Abstract:
A hole cutter machine tool combines the characteristics and properties of a low-cost hole saw with the speed and performance of an annular cutter. The hole cutter comprises a cutter ring portion similar to an end portion of existing annular cutters with a carrier portion similar to the cup of a hole saw. In one embodiment the hole cutter has a threaded aperture which enables use with a standard hole saw arbor or with a replaceable arbor having an annular cutter shank. An embodiment of the method of making the hole saw includes a joining process in which the cutter ring is simultaneously attached to the carrier portion and heat treated.

Description:
[0001]     This application claims the benefit of U.S. Provisional Patent application Ser. No. 60/506,320, filed Sep. 26, 2003, and herein incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to a machining tool and, more particularly, to a hole cutter machine tool which combines the characteristics and properties of a low-cost hole saw with the speed and performance of an annular cutter.  
       BACKGROUND OF THE INVENTION  
       [0003]     Hole saws and annular cutters are machine tools used in drilling operations to cut a hole of a desired size. Hole saws and annular cutters remove a ring of metal leaving a central core or plug which can be removed as one piece. This enables faster hole drilling and requires less energy as only the perimeter is cut as compared to a standard twist drill which requires the entire hole to be reduced to chips.  
         [0004]     A hole saw is typically adapted to be used with a drill press or power drill that allows a user to make circular cut-outs in a material such as wood, steel, fiberglass, plastic, etc. A conventional hole saw includes a saw cup, an arbor, and a pilot bit. The saw cup typically includes a threaded aperture to receive a threaded end portion of the arbor. Other conventional hole saws may have the arbor welded to the saw cup. The pilot bit protrudes from the cutting edge of the saw to guide the saw during cutting. The saw cup generally includes a collection of teeth which are comprised of uniform size and orientation, or may include repetitive groups of different size and orientation. The teeth may also be carbon steel, high speed steel, carbide, diamond grit or tungsten carbide grit tipped. While hole saws have proven to operate in a generally satisfactory manner for relatively shallow holes and softer materials, their performance is often inadequate for deeper holes and harder materials, especially when a large number of holes need to be cut.  
         [0005]     For these more demanding situations, an annular cutter may be used. An annular cutter is a machine tool typically used on magnetic base drills, drill presses, milling machines, and CNC machining applications. A prior art monolithic annular cutter  2  is shown in  FIG. 1  and consists of a hollow cylindrical shell  3  having a shank  4  or stem at one end and axially projecting teeth  5  at the other end. The teeth  5  are separated by helical flutes  6  and helical cutting edges  7  extending from the cutting surface along the exterior of the cylindrical shell  3 . Although not shown, the shank  4  typically includes an aperture for a pilot bit or pin which protrudes from the cutting edge of the annular cutter to guide the annular cutter during cutting. Annular cutters typically employ alternating tooth geometry to help minimize the cut area and evenly distribute chip load to multiple cutting edges, reducing horsepower and drilling feed pressure. Scrap material advances away from cutting edges, forming an easy-to-remove nest of chips above material surface. Annular cutters are manufactured from premium high-speed steel and specially heat-treated for cutting edge toughness increasing tool life between sharpening. Annular cutters are designed to increase through hole drilling productivity while improving hole accuracy, even in tough applications such as structural steel.  
         [0006]     A problem with the prior art monolithic annular cutter is that it is relatively expensive. The annular cutter is typically manufactured from a solid high speed steel bar which must be machined, ground, heat treated, and finish ground. The high speed steel is a premium material, which is expensive. Deeper holes require longer annular cutters, which requires more material and more labor in machining and grinding. Due to the expense of the annular cutters, they are limited in their use to relatively expensive machines such as the magnetic base drills, etc. The cutters utilize a special monolithic shank which prevents their use in regular hand drills.  
         [0007]     One prior art annular cutter has attempted to solve this problem by using tungsten carbide tips fixably attached to the leading end of a steel annular cutter. While these tungsten carbide teeth are particularly suitable for cutting rails and the like; the proper positioning, attaching, and machining of 4, 8, 12 etc. tungsten carbide tips can add significant cost to the production of the tool—especially in tooling required to properly position the tungsten carbide tips for attachment to the annular cutter body.  
         [0008]     Accordingly, there is a need for a machine tool that combines the characteristics and properties of a low-cost hole saw with the speed and performance of an annular cutter. It would be an additional benefit if such a tool was versatile in that it could be used in both a regular hand drill as well as a magnetic base drill.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention overcomes at least one disadvantage of prior art machine tools. These and other advantages are provided by a hybrid machine tool identified as a hole cutter assembly combining the low cost of a hole saw with the performance of an annular cutter. The machine tool comprises a monolithic cutter ring member comprising a plurality of cutting teeth spaced circumferentially around a first end thereof, and a plurality of flutes, each flute formed in an outer cylindrical surface of the cutter ring member and extending from the first end to a second end of the cutter ring member. The machine tool further comprises a body member comprising a cylindrical portion having a first end and a second end, wherein the first end of the body member is fixably attached a second end of the cutter ring member and the second end of the body member comprises a top portion formed generally perpendicular to a longitudinal axis of the cylindrical member.  
         [0010]     These and other advantages are also provided by a removable arbor for a machine tool, the arbor comprising: a cylindrical shank portion having a longitudinal axis and at least one flat formed in the cylindrical shank portion, the flat formed parallel to the longitudinal axis; a threaded portion axially spaced from the shank portion and coaxial with the shank portion; and a cylindrical aperture extending through the rotational axis of the arbor.  
         [0011]     These and other advantages are also provided by a method for forming a machine tool comprising the steps of: providing a monolithic cutter ring of a first material; providing a body member of a second material, the body having a cylindrical portion having a first end and a second end; joining the cutter ring to the first end of the body member for a predetermined time and at a predetermined temperature to simultaneously provide a heat treatment of the cutter ring member; forming a plurality of teeth and a plurality of flutes in the monolithic cutter ring.  
         [0012]     Further advantages of the hole cutter assembly will be apparent upon review of the detailed description of the present invention and associated drawings below.  
       BRIEF DESCRIPTION OF THE DRA WINGS  
       [0013]      FIG. 1  is a perspective view of a prior art annular cutter.  
         [0014]      FIG. 2  is a perspective view of a first embodiment of the hole cutter assembly of the present invention;  
         [0015]      FIG. 3  is a perspective view of a second embodiment of the hole cutter assembly of the present invention;  
         [0016]      FIG. 4A  is a cutting end view of the hole cutter assembly shown in  FIG. 3 ;  FIG. 4B  is a partial cross-sectional view of a first alternating tooth of the cutting end of the hole cutter assembly of  FIG. 3 ;  FIG. 4C  is a partial cross-sectional view of a second alternating tooth geometry of the cutting end of the hole cutter assembly of  FIG. 3 ;  
         [0017]      FIG. 5  is an exploded view of an embodiment of the hole cutter assembly of the present invention having an unfinished cutter ring and a carrier body shank or stem;  
         [0018]      FIG. 6  is a cross-sectional view of an embodiment of the hole cutter assembly of the present invention;  
         [0019]      FIG. 7  is a side elevational view of another embodiment of the present invention showing a demountable cap;  
         [0020]      FIG. 8  is a side elevational view of another embodiment of the present invention showing a removable annular cutter style shank;  
         [0021]      FIG. 9  is an un-wrapped side elevational view of another embodiment of the present invention showing a cutter ring having straight flutes;  
         [0022]      FIG. 10  is an un-wrapped side elevational view of another embodiment of the present invention showing a novel clearance surface on the cutter ring;  
         [0023]      FIG. 11  is an unwrapped cutting end view of a portion of the cutting ring showing an embodiment featuring a novel clearance surface on the cutter ring; and  
         [0024]      FIG. 12  is a cross-sectional view of an additional embodiment of the cutter ring showing a clearance chamfer on the trailing end of the cutter ring.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Referring to  FIG. 2 , a first embodiment of the hole cutter assembly  10  of the present invention is shown. The hole cutter assembly  10  comprises a carrier body  20  and a cutter ring  30 . The carrier body  20  comprises a cylindrical portion  22  and a top portion  24 . The cylindrical portion  22  having a first end  28  and a second end  25 . The top portion  24  typically extends radially inward from the second end  25  of the cylindrical portion  22  of the body  20 . The cutter ring  30  is similar to the cutting end of the prior art annular cutter  2 . The cutter ring  30  comprises a plurality of axially projecting teeth  34  from a first end  36  of the cutter ring  30 . A second end  32  of the cutter ring  30  is fixably attached to the first end  28  of the cylindrical portion  22  of the carrier body  20 . A plurality of flutes  38  and cutting edges  37  are formed in the outer circumferential surface of the cutter ring  30  and extend from the first end  36  of the cutter ring  30  to the second end  32  of the cutter ring  30 . Optionally, as shown in  FIG. 3 , the flutes  138  may be extended to the carrier  120  to help move chips away from the cutting ring  30 . However, referring again to  FIG. 2 , it is contemplated that the flutes  38  limited to the axial length of the cutter ring  30  is sufficient to remove chips from the cutting area. The hole cutter assembly  10  may further comprise an arbor  40  that includes a shank portion of the type used with annular cutters. The annular cutter style arbor  40  may be formed as part of a monolithic body  20  or may be removable as discussed with regard to additional embodiments below. The hole cutter assembly  10  has a rotational axis R which also forms the cylindrical or longitudinal axis for the cutter ring  30  and the body  20  including the arbor  40 .  
         [0026]     A second embodiment of the invention is shown in  FIG. 3 . The hole cutter assembly  110  is shown with a hole saw style arbor  140 . The top portion  124  of the carrier body  120  may have a threaded aperture (not shown) to receive a threaded end portion  142  of the hole saw style arbor  140 . Arbor  140  is of the type typically used for standard hole saws and includes a pilot bit  50  attached to the arbor  140 . The pilot bit  50  extends along the rotational axis R of the hole cutter assembly  110  and protrudes from the cutter ring  30  to guide the hole cutter assembly  110  during cutting. Although a pilot bit  50  is shown, the invention is not intended to be limited to a particular center configuration, alternative known configurations such as a spring loaded center pin (not shown), a solid shank, and any other known configurations are also contemplated. It is also contemplated that no guide or center member is needed for some applications and uses of the present invention. As previously discussed, flutes  138  are shown extended to the carrier  120  to help move chips away from the cutting ring  30 . It is contemplated that flutes  138  may extend any axial distance along the cylindrical portion  122  of carrier  120  and may extend the entire axial distance between the first end  128  and the second end  125  of the carrier body  120 .  
         [0027]     As best shown in  FIGS. 4A, 4B  and  4 C, the teeth  34  of the cutter ring  30 , including cutting edges  37 , may have an alternating tooth geometry to help minimize the cut area, known as the kerf, and evenly distribute chip load to multiple cutting edges reducing horsepower and drilling feed pressure. As best shown by the detail view in  FIGS. 4B and 4C , the A teeth extend radially inward from the exterior of the cutter ring  30  and upward toward the body  120  at an angle θ with a plane perpendicular to the rotational axis, and the B teeth extend radially outward from the interior of the cutter ring  30  and upward toward the body  120  at an angle λ with a plane X perpendicular to the rotational axis. The height of the teeth  34  may also be of varying or alternating heights as is known in the art. In an alternative embodiment of the cutter ring  130 , shown in  FIG. 12 , the teeth  134  may have an apex between the inner and outer edges of the ring  130  and extend radially inward and outward from the apex and upward toward the body (not shown) at an angle α and β, respectively, with a line Y parallel to the rotational axis. The invention is not intended to be limited to the particular tooth geometries shown.  
         [0028]     Referring again to  FIG. 4A , the cutter ring  30  also enables the radial width of the cutting surfaces to be minimized as the additional strength of the carrier body  120  over that of the prior art annular cutter walls enables less material to be used without reducing strength or life of the cutting edges. This allows a smaller kerf and less material removal, further reducing the energy required to make the cut.  
         [0029]     The hole cutter assembly of the present invention may be made significantly cheaper than prior art annular cutters. The cutter ring may be manufactured of premium high-speed steel such as M42, or a carbide material or any other suitable material. It is further contemplated that the cutter ring is formed as a bi-metal ring in a similar fashion as that of bi-metal hole saws. Regardless of the material, the cutter ring requires significantly less of the expensive cutting material than required with a prior art annular cutter. To further reduce costs, the cutter ring can be produced as an investment casting, powder metal, or metal injection mold, with or without flutes, then machined, ground, or machined and ground. Referring now to  FIG. 5 , a cutter ring blank  230  is shown prior to attachment to a monolithic carrier blank  220  having an integral cylindrical shank  260 . The cutter ring blank  230  is not limited to the ring shown and may have preformed flutes and teeth formed or cast therein which can later be finish machined and/or ground after the cutter ring is fixably attached to the carrier body; In the embodiment shown the cutter ring blank  230  is attached to the carrier blank  220  and then the plurality of teeth and flutes are formed on the cutter ring blank. The carrier blank  220  can be manufactured of a relatively inexpensive steel material such as 4150 steel and does not require extensive additional machining or grinding. In the embodiment shown, the carrier blank includes a shank blank portion  260  that is monolithically formed with the carrier body blank  220  similar to the prior art annular cutter  2 . The appropriate attachment features are machined into the shank blank portion  260  such as Weldon flats or other attachment features of the type used with prior art annular cutters. Although shown as a monolithic carrier body blank  220 , it is contemplated that the carrier blank  220  could include a threaded aperture formed before or after the attachment of the cutter ring and the carrier body, for use with a removable arbor.  
         [0030]     With prior art annular cutters, deeper drill depths require longer tools. This significantly increases the material and manufacturing cost of the prior art annular cutter. In the present invention, longer holes can be machined by increasing the length of the carrier body. As the carrier body is made of an inexpensive material, and increasing the length of the cylindrical portion results in a negligible increase in material and production cost. Another advantage is that the carbon steel cylindrical body does not require flutes and can be made significantly thinner than the prior art monolithic annular cutters. This allows a thinner cylinder wall and a thinner cutter ring resulting in a smaller kerf. The smaller kerf allows increased speed of the cut and requires less energy to remove less metal.  
         [0031]     As shown in cross-section in  FIG. 6 , an embodiment of the hole cutter assembly  310  is shown utilizing a carrier  320  adapted for use with a removable arbor and a cylindrical portion  322  shown without flutes. The cutter ring  30  is shown attached to the carrier body  320 . The top portion  324  of the carrier body  320  includes an aperture  52  for connection of an arbor or removable shank. The first end  328  of cylindrical portion  322  of the carrier body  320  has a reduced outer diameter forming a connecting portion with the second end  32  of the cutter ring  30 , which has a reduced inner diameter. The stepped connection of the cutter ring  30  and the carrier body  320  is not intended to be limited to the configuration shown and other configurations may be possible. In manufacturing the present invention, the attachment of the body  320  and the cutter ring  30  may be made by a joining process such as brazing, laser welding, projection welding, friction welding, or other methods. In one embodiment, using a cutter ring  30  of premium high speed steel and a carrier body  320  of carbon steel, a brazing process is used to connect the two parts. The brazing material is selected such that the brazing process is at a predetermined temperature and over a predetermined time period to simultaneously provide a heat treatment of the cutter ring material at the same time and temperature that the brazing material can flow to provide a secure and fixed attachment of the ring  30  and the body  320 . Such a brazing process may be accomplished in a controlled-atmosphere or vacuum furnace, for example. Other such brazing methods are also contemplated and the present invention is not intended to be limited to a particular brazing process.  
         [0032]     It is also noted that the cylindrical portion  322  of the carrier body  320  has an innermost diameter larger than the innermost diameter of the cutter ring  30  and an outermost diameter smaller than the outermost diameter of the cutter ring  30 . This provides clearance for the body  320  when cutting through a material. In addition, as shown in the cutter ring embodiment of  FIG. 12 , the second end  132  or trailing end of the cutter ring  130  may also have a chamfer  131  formed on the radial outwardmost portion at an angle γ to provide clearance leading from the cutter ring  130  to the body. The interior cylindrical surface of the cutter ring  130  may also be provided with a clearance as shown by taper angle δ or an appropriate chamfer.  
         [0033]     Referring to another embodiment of the hole cutter assembly  410  as shown in  FIG. 7 , having a two-part carrier body  420  in which the top portion  424  carrier body  420  may be demountably attached to the cylindrical portion  422  of the carrier body  420 . As shown in the exploded view, end portion  424  is threadably attachable to the cylindrical portion  422 . A locking device, not shown, may be needed to prevent decoupling during reverse operation of the hole cutter assembly  410 . While a threaded connection is shown, the invention may include other demountable configurations and is not intended to be limited to the example shown. The demountable end portion  424  allows easy removal of the machined material core from the hole cutter assembly  410 . Another advantage of the demountable end portion  424  is that each end portion may have a different shank configuration to allow for compatibility on multiple different machines. While a hole saw arbor style shank  442  is shown integrally formed with the top portion  424 , it is contemplated that an annular cutter style arbor shank (not shown) could be integrally formed on another top portion and interchanged as needed with the hole saw arbor style end portion  424 . It is also contemplated that demountable end portion  424  could be formed with a centrally positioned aperture similar to that shown in  FIG. 6  such that arbor  424  is demountably attached to the end portion  424 .  
         [0034]     Another embodiment of the present invention is shown in  FIG. 8 , and comprises a removable arbor  510  that includes a shank portion  512  of the type used with annular cutters. The removable arbor  510  comprises a generally cylindrical shank portion  512  having a longitudinal axis R and at least one flat  516  formed in the cylindrical shank portion. The flat portions  516  are formed parallel to the longitudinal axis R and are typically referred to as Weldon flats. Although not shown, it is contemplated that the cylindrical shank portion  512  may also include various depressions, dimples, grooves, or other features that are used by various annular cutter manufacturers as an alternative shank gripping feature to Weldon flats. The replaceable arbor  510  further comprises a threaded portion  518 , axially spaced from the shank portion  512  and coaxial with the shank portion  512 . The threaded portion  518  mates with the threaded aperture  52  of the hole cutter  310  shown in  FIG. 6 . It is preferred that the threads used on the removable arbor  510  are formed with threads having a tight tolerance such as class 3 threads or the like. This will help ensure that the arbor is properly centered in the tool. Other attachment methods are also contemplated and the invention is not intended to be limited to a threaded connection. The replaceable arbor  510  provides versatility to the hole cutter  310  in that it can be used both as a hole saw with tools that utilize a hole saw arbor and as an annular cutter with tools that utilize the arbor shank of an annular cutter. A further advantage provided by the replaceable arbor  510  is that it will allow existing hole saws to be used with tools that are only compatible with the shank of an annular cutter, such as a magnetic drill.  
         [0035]     Another embodiment is shown in  FIG. 9  which shows an unwrapped side view of a cutter ring  330  having teeth  334  and flutes  338  parallel to the rotational axis of the hole cutter assembly (not shown). The straight flutes  338  and corresponding cutting edges  337  are easier to manufacture than helical flutes  38 ,  138  of the earlier embodiments, providing an even greater time and manufacturing cost advantage. In some cutting applications of some materials, there is no appreciable loss in cutting efficiency and performance.  
         [0036]     Another advantage provided by another embodiment of the invention is a clearance structural feature best shown in  FIGS. 10 and 11 .  FIG. 10  shows an unwrapped side view of a cutter ring  430  having flutes  438  and cutter teeth  434 . A clearance surface  454  is formed on the radially outward surface of the teeth  434  at an angle λ toward the trailing flute  438  and meeting with the flute  438  at a radius r as best shown in  FIG. 11 . The surface  454  provides clearance between the radial outward edge of the cutting tooth  434  and the radial inward portion of cutting edge  437 . This feature prevents drag on the radial outward surface of the ring between the tooth  434  and the cutting edge  437  and provides a significant advantage over existing annular cutters.  
         [0037]     Although the present invention has been described above in detail, the same is by way of illustration and example only and is not to be taken as a limitation on the present invention. Accordingly, the scope and content of the present invention are to be defined only by the terms of the appended claims.