Abstract:
A novel drill for the aerification of turf grasses is disclosed. The drill comprises a chuck and a fluted turf drill bit held by the chuck. The chuck includes a locking mechanism which permits the chuck to rotate freely about its longitudinal axis when loaded in compression (as when the drill is inserted into the ground) but which locks, preventing rotation, when the drill is loaded in tension (such as when the drill is withdrawn from the soil). The drill bit has a smooth upper section and a fluted lower section. The smooth section decreases the probability of entangling the turf in the drill bit with subsequent lifting of the turf when the drill is withdrawn. The tip of the drill bit is adapted to provide a torque to the drill bit during insertion into the ground. Thus, the bit spirals into the ground upon insertion, but locks upon removal, thereby permitting the flutes of the bit to cut a cylindrical hole in the ground while removing soil from the hole by retaining it in the space between the flutes. The drill of the present invention may be used in aerators previously limited to solid or hollow-core tines.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/527,611 filed Mar. 11, 2005, which is a continuation of U.S. Provisional Patent Application Ser. No. 60/450,847 filed Feb. 28, 2003, to which priority is claimed under 35 U.S.C. §120 and which is incorporated herein by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to soil aerification (or “aeration”). More particularly, it relates to a method and apparatus for the aerification of turf grasses using a self-rotating turf drill. 
   2. Description of the Related Art 
   What is Aerification 
   Aerification is a mechanical process that creates more air space in the soil and promotes deeper rooting, thus helping plants stay healthy. In most cases, this is achieved by removing cores (often called plugs) and then filling the holes with topdressing. Topdressing is often a certain grade of sand which may have other amendments added to allow the soil to maintain air space, improve water penetration, and encourage healthy root growth. The sand is brushed or poured into the holes which are usually healed within several days. 
   The condition of turf largely depends on the events occurring below the surface. For grass to grow, deep healthy roots are needed, and roots require oxygen. In good soil, they receive oxygen from tiny pockets of air trapped between soil and sand particles. On a sports field, the everyday traffic from players combined with the weight of heavy mowing equipment causes the soil to become compacted and the air pockets on which the roots depend for oxygen are lost. Aerification is a mechanical process that creates more air space in the soil and promotes deeper rooting, water percolation and compaction relief. 
   The practice of aerating turf is becoming increasingly widespread. The benefits of aerification include:
         Improved water infiltration and better drainage   Deeper penetration of fertilizers   Improved plant rooting   Thatch control   Increased stress tolerance   Break up of sod layers that can restrict rooting and water movement   Release of toxic gases from soils   Increased drying and drainage of persistently wet soils   Loosening of soil, allowing for increased air space   Softening of sports fields to reduce risk of injury       

   In addition, putting green aerification can provide for additional surface smoothing. 
   Compaction Relief 
   Definition of Compaction 
   Compaction of sports playing fields and golf course tees, greens and fairways is an inevitable product of their use—golf carts, maintenance machinery and feet all contribute to the process that is defined as “the consolidation of soil particles.” 
   Compaction decreases water and oxygen movement in the soil, hinders root growth and lessens the ability of the soil to drain. Soil compaction causes these negative effects by turning macropores (larger voids in the soil largely responsible for drainage and air flow) into many micropores (smaller voids that hold water). As compaction increases, bulk density also usually increases, which means that more soil solids occupy a unit volume of soil, reducing the porosity. 
   With turfgrass, techniques used to relieve compaction must be effective without being highly visible. Aerification—either with solid tines that create a hole in the soil, or with hollow tines or drills that remove a core of soil—is one of the more common ways of improving compacted soils. 
   When a soil compaction condition is accompanied by excessive thatch buildup, as is almost always the case in poorly maintained turf, each condition contributes to the effect of the other. Thatch is a mat of undecomposed plant material (e.g., grass clippings) accumulated next to the soil in a grassy area (as a lawn, sports field or putting green). It is a tightly intermingled layer of living and dead stems, leaves and roots of grasses, which develops between the layer of green vegetation and the soil surface. When thatch exceeds about ½ inch of undecomposed material, it acts as a barrier to water and air infiltration into the soil below and will provide an environment encouraging turf diseases and harmful insects. Compacted soils, on the other hand, are subject to greater temperature extremes than loose soils, because of limited air movement; microbial activity necessary to thatch decomposition is reduced or halted. 
   Water that cannot penetrate the soil runs off or accumulates in low spots where it harbors fungus growth. 
   Alleviating either condition will help, but only when thatch is kept under control and the soil is properly aerified will turf have the best chance for healthy, vigorous growth and disease resistance. 
   The accumulation of organic matter (thatch) and fine particles (silt and/or clay) can, over time, produce a surface layer that reduces porosity. Aerification can modify the profile, improving oxygen, water, and root movement, especially when the use of hollow tines or turf drills is combined with core removal and backfilling channels with high-quality topdressing sand. 
   Prior Art Methods of Aerification 
   Turfgrass cultivation activities include hollow tine aerification, solid tine aerification, spiking, slicing, and water injection. These activities, to varying degrees, can reduce thatch, prepare turf for overseeding, and relieve soil compaction. Perhaps the best machine for working large areas is a piston driven aerator that thrusts the core cutters vertically. Direct up and down coring leaves a clearly defined hole. Drum-type roller aerators will work but may cause tearing damage to the remaining grass since this type of cutter enters the turf at one angle, moves in an arc with the drum movement, and is withdrawn at a different angle. 
   Solid Tine 
   Solid-tine aerification allows turf managers to aerate more frequently, since the procedure produces less surface disruption. Solid tines larger than ¼ inch in diameter open turf to allow water and air infiltration, but the process compresses displaced soil downward and to the sides. This actually increases soil compaction around newly created aerification holes. Repeated solid-tine aerification with larger-diameter tines can create a hardpan at the aerating depth. 
   Related to solid tine aerification are slicing and spiking aerifiers. Slicing, spiking, and solid tine aerification do not pull plugs of soil from the turf. Slicing aerifiers cut thin slits into the soil and spiking aerifiers cut thin, triangular-shaped holes in turf. While they do not relieve soil compaction as efficiently as hollow tine aerification, these practices cause less surface disruption and can be done anytime. 
   Hollow Tine 
   These devices pull out plugs of soil that are deposited on the surface. One of the most common operations that one can perform using a hollow tine aerator is conducting a soil exchange program, offering the professional an ideal opportunity to remove soil cores and replace them with a suitable top dressing, altering the soil profile. 
   Self-powered hollow tine aerifiers (core aerifiers) insert hollow tines into the soil, removing a soil plug ¼″ to ¾″ in diameter and 2″ to 12″ deep, depending on soil type, soil moisture, and type of machine. Core spacing varies depending upon the make and model of the machine. In general, the more cores removed per square foot, the more effective the cultivation will be; removing fifteen to thirty cores per square foot is recommended. Hollow tine aerification is considered the most efficient compaction reliever of the prior art methods. It is preferably done during active turf growth. 
   Slitting 
   Using triangular blades ranging in size 100-250 mm (4″ to 10″), these machines create lots of short, narrow, close slits; slitting is useful for getting air down into the soil; it&#39;s quick; it does a fair job in dethatching; however, this approach is not highly effective at reducing compaction. Slitting also has its benefits, particularly in autumn when it can be employed to help ‘connect’ the surface of the soil with the underlying drainage layers. In the spring and summer, slitting ensures that water from rain and irrigation soak through the turf rather than being shed in a sideways fashion by the thatch. 
   Water Injection 
   Water injection aerification is a recently-introduced method of turf aerification. Water, under high pressure, is injected into the turf surface to relieve soil compaction. In addition, it can be used to inject turf management chemicals into the soil. It causes little surface disruption and can be done anytime during the growing season. This new technology has not been commonly available for use outside of golf course applications. 
   Deep Drill Aerification 
   Drill-type aerifiers employ rotating turf drills. The drill bits eliminate compaction along the sides and bottom of the aerification hole, and allow for quick and effective penetration even in heavily compacted soils including hardpan, muck and roots. The “gentle footprint” of drill-type aerifiers, in conjunction with the absence of cyclic vibration and the “straight in, straight out” action of the drill bits, gives this type of machine the capability of aerating fields that are wet, dry or experiencing periods of high stress. 
   Deep drill aerifiers are also preferred for use in all problem areas because the rotating drill bits will penetrate subsoil areas, where other machines tend to walk or bounce, often causing trauma to the playing surface. Turf drill bits fracture the cylinder wall without glazing, thereby allowing lateral movement of air and water. “Drill &amp; Fill” aerifiers are available which back-fill the drilled holes with a selected top dressing, usually sand, thereby modifying the soil profile. 
   Turf drill bits are commercially available in ⅝″×12″, ⅝″×16″, ¾″×12″, and 1″×12″ sizes. One particular deep drill aerifier currently on the market produces 5″ spacing of holes. Drill aerification is especially preferred when one must penetrate hard soils. However, drill aerification is a very slow process as compared to reciprocating type aerifiers. 
   As noted above, aerification has the added benefit of smoothing the surface of a putting green. The process of punching holes and either reincorporating the plugs brought up or removing the plugs and filling the channels can offer some surface smoothing. Surface topdressing alone will fill/smooth low spots. The combination of aerifying and the follow-up topdressing will, over time, both fill low spots and soften high spots, resulting in more efficient surface smoothing than topdressing alone. 
   SUMMARY OF THE INVENTION 
   The method and apparatus of the present invention combines the speed and mechanical simplicity of solid or hollow tine aerification with the penetration depth, clean cutting and cylinder wall fracturing of deep drill aerification. A turf drill is held in a chuck which permits free rotation of the drill bit when it is pushed into the ground (loaded in compression) but which restricts rotation of the bit when it is withdrawn from the ground (loaded in tension). When the chuck is locked and the drill bit is pulled from the soil, the flutes on the bit cut a clean, generally cylindrical hole in the soil with minimal compaction of the surrounding earth. In one embodiment, the drill bit comprises a non-fluted upper portion which helps prevent entanglement and lifting of the turf as the bit is withdrawn. 
   In some embodiments, the distal end of the drill bit is provided with opposing beveled surfaces which impart a rotational movement to the bit as it is pushed into the soil. Since the bit is self-rotating, there is no need for rotational means in the aerifier head, and therefore drills according to the present invention can be utilized in aerifiers previously equipped with solid or hollow-core tines. Since rotational means are not needed in the aerifier&#39;s heads, the tines may be placed in greater proximity to one another which permits greater density of aerification holes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial cut-away view of a simplified, reciprocating-type aerifier equipped with a turf drill according to the present invention. 
       FIG. 2  is a partial cross-sectional view of the chuck of the present invention in its free rotation state. 
       FIG. 3  is a cross-sectional view taken along line  3 - 3  in  FIG. 2 . 
       FIG. 4  is a side view of the lower portion of the central shaft of the chuck. 
       FIG. 5  is a partial cross-sectional view of the chuck of the present invention in its locked, rotation-inhibiting state. 
       FIG. 6  is a side view of a drill bit according to the present invention. 
       FIG. 7  is an end view of the tip of the drill bit illustrated in  FIG. 6  taken along line  7 - 7 . 
       FIG. 8  is an enlarged, side view of the tip of the drill bit illustrated in  FIG. 6 . 
       FIG. 9  is an enlarged, side view of the tip of the drill bit illustrated in  FIG. 6  rotated 90°. 
       FIG. 10  is a partial cross-sectional view of another embodiment of the chuck of the present invention in its free rotation state. 
       FIG. 11  is a cross-sectional view taken along line  11 - 11  in  FIG. 10 . 
       FIG. 12  is a cross section taken along line  12 - 12  in  FIG. 10 . 
       FIG. 13  is a partial cross-sectional view an alternative embodiment of the chuck of the present invention in its locked, rotation-inhibiting state. 
   

   DETAILED DESCRIPTION 
   In the following description, “drill” should be understood to mean an apparatus comprising both a drill chuck and a drill bit held within the chuck. 
   Referring now to  FIG. 1 , a portion of a reciprocating turf aerator is shown as a partial cut-away drawing. The aerator is shown in simplified form to illustrate how the turf drill of the present invention may be used in practice. Aerator  12  may be moved across an expanse of ground such as soil  22  on wheel(s)  14 . Reciprocating heads  20  are connected to crankshaft  16  by connecting rods  18  which cause heads  20  to move generally up and down as crankshaft  16  rotates. Drills  10 , attached to heads  20 , are thereby alternately thrust into and withdrawn from soil  22 . In some commercially-available aerators, crankshaft  16  is driven by the power take off (PTO) of a tractor used to pull aerator  12  across a putting green, for example. 
   As mentioned above, this is a simplified view of a reciprocating aerator. Commercial aerators are typically equipped with articulating heads that additionally move fore and aft relative to the track of the aerator across the ground such that during insertion, withdrawal and the interval there between during which the drill bits are in the soil, the heads and drills (or tines) do not move transversely with respect to the ground. In this way, cylindrical, vertical holes may be achieved while the aerator advances continuously across the ground. Apparatus which provide this type of motion are described in U.S. Pat. No. 6,041,869 entitled “Turf Aerator with Constantly Vertical Tines” and are available from manufacturers such as Redexim/Charterhouse, Jacobsen (under the Ryan brand name) and others. 
   The chuck  24  of one particular embodiment of the present invention is shown in partial cross section in  FIG. 2 . Shaft  26  may be adapted at its upper or distal end to engage the head platforms  20  of a mechanical aerator. Reciprocating aerators are particularly preferred, but the drill embodiments illustrated in the drawing figures can be employed in a variety of aerators. 
   The proximal end (lower end in  FIG. 2 ) of shaft  26  is contained within rotating body  28  of chuck  24  and is rotatably supported by bushing  30  and thrust bearing  32 . In the particular embodiment illustrated in  FIG. 2 , the proximal end of shaft  26  has conical tip  48  (see  FIG. 4 ) which fits within a corresponding conical portion of bearing  32 . Bushing  30  and thrust bearing  32  may be fabricated from a softer metal than that used for shaft  26  to reduce frictional wear. Additionally, chuck  24  may be provided with grease fitting  36  (also known as a Zerk fitting) through which a suitable lubricant may be introduced for lubricating shaft  26  within bushing  30  and bearing  32 . One preferred lubricant is lithium grease. In other embodiments of chuck  24 , self-lubricating bearings and bushings may be used, in which case it may not be necessary to provide means for introducing lubricant from an external supply. 
   Shaft  26  is free to both rotate within bushing  30  and thrust bearing  32  and to slide longitudinally (within limits, as described below) within bushing  30  and the upper, cylindrical portion of thrust bearing  32 . As indicated by the arrow in  FIG. 2 , chuck  24  is shown loaded in compression such as would occur when the drill was being pushed into the ground. The conical tip at the proximal end of shaft  26  is shown fully engaged in thrust bearing  32  in  FIG. 2  as it would be during insertion of the drill in the ground. 
   Chuck  24  comprises a lock which engages when a turf bit held in the chuck is loaded in tension and which disengages when the bit is loaded in compression. In the embodiment illustrated in  FIG. 2 , rotating body  28  has an opposing pair of set screws  34 . The set screws  34  have a conventional threaded portion for engaging the threads of tapped holes within rotating body  28  and also a cylindrical tip  35  of reduced diameter which is sized to project into the upper central bore of rotating body  28 . Such set screws are sometimes referred to as “dog point” set screws. In the embodiment illustrated, the holes in rotating body  28  into which set screws  34  are screwed are not threaded the full thickness of the wall of rotating body  28 . Rather, the threads begin at the exterior surface of rotating body  28  and end prior to reaching the central bore of rotating body  28 . In this way, the insertion of projecting points  35  may be limited. It is preferred that projecting points  35  do not contact shaft  26  when set screws  34  are fully seated within rotating body  28 . The rotation and sliding of shaft  26  within rotating body  28  would be inhibited if projecting tips  35  were to contact shaft  26 . Alternatively, bushing  30  may be sized and positioned such that the shoulders of set screws  34  contact bushing  30 . In this way, over-insertion of set screws  34  may be prevented and bushing  30  may be secured within rotating body  28 . 
   As illustrated in the detail of  FIG. 4 , shaft  26  includes stop collar  44  which prevents withdrawal of shaft  26  from rotating body  28  when a tensile force is applied to shaft  26  (such as occurs during withdrawal of the drill from the soil). Stop collar  44  may be provided on its upper surface with one or more indentions. In the embodiment illustrated, four such indentions are provided spaced 90° apart and each describes an arc of a circle in cross section. Indentations  46  and conical tips  35  of set screws  34  are preferably sized such that projections  35  will seat in indentations  46  when stop collar  44  is brought into contact with set screws  34 . This condition is illustrated in  FIG. 5 . 
     FIG. 5  shows the same embodiment as that illustrated in  FIG. 2 . In this case, however, the drill is loaded in tension, as indicated by the arrow in the drawing. This condition obtains when the drill is being withdrawn from the soil and frictional forces on the drill bit  50  are opposing the upward motion imparted by the aerator. It will be noted that the conical tip of shaft  26  is partly withdrawn from the conical portion of thrust bearing  32  and stop collar  44  is in contact with cylindrical projections  35  of set screws  34 . Further upward motion of shaft  26  relative to rotating body  28  is thereby prevented. Since stop collar  44  may be coated with lubricant, contact of the upper surface of stop collar  44  with cylindrical projections  35  may not inhibit the rotation of shaft  26  relative to rotating body  28  until an opposing pair of indentations  46  align with set screw projections  35  at which point shaft  26  may move slightly further upward, seating projections  35  within indentations  46  at which point further rotation of shaft  26  is significantly inhibited. It will be appreciated that the number and spacing of set screws  34  in rotating body  28  and the number and spacing of indentations  46  in stop collar  44  may vary from that of the embodiment shown in  FIGS. 2 through 5 . 
   Also shown in  FIGS. 2 and 5  is dirt shield  38  which may be used to help deflect dirt, sand and other soil components from the interface of bushing  30  and shaft  26 . Dirt shield  38  may be a stamped metal fitting which is concentric with shaft  26 . Rotating body  28  may also be provided with chamfer  42  to further aid in the shedding of dirt from the top of rotating body  28 . In operation in aerifiers having multiple drills in close proximity one to another, dirt particles are often thrown up by the drills as they are withdrawn from the ground which particles may land on nearby drill chucks. It is, of course, advantageous to shield bearings from the introduction of abrasive particles. 
   Also shown in  FIG. 2  and  FIG. 5  is the upper portion of the shank of turf drill bit  50 . Rotating body  28  is provided with a central bore on its lower surface for receiving drill bit  50 . Drill bit  50  may be provided with notch or flat  52  for engaging set screw  40  which both retains bit  50  within chuck  24  and prevents the rotation of bit  50  relative to rotating body  28 . In the illustrated embodiment, set screw  40  is shown as being a dog point set screw. Set screw  40  may be a conventional set screw, but it may be convenient to have set screw  40  be of the same type and size as set screws  34  so as to reduce inventory and replacement parts requirements and to reduce the chance that a conventional set screw would be inserted in place of set screw  34  thereby impairing the function of chuck  24 . Alternatively, set screw  40  may be a different diameter from that of set screws  34 . 
   As will be appreciated by those skilled in the art, there are many ways a drill bit may be secured in a chuck. The securing method using a set screw described above and illustrated in the drawing figures has been found to be particularly suited to the application of the invention, but other methods may be used. By way of example, a hole may be provided in the chuck with a corresponding hole in the bit shank. A pin (such as a roll pin) or a machine screw passing through the hole in the chuck and into the hole in the bit shank would secure the bit in the chuck. 
   One embodiment of a drill bit of the present invention is shown in  FIG. 6 . Bit or drill tine  50  is comprised of an unfluted, generally cylindrical upper portion  54  and a lower, fluted section  56 . As noted above, the upper portion of the shank of bit  50  may be provided with flat or notch  52  which provides a planar contact area for set screw  40  of chuck  24  used to secure bit  50  in the lower central bore of rotating body  28 . 
   Flutes  58 , which may be generally rectangular in cross-section, are formed in a helical pattern around core or central shaft  62 . Smooth portion  54  is provided to lessen the chance of turf entanglement when the bit is withdrawn from the turf. In practice, the insertion depth may be adjusted such that fluted portion  56  penetrates to a soil depth just below the turf layer while portion  54  is within the turf layer. 
   Details of the tip of bit  50  are shown in  FIGS. 7 ,  8  and  9 . The tip may be formed by grinding generally planar, opposing flats  60  at the angle shown as α in  FIG. 8 . The position of notch  52  is shown as a dashed line in  FIG. 7  to illustrate the angular position of the dividing line or “chisel edge” between the opposing flats  60 . It will be noted that flats  60  are offset from each other with respect to the center line of the bit. Because of this offset, a torque is imparted to bit  50  (counterclockwise as viewed in  FIG. 7 ) when it is inserted into the ground. Thus, when bit  50  is pushed into the ground by an aerator, it tends to rotate about its longitudinal axis and the flutes  58  create a pair of helical grooves in the soil around the central hole created by the displacement of the soil by central shaft  62 . 
   Conventional turf drills typically are carbide tipped to maintain sharpness for an adequate length of time. It has been surprisingly found that the drill bits of the present invention do not require carbide tips or inserts to provide adequate service life. The drill bits of the present invention rotate about 2½ revolutions per insertion. In contrast, bits used in conventional turf drilling machines rotate about 25 revolutions per insertion. It is contemplated that the reduction in friction engendered by the factor of 10 decrease in rotations per insertion is responsible for the longer-wearing nature of the bits of the present invention. 
   In one particularly preferred embodiment, L 1  is about 10½ inches, L 2  is about 7½ inches and D, the drill tine&#39;s diameter, is about ½ inch. The shank diameter may be chosen to fit the head of the particular aerator to be used and it may be greater than, less than, or the same as the tine diameter. In this embodiment, the diameter of central shaft or core  62  is about ¼ inch and the flutes  58  are about 0.1 inch wide (thick) and 0.125 inch high. The twist length, the linear distance over which a flute makes a complete revolution about central shaft  62 , is about 3 inches. The tip angle (α in  FIG. 8 ) is about 45°. A particularly preferred drill tine is fabricated from American Iron and Steel Institute (AISI) Grade 4140 steel heat treated after fabrication to a value of at least about 50 on the Rockwell “C Scale” of hardness. Following heat treatment, drill tine  50  may be shot-peen finished. 
   It will be appreciated by those skilled in the art that there are many means for effecting the locking feature of the chuck of the present invention. By way of example, one such alternative is shown in  FIGS. 10 through 13 , inclusive. In this embodiment, a spline  70  or splines  70  on shaft  26  is used in conjunction with keyway  69  or keyways  69  in locking member  68  held within rotating body  28 . 
   In the embodiment illustrated, bushing  30  is held within upper bore  72  of rotating body  28  by retaining ring  64  which fits within groove  65  in the wall of upper bore  72 . Locking member  68  which may include a plurality of keyways  69  rests on shoulder  73  at the lower boundary of upper bore  72 . Thrust washer  66  may be provided between locking member  68  and bushing  30  to protect the relatively softer material of bushing  30  from impact with splines  70  of shaft  26  when shaft  26  slides upward. Keyways  69  are sized and spaced such that splines  70  will fit within them when shaft  26  is urged upward (loaded in tension) and rotating body  28  rotates relative to shaft  26  until the splines  70  and keyways  69  align.  FIG. 10  shows chuck  24  loaded in compression (as during insertion of the drill into the ground). In this condition, splines  70  are below locking member  68  and thus rotating body  28  can freely rotate relative to shaft  26 .  FIG. 13  shows chuck  24  loaded in tension (as occurs during withdrawal of the drill from the ground). In this condition, splines  70  engage keyways  69  in locking member  68  and rotation of rotating body  28  (and bit  50 ) relative to shaft  26  is prevented. 
   Locking member  68  may be fabricated as an extrusion cross cut to the desired thickness. Rotating body  28  may be heated to expand the diameter of upper bore  72  and locking member  68  inserted while the bore is expanded. Upon cooling and contraction, locking member  68  (if appropriately sized) will be rotatably secured within upper bore  72 . 
   While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.