Abstract:
A calibration disk for use primarily with table saws. In an embodiment, the disk is installed on depth control axle and spaces away from the saw cabinet with a spacing collar. A friction collar provides a frictional engagement between the disk and the axle that may be overcome manually, so that the disk may be zero-set. To set the blade height, the operator rotates the depth control until a line corresponding to the desired cut depth is aligned with an alignment mark affixed to the saw cabinet.

Description:
FIELD OF THE INVENTION 
   The invention relates generally to an apparatus for setting the cutting depth of a saw, and more particularly to an instrument for setting the cutting depth of a table saw. 
   BACKGROUND OF THE INVENTION 
   The table saw is one of the most common and versatile pieces of woodworking equipment. A typical table saw consists of a saw blade mounted on an arbor and driven by a motor. The blade protrudes through the surface of a table, which provides support for the material being cut. 
   The depth of the cut often must be set precisely, particularly when cutting a dado or rabbet. In a typical table saw, the depth of the cut is varied by adjusting the blade height: the distance that the cutting edge of the blade protrudes above the table surface. The higher the blade protrudes above the surface, the deeper the cut. In some table saws, the blade and arbor are fixed and the table is moved up and down. In other table saws, the table is fixed and the blade and arbor are moved up and down. The angle of the cut is typically controlled by adjusting the angle of the blade relative to the table. 
   An operator may control the height of the blade by rotating a control handle, usually in the form of a disk or wheel, which drives a mechanism to lower or raise the saw blade relative to the table. The control handle is commonly mounted on an axle. Typically, table saws present no means for communicating the height of the blade above the table to the operator. Setting the blade height tends to be more difficult for table saws than other machine tools because the relationship between a given rotation of the control handle and a change in the blade height is not constant. 
   Commonly, the operator will measure the height of the saw blade using one of a variety of devices. One such device is a height gauge which functions much like a caliper, where one leg sits upon the surface of the table and the other sits upon the upper edge of the saw blade. The height is displayed on a dial. Another such device is a calibrated fence. A fence is a movable guide that is used to guide material to be cut through the saw blade. When the saw is stopped, the calibrated fence may be placed next to the blade and the height of the blade adjusted against a scale inscribed in the surface of the fence. Similar devices include scales, tape measures, or step blocks. It is common to have to make several adjustments to get precise results using these devices. 
   When using any of these devices, the saw must be stopped for the operator to safely read the height of the saw blade. Stopping the saw and applying an external measurement device to measure the height of the blade is both time consuming and prone to error. Furthermore, there is an incentive for an operator to sacrifice safety and adjust the saw blade while it is still spinning. 
   Another common method is to make a trial cut in a scrap piece of wood. Using this method, the operator makes repeated cuts in a scrap piece, making fine adjustments between each cut and measuring the result. This method is awkward, time consuming, and imprecise. 
   Accordingly, there is a need for an easy to use way to adjust the height of the saw blade accurately and to make fine height adjustments while the saw is spinning. Furthermore, any adjustment device should be inexpensive and easy to install. 
   The same needs exists for many machine tools, such as routers. In a table saw, the blade depth is directly related to the cutting depth. In other tools, the cutting depth is indirectly related to the distance from the cutting edge to the table, but the principle problems are the same. Throughout this specification, cutting depth and blade height are used interchangeably when referring to table saws. 
   SUMMARY OF THE INVENTION 
   An embodiment of the invention includes a calibrated disk that is positioned behind the control handle that raises and lowers the saw blade. The calibrated disk has marks inscribed in the surface and may be rotated independently of the handle to “zero” the dial. When the saw is not operating, the saw blade is typically “parked” in a position where the blade is below the top surface of the table. In operation, the control handle is rotated to raise the saw blade level with the top surface of the table. With the control handle held motionless, the disk is rotated until the zero reference mark is opposite an alignment mark. The control handle is then rotated until a reference line on the disk corresponding to the desired height is opposite the alignment mark. The disk may be frictionally secured to the axle so that it rotates with the axle while making a height adjustment, yet may be manually zeroed. 
   The calibrated disk may be added to an existing table saw or tool merely by removing the control handle, which generally requires removal of only one set screw. The calibrated disk may be quickly and easily installed on the control axle, and the control handle re-installed. 
   The purpose of the foregoing summary is to enable the United States Patent and Trademark Office and the public generally, and especially the scientists, engineers, and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection, the nature and essence of the technical disclosure of the application. The summary is neither intended to define the invention of the application, which is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way. 
   Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein only the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated by carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawings and description of the preferred embodiment are to be regarded as illustrative in nature, and not as restrictive in nature. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side, perspective view of an embodiment of the invention installed on a table saw. 
       FIG. 2  is an exploded view of an embodiment of the invention. 
       FIG. 3  is a perspective view of an embodiment of the invention installed on a table saw. 
       FIG. 4  is a detail view of a disk constructed according to an embodiment of the invention. 
       FIG. 5  shows a reference table constructed according to an embodiment of the invention. 
       FIG. 6  is a detail view of a disk constructed according to an embodiment of the invention to be used with the reference table shown in  FIG. 5 . 
       FIG. 7  shows an embodiment of the invention wherein the blade height is displayed electronically. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While the invention is susceptible of various modifications and alternative constructions, certain embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed; rather, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims. For example, while embodiments of the present invention were developed for a table saw, the invention is not limited to use with table saw and may be used with other saws, woodworking equipment, or machine tools, such as routers. While the invention is not limited to use with saws, it is expected that various embodiments of the invention will be particularly useful in such devices. 
     FIG. 1  shows an embodiment of the invention installed on a table saw. The operator controls the height of the saw blade using a control handle  10 , which sets the position of the saw arbor through a mechanism (not shown). A control axle  12  (see  FIG. 2 ) extends from control handle  10  through a saw cabinet  14 . A disk  16  is installed on the axle so that as control handle  10  turns, disk  16  spins with the axle  12 . An alignment block  18  is inscribed with one or more alignment marks  20  and attached to cabinet  14  so that alignment marks  20  can be viewed either adjacent to or through disk  16 . 
     FIG. 2  shows an exploded view of an embodiment of the invention installed on the axle  12 . Disk  16  has a central passageway  22  large enough to allow disk  16  to spin freely on axle  12 . A spacing collar  24  fits over axle  12  between disk  16  and the wall of cabinet  14  ( FIG. 1 ). The outer diameter of spacing collar  24  is larger than the diameter of passageway  22 . A friction collar  26  fits securely on axle  12  and abuts disk  16 , pressing disk  16  against spacing collar  24 . Disk  16  is inscribed with one or more distance marks  28 . Distance marks  28  are shown as radial lines; however, points, carets, or any other mark suitable for aligning disk  16  may be used. For ease of setting commonly used cut depths, distance marks  20  corresponding to particular blade heights may be identified by one or more labels  34  inscribed on disk  16  ( FIG. 4 ). 
   As can be seen in  FIG. 2 , installation of disk  16 , friction collar  26 , and spacing collar  24  requires only that control handle  10  be removed from axle  12 , typically requiring loosening a set screw (not shown) in control handle  10 . No cutting or drilling of holes in the table saw is required. After removal of control handle  10 , disk  16 , friction collar  26 , and spacing collar  24  are slid onto axle  12 , and control handle  10  may then be re-installed. 
   An embodiment of the invention installed on a table saw is shown in  FIG. 3 . In a typical table saw, saw blade  30  protrudes through the material support surface  32 , also called a saw table. To set the blade height, the operator should first “zero” disk  16 . “Zeroing” means that disk  16  is positioned so that it reads zero when saw blade  30  is at a height where it would contact any material on material support surface  32 , but without cutting the material when saw blade  30  rotates. The operator zeroes disk  16  by rotating handle  10  to withdraw the saw blade  30  through the material support surface  32  until the top of the saw blade and the outermost cutting edge of the saw blade is flush with the top surface of material support surface  32 . The operator then rotates disk  16  until a distance mark  28  corresponding to a zero position opposes alignment mark  20 . Referring again to  FIG. 2 , it can be seen that friction collar  26  presses disk  16  against spacing collar  24 . The operator may rotate disk  16  while holding handle  10  still, overcoming the static friction provided by friction collar  26 . When the operator turns handle  10  without grasping disk  16 , the static friction provided by friction collar  26  rotates disk  16  in concert with axle  12 . 
   To make a cut of a given depth, the operator rotates handle  10  until a first desired distance mark  28  is opposite alignment mark  20 . After making a first cut, the operator may change the cut depth merely by rotating handle  10  until a second desired distance mark  28  aligns with alignment mark  20 . Also, disk  16  may be calibrated so that fine, predictable results may be obtained. In this way, the operator can make a series of cuts of differing depth quickly and easily without stopping rotation of the saw blade. In contrast, using ordinary methods, the operator must stop the saw blade for each cut depth and use a gauge to adjust the saw blade height, or make a series of cuts in a scrap piece using a trial and error method. In table saws, the blade height is a direct proxy for cutting depth; in other machine tools, the distance from the cutting edge to the material support surface sets the cutting depth. 
   On most saws, control handle  10  must be rotated more than 360 degrees to position the blade to the desired height. In this situation, the desired distance mark  28  will pass by alignment mark  20  one or more times before alignment on the final rotation. The final rotation may be determined by visually examining the height of blade  30 . In another embodiment, labels  34  are placed at different radii, each radius corresponding to a different number of rotations of control handle  10  from the zero setting. 
   On most table saws, unlike many machine tools, the relationship between the rotation of handle  10  and the corresponding change in the height of blade  30  is nonlinear, meaning that the change in the height of blade  30  for a given angle of rotation of handle  10  is not constant; rather, the rate of change varies with the initial height. In some table saws, the arbor is mounted on an arm that rotates about a point to change the position of the arbor; thus, the height of blade  30  depends on the sine of the angle of the arm relative to the material support surface  32 . In other saws, the relationship is more complex. In any case, the relationship can be calculated or discovered empirically. The position of marks  28  on disk  16  must be adjusted to accommodate this non-linear relationship, or the marks  28  must be identified with the appropriate labels  34  according to the relationship. 
   Disk  16  may be opaque or clear, to provide additional ease in aligning a mark  28  with the alignment mark  20 . In addition, when disk  16  is clear, other scales and features on the saw behind the handle are visible to the operator. Marks  28  and labels  34  may be etched into the surface of the disk, printed or applied with any means appropriate to make a permanent mark. Labels  34  may contain numeric characters, alphanumeric characters, symbols or glyphs. 
   Friction collar  26  may be made of an elastic or fibrous material and may be formed in the shape of an o-ring. Alternatively, friction collar  26  may fit within passageway  22  so that it is captured between the edge of passageway  22  and axle  12 . 
   Spacing collar  24  may be rigidly secured to the control axle  12 , as in a ring with a set screw. Alternatively, many table saws are manufactured with a ring rigidly attached to the control axle, and spacing collar  24  may be sized to contact both this ring and disk  16 , thus spacing disk  16  away from cabinet  14 . In this embodiment, spacing collar  24  may be made with any flexible material and may be slotted so that the spacing collar can be snapped around axle  12  without removing axle  12  from the saw. 
   Alignment block  18  may be constructed of any suitably durable material and may be affixed to cabinet  14  magnetically or with an adhesive. Alignment mark  20  may be etched, printed or otherwise inscribed in the surface of block  18 . Alternatively, alignment block  18  may be replaced by a label adhesively attached to the surface of cabinet  14 . In another embodiment, alignment mark  20  may be inscribed directly on the surface of cabinet  14 . 
     FIG. 4  shows an embodiment of disk  16  constructed for use with a particular saw. The relationship between the position of control handle  10  and the height of the outermost edge of saw blade  30  above material support surface  32  depends on the diameter of saw blade  30 . Similarly, the relationship between turns of control handle  10  and the height of saw blade  30  depends on the details of the mechanism that sets the arbor position, which varies by saw manufacturer. Thus, the distance mark  28  corresponding to a given cut depth or blade height will vary with blade diameter and saw manufacturer. As shown in  FIG. 4 , disk  16  is inscribed with one or more numeric labels  34  corresponding to a particular blade height or cut depth for a given saw blade diameter and saw manufacturer. A separate disk  16  may be provided with appropriate labels  34  and distance marks  28  for each combination of saw diameter and saw manufacturer.  FIG. 4  shows a disk  16  constructed with adjacent marks  28  approximately 6 degrees apart, corresponding to a change in cut depth of approximately 0.005 inches. However, disk  16  may be constructed to calibrate changes in cut depth as small as 0.002 inches. The operator may need to take care to make changes in one direction, so that backlash in the saw mechanism does not contribute to error in the cut depth. Alternatively, a vernier scale having marks designating graduations to either side of mark  20  may be added to alignment block  18 , so that adjustments as small as 0.002 inches may be made. To use the vernier scale, the operator selects the distance mark  28  corresponding to the blade height that is closest to the desired blade height, and selects the graduation that corresponds to the difference between the desired blade height and the height represented by the selected distance mark  28 . The operator then aligns the selected distance mark  28  with the selected graduation mark. 
   In a preferred embodiment, labels  34  on disk  16  may correspond to entries in a table. An example of such a table is shown in  FIG. 5 . Table  36  has columns  38  corresponding to cut depth or blade height, and rows  40  corresponding to different blade diameters. For example, 8 inch diameter blades are commonly used for dado cuts, and 10 inch diameter blades are commonly for general purpose cuts. The entries at the intersections of columns  38  and rows  40  correspond to marks  28  on a disk  16 , as shown in  FIG. 6 . For convenience, the marks  28  may be identified by one or more labels  34 . To use table  36 , the operator selects the entry at the intersection of the desired cut depth in column  38  and the appropriate blade diameter in row  40 . The selected entry corresponds to a particular distance mark  28 . The operator rotates handle  10  until the distance mark  28  corresponding to the selected table entry oppose alignment mark  20 . Table  36  may be affixed to the cabinet  14  of the table saw or distributed separately as a booklet, card, adhesive label, or the like. Table  36  may be pre-printed with data corresponding to a particular saw manufacturer and blade diameters, or table  36  may be provided with blank entries so that the operator can measure the characteristics of a particular saw and blade combinations and enter the corresponding data. 
   Table  36  may be expanded to accommodate additional rows for different manufacturers of table saws. For example, a first set of rows may contain an 8 inch blade row and a 10 inch blade row for a first manufacturer A, and a second set of rows may contain an 8 inch blade row and a 10 inch blade row for a second manufacturer B. While rows correspond to blade diameter and manufacturer and columns correspond to blade height or cut depth in the exemplary embodiment, any assignment of rows and columns to blade height, blade diameter, and manufacturer may be made to construct table  36 . 
   In another embodiment, disk  16  may be inscribed with a first series of labels displaying numbers corresponding to a particular blade height, and a second series of labels corresponding to entries in table  36 . 
   In some applications, it may be desirable to display the selected cutting depth electronically. In an alternative embodiment, disk  16  may be encoded with electronically readable indicia. In a preferred embodiment, the indicia are printed on disk  16 , appearing as electronically readable marks corresponding to distance marks  28 . Referring to  FIG. 7 , a sensor  42  reads the indicia to produce data corresponding to the angular position of disk  16 . Electronic circuitry  44  processes the data and displays the blade height or cutting depth on a display  46 . Display  46  may be mounted anywhere on cabinet  14  easily viewable by the operator. Sensor  42  may be an optical sensor, a magnetic sensor, or any sensor capable of reading the angular position of disk  16 . If sensor  42  is a magnetic sensor, the indicia may be printed in magnetically readable ink, similar to that used on checks. Electronic circuitry  44  may comprise a computer and memory, and preferably is capable of accounting for the total number of rotations made by disk  16  after disk  16  is zeroed by the operator. Display  46  may be a liquid crystal display, electroluminescent display, or similar display capable of presenting a cutting depth to the operator, and preferably displays numeric data. 
   While there is shown and described the present preferred embodiment of the invention, it is to be distinctly understood that this invention is not limited thereto but may be variously embodied to practice within the scope of the following claims. From the foregoing description, it will be apparent that various changes may be made without departing from the spirit and scope of the invention as defined by the following claims.