Abstract:
A router and other cutting tools with a fixed center such as drills, shapers, milling machines, etc., used for cutting wood, metal or other materials, is provided with a fence mechanism for either a table or the base of a portable tool, for rapid and easy settings of the fence with respect to the center of the cutting tool. This is accomplished by a pivot mounting of the fence on a table or on a portable tool base, with respect to a block pivoted to the table or tool base, wherein the center of the pivot for the block and the center for the pivot for the fence are on opposite sides of the cutting tool and located on a line which passes through the tool center and the respective pivot locations. The desired spacing of the fence to the tool can be achieved using accurate spacers between the fence and the block, even with the tool being mounted in place. A curved slot in the fence structure, of predetermined shape and location with respect to the tool center, can be provided to receive a follower pin extending from the table and function as the fence pivot. The disclosure teaches how to develop such a curved guiding slot. A setup gage plate is also provided, with incrementally spaced holes to receive a post and cooperate with the pivoting fence to set the spatial relationship between the fence face and the bit.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 08/966,628 filed Nov. 10, 1997 now, U.S. Pat. No. 5,881,785. 
    
    
     BACKGROUND OF THE INVENTION 
     The concept of using two pins or posts mounted on a router base to make a self-centering mortising and slotting base is per se well known. Spielman in his book &#34;Router Jigs &amp; Techniques&#34; (1988 Sterling Publishing Co., Inc. New York N.Y.) describes such a base on page 202. A more recent application of the concept is described by Taylor and McDaniel in U.S. Pat. No. 5,423,360 where an apparatus for centering a work-piece relative to a cutting tool is disclosed. That concept could be adapted directly to a router table, T with a router (not shown) mounted to a base plate 14 (or a table for other tools such as drills, shapers etc.) as illustrated in FIG. 1 herein (Prior Art). 
     Thus, two posts 13a and 13b could be fixed to a table with pivots 12a and 12b, the posts being centered on each side of the cutting tool on a line through the center of the cutting tool 15. The posts could be, for example, disks cut from three-quarter inch stock. Although the arrangement illustrated in FIG. 1 could work for centering a work-piece it would be difficult to use and not truly practical. However, with certain unique modifications described hereinafter, such a device can be very useful not only for centering the workpiece but also in setting up the fence of a router table to perform various cuts. 
     SUMMARY OF THE INVENTION 
     Even though a router table is used as an example, it is clear that the concept can be used with various other cutting tools with a fixed center such as drills, shapers, milling machines, etc., whether used for cutting wood, metal or other materials. The most important unique feature of this invention is the provision of a fence mechanism, for either a table or a portable tool, which provides rapid, easy to use, settings of the fence with respect to the center of a cutting tool, such as a router bit. This is accomplished by a pivot mounting of the fence on a table or on a portable tool base, with respect to a block pivoted to the table or tool base, wherein the center of the pivot for the block and the center for the pivot for the fence are on opposite sides of the cutting tool and located on a line which passes through the tool center and the respective pivot locations. The desired spacing of the fence to the tool can be achieved using accurate spacers between the fence and the block, even with the tool being mounted in place. 
     When the invention is installed on a table, a curved slot of predetermined shape and location with respect to the tool center will be formed in either the table or the fence member, and such slot will receive a follower pin extending from the fence member or the table surface, and provides a means for positioning the fence to provide fence centered motion such that when the fence is moved over the table the center of the fence will always align with the center of the cutting tool (i.e. the center of the fence and the center of the cutting tool lie on a line perpendicular to the fence). The disclosure teaches how to develop such a curved guiding slot. 
     The invention also includes various jigs, gages, and relationships which can be used to locate desired centers of pivot locations on the table, or on a tool baseplate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 (prior art) shows two posts pivotally attached to a table and equally spaced from a cutting tool on a line extending through the tool center; 
     FIG. 2 shows the post arrangement of FIG. 1 together with a fence pivotally attached to the table; 
     FIG. 3 illustrates the use of a spacer of known dimension to space the fence a desired distance from the cutting toll; 
     FIG. 4 is a view, from the back of table T, similar to FIG. 3 with exemplary dimensional relationships; 
     FIG. 5 is an illustration the pivoted fence and post on a table as used to develop an equation for the cutting of a groove in the table (or fence) to receive a follower pin in the fence (or table), such that when the fence is moved over the table the center of the fence will always align with the center of the cutting tool. 
     FIG. 6 is a diagram illustrating the development of curves which define the shape of a slot, as in the fence base, to receive a follower in the table top with respect to the cutting tool; 
     FIG. 7 is a diagrammatic expression of the shape of such a slot cut in the table top, to receive a follower in the fence and achieve fence centered motion of the fence with respect to the cutting tool; 
     FIG. 8 is an illustration of a jig for cutting (routing) a fence centered motion curve into the table; 
     FIG. 9 is an illustration of a jig for pivot hole layout on the table; 
     FIG. 10 illustrates of a router baseplate fitted with a pivoted fence and locating post; 
     FIG. 11 illustrates use of the pivoted fence and locating post as a drilling and marking jig. 
     FIG. 12 illustrates the curved slot formed in a fence member; and 
     FIGS. 13 and 14 are top and side views of an auxiliary set-up gage and locating post. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated in FIG. 2, the router fence 16 can be attached to the left-hand post so its face is tangent to the post as shown. The left hand post 13a does not need to be present; all that is required is that the fence 16 be attached to the table T by a pivot 12a located at the center of the original post 12a. The pivot hole in the fence 16 is located relative to the face of the fence 17 at a distance equal to the radius of the post 13b, e.g. 2 inches for the 4 inch diameter post in the example. With this arrangement, the left-hand post is replaced by the fence 16 and pivot 12a. In a similarly way, the right hand circular locating post 13b in FIG. 2 could be replaced with a rectangular locating post, provided that the edge facing the fence is tangent to the original circular locating post 13b. 
     If a board (i.e. work-piece) is placed against the fence face 17 and both are rotated until the work-piece contacts the locating post 13b, then the board is perfectly centered relative to the cutting tool regardless of the thickness or width of the board. The fence 16 can then be clamped to the table T, the locating post 13b removed and, if desired, stop blocks positioned on the fence 16. The fence 16 can then be used to make the desired centered cuts in as many pieces of the same size as required. 
     In order to ensure accuracy over time, means can be provided to adjust the position of one of the pivots 12a and 12b. Using a simple jig, the table can be realigned, e.g. after a new router is installed in the table. 
     The automatic centering feature in itself makes the pivoted fence with locating post worthwhile, however, it is also very simple to accurately set up other jobs that do not require centering. 
     The pivoted fence with locating post is exactly the same as any other pivoted fence when the locating post 13b is removed. In most applications, the fence face 17 is located behind the center of the cutting tool 15, but for some applications the fence face 17 is in front of the center of the cutting tool 15. However, when the fence face 17 is behind the cutting tool, the pivoted fence with locating post is easy to set up for various cuts and will be discussed first. 
     The pivoted fence with locating post can be used easily to accurately set the fence face 17 a required distance from the center of the cutting tool. As shown on FIG. 3, all that is required is a spacer 18 of twice the desired setting: e.g. if want the center of the cutting tool 15 to be 3/16 inch from the edge of the work piece, then use a 3/8 inch spacer 18 between the fence face 17 and the locating post 13b. Most well equipped shops have very accurate spacers available in drill bits, and can be used, as shown in FIG. 3, to accurately set up the fence. If no spacer 18 of the right size is available, then measurements can be made with a square or other suitable means. 
     One edge of the square must be against the fence face 17 and the other along a diameter of the locating post pivot 12b. The measurement, of course, is twice the required spacing at the bit center B from the fence face 17. If the rectangular locating post is used, the edge facing the fence face 17 must be parallel to the fence when the measurement is made; this is easily accomplished with a square. However, a better option is to attach or build into the locating post a means for making accurate measurements, for example a vernier caliper an Incra gauge, or the auxiliary gage plate described below. 
     If the fence face 17 is rotated against the left locating post 13b (i.e. no spacer), then the face of the fence is exactly over the center of the cutting tool 15. If it is desired to set the fence face 17 ahead of the cutting tool, a slightly more complicated approach is required as described hereinafter. 
     If it is desired to set the fence face 17 to a known distance ahead of the cutting tool center 15 or to reference the distance to the front of the cutting tool, smaller locating posts of known radius can be used to set up the fence. The distance that the fence face 17 is advanced ahead of the cutting tool center is one-half of the difference between the smaller radius and the original locating post radius. Thus, if the original locating post has a radius of two inches, and the new locating post has a radius of one &amp; one-half inches, then the fence face 17 of the fence is one quarter inch ahead of the cutting tool center 15 (i.e. 1/4=(2-1.5)/2). Again, it is also possible to use a square and measure to the required small radius. 
     If a rectangular locating post is used, the pivot can be located so that the first edge is set to the same distance from its pivot as the fence face 17 is located from the fence pivot 12a, while each of the other three edges is set closer to the pivot at different distances. Hence, each edge can be used to set the fence face 17 ahead of the cutting tool center 15 by different amounts. Each edge can be set to measure the set up distance from the edge of different size cutting tools. Still another approach can be used as described below for the auxiliary gage plate (see FIGS. 13 and 14). 
     For completeness, the following description explains how the pivoted fence and locating post works and gives the information needed to make a fence with a ratio different than 1/2. 
     Function of the Pivoted Fence &amp; Locating Post 
     FIG. 4 shows a general scheme for setting up a pivoted fence and locating post. In general the centers of the locating post 13a, pivot 13b and cutting tool 15 must all lie on the same line but the spacing distances S1 and S2 need not be the same, i.e. S 1  and S 2  need not be equal. The distance from the face of the fence to the pivot is r 1  and, in general, it does not need to be equal to the radius of the locating post r2. 
     Even with these generalizations, the similar triangles, shown in bold lines in FIG. 4, can be used to describe how the pivoted fence and locating post works. The triangle &#34;acd&#34; is similar to the triangle &#34;abe&#34; and all of the similar sides are in the ratio of S 1  /(S 1  +S 2 ) which is called R; note that if S 1  =S 2  then the ratio, R, is 1/2 as it was in the previous discussion. 
     The sides &#34;eb&#34; and &#34;cd&#34; are similar sides and, therefore are in the ratio R. The side &#34;eb&#34; is the sum of r 1  and the set-up distance (the perpendicular distance from the fence face 17 to the cutting tool center 15). The side &#34;cd&#34; is the sum of r 1 , the spacer 18 (or measured) distance and r 2 . Consequently: ##EQU1## The relation obtained above from the similar triangles can be used to determine how the setup distance is related to the spacer 18 and the physical dimensions illustrated in FIG. 4. The resulting relationship is 
     
         setup=[S.sub.1 /(S.sub.1 +S.sub.2)](r.sub.1)[r.sub.2 /r.sub.1 -S.sub.2 /S.sub.1 ]+[S.sub.1 /(S.sub.1 +S.sub.2)](spacer). 
    
     It should be noted that if the physical dimensions of the locating post 13a and fence pivot 13b are chosen wisely, the term involving only the physical dimensions will not be needed: i. e. chose 
     
         i. e. chose r.sub.2 /r.sub.1 =S.sub.2 /S.sub.1 
    
     Using the above relation for the physical dimensions results in a simple relationship for the setup distance: 
     
         setup=[S.sub.1 /(S.sub.1 +S.sub.2)](spacer) 
    
     For example, if the pivot 12b is located one inch from the face of the fence, 17 then, r 1  is 1 inch. If the locating post 13a and pivot 13b are centered at 15 inches on each side of the cutting tool center 15, on a line through the center 15 of the cutting tool, using a 1 inch radius locating post 13a obtains a ratio of 1/2. Then, using the same fence 16 and table T, by adding two additional holes (not shown) for the fence pivot 12a, along the line through the center of the cutting tool, all of the ratios shown in Table 1 can be obtained. 
     
                       TABLE 1______________________________________Required Dimensions to Obtain Various Ratioswith the same Fence and TableDimension/ratio       1/2        1/3       1/4______________________________________Pivot Radius r.sub.1        1 inch    1 inch    1 inchPost Radius r.sub.2        1 inch    2 inch    3 inchPivot Space S.sub.1       15 inch    71/2 in.  5 inchPost Space S.sub.2       15 Inch    15 inch   15 inch______________________________________ 
    
     It is interesting to note that one can mortise or groove a board at its center or at one fourth of its thickness (or width), or at one third of its thickness (or width). Using a 1&#34; spacer, with a ratio of 1/3, will allow cutting a groove 1/3 inch from the edge. 
     Thus the pivoted fence with a locating post affords a simple and accurate method for centering work and setting up the fence for other cuts. However, the pivoted fence has a drawback when one wants to cut a blind rectangular mortise wider than the bit: when the fence is moved, any stop blocks being used would have to be adjusted to obtain the desired result. Also, if a work piece is held firmly against the fence and the fence is moved then the bit will cut an arc in the piece rather than a cut perpendicular to the edge that was held against the fence. As described in the next section, These problem are solved with the concept of &#34;fence centered motion&#34;. 
     Fence Centered Motion 
     The term &#34;fence centered motion&#34;, means that when the fence is moved, the fence is located so that the center of the fence lies on a line that is perpendicular to the fence and passes through the center of the bit,15. This can be accomplished by cutting a slot in the fence that replaces the fence pivot hole, 12b and by cutting a groove in the table that guides a follower (e.g. a peg) in the fence. Alternatively, the peg can be attached to the table and both a straight slot and a curved slot can be cut into the fence as shown in FIG. 12. The equations for the curve and the location of the peg are developed as follows. 
     One of the difficulties encountered with a pivoted fence is that if it is moved one needs to adjust the position of any stop blocks in order to cut a rectangular blind mortise wider than the bit diameter. Also, if a work piece is held firmly against the fence and the fence is moved then the bit will cut an arc in the piece rather than a cut perpendicular to the edge that was held against the fence. In order to overcome such problems in a pivoted fence we have developed a concept of &#34;fence centered motion&#34;. This can be accomplished by cutting a straight slot in the fence that replaces the fence pivot hole and cutting a curved slot in the table that guides a peg in the fence. Alternately, the peg can be attached to the table and both a straight slot and a curved slot can be cut in the fence. 
     FIG. 5 shows the table T with the fence 16, pivoted at some arbitrary angle θ. Both the fence and the table coordinates are shown on FIG. 5. FIG. 5 also shows the angles and distances referred to in the descriptions of the equations in the following sections. 
     X and Y are the coordinates of a point on the fence which will trace a curve in table coordinates. Sp (see FIG. 5) is the perpendicular spacing of the fence face 17 from the center of the router bit 15, which is the origin of the table coordinates. When the spacing Sp is zero the origin of the fence and the table coincide. The location r of the fence pivot 12a from the face 17 of the fence, is likewise, the radius for the post pivot, 13b. Lower case s is the spacing of the pivot holes, 12a and 12b, from the center of the router bit, 15, (11.09375 in the prototype table). The angle θ 0 . is between the face of the fence 17, and the diameter through the pivot holes when the spacing Sp is zero. 
     
         Sp(θ)=s sin(θ(π/180)-r 
    
     The angle θ above is between the fence face 17 and the diameter through pivot holes 12a and 12b, at the fence position that gives the spacing Sp. 
     
         α(θ)=π/180(θ)-θo(r) 
    
     The angle α, above, is between the fence face 17, and the x axis of the table (the line tangent to both posts 13a and 13b). 
     
         X(x,θ)=y sin(α(θ))+x cos(α(θ)) 
    
     
         Y(x,θ)=y cos(α(θ))-x sin(α(θ))-Sp(θ) 
    
     The above two equations give the trace of the point x, y, that is fixed to the table, on the fence (the values of x&#39; and y&#39; are in fence coordinates) as a function of the parameter θ. FIG. 6 shows such curves for y=r and example values of x as indicated on FIG. 6: the tracing points are located in table coordinates at: (-13, 2), (-12.5, 2), (-12, 2) and at the fence pivot point 12a. 
     Referring to FIG. 12, there is shown a modified fence having a face 45 and a wing part 41 in which a curved slot 42 (i.e. the fence centered curve) and a straight slot 43 are cut. The curved slot 42 is cut into the fence along one of the traces, and a follower pin is located in the table at the corresponding tracing point. The straight slot 43 is located along the pivot point trace, so the fence can pivot and also move along slot 43 to align the center (the origin in fence coordinated) of the fence with the bit. The center of the bit 15 and the origin of the fence lie on a line perpendicular to the fence face. Thus when this fence is mounted to the table and it is moved the center of the fence will always align with the center of the bit. 
     The opening 44 is provided to accept a vacuum connection (not shown), so as to withdraw chips when working. The fence also is provided with holes 46a, 46b, and 47 which function as a set-up jig for adding this fence to a table. In preparation for accurately fitting this fence to a table, hole 48 is used to locate the fence by fitting hole 48 onto a 1/4 inch rod fitted to the router in the table. Then with the fence squared with respect to the table surface, hole 46a is used, for example with a conventional drill guide bushing, to drill the pivot pin hole in the table and hole 46b is used to drill the locating pin hole in the table. Finally, hole 47 is used to locate a drill for making the follower pin hole in the table. 
     If X and Y are the fence coordinates of a point fixed on the fence 16. then the trace of the point X,Y (fixed to the fence) on the table T (x and y are in table coordinates) is given as: 
     
         x(X,θ)=X cos(α(θ))-(Sp(θ)+Y)sin(α(θ)) 
    
     
         y(X,θ)=X sin(α(θ))+(Sp(θ)+Y)cos(α(θ)) 
    
     There is an alternate approach, namely, to cut the trace into the table as shown in FIG. 10. The follower or pivot pin is then placed in the fence 16 at the proper point (here at (10, 2) as in the prototype table) and again the fence 16 (with the straight slot as above) can be moved and the center automatically aligned with the bit. This approach, while feasible and accurate, has a practical disadvantage. Forming the long curved slot in the table top can be unacceptable to a party adding the invention to an existing router table from an esoteric view point. Furthermore such a slot could interfere with the stiffness and integrity of the tabletop. Therefore the type of fence structure shown in FIG. 12 is a preferred choice for the market place. 
     In addition to the above described fence, this invention provides a novel set-up gage which can quickly and accurately set the position of the fence face, with the fence installed, accurately to within (for example) 0.050 inch. This gage is shown in FIGS. 13 and 14, and includes a plate-like body 50 having multiple mounting holes 60, each of which provides a potential location for a post 58 with an upwardly projecting threaded shaft 61 sized to fit within the holes 60, and having a wing nut 57. Post 58 is of a size to fit into the locating post hole formed in the table, i.e. hole 12b of FIG. 2. 
     As can be seen from FIG. 13, holes 60 are spaced from the upper edge of plate 50 at regular setup increments over a range of four inches (-0.75 to +3 inches of setup) each setup increment being equal to 0.050 inch in this example. Thus, post 58 can be located at selected precise distances from the upper edge of plate 50. If, for example, post 58 were mounted in the hole 60 at 0.00 inch, and the gage was mounted to the table with the post inserted into the locating post hole 12b in the table top, and the fence swung into contact with the upper edge of gage plate face bar 51, fence face 45 is then located to precisely intersect the center of the bit. By mounting post 58 in different holes, the spacing of fence face 45 to the bit center can be set as desired. 
     The upper edge of plate 50 preferably is provided with and adjustable face bar 51 which depends in front of the plate upper edge as seen in FIG. 14, and which has ear parts 54a and 54b which rest and slide on blocks 55a and 55b secured to the upper area of plate 50. The ear parts 54a and 54b have extended slots 56a and 56b which receive clamping screws 59a and 59b to hold bar 51 in a set position. A spring loaded threaded adjusting screw assembly 52 is mounted by a threaded plate 53 to plate 50 behind bar 51 and engages the back side of bar 51 to adjust its location with respect to the upper edge of plate 50. This adjustable face bar provides a means to compensate for amall variations in the thickness of a facing that is typically placed on the fence face 45. 
     After the fence face is located, the fence is clamped in position for subsequent use, and plate 50 along with post 58 is removed so the router table can be used without interference. 
     Jigs for Adapting a Table 
     The equations given above can be used in computer controlled equipment used in the manufacture of the tables. However, a simple jig has been developed which allows retrofit cutting of the required curve into an existing table using a router. FIG. 8 shows a schematic of the jig used to cut the curve into the table. The two slots 27 and 28 are perpendicular and the router bit is mounted on the jig at the same relative position as the follower pin will be located, on the fence 16. The pivot pin of the fence is placed through the indicated slot and into the pivot hole in the table and the router bit of the router mounted in the table (not used to cut the curve) is inserted into the slot 28, in FIG. 8. When the router 29 is mounted on the jig and is moved while running, it cuts the required curve for fence centered motion into the table T. 
     As mentioned in the parent application, a simple jig also has been developed for layout of the pivot holes in the table, as shown in FIG. 9. As an example, a 1/4 inch hole in the jig is positioned over a 1/4 inch rod or bit mounted in the router. The jig is rotated to the desired position and clamped to the table. Using the bottom edge of the slots, two lines are drawn. These lines, if extended (line 25), would pass through the center of the cutting tool. The clamp is removed and the jig is allowed to rotate about the bit center. One of the holes provided in the jig is then used to swing an arc across each of the line segments: the intersection of the arcs with the lines precisely locate the centers of the pivot hole for the fence and the locating post. 
     The simple jigs, shown in FIGS. 8 and 9, can be provided in kits, along with instructions, that would allow a user to make, or upgrade, a table in the user&#39;s own workshop. In addition to the fixed table applications, so far discussed, there are numerous applications of the concept for portable tools such as drills and routers (not table mounted). Some of these are discussed in the next section. 
     Portable Power Tool Applications 
     A router baseplate 22 can be equipped with a pivoted fence 19 with locating post 20 for use in portable applications, as shown in FIG. 10. Thus, the centering feature and ease of setup afforded by the pivoted fence with locating post will be available for portable applications. The locating post can be equipped with measurement means for those applications that do not require centering, just as in the table mounted case. 
     It should be pointed out that the pivoted fence with locating post avoids the limitations of both work piece size and mortise location that a traditional baseplate with two pins, centered about the bit, experiences: the work piece must be long enough to permit both pins to contact opposite sides of the work piece for the entire length of the cut. Further, irrespective of the length of the work piece, the cuts cannot be made close to either end of the work piece, since, both pins must stay in contact with the work piece for the entire length of the cut. Even through it may be possible to work around these limitations it is not necessary with the pivoted fence with locating post. Neither of the limitations apply to the pivoted fence with locating post, since, once set up the work piece rides against the fence and, therefore, can be machined from one end to the other regardless of the length of the work piece. 
     The pivoted fence with locating post can also be used with portable drills. The pivoted fence and locating post can be attached to the bottom of a drill fixture, used for drilling holes vertically or at a set, fixed angle. Both the self centering feature and the locating feature can be used for vertical drilling. An alternate approach is to use the pivoted fence with locating post as a self centering jig 31 with means for attaching drill bushings or marking tools at the center of the jig 30, as shown in FIG. 11. After the fence 33 is located at the desired distance, the fence is locked in place and the post 32 removed. Thus, the bushing or marking tool positioned at the jig center 30g is located precisely relative to the fence 33 and as many holes as desired can be drilled, or a straight line can be marked on the work piece. Means (not shown) can be attached to the bushing at 30 to allow for evenly spaced holes: e.g. a holder, with a pin equal to the bit diameter, could be pivoted around the bushing and used to locate the jig for the next hole. 
     While the methods herein described, and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.