Abstract:
An extension for a bit or cutter tool relative to a rotational power source. The extension includes a blind bore receiving the shank of the bit or cutter. The opposite end of the body has structure that can be operatively connected to the source of rotational power. A second bore through the side of the body intersects the first bore. The second bore has two portions. The inner-most portion has a smaller diameter and is internally threaded. The outer portion has a larger diameter and slidably receives a clamping member. Clamping member can be retained by a shoulder bolt and has an end that can enter into the blind bore to clamp the shank in place. Preferably the clamping member is a sleeve having a center bore and a concentric exterior. Another aspect of the invention includes a biasing means that biases the sleeve outward of the bore.

Description:
[0001]     This is a conversion of, and priority under 35 U.S.C. § 119 and/or 120 is claimed to, U.S. Provisional Application 60/533,743, filed Dec. 31, 2003.  
       INCORPORATION BY REFERENCE  
       [0002]     The contents of U.S. Provisional Application 60/533,743, filed Dec. 31, 2003 are incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates to a chuck, or an extension useable with a chuck, for holding cutter or router bits.  
         [0005]     2. Problems in the Art  
         [0006]     Various machines are adapted for interchangeable tools. An example is a wood-working router. A chuck of the router is adapted to receive and fix a router bit shaft. There are a number of other types of machines that utilize such a chuck or an analogous structure.  
         [0007]     The mechanism to fix the bit in the chuck must be durable and robust. It cannot allow longitudinal or rotational movement of the bit during operation, even when substantial forces are experienced by the working end of the bit. Any such movement would reduce the effectiveness of the tool or even be dangerous (e.g. a high speed bit could release and fly off).  
         [0008]     A variety of methods exist for fixing a bit in a chuck. Standard designs for routers use arbor locks or factory two-wrench systems. Some examples can be seen in the following U.S. patents: 
        U.S. Pat. No. 3,091,474     U.S. Pat. No. 5,348,319     U.S. Pat. No. 5,096,212     U.S. Pat. No. 6,332,619        
 
         [0013]     There are times when it is desirable to extend the working end of the bit from the machine. For example, in certain situations, it is desirable to extend the cutting or working end of a router bit farther from the factory chuck of the router than normal. A specific example is where the router is installed upside-down in a table, with the bit chuck at or near the table surface. Placing a standard router bit in the chuck extends the bit a distance above the table top. Even if there is some adjustability of the router or router chuck relative to the table top such that there can be some adjustment of the height of the bit above the table top, there are certain circumstances where it is desirable, or even necessary, that the working end of the router bit be higher than any available adjustment range of the bit in the normal chuck and router.  
         [0014]     Although existing methods of fixing a bit in a chuck and allowing some adjustments of the chuck relative to a table top are adequate for many purposes, there still exists room for improvement in the art.  
         [0015]     Attempts to extend the working end of the bit leave room for improvement in the art because of complexity in terms of manufacture or number of parts, and potential for failure or vibration. Many previous extensions use a standard threaded collet with an extended shank to extend the reach of the bit when needed. They are supplied with internal or external threaded means to compress either a nut or a peripheral set of moveable fingers, or a separate collet sleeve actuated by a nut threaded over the outside diameter of an extension body which, when tightened, compress the fingers of the sleeve onto the bit shank, thereby retaining it. These methods require the use of two wrenches or the arbor lock of the router to tighten and release the bit shank in the extension. They also added an extreme amount of length to the shank requiring substantial space to be fabricated to return the useable stroke of the router. Also, due to the extreme length and slim profile, they are prone to introducing a substantial amount of concentric rotating width into the spinning bit which creates vibration, both with the bit cutting and free running.  
         [0016]     Therefore, an improved extension that deals with these problems is submitted to be needed in the art.  
         [0017]     The above listed patents represent various ways of locking a bit shank into a chuck. They have the benefit of allowing single tool cutter changes without the use of the arbor locks or the factory two wrench system mentioned above. However, disadvantages of these designs include difficulty in manufacturing and inability to use standard and large shank bits. Also, the need for an individual chuck for each brand of router becomes apparent when the wide variety of collet designs used for each manufacturer are taken into account. These types of chucks also do nothing to extend the reach of the cutter when it is needed, such as on the Legacy Mill. Special extra-long bits are needed for these machines, which are hard to find and expensive when located.  
         [0018]     Additionally, at least in U.S. Pat. Nos. 3,091,474 and 6,332,619, eccentric sleeves  26  and  209 , respectively, are difficult to make and require extreme care by the user to ensure proper alignment and correct clamping. These sleeves are also oriented so that if the fastener should fail, the rotation of the bit shank will force the sleeve out of contact with the bit shank, thereby releasing the cutter from the machine. Other disadvantages to these designs are the difficulty of keeping the bore of the chucks concentric with the center line of the arbor due to the cone-shape formed on the bottom of the chuck to mate with the factory taper. Due to the clearance required to insert and remove the cutter when the bit is clamped in operating position, the center line of the bit is no longer concentric with the center line of the arbor on which it is mounted. They also have no means of retaining the bit in the chuck when used in a chuck-down vertical position. Assembly and repair is also hindered by the design of these chucks. The retention pins and spring rings used to hold the various components together are subject to catastrophic failure. If either the spring rings or the tension pins fail, the chucks are free to disengage from the arbor of the machine.  
         [0019]     By referring to FIGS. 5 and 6 of U.S. Pat. No. 3,091,474, and FIG. 5 of U.S. Pat. No. 6,332,619, the eccentric nature of the sleeves is explicit. The bore through the sleeve is offset from the longitudinal axis of the sleeve.  
         [0020]     U.S. Pat. No. 5,096,212 illustrates a clamping method using two sleeves  108  and  109  on a threaded screw  94  (See FIG. 17 of U.S. Pat. No. 5,096,212). This adds complexity and cost to that clamping system.  
         [0021]     U.S. Pat. No. 5,348,319 utilizes a complex shaped member  12  inserted longitudinally into the chuck. Also a separate insert  16  is used to receive the bit shank  18 . The complex shape  12  wedges against the exterior of collet  16  instead of the bit shank. This also is a complex arrangement and requires complex manufacturing of the chuck.  
         [0022]     Vibration problems most acute with U.S. Pat. Nos. 3,091,474 and 6,332,619 cannot be machined out or calculated out because of the different bits and speeds used. Although the offset from the center line is relatively small, it can be enough to cause substantial vibration and unbalancing of the bit because the longitudinal axis of the shank of the bit is slightly offset from the longitudinal axis of the arbor.  
       SUMMARY OF THE INVENTION  
       [0023]     It is therefore a principle object, feature, advantage and aspect of the present invention to provide an apparatus and method which improves over the state of the art.  
         [0024]     Other features, advantages, options or aspects of the invention include an apparatus and method which: 
        a. is non-complex and economical to manufacture;     b. reduces cost and resources for repair or reconstruction;     c. can be used in either a cutting or router bit chuck or in an extension of the same;     d. minimizes the amount of effort needed to attach a bit or remove a bit, or replace a bit;     e. is relatively universal across most brands of routers which have the proper size collet.        
 
         [0030]     These and other objects, features, advantages, and aspects of the present invention will become more apparent with reference to the accompanying specification. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is an enlarged perspective view in exploded form of a router or cutting bit extension according to one aspect of the invention.  
         [0032]      FIG. 2  is similar to  FIG. 1  but shows a router or cutting bit chuck according to one aspect of the present invention.  
         [0033]      FIGS. 3A and 3B  illustrate diagrammatically an elevation view of a standard in-table router with conventional bit chuck.  FIG. 3A  shows the bit in exploded position from the chuck.  FIG. 3B  shows the bit fixed into the chuck in operable position.  
         [0034]      FIGS. 4A and 4B  are similar to  FIGS. 3A and 3B  but show the embodiment of the extension of  FIG. 1  relative to a conventional in-table router.  
         [0035]      FIGS. 5A and 5B  show a side elevation and elevation respectively of the extension of  FIG. 1  illustrating dimensions and manufacturing techniques for one exemplary embodiment.  
         [0036]     FIGS.  6 A-C show, in isolation, enlarged views of a clamping sleeve used in the embodiment of  FIGS. 1 and 5 A-B.  
         [0037]      FIG. 7  is an enlarged sectional view taken along lines  7 - 7  of  FIG. 5A . 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0038]     To provide a better understanding of the invention, specific exemplary embodiments the invention can take will now be described in detail. Frequent reference will be taken to the accompanying drawings. Reference numerals will be used to indicate certain parts and locations in the drawings. The same reference numerals will be used to indicate the same parts and locations throughout the drawings, unless otherwise indicated.  
         [0039]     Environment of Invention  
         [0040]     Exemplary embodiments will be described in the context of a router  70  mounted in a table  80  such that router chuck  75  is oriented upwardly (see FIGS.  3 A-B,  4 A-B). A hole in the top of table top  80  allows access to the chuck to insert and fix a router bit  76  in chuck  75 ; and release and remove and/or interchange another bit. It is to be understood, however, that concepts of the invention embodied in the exemplary embodiments can be applied to other tools needing analogous replaceable working tools.  
         [0041]     General Structure  
         [0042]      FIG. 1  illustrates an exemplary embodiment of a router or cutter bit extension  10  according to the invention. Extension  10  is a generally solid piece of machined steel (e.g. stainless steel) having a cylindrical portion  12 , a conical portion  14 , and a shank  18 . A blind bore  16  extends substantially through portions  12  and  14  along center line  20 . Shank  18  is centered along center line (or longitudinal axis)  20 .  
         [0043]     Shank  18  is configured to fit into and lock into conventional chucks or arbors of most conventional routers  70 . Blind bore  16  is configured to receive the shank of any number of conventional router bits. The internal diameter of blind bore  16  is therefore essentially the same as the external diameter of shank  18  in most cases. However, those dimensions could vary.  
         [0044]     The shank of a bit inserted into blind bore  16  can be clamped by a shoulder bolt  40 /sleeve  30  combination that can be inserted into tangential bore  22  in the side of cylindrical portion  12  of extension  10 . As illustrated in  FIG. 1 , tangential bore  22  extends tangentially to blind bore  16  in such a manner and to such a distance that this major clamping bore  22  exposes part of blind bore  16  (see area indicated at reference number  28 ). The major portion of bore  22  terminates in a wall or step  26  that is orthogonal to the longitudinal axis of bore  22 . A minor bore (threaded)  24  continues along the longitudinal axis of bore  22  from step  26  to the exterior (see reference numeral  25 ) of cylindrical portion  22 .  
         [0045]     Shoulder bolt  40  includes a head  42  with a hex socket  44  extending inwardly therein. Shoulder  46  extends from head  42 . A reduced diameter terminal part of shoulder bolt  40  includes unthreaded portion  47  and threaded end  48 .  
         [0046]     Clamping sleeve  30  is approximately the length of shoulder  46  of shoulder bolt  40 . It has a through-bore  32  having a diameter slightly larger than the outside diameter of shoulder  46  of shoulder bolt  40  such that sleeve  30  slides over shoulder  46  in a mating fashion but freely rotates thereon. Shoulder  46  is hardened and machined. End  48  and portion  47  of shoulder bolt  40  extend beyond sleeve  30  when installed in shoulder bolt  40 . A thin metal washer  50  can be installed between sleeve  30  and head  42  to reduce wear by any friction between the two.  
         [0047]     A combination of sleeve  30  on shoulder bolt  40  can be inserted into major bore  22  in extension  10  and threaded end  48  turned into minor threaded bore  24 . Sleeve  30  is oriented such that flat  34  is parallel with the plane of the end of extension  10  (the plane of the opening into blind bore  16 ). A radius angle cut exists approximately centered 90 degrees clockwise at the innermost end of sleeve  30  and ends up coincident with opening  28  into blind bore  16 , as will be further described below (but which cannot be seen in  FIG. 1 ). By inward threading of shoulder bolt  40 , the inner end of sleeve  30  is brought farther into opening  28 . In this manner a portion of the inner end of sleeve  30  enters within the blind bore  16  and thus can exert clamping force on a bit shank in blind bore  16 .  
         [0048]     The basic concept of using a threadable bolt and sleeve having a portion that extends into the shank bore is described in such patents as U.S. Pat. Nos. 3,091,474 and 6,332,619, mentioned above. However, differences exist between those structures and that of extension  10 .  
         [0049]     First, through-bore  32  of sleeve  30  is generally centered along the longitudinal axis of sleeve  30 . In other words, the wall thickness around through bore  32  is essentially the same around its circumference (except for the flat portion  34 ). This is in direct contrast to the decidedly eccentric shape of the sleeves of the above-mentioned patents.  
         [0050]     Secondly, shoulder  46  of shoulder bolt  40  is hardened and of larger diameter than the remainder of portion  47  and  48  of the shaft or bolt  40 .  
         [0051]     Third, optionally an O-ring (elastomeric and resilient)  52  can be positioned between the inner end of sleeve  30  and step  26  inside extension  10 . In  FIG. 1 , two O-rings  52 A and B can be utilized. The diameter of the opening in the O-rings is slightly less than the diameter of portion  48  and  47  of bolt  40 . When bolt  40 /sleeve  30  is inserted into extension  10  and bolt  40  is threaded into bore  24 , O-rings  52 A and B compress between step  26  and the inner end of sleeve  30 . This biases bolt  40 /sleeve  30  outwardly to assist in deterring backup of bolt  40  or loosening of bolt  40 . But additionally, when bolt  40  is somewhat loosened, O-rings  52 A and B tend to bias it outwardly to assist in removal of the bit shank from blind bore  16 . Conversely, when loosened, they also help deter the bolt/sleeve  40 / 30  combination from falling out of extension  10 . It is to be understood that in this embodiment two O-rings are used. One could also be used or more than two. There are also alternative biasing members (e.g. springs) that could be used.  
         [0052]     Additionally, a threaded bore  54  exists from the end surface of extension  10  parallel to through-bore  16  and in communication with main clamping bore  22  (see  FIG. 1 ). A set screw  56  with a hex socket  58  is adapted to be threaded through bore  54  until its inner end abuts flat  34  of sleeve  30  when screw  40 /sleeve  30  is installed. This primarily deters sleeve  30  from rotating and can assist in preventing longitudinal movement of sleeve  30  relative to bolt  40 . Preferably set screw  56  is tightened enough to stop rotation but allow some longitudinal movement so that bit removal and insertion (and clamping) can be done with just loosening or tightening one thing—bolt  40 .  
         [0053]     Therefore, as can be seen, a simple, easy to manufacture combination exists for clamping a bit shank. One tool can be used to do so by simply rotating shoulder bolt  40 .  
         [0054]      FIG. 2  illustrates an alternative embodiment according to the invention. Instead of an extension having a shank  18  that could be fixed into a router chuck, the invention can be embodied into a chuck  10 B. The clamping mechanism of shoulder bolt  40 /sleeve  30 , and the other structure described with regard to  FIG. 1 , is identical. The only difference is instead of a shank  18 , chuck  10 B would be connected operably to an arbor  60 / 62 / 64  arrangement that in turn is connected to a draw bar  66 . Chuck  10 B would therefore function like any conventional chuck (see descriptions of the same in U.S. Pat. Nos. 3,091,474 and 6,332,619). It would use standard structure for operative connection to the motor of the tool. Therefore this standard connection will not be further described, as it is well known in the art.  
         [0055]      FIGS. 3A  and B and  4 A and B illustrate diagrammatically how extension  10  can be used. Normal in-table routers have a metal base plate  71  that seats into a mating circular cutout in the top of table  80  to hold router  70  in an inverted position. Supporting structure  73  extends from base plate  71  and is connected to the body or motor housing  74  of router  70 . Chuck  75  is at the top of housing  74  and is operatively connected to the motor in housing  74 . An opening  72  exists in base plate  71 .  
         [0056]     A bit  76 , having a shank  77  and cutting head or working end  78 , is insertable shank-first into chuck  75 . Chuck  75  is then adjusted to grab shank  77  to hold bit  76  in operable position (see  FIG. 3B ). As indicated, router  70  is adjusted so that cutting head  78  extends above the plane of table top  80 . For illustration, the plane of table top  80  is indicated at reference numeral  81 . The plane of the top of cutting head  78  is indicated at reference numeral  82 . The distance between planes  81  and  82  is indicated at reference numeral  83 .  
         [0057]     As previously briefly discussed, even though many routers have the capability of adjusting the distance between base plate  71  and chuck  75 , and thus having some range of adjustability of the plane of the top of cutting head  78 , there are certain circumstances where certain cutting bits require extension above plane  81  farther than router  70  can be adjusted. As illustrated in  FIGS. 4A  and B, extension  10  of  FIG. 1  can be fixed into chuck  75  of router  70  and shank  77  of bit  76  fixed into extension  10 . As diagrammatically illustrated in  FIG. 4B , this would result in plane  83  being substantially higher than plane  83  of  FIG. 3B . The top of extension  10 , when inserted into chuck  75 , is indicated at the plane indicated by reference numeral  84  in  FIG. 4B . The difference between plane  81  and plane  83 , when used in extension  10 , would essentially be the length of extension  10  (approximately).  
         [0058]     As stated, bit  76  can be installed into extension  10  with one tool quickly and easily. Its clamping structure robustly grips shank  77 .  
         [0059]     As can be appreciated, the length of extension  10  can be varied according to need or desire.  
         [0060]     Additional Details Regarding Embodiment of Extension  10   
         [0061]     By reference to  FIGS. 5A  and B,  6 A-C and  7 , additional details regarding extension  10  are illustrated. Bore  24  is a 10-32 GH7 threaded hole. The center bore should be concentric within close tolerances. All diameters should also. It is to be understood that these are exemplary of one form extension  10  could take.  
         [0062]      FIGS. 5A  and B illustrate extension  10  body  12 / 14 / 18 , as well as blind bore  16 , major and minor clamping bores  22  and  24 , and set screw bore  54 .  
         [0063]     FIGS.  6 A-C show an exemplary sleeve  30 . In particular, the radius of machined portion  36  is shown in detail. Flat  34  can also be seen in more detail. Also, in this embodiment each opposite end edge is beveled (reference numeral  38 ).  
         [0064]      FIG. 7  illustrates by sectional view bolt  40  and sleeve  30  assembled into extension  10 .  
         [0000]     Options and Alternatives  
         [0065]     The foregoing exemplary embodiments are given by example only and not by limitation. Variations obvious to those skilled in the art will be included within the invention.  
         [0066]     It can therefore be seen that extension  10  allows extension of a router bit outward of the base of a router or machine base plate to get added reach and allow easy bit changing with a single tool without using a factory collet or arbor lock, or two wrenches, when used in conjunction with table/hand-held/machine-mounted router. Its blind bore  16  can be sized to receive cutter bits or router bit shanks sized to fit in the collet of a conventional router or other machine. Its radial clamping mechanism, operated by a single tool, enables it to be used even by persons having less than full use of both hands. It also allows essentially universal use across all brands of routers which have the proper size collet. It does not depend on any threaded means other than the factory supplied collet and clamping means.  
         [0067]     The designs are easy to manufacture due to a concentric clamping sleeve as opposed to an eccentric sleeve. The extension design is far more universal and allows a single size to be used across a wide variety of routers.  
         [0068]      FIGS. 5A  and B show additional details for one example of a bit chuck according to the invention. Variations are possible, such as would be obvious to those skilled in the art.  
         [0069]     One optional feature that can be manufactured into extension  10  is as follows. As mentioned, clamping systems such as U.S. Pat. Nos. 3,091,494 and 6,332,619 have enough play in the bore that receives the bit shank that many times, when clamped, the longitudinal axis of the bit is moved off center of the longitudinal axis of the collet or arbor. This slight offset (even several hundredths or thousandths of an inch) can result in a wobble or vibration when the bit rotates. This is especially apparent at high speed rotations. To compensate for this, optionally the longitudinal axis of shank  18  of extension  10  can be offset from the longitudinal axis of blind bore  16  opposite opening  28  in main clamping bore  22  by approximately the same distance the shank  77  of bit  76  would be moved when turning down shoulder bolt  40  to clamp in bit  76 . Because shanks  76  are essentially all the same diameter, the amount of movement can be averaged or approximated and, during manufacturing, the offset of shank  18  will align it with the operating longitudinal axis of shank  77  of bit  76  sufficiently to reduce or eliminate whipping or vibration. The center line of the bit would be concentric to the center line of the arbor when it is clamped into the extension and the extension is in turn clamped into the machine arbor/collet. This design and the mass of extension  10  help alleviate the whipping problem observed in extensions sold by others. Extension  10  can be made of fatigue-proof steel or other tough steels known in the art. Shoulder  46 , and threaded fastener  40  with the matching bore and sleeve  30 , provide a full bearing surface for torque-loading of the sleeve when clamped.  
         [0070]     Another optional feature can be a balancing hole  45  (see  FIG. 1 ) which can be a formed (e.g. by drilling or otherwise) cavity or void in the side of cylindrical portion  12  of extension  10 . Hole  45  preferably is generally in the same plane as clamping screw or bolt  40  (see plane defined by lines  47  and  49  in  FIG. 1 ). The function of balancing hole  45  is to compensate for the missing mass on the opposite side of cylindrical portion  12  caused by opening  22  and bore  24  that facilitate entry of clamping bolt  40  and sleeve  34  into cylindrical portion  12 . By methods well known in the art (e.g., trial and error or a computer program that calculates any offset in mass), the size of hole  45  is selected to balance extension  10  along its longitudinal axis. The size of hole  45  therefore depends upon the size of any missing mass on the opposite side of extension  10 , including the opening  64  for set screw  56 . Of course, the design would take into account the mass of any structure normally inserted into the openings, including clamping screw  40 , sleeve  45 , set screw  56 , and other parts, but is intended to be quite precise in balancing extension  10 . In the embodiment shown in  FIGS. 5A  and B, hole  45  is approximately {fraction (7/32)} inch in diameter and {fraction (3/16)} inch deep.  
         [0071]     As can be appreciated by those skilled in the art, the position of balancing hole  45  relative the opposite side of extension  10  may not be directly  1800 . There could be an offset. As can be seen in  FIG. 1 , the missing mass caused by voids  22 ,  24 , taken in combination, are somewhat complex. They do not represent a simple cylindrical bore directly or orthogonal into the side of extension  10 . Therefore, balancing hole  45  might be offset a few degrees (e.g. 5°) on the opposite side of a plane through the longitudinal axis of extension  10  that lines up with wall  26 . There is no set range of offset and it would be dependent upon the circumstances. But even with the general embodiment of  FIG. 1 , the offset could be slight, perhaps up to 15° or so.  
         [0072]     Other methods for balancing extension  10  are possible. For example, a flat spot might be machined on the opposite side of extension  10  from opening  22 . However, flat spots tend to create more complexity in achieving balance. Another possibility would be to add mass to the side of opening  22 . Other methods are possible such as within the skill of those skilled in the art.  
         [0073]     Main clamping bore  22  in which sleeve  30  slides is also sized to provide a full bearing surface to prevent deflection of sleeve  30 , which maximizes sleeve  30  to bit shank  77  contact. Flat point set screw  56 , combined with milled flat  34  on sleeve  30 , provides an anti-rotation feature to sleeve  30 . This also ensures maximum bit contact while aiding in the accurate milling of the radius in the edge of sleeve  30  for, again, maximum shank  76  contact. Sleeve  30  is also oriented to work with the rotation of the bit to affect a self-clamping or enhance clamping force provided by threaded fastener  40 . Even if the fastener  40  should fail, the rotation effect of shank  77  on sleeve  30  will work to draw sleeve  30  into the body of extension  10  and not outward away from bit shank  77 , therefore acting as a self-restraining mechanism for bit retention.  
         [0074]     Resilient ring or rings  52  provide a method of biasing sleeve  30  to a released position when clamping force is released. It (or they) also act to retain the bit in extension  10  when used in a bit-down vertical position, such as a Legacy Mill or pin routing machine.  
         [0075]     Since no parts but the factory collet components are used to retain extension  10  to the arbor, the chances of failure or release from the machine arbor are greatly reduced. Balancing is greatly enhanced due to the fact that the clamp position of the bit is concentric with the extension shank center line and therefore the machine arbor center line. This eliminates what can be called variable mass from the balancing equation, making balancing easier and far more accurate. The variable mass is created by the use of various diameters and lengths of bits, and also the weight of these bits.  
         [0076]     As stated, the invention can be used for routers and analogous uses. By analogous uses it is meant any rotary tool that is gripped by a collet-like member or chuck. Shaping machines are another example. The primary application described above is with table or machine mounted routers of either the fixed base or plunge router type. But this is not limiting to its use.  
         [0077]     In operation, extension  10  is mounted to the factory supplied arbor or into the factory supplied collet of the router and the bolt  40  tightened. Extension  10  is then checked for run out, which a maximum is supplied with instructions for use. If the run out is found to be excessive, the collet is then loosened and extension  10  or collet sleeve are repositioned and the collet retightened. Run out is again checked and the process is repeated until the run out is brought to the absolute minimum. The router bit of choice is now selected and inserted into the bore of the extension. A supplied Allen wrench is used to rotate the clamping screw which, in turn, applies the clamping force to the clamping sleeve which bears on the shank of the bit, effectively clamping the bit into working position in the extension  10 . To remove the bit, the clamping screw is rotated counterclockwise, which releases the clamping force of sleeve  30 . The resilient members  52  can then bias the sleeve to the unclamped position and the bit can be withdrawn.  
         [0078]     In one embodiment a combination of features and aspects could include: 
        an extension with a body,     a round tool shank sized and shaped at its first end design to be inserted into the factory collet/chuck of a woodworking router and be retained by the collet,     a blind unthreaded bore at the opposite end into which the shank of the router bit can be inserted,     a peripheral clamping mechanism perpendicular to said bore,     said clamping mechanism consisting of,     a bore perpendicular to the blind bore,     said bore being situated so as to work with the forces of rotation of the bit when in use allowing the clamping mechanism to self tighten to some degree,     said bore being of two dimensions in cross section,     one section of said bore being sized to receive a clamping sleeve,     this first bore being located so as to allow the sleeve edge to penetrate the blind bore for the shank,     the remainder being of a reduced size to accommodate the threaded clamping method,     the reduced size remaining bore containing internal threads,     a threaded clamping method to load and retain the sleeve,     a sleeve of uniform wall thickness and being less than half the depth of the bore in length, in which the sleeve is inserted and retained,     the sleeve having a flat machined onto it, the sleeve having a radius perpendicular to the centerline machined onto it at one end,     a washer/ring positioned under the head of the threaded clamping method to reduce wear and friction,     a resilient ring or rings to bias the sleeve to an unclamped position,     said rings also acting to retain the bit when the router is used in the chuck down position,     the threaded clamping method includes a hex shaped recess in its first end,     the threaded clamping method includes a shoulder about its center line biased to an end upon which the sleeve resides,     the threaded clamping method which includes at its second end a threaded portion,     an anti rotation method,     the anti-rotation/and secondary retention means method consisting of a bore,     the bore being located in the same face as the blind bore,     the bore being in the periphery of the top face,     the bore being threaded or smooth,     the bore intersecting the periphery clamping bore,     the bore being blind or through.        
 
         [0107]     However, it is to be understood that many of the above aspects are optional. Variations of the above-combination can be practiced, including or not including certain of the aspects, achieve different functions and advantages. And variations obvious to those skilled in the art can be made to any of the features or aspects. The invention is defined solely by the claims appended hereto.  
         [0108]     Also included in the invention is a method of machining which accurately locates the blind bore centerline and the center line of the tool&#39;s arbor/collet, which eliminates or reduces the off-center rotation of the cutter/bit which reduces vibration and makes balancing the assembly consistent regardless of the mass inserted into the blind bore (i.e., size, length and diameter of cutter bit).