Abstract:
A post driver for driving hollow posts, especially plastic posts, has an elongated central guide shaft and a hollow outer sleeve. The guide shaft has a length and diameter sized to pass fairly freely through but generally fill the post&#39;s hollow core to protect against the post buckling during pounding strokes. The outer sleeve annularly surrounds a substantial upper portion of the post for similar reasons. The outer sleeve transmits pounding strikes to a stop formation that rests stationary on the post&#39;s top end. That way, a user manually applying pounding strokes to the stop formation&#39;s upper surface transmits force to not only the post&#39;s top end but also the guide shaft&#39;s bottom end. Optionally, the guide shaft&#39;s bottom end is tipped and sticks out a little in order to pierce a pilot hole in the ground, and clear a path, for the post to follow.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 61/336,800, filed Jan. 27, 2010. 
     This application is a continuation in part of U.S. patent application Ser. No. 12/459,028, filed Jun. 25, 2009 now abandoned, which claims the benefit of U.S. Provisional Patent No. 61/133,045, filed Jun. 25, 2008. All the foregoing disclosures are incorporated by this reference thereto. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention generally relates to hollow posts and drivers therefor and, more particularly, to a combination post and insertion tool which supports the post and transmits the impacts from a hammer during insertion of the post (driving of the post) into the ground. 
     A number of additional features and objects will be apparent in connection with the following discussion of preferred embodiments and examples. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       There are shown in the drawings certain exemplary embodiments of the invention as presently preferred. It should be understood that the invention is not limited to the embodiments disclosed as examples, and is capable of variation within the scope of the skills of a person having ordinary skill in the art to which the invention pertains. In the drawings, 
         FIG. 1  is a perspective view of a row of posts in accordance with the invention for forming a fence line as a matter of illustrating an example end use of the posts; 
         FIG. 2  is an enlarged-scale perspective view of a first embodiment of post driving apparatus in accordance with the invention, with a post to-be-driven shown to illustrate operative use; 
         FIG. 3  is a further perspective view thereof except on an enlarged scale and with intermediate portions broken away at two places to foreshorten the view; 
         FIG. 4  is a perspective view of comparable to  FIG. 1  except of a second embodiment of post driving apparatus in accordance with the invention, with a post to-be-driven likewise shown to illustrate operative use; 
         FIG. 5  is a further perspective view of the  FIG. 4  embodiment except on an enlarged scale and with intermediate portions broken away at one place to foreshorten the view; 
         FIG. 6  is a reduced scale, exploded perspective view of the post driving apparatus in accordance with  FIG. 4  embodiment in combination with a T-Post driver of the prior art, wherein portions of the post to-be-driven are broken away at one place to foreshorten the view; 
         FIG. 7  is an exploded perspective view of an alternate embodiment of a combination post and insertion tool therefor in accordance with the invention; 
         FIG. 8  is a perspective view comparable to  FIG. 7  except the post and insertion tool coupled together; 
         FIG. 9  is an enlarged scale partial sectional view taken along line IX-IX in  FIG. 7  (ie., with the post not shown), and the spike foreshortened; 
         FIG. 10  is an enlarged scale partial sectional view taken along line X-X in  FIG. 8  (ie., with the post indeed shown), and the spike and portions of the post foreshortened; 
         FIG. 11  is an enlarged scale bottom plan view of  FIG. 8 ; 
         FIG. 12  is a sectional view taken along line XII-XII in  FIG. 9  and on an enlarged scale; and, 
         FIG. 13  is an enlarged scale detail view taken from the sectional view of  FIG. 10  and showing the post and spike of the insertion tool therefor cooperatively working together while being driven through rocky ground. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a row of posts  70  in accordance with the invention forming a fence line. This view is included as a matter of illustrating an example end use of the posts  70 . The fence line might be electric. More significantly, the fence posts  70  will be un-typically flexible. 
     There is one installation of these fence posts  70  in accordance with the invention on a farm that uses a large-scale type of irrigation system known as a center-point pivot system. Center-point pivot irrigation is a form of sprinkler irrigation consisting of several segments of pipe (usually galvanized steel or aluminum) joined together and supported by trusses on wheeled towers, maybe eight to ten feet ( ˜ two-and-a-half to three meters) tall. In other words, the wheeled tower should have ample enough height so that the trusses can clear the crop height of, for example, corn. Sprinklers are positioned along the length. The system moves in a circular pattern and is fed with water from the pivot point at the center of the arc. These systems are found and used in all parts of the nation and allow irrigation of all types of terrain. 
     The tires are heavy. They are nearly truck tires (more likely, trailer tires). On this particular farm, the farmer just runs the wheeled towers right over the fence line. The fence posts  70  in accordance with the invention yield by bending over on their side until pretty much flattened out on the ground. Then, once the wheeled-towers have passed, the fence posts  70  spring back up and restore themselves to their original upright posture. 
     It is an aspect of the invention that the fence posts  70  are a specially blended material in order to enable this characteristic thereof. 
       FIGS. 2 and 3  show the first embodiment of post driving apparatus  20  in accordance with the invention. The post driving apparatus  20  comprises a central guide shaft  22  and combination anvil/outer sleeve  24 / 26  which slides on the central guide shaft  22  between upper and lower extremes. It is preferred that the post driving apparatus  20  be used to drive hollow posts (eg.,  40 ) into the ground whether they be metal or plastic. The invention is particularly advantageous for plastic posts in that the central guide shaft  22  is designed to insert inside the full length of the hollow core of the plastic post (eg.,  40 ) and thereby provide protection against buckling under the force of the pounding strokes. In this embodiment, the combination anvil/outer sleeve  24 / 26  is the drive weight that pounds the post  40  into the ground. The guide shaft  22  not only provides temporary rigidity to the post to-be-driven  40  while being pounded but also pierces a pilot hole in the ground (this is not shown) for the post  40  to follow, thereby clearing a path for the post  40 . The guide shaft  22  also provides a track portion  28  for the combination anvil/outer sleeve  24 / 26  to slide on during pounding strokes. 
     The outer sleeve  26  is preferably produced from a heavy-gauge metal pipe. The anvil  24  is preferably produced from a heavy, metal bushing. That is, the anvil  24  is a thick-walled cylinder (ie., bushing) extending between annular ends or faces. It is preferred that the outer sleeve  26  be about twenty inches long or, in other words, sufficiently long for ample up-and-down sliding strokes. The anvil  24  (bushing) is preferably a fraction of the length of the outer sleeve  26 , perhaps something like three inches long. The anvil  24  (bushing) preferably has an outer diameter that closely nests inside the outer sleeve  26 &#39;s hollow core. The anvil  24  (bushing) preferably has an inner diameter that allows sliding travel up and down on the guide shaft  22 , as between extremes more particularly described below. The anvil  24  (bushing) is fixed in and/or welded to the outer sleeve  26  at one end of the outer sleeve  26 , with one annular end about flush with one end of the outer sleeve  26 , and the other annular end or face defining the pounding face for delivering the pounding force. The remaining extent of the outer sleeve  26  not occupied by the anvil  24  (bushing) forms sort of a skirt portion  34  therefor. 
     The outer sleeve  26  extends axially between the one end with the anvil  24  therein and an another end with an annularly inward flange portion  35  that is axially-spaced away from the anvil 24 .  FIG. 3  that this annularly inward flange portion  35  is sized to closely surround the post  40 &#39;s outer sidewall The annularly inward flange portion  35  of the outer sleeve  26  should be sized to let the post to-be-driven  40  pass freely through during the up-and-down sliding strokes, but not the anvil  24 . That is, the anvil  24 &#39;s annular driving face is what delivers the applied pounding force that gets transmitted to the post  40 . In other words, the inner diameter of the anvil  24 &#39;s hollow core is less than that of the post  40 , and hence the post  40  gets driven instead of passed through. Correspondingly, the inner diameter of the anvil  24 &#39;s hollow core is greater than that of the guide shaft  22 , which allows free sliding travel on the track portion,  28  thereof. The track portion  28  guides the path of the anvil  24  and keeps it aimed on target for the top of the post to-be-driven  40 . 
     The guide shaft  22  is preferably produced from a solid metal rod that extends between a lower tip end and an upper butt end. The tip end is somewhat sharpened, not too much so to present a danger to users but sufficiently so to pierce the ground with pounding strokes. Indeed, it is preferred to sharpen the tip end into a cone, either with or without flats or flutes (none shown). In this embodiment, the guide shaft  22  acts as a guide for the combination anvil/outer sleeve  24 / 26  and a stabilizer for the post. It is preferred that the length of the guide shaft  22  be the sum of (A) the length of the post to-be-driven  40  plus (B) a length corresponding to about an inch less than the length of the outer sleeve  26 . 
     For example and without limitation, assume a post driving apparatus  20  in accordance with the invention sized to sink a four foot long plastic post (eg.,  40 ) about one foot into the ground. Assume further that the outer sleeve  26  is about twenty inches long, and the anvil  24  plugs about the last three inches of the outer sleeve  26  (which, as an aside, leaves a skirt portion  34  that is about seventeen inches long). Given the foregoing, the length of the guide shaft  22  should be the sum of (A) four feet, the length of the post to-be-driven  40 , and that&#39;s not including the measure of the guide shaft  22 &#39;s tip end&#39;s cone section, plus (B) about nineteen more inches at the top, which is a short measure ( ˜ one inch) less than the twenty inch length of the outer sleeve  26 . This nineteen more inches serves as the track portion  28  of the guide shaft  22  for the anvil  24  to slide up and down on. 
     The guide shaft  22  further includes a stop collar  36  welded to it at the transition between the height of the post to-be-driven  40  (eg., the four foot elevation) and the slide track portion  28  (eg, the about nineteen more inches). The collar  36  has an outer diameter slightly less than the outer sleeve  26 &#39;s skirt portion  34 &#39;s inner diameter so that the skirt portion  34  can freely pass by this stop collar  36  during the up and down sliding strokes. The collar  36  might also be fairly thin, and therefore more nearly resemble a washer. As for the anvil  24 , however, this stop collar  36  defines the lower limit of the anvil  24 &#39;s downstroke (ie., pounding stroke). In use, it is preferred that the stop collar  36  is rested against the post to-be-driven  40 &#39;s top end. That way, the pounding strokes of the anvil  24 &#39;s pounding face are delivered directly to the stop collar  36 , which directly transmits the force of the pounding stroke to the post  40 &#39;s top end. In other words, the anvil  24 &#39;s pounding face does not directly strike the post  40 &#39;s top end, but the stop collar  36  (which, as said, rests on the post  40 &#39;s top end). 
     The guide shaft  22  might optionally include a cap or retainer at its upper end (not shown) when stood vertically. The retainer might be a round metal disc welded or bolted to the guide shaft  22 &#39;s top end (again, this is not shown). When the retainer is included, it will serve as the anvil  24 &#39;s upper (travel) limit during the up stroke (eg., the back or retraction stroke). It is also preferred that the guide shaft  22 &#39;s sharpened tip end project out the post  40 &#39;s bottom end so that the guide shaft  22 &#39;s conic tip end forms a smooth tip end for the post  40  as a whole (again, with the post  40 &#39;s top end abutted against the stop collar  36  at the bottom of the track portion  28  of the guide shaft  22 ). That way, with the guide shaft  22  inserted through the whole length of the post to-be-driven  40 , the guide shaft  22 &#39;s tip end will do the actual piercing into the ground and thereby save the post  40 &#39;s bottom end from unwanted damage. The guide shaft  22 &#39;s sharpened end will aid in an easier driving through the ground. 
     To drive the post  40  into the ground, the guide shaft  22  is inserted inside the post  40 , with the stop collar  36  bottoming out on the post  40 &#39;s top end, the guide shaft  22 &#39;s tip end poking out the post  40 &#39;s bottom end. Then the user sets the post  40  up vertically on the ground where it is desired to be driven by the user (not shown), with the guide shaft  22 &#39;s tip end resting on the ground at the point of entry (again, not shown). As a result, the guide shaft  22 &#39;s track portion  28  (eg., the upper nineteen inches in the example) will extend upwardly out of the post  40 &#39;s top end. This track portion  28  shall be the ‘guide’ or track portion  28  for the path of the combination anvil/outer sleeve  24 / 26  during the up-and-down sliding strokes. The remainder of the guide shaft  22  inside the post  40  will act as a stabilizer for the post  40 , providing the post  40  with rigidity against buckling while being driven. 
     The outer sleeve  26 &#39;s skirt portion  34  passes freely past the stop collar  36  and the post  40 &#39;s outer sidewall—until the anvil  24 &#39;s pounding face comes to rest on the fixed stop collar  36 . Now the user can slide the anvil  24  between up and down sliding strokes, thrusting each down stroke with force as a pounding stroke to deliver a pounding blow to the stop collar  36 , which directly transmits the force to not only the post  40 &#39;s top end but more significantly to the guide shaft  22 &#39;s tip end. The user continues with pounding strokes alternated with retraction (back) strokes, progressively driving the tip end of the guide shaft  22  deeper into the ground, with the post  40  directly following. 
     Again, to drive the post  40  into the ground, the user grasps the outer sleeve  26  of the combination anvil/outer sleeve  24 / 26 . The user hoists the combination anvil/outer sleeve  24 / 26  up vertically for a back (or retraction) stroke, and then thrusts the combination anvil/outer sleeve  24 / 26  down for a pounding stroke. Since the guide shaft  22  is inserted through the central bore in the anvil  24 , the combination anvil/outer sleeve  24 / 26  should stay tracking on the guide shaft  22 . As further assurance of this, the outer sleeve  26 &#39;s skirt portion  34  should track on the stop collar  36  concurrently with the annularly inward flange portion  35  on the upper portions of the post  40 &#39;s outer side wall, which should further help prevent the anvil  24  from binding on the track portion  28  of the guide shaft  22 . This will keep the combination anvil/outer sleeve  24 / 26  moving straight on the central axis of the guide shaft  22  (and post  40  as well) during the pounding and retraction stroke, without getting crooked. Staying on axis is important for driving the post  40  in straight or otherwise not damaging the post  40 . Also, the retainer on the upper end of the guide shaft  22  (if used, and not illustrated) will prevent the user from backing the combination anvil/outer sleeve  24 / 26  off too high or, that is, limit the combination anvil/outer sleeve  24 / 26  from sliding off the top of the guide shaft  22  completely. 
     The user should thrust the combination anvil/outer sleeve  24 / 26  down the guide shaft  22  upon the stop collar  36  with force. The weight of the combination anvil/outer sleeve  24 / 26  acts as the pile-driving weight. The pounding upon the collar  36  will drive the guide shaft  22 &#39;s tip end into the ground. Since the combination anvil/outer sleeve  24 / 26  is purposely heavy, it is easy for the user to generate a lot of force to pound the post into the ground without much exertion. That is, the user to relies partly upon the gravity to assist his or her own exertions. The placement of the stop collar  36  between the anvil  24 &#39;s pounding face and the post  40 &#39;s top end acts as a barrier between the anvil  24  and post  40 . This will prevent the anvil  24  from shattering or otherwise damaging the post  40 . 
     Pounding strokes are applied until the post  40  is driven into the ground to the desired depth, of about a foot or whatever. When the user is finished, all he or she must do is remove the guide shaft  22  from the ground and post  40  by sliding it out the top end of the post  40 . 
       FIGS. 4 and 5  show a second embodiment of post driving apparatus  50  in accordance with the invention. In this embodiment, the guide shaft  52  has the combination anvil/outer sleeve  24 / 26  fixed to it. The anvil  24  is fixed to the guide shaft  22 , that is, with the anvil&#39;s pounding face fixed at the elevation of the stop collar  36  of the  FIG. 2  embodiment (which is eliminated in this embodiment). The anvil  24  can be fixed to the guide shaft  22  by welding or the like. 
     The excess portions of the guide shaft  52 —which in the  FIG. 2  embodiment of the guide shaft  22  serve as the track portion  28 —are another difference in this embodiment, because they are eliminated. Hence the guide shaft  52  is relatively abbreviated compared to the guide shaft  22 . The guide shaft  52  inserts all the way into the post to-be-driven  40  as shown, with the sharpened tip end projecting from the post  40 &#39;s bottom end while the anvil  24 &#39;s pounding face rests on the post  40 &#39;s top end. 
     In contrast to  FIG. 2 , the guide shaft  52  here only serves as a stabilizer for the post  40 . More significantly, the combination anvil/outer sleeve  24 / 26  does not reciprocate relative the post to-be-driven  40  (or the guide shaft  52  either) during use. 
     Instead, as  FIG. 6  shows, the pounding action is delivered by a conventional, T-post driver  60  in accordance with the prior art, such as and without limitation like what is disclosed by U.S. Pat. No. 2,098,146-Hunt, the disclosure of which is incorporated herein by this reference. The conventional T-post driver  60  slips over the outer sleeve  26  and is utilized to pound this embodiment of the post driving apparatus  50  as a unit in unison with the post to-be-driven  40 . As soon as the post to-be-driven  40  is sunk into the ground to the desired depth (not shown), the conventional T-post driver  60  is set aside. Then this embodiment of the post driving apparatus  50  is withdrawn completely, out through the top of driven post (this is not shown). Again, the guide shaft  52  stabilizes the post  40  and is driven along with the post  40  into the ground, after which the user then extracts the post driving apparatus  50  as a whole when finished. 
       FIGS. 7 through 10  show an alternate embodiment of a combination post  70  and insertion tool  72  therefor in accordance with the invention. 
     The insertion tool  72  comprises an elongated spike  74  and an abbreviated outer sleeve  76  telescoped over the top end  78  of the spike  74 . The spike  74  extends between a butt end  78  and conically-tapered pointed end  80 . The outer sleeve  76  extends between a lower open end  82  and top end  84  plugged by an anvil  86 . 
     The anvil  86  interconnects the outer sleeve  76  and spike  74 . The anvil  86  and outer sleeve  76  are preferably produced of steel that accepts welds. The spike  74  is preferably made of the same material.  FIG. 9  shows that the outer sleeve  76 &#39;s open bottom end  82  is lined with a scuff-protecting ring  88 .  FIG. 10  shows that the purpose of the scuff protecting ring  88  is to protect the post  70  from being marked and scuffed during use. 
     Optionally, the anvil  86  and outer sleeve  76  are permanently fixed together. Preferably, the central spike  74  and anvil/outer sleeve unit  86 / 76  are releasably coupled together.  FIGS. 7 through 10  and  FIG. 12  show a system comprising a quick release pin  90 . One advantage of the foregoing is to allow the exchange of one spike  74  of one length and/or diameter for another spike  74  of another length and/or diameter, and in accordance with the length and diameter of the given post  70 . 
     The post  70  is relatively slender and hollow and also, like the spike  74 , is elongated between spaced ends  92  and  94 , one comprising an open top end  92  and the other comprising an open pointed end  94 . Whereas this hollow post  70  is indeed relatively slender, it comprises substantial wall thickness. Indeed, for buckling and bending analysis, it might qualify for short column status (in contrast to long column). 
     Engineers typically perform buckling (bending) analysis according to the ‘area’ or ‘second’ moment of inertia. 
     Applicant typically prefers a post with a Modulus of Elasticity in Bending (MOE) in the range of 250,000 psi, and a Modulus of Rupture in Bending (MOR) in the range of 4,000 to 4,500 psi. 
     Wherein, the ‘area’ or ‘second’ moment of inertia “I a ” equals:
 
 I   a =(π/4)·( r   o   4   −r   i   4 )  (1)
 
r o =outside radius,
 
r i =inside radius.
 
The radius of gyration “R g ” equals:
 
( R   g ) 2   =I   a   /A.   (2)
 
The critical force “F” to buckling equals:
 
 F =(π 2   ·E·I   a )/( K·L ) 2   (3)
 
E=elastic modulus
 
L=length, and
 
K=factor changing true length to an effective length, &amp; according to end restraint or not.
 
The Modulus of Rupture in Bending (MOR) is given by:
 
MOR=(1.75)( P )(O.D.)/( I   a ).  (4)
 
P=pressure of applied load, and
 
O.D.=outside diameter.
 
     However, the post  70  need not withstand all the impact of the T-post driver  60  without help. That is, the insertion tool  72  in accordance with the invention provides support against buckling and fragmenting under the impacts of the T-post driver  60 . 
     It is an aspect of the invention that the combination in accordance with the invention of this post  70  and this insertion tool  72  are only matched together about once in the life of the post  70 . And that one time is, needless to say, at the instance of driving this post  70  into the ground. 
       FIGS. 10 and 13  show that the lengths of the post  70  and spike  74  are selected correspondingly so that the post  70 &#39;s open pointed end  94  aligns with the spike  74 &#39;s pointed end  80  so as to form a nearly smooth continuation thereof. Likewise,  FIGS. 10 and 13  along with  FIG. 11  show better that the outside diameter of the spike  74  is chosen to closely fill the inside diameter of the post  70 &#39;s hollow core. Again, both the bottom of the post  70  and bottom of the spike  74  are conically tapered, and preferably as close to the same angle as practical. The length of the post  70  should be shorter than the spike  74  so that the open tapered end  94  of the post  70  more or less meets the spike  74 &#39;s transition point where the pointed end  80  transitions into the spike  74 &#39;s cylindrical sidewall. That way, the spike  74 &#39;s pointed end  80  is exposed beyond the post  70 &#39;s bottom end  94 . The taper of the post  70 &#39;s tapered end  94  begins where the taper of the spike  74 &#39;s pointed end  80  leaves off. 
     When the central spike  74  is inserted inside the post  70 , these two tapered formations are meant to work with each other so that they form a fairly continuous uniform conic taper with each other in unison. This is shown best in  FIG. 13 . 
     Again,  FIG. 13  shows better the following. That, the close matching match-up between the length as well as taper of the spike  74  and the length as well as taper of the post  70  allows for easier piercing of rocky ground, and driving into the ground, when the post  70  is being driven. The ground spike  74  has a hardened pointed end  80  and can push aside aggregate in the soil that the plastic post  70  could not. In the absence of the spike  74 , a direct strike into a rock might shatter the plastic post  70  or overcome the critical buckling strength of the plastic post  70  alone. But not so in accordance with the invention. The pointed end  80  of the steel spike  74  might do any of the following:
         push the rock aside,   steer the course of the post  70  around the rock,   do a bit of both, or   stop downward progress in its tracks, without destruction of the plastic post  70 . In the last case scenario, the post  70  and spike  74  of the insertion tool  72  can be pulled out (withdrawn) for another try. The spike  74  can be used alone for a while to probe the ground for a pathway around the obstructing rock. Given the new spot, the post  70  can be re-driven into the ground except this time into the new spot. The pointed end  80  will lead the way. The spike  74  will stiffen the post  70  against buckling.       

     During the instances where the spike  74 &#39;s hardened pointed end  80  moves a rock aside, the plastic post  70 &#39;s tapered open end  94  has sufficient compression strength to continue the pushing aside of the rock, being reinforced on the inside sidewall by the steel spike  74 , to produce an applied force against the aggregate normal to the angle of the taper. 
     Again, with the plastic post  70  experiencing a compressive force between the inside spike  74  and the outside aggregate, the plastic post  70  has sufficient compressive strength to withstand this. 
     The post  70  also has thick walls and an inside diameter such that the central guide shaft fills the hollow core for a close fit. 
     After the post  70  has been driven to the desired depth (as shown by  FIG. 13 ), the insertion tool  72  is withdrawn, and the post  70  remains. 
     The invention having been disclosed in connection with the foregoing variations and examples, additional variations will now be apparent to persons skilled in the art. The invention is not intended to be limited to the variations specifically mentioned, and accordingly reference should be made to the appended claims rather than the foregoing discussion of preferred examples, to assess the scope of the invention in which exclusive rights are claimed.