing is positioned in the drop arm assembly  194  while the hardened steel pins extend from the pyrotechnic housing  322 . In further embodiments, the alignment features are integrated into the latch  300  and/or the shots. 
     The slit  330  in the housing  322  receives the bridge  320  of the cartridge  314 . The slit  330  thus allows for a spare shot to be incorporated into the cartridge  314 . The slit  330 , however, weakens the pyrotechnic housing  322 . Consequently, support is required at both a forwardly location and a rearwardly location with respect to the slit  330  to preclude failure of the pyrotechnic housing  322 . While the rearward mounting plate  326  is firmly bolted to the height adjust carriage  142  with two bolts  346  and a pin  348  shown in  FIG. 23 , bolting of the forward portion of the pyrotechnic housing  322  would result in unacceptably high stresses, even with the provision of the rounded end portion  332  which inhibits cracking at the end of the slit  330 . It is for this reason that the finger plate  328  is used. 
     As depicted in  FIG. 17 , the forward portion of the pyrotechnic housing  322  is supported by contact between the finger plate  328  and finger ribbing  344  on the height adjust carriage  142 . The finger plate  328  thus transfers force in the direction of the pyro firing (beneath the pyrotechnic housing  322 ), but does not constrain the pyrotechnic housing  322  in any other degree of freedom, which greatly reduces the stress levels in this part and allows the pyrotechnic housing  322  to be made from affordable and lightweight material. In this embodiment, three fingers are provided. In other embodiments, more or fewer fingers are provided. 
     The disclosed pyrotechnic system provides a number of additional features. By way of example, the pyrotechnic assembly  350  of  FIG. 24  includes two shots  310 / 312 . While the saw control system in some embodiments provides an electrical check to make sure that an unused shot is connected, the safety control system in some embodiments is not configured to ensure that the connected shot is properly installed in the pyrotechnic housing  322  and thus aligned with the semi-spherical strike pin  280 . The pyrotechnic assembly  350  shown in  FIG. 24 , however, is configured to ensure that a user does not mistakenly connect the wrong shot. 
       FIG. 24  depicts the pyrotechnic assembly  350  which includes the pyrotechnic housing  322 , the cartridge  314 , and the shots  310 / 312  which have been described above. The pyrotechnic assembly  350  further includes an electrical connector  352 , a connecting wire  354 , and a reaction plug  356 . 
     Typically, the shots  310 / 312  and the cartridge  314  are provided as a single unit. Additionally, the table saw  102  is provided with the connecting wire  354  inserted through an opening  358  of the reaction plug  356  as shown most clearly in  FIG. 25 . One end of the connecting wire  354  is permanently attached to the saw control unit, while the other end is attached to the electrical connector  352 . 
     The pyrotechnic assembly  350  is assembled by providing the shots  310 / 312  in the cartridge  314 . The shots  310 / 312  and the cartridge  314  are then inserted into the pyrotechnic housing  322 . For a new unit, either shot  310 / 312  is aligned with the housing axis  366  and inserted into the internally threaded chamber  324 . If the unit has previously been used, then the unused shot is inserted into the internally threaded chamber  324 . 
     Next, the electrical connector  352  is inserted into a plug of the shot  310 / 312 . The reaction plug  356  is then threaded into the internally threaded chamber  324 . Because the electrical connector  352  is larger than the opening  358  (see  FIG. 25 ), the reaction plug  356  can only be threaded into the internally threaded chamber  324  if the electrical connector  352  is connected to a shot located in the internally threaded chamber  324 . The incorporation of the electrical connector  352  and a mating connector on the shots thus enables the incorporation of a mechanical/electrical lockout as described above. 
     In other embodiments, the reaction plug  356  and electrical connector  352  can be replaced with a snap-on cap or a flashlight-like cap. Additionally, the electrical connector  352  can be omitted in such embodiments and replaced with a simple pigtail connector. 
     The reaction plug  356  further assists in a lock-out function which ensures that the cartridge  314  is adequately seated within the pyrotechnic housing  322 . As shown in  FIG. 26 , the spring  308  biases the latch  300  in a clockwise direction. When the reaction plug  356  is not adequately threaded into the internally threaded chamber  324  as depicted in  FIG. 26 , the prongs  306  force the shot  312  upwardly within the internally threaded chamber  324  and the latch  300  is rotated in a clockwise direction to a position whereat a lower surface of a lower portion  360  of the latch  300  is located within the drop path of the latch pin  282 . Accordingly, counterclockwise orbiting of the drop arm assembly  194  is constrained by contact between any portion of the drop arm assembly and the lower portion  360 . Consequently, the latch pin  282  cannot be received within the latch pin receiving area  304 . 
     By rotating the reaction plug  356  in a direction to further engage the internally threaded chamber  324 , the reaction plug  356  is forced against the cartridge  314  or the shot  310 , forcing the shot  310  or the cartridge  314  against the prongs  306 . This forces the spring  308  into compression, and rotates the latch in a counterclockwise direction resulting in the configuration of  FIG. 27 . In  FIG. 27 , counterclockwise orbiting of the drop arm assembly  194  is still constrained by contact between the latch pin  282  and the lower surface of the lower portion  360 . 
     Continued rotation of the reaction plug  356  fully seats the cartridge  314  within the internally threaded chamber  324 , further rotating the latch  300  to the configuration of  FIG. 28 . In  FIG. 28 , the latch  300  has been rotated so that a side surface of the lower portion  360  is within the drop path of the latch pin  282 . Accordingly, by orbiting the drop arm assembly  194  in a counterclockwise direction, the latch pin  282  presses against the side surface of the lower portion  360  further compressing the spring  308  and rotating the latch  300  in the counterclockwise direction as the latch pin  282  slides upwardly along the side surface of the lower portion  360 . 
     Continued counterclockwise orbiting of the drop arm assembly  194  moves the latch pin  282  above the side surface of the lower portion  360 . Accordingly, the spring  308  forces the latch  300  to rotate in a clockwise direction resulting in the configuration of  FIG. 29 . In  FIG. 29 , the latch  300  has rotated in the clockwise direction such that the latch pin  282  is received within the latch pin receiving area  304 . 
     Accordingly, if the reaction plug  356  is not sufficiently threaded into the pyrotechnic housing  322 , the latch  300  provides a mechanical “lockout” and the drop arm assembly  194  cannot be raised into a cutting/latched position. While described with respect to a pyrotechnic device, the reaction plug  356  can be used with actuators of any desired type to provide both mechanical and electrical lockout capabilities. 
     The reaction plug  356  is typically configured such that it can be easily turned by hand. In one embodiment, the reaction plug  356  includes ribs  362  (see  FIG. 24 ) which are configured to allow for tightening/loosening. The ribs  362  are further configured to allow for tightening/loosening of the reaction plug  356  with a spanner wrench (not shown). In some embodiments, the reaction plug is a hex shaped plug that can be turned with a standard hex wrench instead of a spanner. In further embodiments, a locking feature separate from the reaction plug is provided which requires a tool to allow rotation of the reaction plug. By way of example, the locking feature may be a spring loaded component (ball bearing, spring tab) which is operated by pushing on a locking tab that needs a screwdriver or similar tool to release. In other embodiments, a hole and extruded pin with a circular reaction plug are used which require a special wrench to tighten and loosen the reaction plug. 
     The biasing of the latch  300  into the active shot by the spring  308  also assists in removal of the cartridge  314  as explained with initial reference to  FIG. 30 .  FIG. 30  depicts the cartridge  314  fully seated within the pyrotechnic housing  322 . For removal of the cartridge  314 , the reaction plug  356  is removed. Because the latch  300  is biased against the active shot, removal of the reaction plug  356  allows the cartridge  314  to be pushed upwardly to the position depicted in  FIG. 31 . A user can then grasp the upper portion of the cartridge  314  above the inactive shot rather than pulling the cartridge  314  using the connecting wire  354 . 
     Referring back to  FIG. 16 , when the active shot  310  is activated by a saw control system, the shot  310  applies force to the drop arm assembly  194  through the semi-spherical strike pin  280 . This force is transferred to the latch pin  282  (see  FIG. 29 ) which forces the latch  300  to compress the spring  308  and moves the latch pin receiving portion  304  of the latch  300  out of the drop path of the latch pin  282 . The drop arm assembly  194  then orbits in a clockwise direction moving the blade  118  (see  FIG. 2 ) which is mounted to the arbor shaft  240  under the workpiece support surface  104 . 
     As discussed above, the location of the drop arm orbit axis  201  is controlled to be located between the axis of rotation  202  of the offset drive shaft  164  and an axis of rotation of the slave pulley  192 . This arrangement provides for increased dropping speed of the drop arm assembly  194  and prevents damage or stretching of the belt that would lead to degradation of powertrain performance as explained with further reference to  FIGS. 6, 15A, and 32 .  FIG. 32  shows the drop arm orbit axis  201 , the axis of rotation  202  of the offset drive shaft  164 , and the axis of rotation  183  of the slave pulley  192 . Since the pulley  166  is mounted to the height adjust carriage  142  and the slave pulley  192  is mounted on the drop arm assembly  194 , tensioning of the belt  162  as described above moves the pulley  166  away from the drop arm orbit axis  201  (to the left in  FIG. 32 ). As a result, during a drop arm drop the slave pulley  192  moves toward the pulley  166 . Accordingly, the axis  183  moves closer to the axis  202 . This reduction in distance de-tensions the belt which results in a faster drop time. 
     The impact of the drop arm assembly  194  is absorbed in part by contact between the pad  276  and a surface  374  as shown in  FIG. 33 . The pad  276  is mounted on the drop arm assembly  194  using any desired mounting means such as glue, fasteners, clamp plate, etc. Positioning the pad  276  on the drop arm assembly  194  allows a pad with a smaller sized geometry than mounting the pad on the surface  374 . 
     For example,  FIG. 33  depicts the location of impact between the drop arm assembly  194  and the surface  374  when the height adjust carriage  142  is initially in a fully raised position as depicted in  FIG. 2 . When the height adjust carriage  142  is at a lowermost position as depicted in  FIG. 34 , the drop arm assembly  194  contacts the surface  374  at a lower location as depicted in  FIG. 35 . Consequently, covering the span of the surface  374  which is contacted by the drop arm assembly  194  would take more material than is required to cover the portion of the drop arm assembly  194  which contacts the surface  374 . Consequently, mounting the pad  276  on the drop arm assembly  194  reduces the amount of pad material that is required. 
     The configuration of the drop arm frame  242  is thus selected in part to provide the desired surface for contacting the surface  374 . Returning to  FIG. 22 , the configuration of the drop arm frame  242  is further selected to reduce the weight of the drop arm frame  242 . As depicted in  FIG. 22 , a number of ribs  376 / 378 / 380 / 382  extend from a lower surface  384  to an opening  386  which receives the arbor shaft  240 . The ribs  376 / 378 / 380 / 382  provide strength which allows for less material to be used and/or for lighter materials to be used. In the context of the drop arm assembly  194 , this translates into a reduced moment of inertia thereby providing a more rapid lowering of the drop arm assembly in response to a sensed unsafe condition. 
     The ribs  376 / 378 / 380 / 382  also reduce the rebound force of the drop arm assembly  194  once the pad  276  contacts the surface  374 . As shown in  FIG. 22 , the ribs  376 / 378 / 380 / 382  each define a respective axis  388 / 390 / 392 / 394 . The axes  388 / 390 / 392 / 394  intersect at a locus  396  which coincident with, adjacent to, in proximity to the center of gravity  340 . This configuration reduces bounce-back energy and allows further reduction in the amount or weight of materials. 
     The above described configuration is typically insufficient for dissipation of all bounce back energy of the drop arm assembly  104 . Accordingly, a bounce back latch assembly  400  is provided as shown in  FIG. 36 . The bounce back latch assembly  400  includes a lower latch  402  and an upper latch  404  independently movably connected to the orbit bracket  203  by a pin  406 . The pin  406  in some embodiments is sized longer than necessary to provide for tolerance. A wave washer (not shown) may be used between the head of the pin  406  and the latch  404  to allow for the tolerance while providing desired tension to the system. 
     The lower latch  402  and an upper latch  404  are biased into contact with a rebound surface  408  of the drop arm frame  242  by two springs  410  and  412 , respectively. The springs  410 / 412  are anchored to the orbit bracket  203  by a bolt  414 . The bounce back latch assembly  400  further includes a reset lever  416  which extends from the lower latch  402  to a location above the orbit bracket  203 . 
     During orbiting of the drop arm assembly  194  in response to a sensed unsafe condition, the rebound surface  408  orbits in a clockwise direction (viewed as in  FIG. 36 ). As the rebound surface  408  orbits, the rebound ledge  275  (see  FIG. 15A ) orbits past the lower latch  402 . Accordingly, the spring  410  biases the lower latch  402  into contact with the rebound surface  408  at a location inwardly of the outermost extent of the rebound ledge  275 . Subsequently, the drop arm assembly  194  contacts the surface  374  as described above. When the drop arm assembly  194  rebounds away from the surface  374 , the lower latch  402  comes into contact with the rebound ledge  275  precluding further upward (counterclockwise) movement of the drop arm assembly  194 . 
     The rebound ledge  274  (see  FIG. 15A ) and the upper latch  404  operate similarly. The main difference is that for the rebound ledge  274  to orbit beneath the upper latch  404 , more clockwise orbiting of the rebound surface  408  is required. This occurs, for example, when the height adjust carriage  142  is positioned toward its highest location such as the height depicted in  FIG. 16 . Accordingly, at higher locations, rebound protection is provided by the rebound ledge  274  and the upper latch  404  while at lower heights, such as the height depicted in  FIG. 34 , rebound protection is provided by the rebound ledge  275  and the lower latch  402 . 
     When a user wishes to return the drop arm assembly  194  to a latched position, the user pushes against the reset lever  416  which moves the lower latch  402  away from the rebound surface  408 . Additionally, a lip  418  of the lower latch  402  contacts the upper latch  404 , moving the upper latch  404  away from the rebound surface  408 . The drop arm assembly  194  can then be raised into a latched position held by the latch  300 . 
     The above described use of ribbing to reduce the weight of the drop arm assembly  194  also reduces the overall weight of the table saw  102 , making the table saw  102  more portable. Ribbing is used in other areas of the table saw for the same purpose. For example,  FIGS. 37-39  depict various views of the height adjust carriage  142 . Extensive ribbing  420  is provided in order to accommodate the large impact forces from the shots  310 / 312 . 
     Similarly, the bevel carriage  134  includes ribbing  422 / 424 / 426 / 428  along with other structural features as depicted in  FIGS. 40-41 . Also shown in  FIGS. 40-41  are openings  430  and  432 . The ribbing  424  and  428  provides structural support for the surface  374  which is impacted by the drop arm assembly  194  as discussed above. The ribbing  422  and  426  and other structural features provide support which allows for the openings  430  and  432  to be accommodated. The opening  430  is needed in order to allow for mounting of the motor assembly  160  ( FIG. 4 ) while the opening  432  is provided to enhance operation of the saw control unit as will be discussed in further detail below. In addition, the removal of the material to form the opening  432  reduces the weight of the saw. 
     Accordingly, in one embodiment ribbing is used throughout the table saw  102  to keep the table saw  102  light and portable without compromising structure. Nonetheless, selective areas and components of the table saw  102  are provided in the form of stronger materials to ensure optimal functioning of the table saw  102  even after multiple pyrotechnic activations. For example, forces of the impact of a drop transfer through the drop arm, orbit bracket and into the height adjust rods. Accordingly, the orbit bracket  203  ( FIG. 10 ) and the area of the bevel/height adjust carriages around the height adjust rods are typically formed with stronger and or heavier material. Likewise the alignment housing  342  ( FIG. 17 ), the pyrotechnic housing, and the latch  300  in some embodiments are made from stronger material such as by using powder metallurgy, zinc die-casting, or the like. 
     Because many of the structural components are formed of lightweight material, forces from the pyrotechnics and from arresting the drop arm assembly  194  are not damped. The transferred forces must therefore be accounted for when positioning sensitive components. One such sensitive component is housed within a saw control unit assembly  450  in  FIG. 42  which is mounted to the bevel carriage  134 . The saw control unit assembly  450  includes electronics used to control the table saw assembly  100 . Such electronics include a memory with program instructions stored therein which, when executed by a processor of the saw control unit assembly  450 , controls the safety control system. 
     As shown in  FIG. 43 , the saw control unit assembly  450  includes a printed circuit board (PCB)  452  which is mounted to an outer housing  454 . The outer housing  454  is in turn mounted to an inner housing  456 . The saw control unit assembly  450  is then mounted to the bevel carriage  134 . The inner housing  456  and the outer housing  454  electrically isolate the PCB  452  from the bevel carriage  134 . A USB port  458  (see  FIG. 42 ) provides for electronic access to the PCB  452 . 
     The foregoing configuration of the saw control unit assembly  450  provides damping of the forces from the pyrotechnics and from arresting the drop arm assembly  194 . Nonetheless, some of the forces may still be transferred to the PCB  452 . Accordingly, if the PCB  452  is mounted perpendicular to either of these force vectors, a large impact/vibration load will be applied to the PCB  452 , which can cause damage to the PCB  452 . Accordingly, as best viewed in  FIG. 44 , the PCB  452  is mounted at about a 15 degree angle with respect to the plane in which the forces of the shot and the impact on the surface  374  are applied. 
     If the PCB  452  is mounted in close proximity and parallel to a conductive body that is carrying a signal such as the bevel carriage as discussed in further detail below, the signal can be capacitively coupled to the PCB  452  and cause unwanted noise in other signals. Consequently, the bevel carriage  134  and the saw control unit assembly  450  are configured such that there are no parallel metal surfaces to couple noise to the PCB  452 . It is for this reason that the opening  432  is provided in the bevel carriage  134 . 
     While the mounting of the PCB  452  on the bevel carriage  134  is convenient for purpose of wire routing as discussed further below, in some embodiments the PCB  452  is mounted on a plastic base or underside of the workpiece support surface. In these embodiments, the transfer of force and signal coupling are reduced, but wire routing is typically less optimal. Mounting the PCB  452  to the underside of the workpiece support surface has the added advantage of using the workpiece support surface as a heat sink for heat generating components of the PCB  452  such as a triac. In another embodiment, a component such as a second PCB that generates heat other than the PCB  452  is mounted to the underside of the workpiece support surface and uses the workpiece support surface as a heat sink. 
     As noted above, the positioning of the saw control unit assembly  450  is selected in one embodiment for the convenience of wire routing. Wire routing for one embodiment is depicted in  FIG. 45 . In  FIG. 45 , the PCB  452  is connected to the CCP  262  by a coaxial cable  460 . The coaxial cable  460 , shown in  FIG. 46 , includes a center conductor  462  which is insulated from a shield  464  by an insulator  466 . An outer plastic coat  468  protects and insulates the shield  464 . As shown most clearly in  FIG. 47 , the center conductor  462  of the coaxial cable  460  is connected to the connector tab  264  of the CCP  262  to provide a reliable connection that can withstand the shock loading of the pyrotechnic firing event. 
     Returning to  FIG. 45 , the coaxial cable  460  is connected to the height adjust carriage  142  at location  470  and sufficient slack is provided in the wire  460  between the location  470  and the connector tab  264  to allow for the drop arm assembly  194  to move without detaching the coaxial cable  460  from the connector tab  264 . 
     The coaxial cable  460  is further connected to the bevel carriage  134  at locations  472  and  474  and the height adjust carriage  142  at location  476 . Sufficient slack is provided in the coaxial cable  460  between the locations  474  and  476  to allow for movement of the height adjust carriage  142  with respect to the bevel carriage  134 . 
     At various locations the outer plastic coat  468  is stripped to expose the shield  464 . By way of example,  FIG. 48  depicts a stripped area  478  associated with the location  474 . The stripped area  478  is placed in direct contact with the bevel carriage  134  at location  474 . Typically, a protective covering  480  (see  FIG. 49 ) is then attached over the stripped area  478  to protect the stripped area  478  and to ensure good contact between the shield  464  and the underlying metallic component. 
     Depending upon the location of the connection, a dual screw protective covering, such as the protective covering  480 , or a single screw protective covering such as the protective cover  482  of  FIG. 50  may be used. One or more of the protective coverings in some embodiments are formed from a plastic, while in other embodiments one or more of the protective covers are formed from metal to provide increased connectivity. Alternatively, the coaxial cable shield  464  can be soldered directly to other components or surfaces. 
     In some embodiments, only connection locations provided with a protective cover  480 / 482  are stripped. Thus, in some embodiments the cable is stripped at the locations  472  and  476  of  FIG. 45  but the cable is not stripped at the location  474 . 
     The coaxial cable shield  464  is thus connected to metallic components in such a way that the shield  464  can be connected to multiple points without terminating, and also in such a way as to provide protection to the coax cable  460  where the outer plastic coat  468  is stripped away. This ensures uninterrupted shield connection to all metal parts in the undercarriage assembly. The coaxial cable  460  is thus used to connect shield to the bevel carriage  134 , height adjust carriage  142 , the riving knife  116  and associated components, etc. 
     Shield connection to the angle indicator  130  ( FIG. 1 ) is also provided by the location  472 . As discussed above, the location  472  is in electrical communication with the bevel carriage  134 , also shown in  FIG. 51 . The bevel carriage  134  is in turn in electrical communication with a bevel clamp  133 . Finally, the bevel clamp  133  is pressed into electrical communication with the angle indicator  130  when the bevel carriage  134  is locked by the bevel adjust lock  132 . Thus, the angle indicator  130  is placed in electrical communication with the shield  464 . 
     The angle indicator  130  is electrically isolated from the workpiece support surface  108  by a non-conductive front plate  486 . This allows the workpiece support surface  108  to be maintained at “neutral” while the angle indicator  130  is at “shield”. In other embodiments electrical isolation is provided by plastic isolators as table connections, by using an all plastic front plate or a plastic front plate with a small insert for bevel clamping, or by using an all metal front plate with non-conductive isolators to the bevel lock and the workpiece support surface. If desired, the workpiece support surface  108  may be connected to earth ground to reduce interference to the sensing system from static electricity. Static electricity from the blade and components connected to shield can be ameliorated by connecting those components to earth ground through a high resistance cable. 
     Because the bevel carriage  134  is suspended from the workpiece support surface  108 , the support mechanisms must also be insulated. As shown in  FIG. 52 , the bevel carriage  134  includes a pair of beveling trunnions  488  (only one is visible in  FIG. 52 ) which are pivotably supported by a pair of trunnion blocks  490  attached to the workpiece support surface  108 . The trunnion blocks  490  are insulated from the beveling trunnions  488  by a pair of plastic trunnion inserts  492 . 
     The angle indicator  130  is connected to shield in some embodiments, either alternatively or additionally, through the bevel carriage  134  or height adjust carriage  142 . By way of example,  FIG. 45  shows the bevel carriage  134  connected to “shield” at the locations  472  and  476 . Electrical communication with the locations  472  and  476  may be provided through a powder metallurgy bracket  496  (see  FIG. 51 ) in electrical communication with the height adjust rod  484  and/or through a threaded rod bracket  498  in electrical communication with the height adjust rod  484 . Thus, while the PM brackets  496 / 498  provide additional strength which allows for other portions of the table saw  102  to be made with lightweight metals, they can also provide for good electrical communication between components. 
     As noted above, the height adjust carriage  142  is connected to the shield  464 . The drop arm frame  242  is in turn in electrical communication with the height adjust carriage  142  through the orbit bracket  203 . Accordingly, the arbor shaft  240  and blade  118  are electrically isolated from the drop arm frame  242 . As shown in  FIG. 53 , the arbor shaft  240  is electrically isolated from the drop arm frame  242  by a plastic bearing housing  500  which houses a bearing  501  which supports a blade side  502  of the arbor shaft  240 . A pulley side  504  of the arbor shaft  240  is supported by a bearing unit  506 . The drop arm frame  242  includes a plastic over-mold  508  which supports a back bearing  510 . Accordingly, the blade  118 , as well as the arbor shaft  240 , arbor nut  336 , and blade washers  512 / 514  are each electrically isolated from the drop arm frame  242 . In an alternate embodiment, the bearing  510  is isolated by a component (not shown) wherein the component can be incorporated into the back bearing  510  either by pressed fit, adhesive, over-mold, or other techniques. The bearing can be made from non-conductive material such as ceramic material, as an example. 
     The arbor shaft  240  is further electrically isolated from the conductive belt  162  ( FIG. 15A ) by the pulley  192 . As depicted in  FIGS. 53 and 54 , the pulley  192  includes an inner core  520 , an intermediate core  522 , and an outer shell  524 . A shim  526  is provided between the arbor shaft  240  and an inner shim lip  528  of the slave pulley  192 . In another embodiment, more than one shim may be used in the system. A jam nut  530  maintains the pulley  192  on the arbor shaft  240 . 
     The shim  526  provides the correct alignment between the pulley  192  and the pulley  166 . The motor end pulley  166  attaches to the motor assembly  160 . The driven pulley  192  is attached to the drop arm assembly  194 . Because of the tolerance build up, it is possible for the two pulleys  192 / 166  to be offset. Accordingly, in this embodiment one of the pulleys is fixed and the other is adjustable. While in the embodiment of FIG.  53  a shim is used, in other embodiments the shim is replaced by a sliding collar or a collar that can be adjusted by turning on an external thread. Further embodiments incorporate an adjustable collar, a movable collar with jack screw in the pulley, inclined planes on the pulley and shaft, a c-ring instead of the jam nut, an adjustable multi-piece pulley, or a method using differently sized pulleys based on actual shaft offset measurements. 
     Returning to  FIG. 54 , the inner core  520  is wear resistant and may be made from a conductive material. The inner core  520  includes a bore  532  configured to couple with the arbor shaft  240  such as by a threaded engagement. Other methods of engagement such as splined, a keyed, press fit connection, or the like may also be used. The outer shell  524  is also wear resistant and may be made from a conductive material. The outer shell  524  includes an outer surface  534  configured to engage the belt  162 . 
     The intermediate core  522  is formed from a non-conductive material which in one embodiment is an insert molded plastic. The outer surface  536  of the inner core  520  and the inner surface  538  of the outer shell  524  include features to prevent slipping of the intermediate core  522  with respect to the inner core  520  or the outer shell  524 . The features include, but are not limited to, knurl, splined, dove-tail, protruded structure, anti-slip structure, locking structure, or the like. 
     As depicted in  FIG. 54A , the outer shell  524  in this embodiment includes splines  540  which are dovetailed. The outer faces exhibit an angle  542  of about 6°. This provides increased locking which is beneficial when materials exhibiting different thermal expansion and contraction characteristics are used. Accordingly, when the intermediate core  522  is formed, complementary dovetail structures are formed in the intermediate shell as depicted in  FIG. 54 . Thus, the outer component and the inner component of the pulley define a plurality of dovetail connections therebetween. 
     In other embodiments, electrical isolation between the arbor shaft  240  and the belt  162  is provided using an all plastic pulley, an anodized aluminum pulley, or a plastic over-mold pulley. 
     In some embodiments, a non-conductive belt is used in place of the conductive belt  162 . In this embodiment, a conductive pulley can be used with the non-conductive belt. In another embodiment, a conductive belt can be used with one conductive pulley and one non-conductive pulley. 
     The motor assembly  160  shown in  FIG. 6  is thus isolated from the arbor shaft  240  by the pulley  192 . As depicted in  FIG. 6 , the motor assembly  160  is further isolated by the pulley  166  which is made like the pulley  192  with a non-conductive intermediate core  580  between an inner core  582  and an outer shell  584 . 
     While the motor assembly  160  is thus electrically isolated from the arbor shaft  240  and blade  118 , the motor is nonetheless capable of generating electromagnetic interference. Accordingly, the motor assembly  160  is configured to reduce the potential transmission of interfering electromagnetic energy. As depicted in  FIG. 6 , the power shaft  168  is radially supported within a casing  586  by a bearing  588 . The other end of the power shaft  168  is radially supported within the motor gear housing  176  by a bearing  590 . The offset drive shaft  164 , containing the gear  170 , is radially supported within the motor gear housing  176  by a bearing  592 . A bearing  594  is supported by a cover plate  596 . The cover plate  596  is attached to the motor gear housing  176  and encloses the gear  170  and positions the gear  170  to be driven by an armature pinion. 
     If all of the foregoing components were made from metals, the motor assembly  160  would act like an antenna and transmit noise which could interfere with the sensing system. Specifically, the offset drive shaft  164  (also called a gear shaft) and the bearings  588 ,  590 ,  592 , and  594  all transmit noise which if coupled to a large component like the motor gear housing  176 , the motor casing  586 , or the cover plate  596  would be transmitted in the vicinity of the sensing system if those components were made from metal. In order to reduce interference with the sensing system, the motor gear housing  176 , the casing  586 , and the cover plate  596  are therefore made from plastic, significantly reducing the noise transmitted by the motor assembly  160 . In alternative embodiments, a non-metallic barrier is positioned between the shafts/bearings and the cover plate/gear housing. 
     In addition to interference from electrical noise, the motor assembly  160  also generates carbon dust which can interfere with the operation of the sensing system including the CCP  262 . For example, carbon dust from universal motor brushes can build up on components and may form a conductive path that will affect the sensing system. Accordingly, unlike typical motor housings, the motor gear housing  176  is provided with a number of radial air vents  610  as shown in  FIG. 55 . The radial air vents  610  divert cooling air which is axially driven by a fan  612  (see  FIG. 6 ) and divert the air radially. Accordingly, any carbon entrained within the fan driven air is forced in a direction away from electrically isolated components including the CCP  262  thereby reducing the possibility of carbon dust buildup between the isolated components. 
     In some embodiments, additional reductions in electrical noise interference are realized by incorporating an electronically commutated motor rather than an AC universal motor. An electronically commutated motor provides a more consistent noise level which is more easily mitigated and may reduce generated noise. Other noise reducing features include the incorporation of ceramic bearings instead of plastic bearing isolators, isolation of gear to pulley shaft with thermoset or thermoplastic, isolating the blade locally such as by using non-conductive blade washers, incorporation of non-conductive couplers on shaft, incorporating a partly non-conductive arbor shaft, or using an aluminum gear housing with isolated bearings. 
     The fence  114  of  FIG. 1  is also configured to reduce potential interference with the sensing system. Specifically, the fence  114  is removably and movably attached to rails  620 / 622  which are mounted to the workpiece support surface  108 . The fence  114  is optionally in electrical communication with the workpiece support surface  108 . Because the fence  114  is movable, it is possible for the fence to come into contact with the blade  118  or the riving knife  116  (or associated pawls). To reduce the potential for inadvertent contact which could affect the sensing system, the sides and top of the body portion of the fence  114  are formed with isolating components  624 ,  626 ,  628 , respectively. This allows for internal components and end portions of the fence  114  to be formed from metal. 
     In one embodiment, one or more of the isolating components  624 ,  626 ,  628  can be removed and reinstalled by the user to allow use of custom made jigs or fixtures with the tool. In another embodiment, a single isolating component is used. The one isolating component may be “U” shaped to cover all three surfaces or simply cover one side of the fence. 
     In further embodiments, the body portion of the fence is over-molded with an isolation material. In some embodiments the riving knife and associated pawls are isolated from the shield signal or formed from non-conductive materials. In some embodiments, the isolating component  628  is omitted and kickback pawls are provided with a “lock-up” feature similar to those common with the overhead guard which lock up to prevent contact with the top of the fence. In further embodiments the isolating component  628  is omitted and the fence is configured to extend only across the workpiece support surface  108  to a location at which it cannot contact the kickback pawls. 
     The throat plate  122  of  FIG. 1  is also configured to reduce electrical interference as explained with reference to  FIG. 56 . The throat plate  122  includes an insert receiving area  640  in which an insert  642  is mounted. The throat plate  122  is configured to fit within the throat plate opening  334  in the upper surface of the workpiece support surface  108 . The throat plate  122  is removably mounted to the workpiece support surface  108  by first inserting two tabs  646 / 648  within slots (not shown) in the workpiece support surface  108  or under a lip (not shown) of the workpiece support surface  108 . A knob  650  is then rotated to lock the throat plate  122  in place. 
     The knob  650  has a body portion  652  and a stem  654 . The body portion  652  is rotatably positioned in a knob well  656  in the workpiece support surface  108 . The stem  654  extends through a hole (not shown) in the knob well  656  to the underside of the workpiece support surface  108 . A spring assembly  658  is positioned on the stem  654  (see  FIG. 57 ) beneath the workpiece support surface  108  biasing the body portion  652  against the bottom of the knob well  656 . 
     Turning to  FIG. 58 , the body portion  652  of the knob  650  includes two finger holes  660 , a locking cam  662  and a lifting cam  664 . The finger holes  660  provide an area for a user to gain leverage so as to rotate the knob  650 . In other embodiments, other geometry is provided to allow a user to gain leverage. In some embodiments, the body portion includes a coupling feature which allows a tool such as a screw driver, Allen wrench, or other tool to engage the knob  650  when rotation of the knob  650  is desired. 
     The cams  662  and  664  selectively engage a cam ramp  666  located in a knob recess  668  of the throat plate  122  shown in  FIG. 59 . By rotation of the knob  650  in a clockwise direction, the lifting cam  664  is rotated beneath the cam ramp  666  forcing the throat plate  122  upwardly so as to allow a user to more easily grip and remove the throat plate  122 . Rotation of the knob  650  in a counter clockwise rotates the locking cam  662  over the top of the cam ramp  666  thereby locking the throat plate in position. 
     The knob  650  and the throat plate  122  in one embodiment are made of plastic to preclude interference with the sensing system. In areas which are subject to increased wear, metal inserts such as the insert  642  may be used to provide increase wear resistance. Such metal inserts are insulated from the workpiece support surface  108  by the plastic throat plate  122 . 
     Removal of the throat plate  122  is typically desired in order to facilitate changing of the blade  118 . Accordingly, a user simply rotates the knob  650  in a clockwise direction to force the throat plate  122  upwardly as described above and then removes the throat plate to expose the arbor nut  336  as depicted in  FIG. 21 . Because the drop arm assembly  194  is supported solely by the latch  300  (see  FIG. 29 ), it may be possible for the user to dislodge the drop arm assembly  194  inadvertently while loosening or tightening the arbor nut  336 . For example, when a blade wrench is used to turn the arbor nut in the tightening direction, a moment is generated which acts on the drop arm orbiter  272  in a direction that acts against the supporting force of the latch spring  308  and can cause de-latching. The arbor lock  250  is used to preclude such de-latching as described below. 
     With reference to  FIG. 15B , once the throat plate  122  is removed, a user pushes the activation arm  252  in the direction of the arrow  670 . Referring now to  FIG. 21 , as the activation arm  252  is pushed in the direction of the arrow  670  of  FIG. 15B , the flange  248  compresses the spring  246  and the arbor lock  250  is forced in the direction of the arrow  672 . The arbor lock  250  thus slides along the shoulder screws  258  and the arbor shaft  240  by way of the guide slots  260  and the arbor slot  256 . 
     As the arbor lock  250  moves to the left as depicted in  FIG. 15B , a narrow portion  674  of the arbor slot  256  moves into a notch  676  in the arbor shaft  240  locking the arbor shaft which allows a user to rotate the arbor nut  336  (see  FIG. 21 ). 
     Additionally, the locking ramp  254  is positioned onto the locking ramp  364  as depicted in  FIG. 60 . Since the locking ramp  364  is a part of the pyrotechnic housing  332  which is mounted to the height adjust carriage  142 , the drop arm assembly  194  cannot be de-latched from the latch  300  even while tightening the arbor nut  336 . In alternate embodiments the arbor lock interfaces with other components attached to or a part of the height adjust carriage  142 . 
     Removal of the throat plate  122  further allows the user to reset the drop arm assembly  194  in the event of de-latching of the drop arm assembly  194  from the latch  300  either as a result of the saw control unit or other de-latching. As shown in  FIG. 61 , the drop arm assembly  194  may be reset by first pushing the reset lever  416  in the direction of the arrow  678  which moves the upper latch  404  and the lower latch  402 , as described above with respect to  FIG. 36 , allowing the drop arm assembly  194  to be orbited upwardly. The user then positions a blade wrench  680  about the arbor nut  336  or the arbor shaft  240  to pull the drop arm assembly  194  back into a latched position as described above with respect to  FIGS. 26-29 . 
     In some embodiments, a push stick or some other removable tool are used to raise the drop arm assembly  194 . In further embodiments, a hand hold is provided on the drop arm assembly itself. In still other embodiments, the drop arm assembly  194  is automatically raised such as by using energy stored during movement of the drop arm assembly  194  after de-latching. In some of the embodiments, some of the energy from movement of the drop arm assembly is stored in a spring positioned at the surface  374 . 
     The HMI unit  124  of  FIG. 1  is shown in greater detail in  FIG. 62 . The HMI unit  124  includes a housing  700 , an access point  702 , a near field communication (NFC) access point is illustrated herein, and a number of status indicators  704 . Other types of communication protocol such as Bluetooth, zigbee, Wi-Fi, data protocol, mobile protocol, ultra wide band (UWB) protocol, or any frequency band are possible. The housing  700  protects the other components of the HMI unit  124  while providing user access to components of the HMI unit  124 . The NFC access point  702  is a location at which an electronic device such as a smart phone can be positioned in order to transfer data from a transceiver of the HMI unit  124  to the smart phone. To this end, a user smart phone is provided with an application which includes communication protocols. A user can use the NFC access point  702  to obtain current status of the table saw  102  as well as unique identification information for the table saw. The application can then be used to obtain maintenance recommendations, reset procedures or trouble-shooting procedures, and to provide registration of the table saw. The application can further lock or unlock the system. For example, the application is used to lock or unlock one or more of the bypass switch and the motor power switch using a personal identification number or code. 
     The status indicators  704  are used to provide desired alerts or status indicators to a user. In some embodiments, the status indicators  704  indicate power available, safety system in bypass, safety or system error which is correctable by the user, and safety or system error which is correctable by a service center. In different embodiments, more or fewer status indicators  704  are provided. The construction of the HMI unit  124  enables viewing of the status indicators  704  even in bright sunlight as discussed with further reference to  FIG. 63 . 
     As shown in  FIG. 63 , the status indicators  704  are illuminated by four LEDs  706  on a printed circuit board (PCB)  708 . In some embodiments, the LEDS  706  are each provided as a colored LED having a color different from the other of the LEDSs. An NFC antenna  710  is also provided on the PCB  708 . The PCB  708  is supported by a support  712  which is attached to the housing  700 . A spacer  714  is attached to the support  712  by a number of clips  716 . The spacer  714  includes a number of wells  718  which include openings (not shown) at a lower portion of the wells  718  which receive a respective one of the LEDs  706 . The spacer  714  provides the proper spacing between LEDs and a diffuser  720 , as well as the proper spacing between the NFC antenna  710  and the smartphone access point  702 . The wells  718  of the spacer  714  also prevent light bleed between the different colored LEDs  706 . The wells  718  of the spacer  714  further include one or more openings or passageways  719 . The passageways channel dust away from the LEDs  706  thereby preventing the LEDs  706  from being covered. 
     The diffuser  720  includes a number of lenses  722 , each lens associated with a respective one of the wells  718 . The diffuser  720  retains LED brightness while diffusing light to look uniform across the exposed surface. The diffuser  720  is made of material that is scratch and shatter resistant. 
     While some components of the table saw  102  are thus configured to provide ease of access or use, access or use of some components by a user is not desired. By way of example, the PCB  452  must be electronically accessible during assembly of the table saw  102  and in some instances by a service technician, but should not be accessed by a user. Accordingly, the USB port  458  is positioned to provide access to a technician while limiting access to a user as discussed with initial reference to  FIG. 64 . 
     In  FIG. 64 , the table saw  102  is depicted with a zero bevel angle. Accordingly, a dust port  730  is positioned adjacent to a lower end portion of a dust port access slot  732  in the base housing  106 . The dust port  730  is part of a dust shroud  734  which is attached to the bevel carriage  134  (not visible in  FIG. 64 ). In this position, neither the outer housing  454  nor the USB port  458  of  FIG. 42  are visible to a user. 
       FIG. 65  depicts a rear view of the table saw  103  when the table saw  102  is positioned at a forty-five degree bevel angle (the dust shroud  734  is not depicted in this view). At this position, the outer housing  454  and the USB port  458  are viewable through the dust port access slot  732 . Accordingly, the USB port  458  is accessible by a service technician. Since a user is not expected to frequently look through the dust port access slot  732  at the angle depicted in  FIG. 65 , however, a user will generally not see the USB port  458 . Accordingly, the USB port  458  is shielded from the user under most scenarios. 
     In some embodiments, access to the USB port  458  is further protected such as by providing a protective plastic or rubber plug  736  ( FIG. 66 ) or a cover  738  screwed down with tamper resistant screw  740  ( FIG. 67 ). In some embodiments, the outer housing  454  must be removed to provide access to the PCB  452 . 
     While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.