Abstract:
The saw table guide bar has magnets thereon so that when it is inserted into the slot in an iron saw table it is urged to slide along the side of the slot. The magnetic saw table guide bar is used to support various measuring devices and overcomes measuring difficulties resulting from table slots of varying width.

Description:
CROSS REFERENCE 
   This application relies for priority on the Provisional Application entitled “Magnetic Miter Slot Bar,” filed Apr. 7, 2004, Ser. No. 60/560,776. 

   BACKGROUND OF THE INVENTION 
   Many woodworking and other machines have a spindle rotating on an axis. This axis is used as a reference for setting the various tools guides and surfaces on the machine. On a table saw, a circular saw blade is mounted on the spindle. This blade is flat and lies in a plane at a right angle to the spindle axis. The table saw has a ferrous table with a saw slot therein. The saw blade extends up through the saw slot, to extend above the table surface. For most purposes, the table surface is at a right angle to the plane of the saw blade so that square cuts are made. The workpiece has a flat surface which lies against the plane of the table surface. Moving the workpiece past the blade makes the cut surface at a right angle to the table surface, as long as the spindle is positioned correctly. The surface of the ferrous saw table has a miter slot therein which is used to guide workpieces past the saw blade. Therefore, the direction of the miter slot must be parallel to the plane of the saw blade. In addition, the rip fence must be parallel to the plane of the blade. If the rip fence or the miter slot are not parallel to the plane of the blade, then the workpiece will be moved toward or away from the blade during the cut. This is undesirable for several reasons, including the fact that smooth cutting is not achieved. In addition, saw noise is increased. In other cases, the cut surfaces have burn marks from the saw blade. Another important reason is that there is a threat of kickback of the workpiece as it is being cut. 
   In the past, setting up the table saw has been very time-consuming and filled with a large amount of trial and error. The most successful alignment has been done by craftsmen who have had many years or experience. However, machinery of this type does not stay in adjustment because the machinery is hard-working and is subject to heavy loads and pounding from the lumber which it cross-cuts, rips or dados. There is need for tools which permit a craftsman who is skilled in woodworking but who is not skilled in machinery to adequately align and calibrate table saws to their optimum adjustment. The procedure must be easy to accomplish and must allow the operator to adjust and calibrate the saw quickly and accurately. 
   The prior U.S. Pat. No. 6,665,946 to Paul J. Reilly discloses a machine alignment system which aids in the alignment of the table surface at a right angle to the plane of the saw blade and relates the adjustment of the table so that the miter slot is parallel to the plane of the saw blade. It also discusses the problems of accurate engagement with the miter slot. 
   BRIEF SUMMARY OF THE INVENTION 
   In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to a miter slot bar for sliding in the table slots of table saws and the like to carry a measuring instrument thereon. The measuring instrument is for interacting so that the parallelism of the miter slot with respect to the plane of the saw blade can be established. The miter bar has a reference side surface for engagement against one side of the miter slot and has magnets on the miter slot bar which magnetically urge the miter slot bar toward that side of the miter slot. 
   It is, thus, a purpose and advantage of this invention to provide a magnetic miter slot bar which is part of an alignment system that assures correct alignment between the miter slot, saw blade, rip fence and miter gages in table saws, top saws and the like so that the saws can be accurately set up to make clean, safe and accurate cuts. 
   It is another purpose and advantage of this invention to provide a magnetic miter slot bar which is part of an alignment system which is useful for aligning and calibrating various machinery which has tables with miter slots therein so that the tables, spindles, rip fences and miter gages can be adjusted. 
   It is another purpose and advantage of this invention to provide an alignment system which includes a slide bar which carries a measuring device thereon so that the slide bar can slide along the miter slot and the table and the measuring device indicates parallelism of the miter slot to the saw blade or fence. These adjustments are critical for safe and maximum performance use of the table saw. 
   It is another purpose and advantage of this invention to provide an alignment system which includes a slide bar which fits into the miter slot of a table and fits within the slot and can travel the full length of the miter slot with precision so as to ensure accurate measuring readings from the miter slot to the plane of the saw blade. 
   It is another purpose and advantage of this invention to provide a slide bar which can carry a dial indicator for measurement of the distance from the table miter slot to the plane of the saw blade on a saw fence. 
   It is a further purpose and advantage of this invention to provide a miter slot bar which fits within the miter slot of a saw table and to place magnets on the miter slot bar so that the magnets pull the miter slot bar toward one side of the miter slot. 
   Other purposes and advantages of this invention will be noted from the study of the following portion of the preferred embodiment and the attached claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of a table saw showing a miter slot in the table and showing the alignment system of this invention associated with the table top and the miter slot. 
       FIG. 2  is an enlarged end view thereof, with the table taken in section and part of the miter slot bar broken away. 
       FIG. 3  is a bottom view of the miter slot bar, with parts broken away. 
       FIG. 4  is an isometric view of the alignment system of this invention wherein the magnetic miter slot bar carries and guides a Master Gage. 
       FIG. 5  is a left-end view thereof, with a section taken through the table at the miter slot. 
       FIG. 6  is a view similar to  FIG. 4 , but showing a dial indicator mounted on the miter gage for measuring the distance to the saw blade. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   This invention is directed to an alignment system which is particularly useful for table saws and the like. The alignment system assures correct alignment between the miter slot, rip fence and miter gages with respect to the plane of the saw blade. It is particularly useful in table saws and the like so that the saws can be accurately set up and make clean, safe, accurate cuts. The system is particularly useful with any machinery which has a miter slot in the table. 
   Table saw  10 , seen in  FIGS. 1 and 4 , has a saw table  12  which has a planar top surface  14 . There is a saw slot  16  in the table. A spindle below the table top defines an axis. Mounted on this spindle is saw blade  18 . It is the spindle axis which defines the line to which all relevant surfaces are related. Sometimes the spindle is tiltable with respect to the top surface of the saw table, but for the purpose of this discussion, this preferred embodiment of the magnetic miter slot bar will describe the situation in which the axis is parallel to the top surface  14 . This places the side surface  20 , see  FIG. 6 , at a right angle to the top surface  14 . 
   In addition, the saw table  12  has first and second miter slots  22  and  24  cut into the table below the surface  14 . These miter slots are presumably straight and parallel. Another conventional device on the table saw is fence  26 , see  FIG. 1 . The fence is movable in the direction of the spindle axis and is intended to lie parallel to the side surface  20  of the saw blade. 
   In order to measure the relationship between the miter slot and the saw blade, which represents the spindle axis, a bar  28  is provided, see  FIGS. 1 ,  2  and  3 . The bar  28  is narrower than the miter slot, see  FIG. 2 . The bar has ride pins  30  and  32  extending therethrough, which ride pins are spaced close enough to the bottom of the miter slot bar that, when the ride pins are on the top surface of the saw blade, the bar  28  does not reach to the bottom of the miter slot, see  FIG. 2 . This prevents accumulated detritus in the bottom of the miter slot from interfering with motion of the bar along the length of the miter slot. The ride pins may be held in place by any convenient structure, such as socket head set screws  34  and  36  seen in  FIG. 3 . The ride pins may be made of low friction material to provide a good bearing pair. The ride pins may be renewed, as required, by loosening the set screws. 
   In addition, as seen in  FIG. 2 , the width of the bar  28  is smaller than the width of the miter slot. Sometimes the miter slot may be of a different width at different positions along its length due to poor machining, warpage of the table during the manufacturing process or aging. In order to maintain the guide bar in position against one wall of the miter slot, magnets are provided.  FIG. 3  shows magnets  38  and  40  which are inset into the side of guide bar  28 . They are preferably flush with that side of the guide bar. The may be held in place by any convenient structure, such as adhesive, set screw or pin. The guide bar is preferably non-magnetic in order not to interfere with the magnetic field set up by these magnets. The magnets attract the guide bar to one side of the slot. In this case, it is the side of the slot toward the saw slot. The magnets have considerable strength in preventing the guide bar being moved away from the side surface of the slot, but the magnets do not significantly restrain the slide bar from moving along the length of the slot. The magnet can slide along the length of the slot with considerably less force than necessary to move the magnet away from its closest slot wall. Making the slide bar considerably narrower than the miter slot and positioning the embedded magnets in one side of the slide bar will cause the slide bar to cling to the closest side of the miter slot. The slide bar will traverse the full length of the miter slot, all the while clinging to that one wall of the miter slot. 
   Dial indicator  42  is mounted on the guide bar  28  by any convenient means. In this case, a tang on the dial indicator enters into a crosswise slot in guide bar  28 , and machine screw  44  holds it in place. The finger  46  on the dial indicator can be used to measure distances as the slide bar is moved along the length of the miter slot. In  FIG. 6 , the dial indicator is used to measure side surface  20  of the saw blade. It is this measurement which is used to adjust the table to make the table slot  22  parallel to the plane of the saw blade. In  FIG. 1 , presumably the saw table has already been adjusted so that its miter slot is parallel to the plane of the saw blade. In  FIG. 1 , the miter slot  22  is the reference, and it is used to set the fence  26  parallel to the miter slot. The parallel measurements from the one side of the miter slot wall to the saw blade and to the rip fence  26  are extremely accurate since there are no inaccuracies of miter slot width to contend with. 
   This results in measurement which is free of perturbations resulting from differences in the width of the miter slot. The slide bar will move along the length of the miter slot with little effort, yet will resist becoming detached because the force holding the slide bar against the slot wall is far greater than the force required to move the guide bar along the miter slot. This magnetic miter slot bar assures that there will be no measurement errors resulting from differences in miter slot width. When the magnetic miter slot bar is employed in an alignment system, errors due to differences in miter slot width are avoided. This assures correct alignment between the saw blade, the miter slot and the rip fence in table saws. The alignment system is also useful in aligning and calibrating various machinery which has miter or similar slots. 
   A magnetic miter slot bar can also be used in connection with a gage block, such as gage block  48  shown in  FIGS. 4 ,  5  and  6 . The gage block  48  is in the form of a rectangular tubing and has a bottom surface  50  for engagement against the top surface  14  of the saw table. Front face  52  is at a right angle with respect to the bottom surface  50 . Front face  52  carries two parallel upright cylindrical guide bars  54  and  56 . These guide bars are at a right angle to the bottom surface  50 , which is planar. Level arm  58  has two V-shaped guide notches which are spaced apart the same distance as the guide bars. These notches engage over the guide bars to retain the level arm  58  always parallel to the planar bottom surface  50 . Thus, the under surface of the level arm serves as a height measure with respect to the table top. The level arm can be clamped in a selected position with respect to the bottom surface by means of a clamp screw  60  which extends through the level arm and engages in a T-nut in T-slot  62 . More detail of the gage block  48  can be found in U.S. Pat. Nos. 5,491,906 and 5,826,346, the entire disclosures of which are incorporated herein by this reference. As seen in  FIG. 6 , the dial indicator  42  is secured to the outer end of the level arm by any convenient means, such as a clamp bolt  63  through the boss on the bottom of the dial indicator and through a hole through the end of the level arm. The dial indicator can thus be used as a measurement to the saw blade or other reference surface, such as an alignment plate or a saw fence. 
   The bar  64 , shown in  FIGS. 4 ,  5  and  6 , is sized to engage into the miter slot  22  and is sized with respect to the miter slot so that there is clearance at both the bottom and the one side thereof, similar to that shown in  FIG. 2 . Two magnet inserts  66  and  68  magnetically retain the miter bar  64  to the one side of the miter slot. In this case, it is on the side toward the saw blade. Most of the length of the miter slot bar  64  is flush with the top of the table. However, bosses  70  and  72  extend above the table top in order to permit utilization of larger magnets. With this structure, the magnets can be positioned so that they reach upward with respect to the slot at least to the top surface of the table. 
   The top and bottom surfaces of the gage block contain T-slots  74  and  76 . The top surface of the gage block is parallel to the bottom surface, and the T-slots are the same so that the gage block can be turned over, if desired. T-nut  78  is positioned within T-slot  76 . Clamp screw  80  engages in the T-nut to tighten the miter slot bar  64  against the bottom of the gage block  48 . In this position, with the bottom surface  50  of the gage block against the top surface  14  of the saw table, the miter slot bar  64  is above the bottom of the miter slot  22 . In this way, it avoids detritus in the bottom of the slot. In addition, there is a rectangular boss  82  on the top of miter slot bar  64 . The rectangular boss  82  is sized to fit tightly between the sides of the T-slot. The boss  82  is directed so that, when it is engaged in the T-slot, the front surface of the gage block is at a right angle to the magnetic side of the miter slot bar. With this structure, when the miter slot bar is engaged into the T-slot and magnetically retained against one wall thereof, the plane of the front face  52  is at a right angle with respect to the plane of the saw blade. The gage block  48  could be used in this way to measure parallelism of the miter slot  22  with respect to the plane of the saw blade, in the manner shown in  FIG. 6 . The gage block  48  can also be used for other purposes, such as measuring the height of the saw blade above the table surface  14 , in the manner shown in  FIG. 4 . In this case, the level arm is positioned above the top surface of the saw table at a height desired for the depth of cut of the saw blade  18 . The saw spindle height with respect to the table surface is adjusted so that the blade extends up to the bottom surface of the level arm  58 , shown in  FIGS. 4 and 5 . In this way, the depth of cut is accurately established. 
   This invention has been described in its presently preferred embodiment, and it is clear that it is susceptible to numerous modifications, modes and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.