Abstract:
A power table saw of the type which has a generally rectangular table with front and rear end portions, a motor operatively coupled to drive a rotary cutting blade extending upwardly through a top of the table, the table saw including an elongated fence having front and rear end portions, and being configured to be laterally movable along the width of the table and be secured to the front and rear end portions of the table, front and rear releasable locking mechanisms operatively associated with the front and rear end portions of the fence for locking each end portion to the end portions of the table, and at least one positional sensor provided with each of the front and rear end portions of the fence for determining the lateral position of each end portion of the fence along the width of the table.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Table saws are valuable tools used for a variety of tasks, such as cross-cutting wood and plastic, and ripping long boards into narrow strips. While there are a variety of table saw designs, most table saws include a circular saw blade mounted on an arbor that is turned by one or more belts that are driven by a motor. The saw blade extends through an opening in the surface of a saw table, on which surface the workpiece rests and is supported. The depth of cut is varied by adjusting the amount of the blade that extends above the table surface such that the higher the blade extends above the table, the deeper the cut that is made in the material. Angle of the cut with respect to the table surface is typically controlled by adjusting the angle of the arbor to which the blade is affixed.  
         [0002]     Additionally, table saws nearly always include a fence or guide that extends from a side of the table nearest the operator to a side furthest from the operator, and is oriented to be generally parallel to a cutting plane of the blade. The rip fence is used to guide the workpiece during the process of making a “rip cut,” which is a cut made parallel to a grain of the wood, and guides the workpiece as the workpiece is fed onto the saw blade. A distance of the fence from the blade may be adjusted, thereby determining a location of the cutting surface on the workpiece. Accurate and precise positioning of the workpiece is important to accurate and precision cutting tasks.  
         [0003]     However, while conventional rip fences provide some adjustability with respect to a distance at which it is disposed from a cutting plane of the saw blade, the parallelism of the rip fence with the cutting plane of the saw blade can sometimes be compromised depending upon the particular design of the rip fence mechanism. Unfortunately, lack of parallelism or “trueness” not only accounts for inaccurate and imprecise cutting, it may result in a flawed workpiece that exhibits “burning” as the saw blade cuts at an unintended angle. Moreover, lack of parallelism may also result in a dangerous condition wherein the workpiece is kicked back toward the tool operator.  
         [0004]     Accordingly, precision alignment of the fence and its parallelism with the cutting plane of the saw blade are of critical importance in making precise and accurate cuts in the workpiece.  
       SUMMARY OF THE INVENTION  
       [0005]     The instant invention includes various embodiments of a device and method for promoting parallelism, or “trueness,” between a plane of a rotary cutting blade that is at a right angle to a surface of a table and a rip fence of a table saw assembly. Specifically, embodiments of the invention include a rip fence that may be zeroed at a predetermined location, such as when near or in abutment with a the rotary cutting blade, and then moved away from the rotary cutting blade for a predetermined distance such that the distance from a cutting surface of the rotary cutting blade as well as its orientation with respect to the rotary cutting blade may be determined. Preferably, a front and a rear end of the rip fence include a mechanism whereby the respective distances from the rotary cutting blade may be determined, and that even minute differences in the respective distances may be reconciled to promote trueness between the rip fence and the cutting surface of the rotary cutting blade.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a front perspective view of a table saw, rip fence, and front and rear sensor assemblies according to a preferred embodiment of the invention;  
         [0007]      FIG. 2  is a front perspective view of a table saw and rip fence according to another embodiment of the invention;  
         [0008]      FIG. 3  is a side perspective view of a front sensor assembly illustrated in  FIG. 2 ;  
         [0009]      FIG. 4  is a rear perspective view of a table saw, rip fence and rear sensor assembly according to the embodiment illustrated in  FIG. 2 ;  
         [0010]      FIG. 5  is a side perspective view of the table saw, rip fence and rear sensor assembly illustrated in  FIG. 2 ;  
         [0011]      FIG. 6  is a front perspective view of the rear sensor assembly according to  FIG. 2 ;  
         [0012]      FIG. 7  is a front perspective view of a table saw, rip fence, and front and rear sensor assemblies according to an alternate embodiment of the invention;  
         [0013]      FIG. 8  is a front perspective view of a table saw and rip fence according to another embodiment of the invention;  
         [0014]      FIG. 9  is a side perspective view of the front sensor assembly of the embodiment illustrated in  FIG. 8 ; and  
         [0015]      FIG. 10  is a side sectional view of the table saw and rip fence illustrated in  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     While it is contemplated that the invention may be used with a variety of conventional table saw assemblies, such as those manufactured under the SKIL and BOSCH brands by the S-B Power Tool Corporation of Chicago, Illinois, one exemplary table saw assembly, indicated generally at  10 , is illustrated in  FIG. 1  in connection with a first embodiment of the invention. According to the embodiment illustrated in  FIG. 1 , a rotary cutting blade  12  extends upwardly through a blade bracket  14 , which is an elongated slot disposed in a generally middle portion of a table  16 . A pair of miter gauge slots  18  (best shown in  FIG. 2 ) are also preferably provided, one on each side of the blade bracket  14 , and extending from a front end  20  of the table  16  to a rear end  22  of the table. While the rotary cutting blade  12  may be tiltable for miter cutting, a radial plane  24  of the rotary cutting blade  12  generally extends perpendicularly with respect to a plane of the table.  
         [0017]     An elongated, generally rectangular rip fence, indicated generally at  26 , is also provided with the exemplary table saw assembly  10 , wherein the rip fence has a length corresponding generally to a length of the table  16 , which is defined as a depth of the table as measured from the front end  20  to the rear end  22  of the table. The rip fence  26  is configured to be slidable with respect to a top surface of the table  16 . Thus, the rip fence  26  has a front end  28  that engages the front end  20  of the table  16  and a rear end  30  that engages a rear end  22  of the table and has an elongated rectangular body  32 . The rip fence  26  can move along a width of the table between the rotary cutting blade  12  and a predetermined location on the table, where the width of the table is defined as extending between side ends  33 . A guide plane  34  of the rip fence  26  is configured and arranged to face the blade bracket  14 .  
         [0018]     This embodiment contemplates that the table  16  and the rip fence  26  include complementary measurement mechanisms whereby a distance from the radial plane  24  of the rotary cutting blade  12  to a predetermined location on the table may be accurately and precisely measured, and whereby parallelism between the radial plane and the rip fence  26  may be accurately and precisely ascertained to promote accurate and precise cutting. Specifically, it is contemplated that the rip fence  26  may include one or more of a plurality of positional sensing mechanisms for sensing and/or displaying a location of the rip fence  26  relative to a predetermined reference point, such as the rotary cutting blade  12 . The sensing mechanisms may include, but should not be construed as being limited to, electronic sensors, digital readouts, pointers, or measurement indicia such as scoring or other markings disposed on the rip fence  26 , preferably at the front and rear ends  28 ,  30 . Similarly, it is contemplated that the table  16  includes corresponding positional sensing indicators for detecting a position of the rip fence  26 , such as electronic indicators, digital readouts, pointers or measurement indicia to reference or communicate with the rip fence to give visual or other indication to an operator as to the position of the rip fence relative to the blade.  
         [0019]     For example, turning again to  FIG. 1 , the rip fence  26  according to the preferred embodiment includes a front sensor assembly, indicated generally at  36 , and a rear sensor assembly, indicated generally at  38 , each of which preferably includes a positional sensor  40 . At least one LCD screen  44  is preferably provided to indicate a variety of parameters, such as displacement of the rip fence  26  from the rotary cutting blade  12  and the parallelism of the rip fence to the rotary cutting blade. The positional sensors  40  may be one of a plurality of mechanisms, such as an optical reflective reader, a capacitor, a magnet, or a pointing device, to name a few.  
         [0020]      FIG. 1  illustrates the front and rear positional sensors  40  to be optical reflective readers. The table  16  correspondingly includes positional indicators, such as a plurality of sensor reference points  46 , which may be sensed by the respective positional sensors  40 . Sensor reference points  46  may include one of a plurality of mechanisms, such as a strip of electrical contacts to be read by the positional sensors  40 , magnets, a series of bar codes disposed at predetermined increments (e.g., 1/64″), or contrasting stripes to be read by an optical reflective reader, to name a few.  
         [0021]     As illustrated in  FIG. 1 , the sensor reference points  46  include a strip having a plurality of contrasting stripes, wherein the stripes have a predetermined width, preferably 1/16″. A predetermined number of sensors disposed within each of the contrasting stripes, preferably four, electronically divide the contrasting stripes, thereby rendering an enhanced resolution. For example, where four sensors are included in each of the contrasting stripes gives a resolution of 1/64″.  
         [0022]     In contrast,  FIG. 2  illustrates another embodiment according to the invention whereby the positional sensors include positional transducer sensing head  47   a  and interacting strip  47   b,  which may be optical, mechanical magnetic or capacitive, to name a few. Alternatively, a string driven positional transducer (not shown) may also be used. For example, a capacitive-based interacting strip would have a series of copper pads at equal intervals such as ⅛″ shown as item  46  on item  47   b.    
         [0023]     The table  16  also preferably includes structural features that promote sliding of the rip fence  26  along the surface of the table  16 . These features are commonly known in the art, and include rails on which the fence can slide. Depending on the particular embodiment, additional structural features may be provided to promote sliding of the positional sensors  40  with the rip fence  26 .  
         [0024]     For example, turning again to the embodiment illustrated in  FIGS. 2-5 , the table  16  may also include front and rear sliding brackets  48 ,  50 , one at each of the respective front and rear ends  20 ,  22  along the width of the table as measured from between the sides  33  of the table, for purposes of convention. Depending on the particular sensor assembly used with the table, the sliding brackets  48 ,  50  may assume a variety of configurations. The front and rear sensor assemblies  36 ,  38  are operatively coupled to the rip fence  26 , and reciprocate along the respective front and rear sliding brackets  48 ,  50  when the rip fence is moved.  
         [0025]     Turning to the front sliding bracket  48  of the embodiment illustrated in  FIGS. 2 and 3 , the front sliding bracket is generally rectangular in shape, having a length extending between sides  33  of the table  16 , with an outside surface  56  including a longitudinal slot  58  therein. A lower portion  60  of the front sliding bracket  48  depends downwardly from a top surface of the table  16 , and the front sensor assembly  36  is coupled to the lower portion of the front sliding bracket  48  such that the front sensor assembly is lower than the top surface of the table  16 , while the rip fence  26  is coupled to an upper portion of the front sliding bracket, thereby operatively coupling the rip fence and the front sensor assembly. Thus, the front sensor assembly  36  moves along the longitudinal slot  58  as the rip fence  26  moves along a surface of the table  16 .  
         [0026]     A front mounting bracket, designated generally at  61 , is preferably provided to couple the rip fence  26  to the front sliding bracket  48 . The front mounting bracket  61  includes includes a generally horizontal portion  61   a  and a generally vertical portion  61   b  disposed at right angles to one another to receive the generally rectangular sliding bracket  48  therein. The front mounting bracket  61  is thereby operably coupled to both the rip fence  26  and the sliding bracket  48 , and may slidably engage the sliding bracket to promote movement of the rip fence along the width of the table  16 .  
         [0027]     Similarly, the rear sensor assembly  38 , which is best illustrated in  FIGS. 4 and 5 , is also operatively coupled to the rip fence  26  such that as the rip fence moves, the rear sensor assembly moves. Specifically, the rear sliding bracket  50  (best shown in  FIGS. 4 and 5 ) includes a sliding rail  62  that is coupled to an extreme rear end  22  of the table  16  and is vertically displaced from the top surface of the table to be elevationally lower than the top surface of the table. A mounting bracket  64  is mounted to the sliding rail  62  and configured to be slidingly engaged thereto.  
         [0028]     The mounting bracket  64  is preferably generally rectangular in shape, with a longitudinal groove  66  extending along a top portion thereof. The rip fence  26  is mounted to the mounting bracket  64 , preferably via a mounting extension  68  having a downwardly depending fastening element  70 , such as a pin, configured to lockingly engage the longitudinal groove  66 . Similarly, the rear sensor assembly  38  is coupled to the mounting extension  68  on a mounting side  72  thereof, and a lower rear end portion  74  is lockingly engaged to the mounting bracket  64 .  
         [0029]     Thus, the rear sensor assembly  38  is operably coupled to both the rip fence  26  and the mounting bracket  64  such that the rear sensor assembly moves with the rip fence as it moves. The positional sensor  40  is disposed at a right hand side of the rear sensor assembly  38  as viewed in  FIG. 3 .  
         [0030]     In the preferred embodiment illustrated in  FIG. 1 , a single LCD screen  44  is configured and arranged on a top surface of the rip fence  26 , whereas in alternative embodiments, LCD screens  44  may be disposed at each of the front and rear sensor assemblies  36 ,  38 . As illustrated in  FIGS. 2 and 3 , where LCD screens are provided on each of the front and rear sensor assemblies  36 ,  38 , the LCD screens preferably face the front end of the table for easy reading by the operator.  
         [0031]     Thus, in operation of any of the embodiments, the rip fence  26  is brought into abutment with the radial plane  24  or other predetermined position, at which point the sensors are zeroed by activating a zeroing mechanism  76  disposed on the rip fence. The operator may then move the rip fence  26  to a predetermined location at a desired distance from the rotary cutting blade  12 , and may determine the distance from the blade by reading the one or more LCD screens  44  disposed within the front and rear sensor assemblies  36 ,  38 , or within the rip fence  26  itself. The distance of the rip fence  26  from the rotary cutting blade  12  is an average of the respective distances of each of the positional sensors  40 , which may be expressed as follows: (x 1 +x 2 )/2, where x 1  is a displacement of a first positional sensor and x 2  is a displacement of a second positional sensor.  
         [0032]     Parallelism, on the other hand, may be determined by the absolute value of the difference between x 1  and x 2  as follows: |x 1 −x 2 |. Once the operator knows the parallelism, the operator may readjust the fence to resolve any discrepancy such that the absolute value of the difference between x 1  and x 2  approaches zero, indicating parallelism of the rip fence  26  with the rotary cutting blade  12 . A locking mechanism, such as a clamping lever  79  disposed at the front end  28  of the rip fence  26 , may then be pivoted into a locking position to lock the rip fence into position.  
         [0033]      FIG. 7  illustrates yet another embodiment of the invention that includes a rip fence  26  wherein the positional sensors  40  consist of physical indicators, such as pointers  80  disposed at each end of a mounting bracket  82  coupled to the rip fence. Correspondingly, top surfaces of the sliding brackets  48 ,  50  include measurement indicia  84  at predetermined increments. The measurement indicia  84  on each of the respective sliding brackets  48 ,  50  are calibrated with one another such that corresponding measurements oppose one another across the table from a front end  20  to a rear end  22 . Thus, as the rip fence  26  is moved away from the rotary cutting blade  12 , the pointers  80  will point to a specific measurement such that the operator can readjust and reposition the rip fence until each respective pointer is pointing at the same measurement, indicating a common distance from the radial plane  24  by front and rear ends  28 ,  30  of the rip fence, thereby indicating parallelism.  
         [0034]     Turning now to  FIGS. 9-10 , to promote a greater range of motion for the rip fence  26 , some table saws also include a side extension  86  that is configured to be extendable in a direction of the right side  54  of the table  16 . More specifically, the side extension  86  is typically a slideable panel that is coupled to the table  16  via one or more rails  87 . While it is possible to have the side extension  86  slide relative to the rails (not shown) via a coupling mechanism disposed on an underside of the slide extension, it is also plausible that the rails themselves slideably and telescopically extend from the table  16  to thereby move the side extension. Irrespective of the manner in which it extends, the side extension  86  provides for a predetermined length of extra movement of the rip fence  26 .  
         [0035]     For example, typically the distance from the radial plane  24  and the guide plane  34  of the rip fence  26  reaches a maximum at a predetermined location toward the right end  54  of the table  16 , such as between approximately 13 and 18 inches, with restriction placed on further movement by a hard stop (not shown) disposed at the right end  33  of the table, which abuts a right end of the sliding brackets  48 ,  50 , as well as by a partial length of the sliding brackets themselves, wherein a right side of each abuts the hard stop. Accordingly, the side extension  86  provides for a predetermined increment of extra movement, such as between approximately 11 and 20 inches.  
         [0036]     In operation, the operator would slide the rip fence  26  to an extreme rightward position, at which point the operator would extend the slide extension  86  away from the table  16  to provide for an additional length of movement. However, because the rip fence  26  is no longer moving relative to the table  16  as the slide extension  86  is moved, additional provision is optionally contemplated by the invention to promote continued measurement of both the displacement and parallelism of the rip fence.  
         [0037]     Any one of a plurality of mechanisms is contemplated by the invention to address parallelism and distance in table saw assemblies  10  that include the slide extension  86 . For example, spooled measuring devices  88 , such as tape measures, may be provided, with a spindle thereof coupled to the table  16  at a the front and rear ends  20 ,  22 , and a leading end of a tape coupled to the side extension  86  at front and rear ends such that as the side extension is moved, the tape would uncoil to indicate the additional displacement on either side. A disparity in the displacement would indicate a lack of parallelism, which may then be corrected by the operator.  
         [0038]     As illustrated in  FIG. 9  for example, the spooled measuring device  88  is preferably coupled to the table  16  such that it spools out the measuring tape as the sliding rail  87  moves relative to the table. More particularly, the spooled measuring device  88  is preferably coupled to the table  16  via fasteners, preferably bolts  92 , where the bolts extend through a length of the mounting block and into the table  16  to secure the mounting block and spooled measuring device to the table. A slot  94  is provided in the sliding rail  87  such that sliding rail may move relative to the stationary mounting block  90  for a predetermined distance, as a corresponding amount of measuring tape is spooled out from the spooled measuring device  88 .  
         [0039]     While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.  
         [0040]     Various features of the invention are set forth in the following claims.