Abstract:
A drive system for rotating rollers advancing a board through a board cutting machine. Sprockets and chains in the drive system are positioned such that adjustment of a set of rollers on one side of the board to accommodate varying board thicknesses will not require adjustment of a tension sprocket manually or by a spring.

Description:
RELATED APPLICATIONS 
     This application is related to U.S. application Ser. No. 09/330,411, filed Jun. 11, 1999, entitled “Improved Tool Holder and Tab System for Board Cutting Machine”, invented by R. Ashley Cunningham, the disclosure of which is incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to fiber board cutting machines and, more particularly, to an improved tool holder and tab system for cutting insulation fiber board of the type which has an impermeable barrier on one face thereof. 
     BACKGROUND OF THE INVENTION 
     Machines have heretofore been used to cut grooves in fiber board of a matted fiberglass type having a barrier on one face thereof, such as aluminum foil. U.S. Pat. No. 3,605,534 for such a machine was issued to William H. Barr in 1967. Subsequent to the Barr patent, several other fiber board cutting machine patents have issued with improvements thereto, including U.S. Pat. No. 3,941,018 issued to Jimmy L. Williams, and U.S. Pat. Nos. 3,996,824 and 4,091,697 issued to Ronald J. Cailey. The disclosures of the above-mentioned patents are included herein by reference. 
     In the prior art board cutting machines, a blade assembly is fixably mounted on a tool holder. A plurality of the prior art tool holders are adjustably positioned at predetermined spacing along the tool bar assembly, and the fiber board is fed through the cutting machine to form grooves spaced across the board. Adjustment of the position of the tool holder, including the blade assembly, results in grooves of different positions on the fiber board and thereby provides for forming the fiber board into duct work of different sizes and cross-section configurations. 
     In the prior art cutting machines, the blade assembly is permanently fixed to the tool holder. Different blade configurations are used to cut various groove profiles in the board as taught in the Barr patent (3,605,534). A need has existed for a tool holder that provides for adjustability of the blade position in the tool holder. A further need exists for a simple, inexpensive, reliable tab system for use in connection with the tool holder to position the tool holder to form grooves at correct spacings on the fiber board. 
     SUMMARY OF THE INVENTION 
     The present invention comprises an improved tool holder that provides for adjustability and interchangeability of blade assemblies and further provides that one tool holder may accept any one of a number of the blade assemblies for cutting grooves in fiber board of varying thickness. 
     In one embodiment, the present invention comprises an improved tool holder for a board cutting machine. The board cutting machine has an input side and an output side and a predetermined direction of feed of a board to be cut. The cutting machine includes at least one tool holder bar disposed transverse to the direction of feed of the board. 
     The improved tool holder comprises a first member having a bottom and at least one upstanding wall, the upstanding wall terminates in an outwardly turned flange that is adapted to be received on the tool holder bar of the board cutting machine. The first member has at least one downwardly disposed bracket for receiving an adjustment mechanism. 
     A blade assembly is removably attached to the adjustment mechanism, wherein the blade assembly may be adjustably moved in a transverse direction to the feed direction of the board. At least one blade is mounted on the attachment member. 
     The present invention further comprises a tab system for cutting grooves in a fiber board used for forming insulation duct work into a predetermined shape using the previously described board cutting machine. The tab system comprises at least one tool holder having a first blade assembly for cutting a board of a first predetermined thickness removably attached to an adjustment mechanism, wherein the blade assembly may be moved in a transverse direction to the feed direction of the board into the machine, as previously described, and a second blade assembly for cutting a board of a second predetermined thickness for interchanging with the first blade assembly. The second blade assembly is adapted to be removably attached to the adjustment mechanism, wherein the blade assembly may be moved in a transverse direction to the feed direction of the board into the machine. 
     A tab is disposed on the tool holder wherein the tab includes a first indicator mark for indicating the desired predetermined position of a first blade in the first blade assembly for cutting longitudinally a first side of a groove in material of a first predetermined thickness and a second indicator mark for indicating the desired predetermined position of a second blade in the first blade assembly for cutting longitudinally a second side of a first groove in a material of a first predetermined thickness. The first tab further includes a third indicator mark for indicating the desired predetermined position of a first blade in the second blade assembly for cutting longitudinally a first side of a first groove in material of second predetermined thickness and a fourth indicator mark for indicating the desired predetermined position of a second blade in the second blade assembly for cutting longitudinally a second side of a first groove in a material of a second predetermined thickness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The disclosed invention will be described with reference to the accompanying drawings, which show important sample embodiments of the invention and which are incorporated in the specification hereof by reference. A more complete understanding of the present invention may be had by reference to the following Detailed Description when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1A is a perspective view of a tool holder and tab system of the present invention used in connection with a board cutting machine. 
     FIG. 1B is a perspective view of a duct formed from fiber board grooved by the tool holder of the present invention. 
     FIG. 2A is a top view of a plurality of the tool holders and a tab system of the present invention positioned on parallel tool bars of the board cutting machine of FIG.  1 A. 
     FIG. 2B is a section view of the tool holders of FIG. 2A looking at the front edge of the blades. The fiber board is illustrated as it would appear with the grooves as cut after passing through the blades. 
     FIG. 3 is a top view of the tool holder and one of the tabs of the present invention. 
     FIG. 4 is a side view of the tool holder of FIG.  3 . 
     FIG. 5 is an end view of the tool holder of FIG. 3 looking at the front edge of the blade, and 
     FIG. 6 is a perspective view looking down on the top of the tool holder and one of the tabs of the present invention. 
     FIG. 7 is a perspective view looking up on the bottom of the tool holder of the present invention. 
     FIG. 8A is a top view of a plurality of prior art tool holders and a prior art tab system positioned on parallel tool bars of the board cutting machine of FIG.  1 A. 
     FIG. 8B is a section view of the prior art tool holders of FIG. 8A looking at the front edge of the blades. The fiber board is illustrated as it would appear with the grooves as cut after passing through the blades. 
     FIG. 9 is a top view of the prior art tool holder. 
     FIG. 10 is a side view of the prior art tool holder of FIG.  9 . 
     FIG. 11 is an end view of the prior art tool holder of FIG. 9 looking at the front edge of the blade. 
     FIG. 12 is a top view of one of the tabs of the tab system of the present invention. 
     FIG. 13 is a top view of another of the tabs of the tab system of the present invention. 
     FIG. 14 is a top view of another of the tabs of the tab system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is now made to the drawings wherein like reference characters denote like or similar parts throughout the Figures. 
     Referring now to FIG. 1A, therein is illustrated a perspective view of the board cutting machine  100  of the present invention. Fiber board material  10  is fed into the machine and forced through the machine by compression rollers as illustrated and described in U.S. Pat. Nos. 3,605,534 and 3,941,018. The board exits the machine  100  on the opposite side having grooves  20 ,  30 ,  40 ,  50  and  60 , cut therein. The partial piece  12  of board  10  is not a part of a predetermined duct configuration and is either waste or recycled for other duct shapes. The material  22 ,  32 ,  42 ,  52  and  62  cut from grooves  20 ,  30 ,  40 ,  50  and  60  is illustrated as curved and partially removed from grooves  20 ,  30 ,  40 ,  50  and  60  for purposes of viewing the profile of the grooved board  10 . Those skilled in the art will appreciate that the material  22 ,  32 ,  42 ,  52  and  62  will have to be manually removed from board  10 . In other prior art embodiments of the cutting machine  100 , the material  22 ,  32 ,  42 ,  52  and  62  will be extracted from grooves  20 ,  30 ,  40 ,  50  and  60  by the machine as taught in U.S. Pat. Nos. 3,996,824 and 4,091,697. 
     It will be appreciated by those skilled in the art that the board material may be of any suitable material which is useful as insulation for Heating, Ventilation and Cooling (“HVAC”) duct work, and may include a facing on one side or both faces thereof. The facing may be foil or polymeric material. Such a board is presently available from suppliers including Owens-Corning Fiberglas, Johns-Manville corporation, Certainteed Corporation, Knauf Fiberglas and other suppliers and comprises fiberglass held together by a suitable binder with an impervious facing of aluminum foil on one side. It will be appreciated that the machine  100  and the tool holders  200 ,  300 ,  400 ,  500  and  600  can be used with any suitable insulation material compressed in a board shape. 
     In accordance with the present invention, the passing of the board  10  through the machine will result in a shiplap or other suitable cuts which remove the fiberglass and binder from a desired area such as indicated in the grooves  20 ,  30 ,  40 ,  50  and  60 . The shiplap cuts  20 ,  30 ,  40 ,  50  and  60  provide for strength and integral sealing of the duct when assembled. 
     Referring now to FIG. 1B, therein is disclosed a typical assembled square one-piece HVAC duct  70  formed from a board cut as illustrated in FIG.  1 A. Grooves  20 ,  30 ,  40 ,  50  and  60  are illustrated in their interlocked position. 
     Prior art machines capable of cutting such grooves for assembly into one-piece duct work, and the assembly of such duct work, are illustrated in the Barr patent, U.S. Pat. No. 3,605,534, and subsequent U.S. Pat. Nos. 3,941,018; 3,996,824; and 4,091,687, the disclosure of which is incorporated herein by reference. 
     It will be appreciated by those skilled in the art that ducts of rectangular, and even circular shape, may be formed using different spacing of the tool holders  200  through  600  and additional tool holders with differing blade assemblies in the board cutting machine  100 . 
     Referring now again to FIG. 1A, the board cutting machine  100  includes two leg assemblies  110  and  112  disposed on either side of the machine and a bed and roller assembly (not shown, but of the type known in the prior art) that supports the board  10  as it is fed through the machine  100 . Parallel tool bars  120  and  122  are positioned transverse to the feed direction of the board  10 . 
     The tool bars  120  and  122  may be formed from material having various cross sections. In the present invention, the tool holder bars are formed from a tubular box beam. 
     Referring now to FIG. 2A, therein is illustrated a top view of a portion of tool bars  120  and  122  with the tool holders  200 ,  300 ,  400 ,  500 , and  600  adjustably positioned thereon. Referring also to FIG. 2B, there is illustrated a section view of the tool holders  200 ,  300 ,  400 ,  500  and  600  positioned on tool bar  120 . FIG. 2B is looking at the front edge of the blades. The fiber board  10  is illustrated as it would appear with the grooves as cut therein after passing through the blades. 
     The tool holders  200  through  600  may be positioned along the tool bar in different positions in order to position blade assemblies  280 ,  380 ,  480 ,  580  and  680  at different positions in relation to the board  10 , and thereby adjust the position of grooves  20 ,  30 ,  40 ,  50 , and  60 . Adjusting the location of the grooves on the board  10  allows for the formation of HVAC duct work of differing sizes and configurations. 
     The configuration of blades  282 ,  382 ,  384 ,  482 ,  484 ,  582 ,  584 ,  682  and  684  are well known in the art and described in U.S. Pat. No. 3,605,534 (particularly in FIGS. 11A through 18A thereof). It will also be appreciated by those skilled in the art that there are other additional blade configurations that are known in the art used to cut grooves having different profiles used to form HVAC duct work of differing cross sectional profiles, or to form grooves and cuts necessary for forming corners, and Tee intersections as taught in U.S. Pat. No. 3,605,534 and known in the art. 
     It will be understood that any number of tool holders may be positioned on the tool bar  120  and  122  to form an almost infinite number of arrangements for grooving the board  10 . It will be understood by those skilled in the art that board cutting machines may have a single tool holder bar of any configuration and the tool holder assembly may have different configurations. 
     As illustrated in FIGS. 1A and 2A, the tool holders  200 ,  300 ,  400 ,  500 , and  600  are held in place with clamp mechanisms  290 ,  390 ,  490 ,  590  and  690 . The clamp mechanism  390  is illustrated in more detail in FIG.  6 . Such clamps are well known in the art. It will be appreciated by those skilled the art that any clamping mechanism may be used to secure the tool holders to the tool bar or bars. Clamping mechanism  390  is secured to tool holder  300  by bracket  392 . 
     The body of tool holder  200  is identical and interchangeable with tool holders  300 ,  400 ,  500  and  600 . The only difference in the tool holder being in the blade assemblies  280 ,  380 ,  480 ,  580  and  680  and the corresponding tab indicators  252 ,  352 ,  452 ,  552  and  652 . The interchangeable nature of the body of tool holders  200 ,  300 ,  400 ,  500  and  600  is an important advantage over the prior art tool holders and will be discussed in more detail later in this application. 
     Referring now to FIGS. 3 through 7, wherein the tool holder  300  of the present invention is illustrated. The tool holder is comprised of a first member  322  having a bottom  324 , two parallel upstanding walls  326  and  328  disposed transverse to the longitudinal axis of the tool holder, and which terminate in outwardly disposed flanges  332  and  334  sized and adapted to be received on tool bars  122  and  120 , respectively. The bottom  324  includes outwardly and downwardly turned side members  342  and  344  disposed longitudinally. Side members  342  and  344  serve as brackets for securing the blade assembly  380  to tool holder  300 . Disposed between upstanding walls  326  and  328  is shelf  350 . The shelf  350  may be secured by any conventional manner such as welding, brazing, riveting or by use of the threaded fasteners. The shelf  350  holds tab  352 . Tab  352  is an important feature of the tab system of the present invention and will be discussed in more detail later in the application. 
     Turning now to the important adjustment mechanism  370 . The downwardly disposed side members  342  and  344  of member  322  include openings for receiving threaded rods  372  of the adjustment mechanism. It will be understood that threaded machine screws or bolts may be substituted for rods  372 . Rods are secured in place in the tool holder  300  by nuts  374  or alternative means. 
     The blade assembly  380  is comprised of an attachment member also known as a skid  381  (see FIG. 5) formed from a channel section  385  with the legs  386  and  388  disposed downwardly (see FIGS.  5  and  6 ). It will be understood that the legs of the channel may be disposed upwardly or other structural equivalents including, but not limited to, two sections of angle may be used for the skid. Additionally, two plates held in position with threaded nuts may be used as a skid assembly. It will be understood by those skilled in the art that skid  381  of the blade assembly may be formed as a solid block with openings therethrough to receive the threaded rods or pairs of opposed brackets or other functional equivalents. It will also be understood by those skilled in the art that the width (b) of the base of the channel  385  between the legs  386  and  388  will vary depending on the desired width of the grooves  10 ,  20 ,  30 ,  40 ,  50  and  60  (see also FIG.  2 B). The width of the grooves has been empirically determined as a function of the thickness (t) of the board  10 . 
     Referring to FIG. 5, the leg members  386  and  388  of skid  381  include openings  383  for passing rods  372  therethrough. The adjustment mechanism&#39;s internally threaded nuts  389  may be rotated to move them on the rod  372  thereby repositioning blade assembly  380  transverse to the longitudinal axis of tool holder  300  and transverse to the direction of feed of board  10 . The blade assembly further includes blades  382  and  384  that are attached to leg members  386  and  388  by any conventional means such as welding, riveting or as indicated herein by the use of conventional bolts and nuts. By adjusting the position of blade assembly  380  the position of blades  382  and  384  are adjusted transverse to the direction of feed of board  10 . 
     In the embodiment illustrated, the blade is illustrated as fixed to the skid. However, it will be understood by those skilled in the art that the blade may be adjustably mounted to the skid or, alternatively, a rolling blade such as the type used on a conventional hand-held pizza cutter may be used in the practice of the present invention. 
     In order to appreciate the advantages of the tool holder  300  of the present invention it is important to illustrate the prior art tool holders and discuss the limitations thereof. 
     Referring now to FIG. 8A, therein is illustrated a top view of a portion of tool bars  120  and  122  with prior art tool holders  1200 ,  1300 ,  1400 ,  1500 ,  1600  and  1700  adjustably positioned thereon. Referring also to FIG. 8B, therein is illustrated a section view of tool holders  1200 ,  1300 ,  1400 ,  1500 ,  1600  and  1700  positioned on tool bars  120  and  122 . FIG. 8B is looking at the front edge of the blades. The fiber board  10  is illustrated as it would appear with the grooves as cut therein after passing through the blades. 
     The tool holders may be positioned along the tool bars  120  and  122  in different positions in order to position blade assemblies  1280 ,  1380 ,  1480 ,  1580 ,  1680  and  1780  at different positions in relation to the board  10 . 
     As illustrated in FIGS. 8A and 8B, the tool holders  1200 ,  1300 ,  1400 ,  1500 ,  1600  and  1700  are held in place by a clamping mechanism  1290 ,  1390 ,  1490 ,  1590 ,  1690  and  1790 . Clamping mechanism  1390  is secured to tool holder  1300  by bracket  1392  (FIG.  9 ). 
     Tool holder  1300  is similar to, but not interchangeable with, tool holders  1200 ,  1400 ,  1500 ,  1600  and  1700 . Blade assemblies  1280 ,  1380 ,  1480 ,  1580 ,  1680  and  1780  are fixed by welding to the respective tool holder and the position of the blades is not adjustable in relation to the tool holder. Tabs  1252 ,  1352 ,  1452 ,  1552  and  1652  are different for each respective tool holder. 
     Referring now to FIGS. 9,  10  and  11 , wherein the prior art tool holder  1300  is illustrated in more detail. The tool holder is comprised of a first member  1322  having a bottom  1324 , two parallel upstanding walls  1326  and  1328  which terminate in outwardly disposed flanges  1332  and  1334 , sized and adapted to be received on tool bars  122  and  120 , respectively. 
     Disposed between upstanding walls  1326  and  1328  is shelf  1350 . The shelf  1350  holds tab  1352 . As illustrated in FIG. 8A, tabs  1252 ,  1352 ,  1452 ,  1552  and  1652  are different and must be customized for each respective tool holder. 
     Disposed on the lower surface of bottom  1324  are two blade holder brackets  1386  and  1388 . Blades  1382  and  1384  are attached to brackets  1386  and  1388  by any conventional means such as welding, riveting or as indicated herein by the use of conventional bolts and nuts. 
     When the prior art tool holder  1200  is assembled, the blade assembly  1280  is permanently fixed to the base of the tool holder. The tool holder is placed on the tool bars  120  and  122  on the machine  100 . The fiber board  10  is fed into the machine and the position of the groove  20  is noted (see FIG.  2 B). The tab  1252  is then positioned on the top shelf  1250  of the tool holder to indicate where the cut is made. Next, a tool holder  1300  is assembled and the blade assembly  1380  is permanently affixed to the tool holder  1300 . By trial and error, tool holder by tool holder, the proper tab position is determined and the tab is fixed. The tab  1352  is positioned on the shelf  1350  to indicate where the groove  30  has been cut. This process is followed for each of the tool holders  1400 ,  1500  and  1600 . It is important to understand that each of the prior art tool holders is individually customized in order to generate a matched set necessary to manufacture the fiber board with the grooves  20 ,  30 ,  40 ,  50  and  60 . Tool holder  1700  is used to hold blade assembly  1780  having a cutoff blade  1782  for cutting off the end of board  100 . In alternate prior art embodiments, blade  1782  is mounted on tool holder  1600 . It will be understood by those skilled in the art that often a matched set of eight tool holders is sold with machine  100 . The additional tool holders are used to make different cut configurations and also for use in cutting excess board piece  12  into a usable product configuration. 
     The fiber board  10  is typically manufactured in 1 inch, 1½ inch and 2 inch thickness. The distance between the feed rollers of machine  100  can be adjusted in order to accommodate different thicknesses of board  10 . Different blades  1282 ,  1382 ,  1482 ,  1582  and  1782  and  1384 ,  1484 ,  1584  and  1684 , and blade assemblies  1280 ,  1380 ,  1480 ,  1580 ,  1680  and  1780  must be used with each thickness of fiber board  10 . When using a prior art tool holder system, it is necessary to have a matched set of tool holders for each thickness. This means that in order for maximum flexibility it is necessary to have at least five or more tool holders for each thickness. 
     The improved tool holder  200  of the present invention has the advantage that the tool holder bodies  200 ,  300 ,  400 ,  500  and  600  can be used interchangeably by replacing the adjustable blade assemblies. The tool holders  200 ,  300 ,  400 ,  500  and  600  may also be used for 1 inch, 1½ inch, 2 inch and other thicknesses of fiber board by changing the blade assembly and without adjusting the height of the tool holder bars above the board to be cut. 
     Referring now to FIGS. 3 through 7, when the tool holder  300  is assembled, the tab  352  is fixed to the top shelf  350 . The blade assembly  380  is adjustably mounted on the tool holder. Subsequent to fixing the tab  352 , the blade assembly  380  is adjusted by rotating the nuts  389  which allows the skid  381  and blades  382  and  384  to move into the desired position into alignment with the tab indicator  352 . Referring to FIGS. 2A,  3 ,  4  and  5  when tool holder  300  is assembled, the tab  352  is fixed to the top shelf  350 . The blade assembly  380  is adjustably mounted on the tool holder. The blade assembly is adjusted by rotating the nuts  389  which allows the skid  381  and blades  382  and  384  into the desired position into alignment with the tab indicator  352 . This process is followed for each of the tool holders  400 ,  500  and  600  (and other holders making up a set). 
     When a blade breaks in the tool holder of the present invention, the blade is replaced on the blade assembly  380  and the assembly is adjusted such that the blade aligns with the tab  352 . Likewise, if a blade breaks on one of the other tool holders  200 ,  400 ,  500 , or  600 , the blade is replaced on the blade assembly  280 ,  480 ,  580  or  680  and then repositioned into alignment with the tab  252 ,  452 ,  552  or  652 . 
     Additionally, if a user of the machine desires to change from cutting fiber board  10  of one thickness to a different thickness, it is not necessary to purchase an additional set of five more tool holders. The blade assemblies  280 ,  380 ,  480 ,  580  and  680  for one thickness are removed and the skids  281 ,  381 ,  481 ,  581  and  681  (FIGS. 2A, and  3  through  5 ) for one thickness is removed. A blade assembly  380 , including the skid  381 , and blades  382  and  384 , is inserted on the threaded rod  372  and positioned in alignment with the tab  352 . In a similar manner, the remaining tool holders in the set are retrofitted with blade assemblies for the different thickness of fiber board. Such interchangeability and retrofitting is made possible by the adjustable mounting of the blade assembly  380  in conjunction with the unique design of the tabs  252 ,  352 ,  452 ,  552  and  652 . 
     When using a prior art tool holder, if a machine operator desired to cut a board  10  of different thickness, it was necessary to raise or lower the tool bar or bars to adjust the positioning of the bar or bars in relation to the board to be cut. With the tool holder of the present invention, it is not necessary to adjust the tool bar for different thickness of material. In a new machine manufactured in accordance with the present invention, the bar is initially fixed in the highest position which will accommodate the passage of fiber board of multiple thicknesses. In the retrofit of a prior art machine, the tool bar is raised to the highest adjustment which will accommodate the passage of fiber board of multiple thicknesses. The tool holder blade assembly is removed and a blade assembly designed for the desired thickness material is installed. The blade assembly  380  of the present invention includes the skid  381  having leg members  386  and  388 . The length of the leg members  386  and  388 , extending in a downwardly direction, is carefully selected in order to position the blades  382  and  384  attached thereto correctly in relation to the board. 
     Referring to FIG.  2 A and FIGS. 12 to  14 , each of the tabs  252 ,  352 ,  452 ,  552  and  652  include a step design with tab settings indicated for 1 inch, 1½ inch and 2 inch thick fiber board. Since each tab includes tab settings for all three common thickness and is permanently affixed to the tool holder, one tool holder is capable for use in any position with any thickness merely by changing the blade assembly and bringing it into alignment with the tab indicator. 
     Use of the tool holders  200 ,  300 ,  400 ,  500  and  600 , including tab indicators  252 ,  352 ,  452 ,  552  and  652  and blade assemblies  280 ,  380 ,  480 ,  580  and  680  as an integrated system, is illustrated in FIGS. 2A and 2B. In order to simplify operation of the cutting machine  100 , the inventor has labeled tab  252  as tab A; tab  352  as tab B; tab  452  as tab C; tab  552  as tab D; and tab  652  as tab E. Therefore, the operator can easily know the position of the tool holder in the series used to make the necessary cuts to form the square duct of FIG. 1B. A series of rulers R 1 , R 2 , R 3  and R 4  illustrate how the operator of the machine  100  uses the improved tool holders  200 ,  300 ,  400 ,  500 , and  600  of the subject invention. If a square duct, such as the one illustrated in FIG. 1B, is to be constructed from 1 inch thick fiber board  10  and the desired interior dimension is to be 6 inches inside from wall intersection to wall intersection, the operator positions tool holder  200  against a stop of the machine  100  and measures six inches between the 1 inch tab indicator mark on tab A and the 1 inch tab indicator on tab B. Likewise for tabs C, D and E. The unique design of the tabs takes into account the calculations necessary for positioning the blade assemblies to cut the desired grooves  20 ,  30 ,  40 ,  50  and  60  in board  10 . 
     Referring to FIGS. 2A,  2 B and FIG. 13, it will be understood by those skilled in the art that the right side and left side indicator marks  353  and  355  of tab  352  does not necessarily indicate that blades  382  and  384  are positioned directly below the tab indicator mark. Indeed, one of the features of the tab system of the present invention is that when the tool holders  300 ,  400 ,  500 , etc. are positioned using the R 2 , R 3  (desired inner duct dimensions) between tab indicator marks  355  and  453 , the position of the blades will automatically be positioned to make the desired predetermined cut spacings necessary to form the completed duct as illustrated in FIG.  1 B. As illustrated in FIGS. 2A and 2B, the position of blade  384  is offset by the distance (a) from the edge of tab indicator mark  353 , while blade  382  is positioned directly below tab indicator mark  355 . The offset distance (a) is equal to one-half the thickness (t) of the board  10  being cut. FIGS. 2A and 2B illustrate a like manner of the offset distance (a) for tabs  252 ,  452  and  552 . The tab  652  does not have an offset a. 
     Referring now to FIG. 12, therein is indicated a top view of tab A. The critical measurements for the unique three step profile are a 1  of 2.1250 inches; a 1.5  of 2.875 inches and a 2  of 3.625. The height dimension of the tab is irrelevant to the calculation and placement of the grooves. In the embodiment illustrated, the height of each step on the tab is 1 inch. Calculation of the a 1  distance of a 1 inch thick board is arrived at by adding 1.625 inch+½ the board  100  thickness. The dimension 1.625 inch is determined empirically for a desired flap width. Calculation of the a 1.5  for a 1½ inch board is arrived at by adding 2.125 inch (empirically determined)+½ the board thickness. Calculation of the a 1  for a 2 inch board is arrived at by adding 2.625 inch (empirically determined)+½ the board thickness. 
     Referring now to FIG. 13, therein is indicated a top view of tabs B, C and D. The critical measurements for the unique three step profile are b 1  of 1.625 inch; b 1.5  of 2.5625 inch and b 2  of 3.500. The height dimension of the tab is irrelevant to the calculation and placement of the grooves. In the embodiment illustrated, the height h is 1 inch. Calculation of the b 1.0  distance of a 1 inch thick board is arrived at by adding 1.125 inch (desired groove width determined empirically)+½ the board thickness. Calculation of the b 1.5  for a 1½ inch board is arrived at by adding 1.8125 inch (empirically determined)+½ the board thickness. Calculation of the b 2.0  for a 2 inch board is arrived at by adding 2.5 inch (empirically determined)+½ the thickness of the board. 
     Referring now to FIG. 14, therein is indicated a top view of tab E. The critical measurements for the unique three step profile are e 1.0  of 0.7500 inch; e 1.5  of 1.250 inch and e 2.0  of 1.75. The height dimension of the tab is irrelevant to the calculation and placement of the grooves. In the embodiment illustrated, the h is 1 inch. Calculation of the e 1.0  distance of a 1 inch thick board is arrived at by subtracting ¼ inch from the thickness of the board. Calculation of the e 1.5  for a 1½ inch board is arrived at by subtracting ¼ inch from the thickness of the board. Calculation of the e 2.0  for a 2 inch board is arrived at by subtracting ¼ inch from the thickness of the board. It will be readily apparent that the principles disclosed in this invention may be applied to board thickness other than 1 inch, 1½ inch and 2 inch by applying the appropriate mathematical calculations as disclosed herein. It will also be apparent to one skilled in the art that not only insulation fiber board may be cut and manufactured in accordance with the teachings of the present invention, but other board materials which require precision cutting may use the principles taught by the present invention. It will be apparent to those skilled in the art that the tool holder and tab system of the present invention may be used with newly manufactured cutting machines and/or used as retrofit equipment for prior art cutting machines. 
     A preferred embodiment of the invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous modifications without departing from the scope of the invention as claimed.