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CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/587,409, filed Jan. 17, 2012. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to borehole drills, and more particularly to a manual or human-powered borehole drill 
     2. Background and Related Art 
     Tanzania is one of the many countries in the world that suffers from extreme poverty. Many of the hardships in Tanzania can be attributed to the lack of clean water. Despite the facts that the country is surrounded by three major lakes and an ocean, and 7% of its area is covered by fresh water, it is difficult to find clean water because the water is contaminated and not suitable for human consumption. 
     Potable, or drinkable, water is the basis for a better life. It is estimated that Tanzanian women and children spend an average of 2 hours a day just collecting water, and it is common to find people who walk 6 hours just to find water. Other than the time concerns, 80% of all disease in developing countries is caused by bad water. Many of these people die because of the lack of medicine and health care. Since these people are collecting contaminated water, they spend their time being sick, visiting doctors, and paying for medicine they cannot afford. Although the people know the water makes them sick, they have no alternative. 
     Installing a village water well dramatically reduces all of these concerns and provides clean water for up to 1,500 families. Not only can the children go to school and the people have more time to help themselves financially, but they also have more opportunities to start businesses and in turn help the village progress. 
     Unfortunately, many villages lack clean water wells because the current methods of drilling in Tanzania are limited by opposite extremes. One option for drilling a well is a professional drilling rig, which is too expensive (from $15,000 to $20,000), while the other option is a homemade drilling system, which is too primitive and therefore unsuccessful drilling beyond 100 feet, where potable water is reached. 
     Of course, a professional drilling rig can drill to depths sufficient to access clean drinking water, but it costs upwards of $20,000 to hire the rig for the few days required to drill the borehole. The villages that need these wells cannot afford to spend this extreme amount of money. As a result, they turn to homemade drilling systems, which often are insufficient. The primitive, manual methods with which they dig or drill simply cannot penetrate deep enough to access clean water. The two main manual methods in most developing countries are hand augering and Rota-sludge. Hand augering simply uses an auger to dig the earth away and is effective only in soft soil formations, reaching depths of no more than 30 m (about 100 ft). Rota-sludge is a less effective method because it reaches the same depths but has success in much less diverse formations. In all manual techniques, due to limited mechanical advantage and strength of tools, these methods generally are not sufficient to reach the depths required to access clean water. 
     BRIEF SUMMARY OF THE INVENTION 
     A human-powered borehole drill bridges the gap between the large drilling rigs and the other less effective manual methods. A human-powered borehole drill will enable the people to drill their own wells for roughly $1,500, or even less. Intended mainly for developing countries such as Tanzania, the design is affordable and also extremely simple, as very little product support or spare parts will be needed. The drill uses conventional drill pipe and drill bits allowing the drill system to mimic more conventional methods of drilling and existing hardware to maintain uniformity in drilling and easier access to more drilling products. 
     The human-powered borehole drill will provide clean drinking water to almost any location having an aquifer at a reasonable depth, including remote locations such as villages in Tanzania at an affordable cost. The drill is capable of drilling a six-inch borehole reaching 250 feet through various soil formations to reach potable water. In an effort to bridge the gap between expensive professional rigs and less effective homemade systems, the drill uses existing drill pipe and bits, operates strictly on human power and is portable to move from village to village. 
     The design consists of three major components: the structure, the wheel support, and the wheel. The structure is designed to withstand loads of over three times the weight of 250 feet of drill pipe before yielding. Additionally, the structure is designed with a low center of gravity to prevent tipping and to add stability to the drilling process. The lifting of the pipe is accomplished through the use of a winch and pulley system, which also allows the operators to control the penetration rate of the drill bit. The wheel support is able to stabilize and support the weight of the wheel and allows ready access to the borehole and the drill pipe beneath the wheel. The innovative design of the wheel consists of a hub that is permanently attached to the wheel support via a bearing and eight removable spokes. Each of the spokes is pinned in place on the hub, and additional strength is gained from cross braces that are placed between the spokes. This design also allows for easy transportation. 
     In addition to meeting the quantitative specifications for drilling a borehole, the final design also meets the economic specifications. It can be manufactured for less than $5,000 and because the design consists mostly of welded steel, the majority of manufacturing can be performed in local regions. The entire drilling rig can also be easily disassembled and transported in the bed of a regular-sized truck or on a small trailer and can even be manually transported for transportation to remote areas. 
     The design has been tested in both theory and reality. Many tests were conducted, culminating in a final test with a fully functional steel prototype in which a six-inch-diameter borehole, 27 feet deep, was drilled in a sandy soil condition. Including setup, drilling, and cleanup, the entire test was completed in a five-hour period. More than a dozen boreholes fitted with working hand pumps have been completed. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The objects and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  shows an embodiment of a human-powered borehole drill; 
         FIG. 2  shows a surface preparation of an underlying surface, the preparation being configured to receive the drill of  FIG. 1 ; 
         FIG. 3  shows a drill base placed on the surface of  FIG. 2 ; 
         FIG. 4  shows vertical columns being inserted into the base of  FIG. 3 ; 
         FIG. 5  shows a cantilevered beam being attached to the vertical columns of  FIG. 4 ; 
         FIG. 6  shows a wheel support being attached to the vertical columns of  FIGS. 4 and 5 ; 
         FIGS. 7-8  show steps for securing the components of  FIGS. 3-6  together; 
         FIGS. 9-13  show steps for assembling a wheel; 
         FIG. 14  shows the assembled wheel attached to the assembly of  FIGS. 3-6 ; 
         FIGS. 15-21  show steps for assembling a Kelly bar and pipe string to the assembly of  FIG. 14  in preparation for drilling a borehole; 
         FIG. 22  shows a configuration of operators using the drill of  FIGS. 1-21 ; 
         FIGS. 23-30  show steps for drilling a borehole and for adding an additional pipe segment to the pipe string; and 
         FIGS. 31-42  show steps for disassembling the drill and removing the pipe string when the borehole is complete. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of embodiments of the present invention will now be given with reference to the Figures. It is expected that the present invention may take many other forms and shapes, hence the following disclosure is intended to be illustrative and not limiting, and the scope of the invention should be determined by reference to the appended claims. In addition, headings are provided to guide the discussion, but such headings are not intended to in any way be limiting of the scope of the invention. 
     Exemplary Functional Specifications: 
     Based on anticipated plans, goals, and research, various functional specifications to which the human-powered borehole drill would conform were originally defined. Of those, the ones that were deemed most influential on the design of the drill are set forth below in Table 1. The specific embodiments and examples set forth herein have been based on meeting or exceeding the functional specifications contained in Table 1. It should be understood that the illustrated embodiments and examples are merely examples of one potential design and configuration intended to meet one set of functional characteristics. It should also be understood that the embodiments and examples might be varied while still satisfying or exceeding the functional characteristics shown in Table 1, or that the embodiments and examples might also be varied to satisfy or exceed other functional characteristics depending on the specific needs. Therefore, the illustrated examples and embodiments are intended to be instructional and are not to be deemed limiting of the invention in its various forms. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Functional Specifications 
               
             
          
           
               
                   
                   
                   
                 Ideal 
                 Marginal 
               
               
                 Interpreted Needs 
                 Metric 
                 Units 
                 Value 
                 Value 
               
               
                   
               
             
          
           
               
                 The drill provides access to 
                 Borehole depth 
                 feet 
                  250 
                 200 
               
               
                 clean, potable water 
                   
                   
                   
                   
               
               
                 The drill structure supports 
                 Maximum weight able to be 
                 pounds 
                 10000 
                 5000 
               
               
                 the weight of the drill pipe 
                 supported by structure 
                   
                   
                   
               
               
                   
                 Weight of 250 feet of drill pipe 
                 pounds 
                  3000 
                 1500 
               
               
                   
                 Maximum pull-back force 
                 pounds 
                  6000 
                 3000 
               
               
                 The drill overcomes the 
                 Downward force on drill bit 
                 pounds 
                  3000 
                 500 
               
               
                 compressive strength of 
                 Applied torque to drill pipe 
                 ft-lbs 
                  1500 
                 500 
               
               
                 rock 
                   
                   
                   
                   
               
               
                 The drill turns fast 
                 Rotations per minute 
                 rpm 
                   60 
                 20 
               
               
                 The drill uses existing drill 
                 Percentage of on-market drill 
                 % 
                  100 
                 90 
               
               
                 pipe 
                 pipe 
                   
                   
                   
               
               
                 The drill uses existing drill 
                 Percentage of on-market drill 
                 % 
                  100 
                 90 
               
               
                 bits 
                 bits 
                   
                   
                   
               
               
                 The drill is affordable 
                 Total develpment cost 
                 USD 
                 $1500 
                 $5000 
               
               
                   
                 Cost to remanufacture 
                 USD 
                 $1000 
                 $5000 
               
               
                   
               
             
          
         
       
     
     Description of Exemplary Drill: 
       FIG. 1  shows a depiction of a human-powered borehole drill  10  in its assembled state. The structure of the drill  10  has three main components: a supporting structure  12 , a wheel support  14 , and a wheel  16 . The various components of the drill  10  can be manufactured of any materials having desired cost, strength, and availability characteristics, as is known in the art. In one exemplary embodiment, the drill  10  is mostly constructed of steel parts that are welded and/or bolted together to assemble the complete structure. As such, the drill  10  can be largely manufactured locally without the need of expensive and specialized machining equipment, reducing manufacturing and distribution costs. The entire structure can be disassembled and transported in the bed of a regular size pick-up truck (approximately five and one-half feet wide and seven feet long). This falls well within the ideal value of being transported on a six-foot by ten-foot trailer. As a whole, the final design costs less than $5,000 to manufacture, and will presumably cost less if manufactured at higher quantities. 
     The components and assembly of the supporting structure  12  are shown in  FIGS. 2-5 and 8 . The final bolting of the supporting structure  12  shown in  FIG. 8  occurs after the wheel support  14  is attached to the supporting structure  12  as shown in  FIG. 7  and discussed below. The supporting structure  12  is roughly composed of four parts: a base  20 , a first vertical column  22 , a second vertical column  24 , and a cantilevered beam  26  for lifting a drill pipe  28 . As depicted more clearly in  FIG. 3 , the base  20  has two horizontal legs  30  sufficiently long and spaced wide enough apart to keep the structure  12  balanced and stable. The base  20  overall is approximately forty-seven inches wide and eighty-four inches long. It is constructed of three-and-one-half-inch square tubing, ⅜ of an inch thick. The size and mass of the base  20  keep the center of gravity for the whole structure  12  low to prevent tipping over. In order to tip, the structure has to rotate 36.7 degrees from the vertical. To cause this rotation a horizontal force of 220 pounds must be applied to the high-end of the cantilever beam  26 , or a horizontal force of 352 pounds must be applied at the top of the five-foot second vertical column  24 . The likelihood that these large forces will be applied to the structure  12  is extremely low. 
     The first vertical column  22  and the second vertical column  24  are three-inch square tubes, ¼ of an inch thick. This allows enough clearance to slide into a first sleeve  32  and a second sleeve  34  of the base  20 , while remaining strong enough to withstand the applied loads. A series of rectangular steel tubing sections are welded between the legs of the base over the borehole for additional support. They also provide a rest for a slip plate  38  (see  FIG. 24 ), which is used to secure the pipe  28  during changeover (adding or removing sections of pipe  28 ). 
     The cantilevered beam  26  is a five-inch square steel tube that is seven feet long with a thickness of 3/16 of an inch. The beam  26  has two sleeves  40  of three-and-one-half-inch steel tubing welded at a 45-degree angle that allow the beam  26  to be slid securely on top of the first and second vertical columns  22 ,  24 . The beam  26  will be pinned to the columns  22 ,  24  by four four-inch-long clevis pins. The high end of the beam  26  is nine feet above the ground, directly above the borehole. Both ends of the beam  26  have a pulley  42  inside, and a winch  44  is attached to the low end of the beam  26 . The wire rope or cable from the winch  44  goes through the beam  26  and can then hook onto the pipe  28  or a Kelly bar  46  (see below) for lifting. 
     The functional specification for the lifting system is to be able to support and lift the weight of 250 feet of drill pipe. Based on the density of steel (490.6 pounds per cubic foot), a pipe wall thickness of 0.25 inches, and an outer diameter of 2.875 inches, the weight of 250 feet of pipe is 1725 pounds. While drilling, the borehole may cave in on top of the pipe; thus necessitating the ability to lift more than the just the weight of the drill pipe. 
     The three major components of the lifting system are the hoist structure, the winch  44 , and the pulleys  42 . The hoist structure was designed to never yield, even under extreme lifting conditions. Because of the length of the cantilevered beam  26 , the highest stresses occur in the beam  26  at the junction with the first vertical column  22 . This stress is due to a combined bending load and axial load. Therefore, to select the appropriate beam size of the beam  26 , the von Mises stresses were calculated at this point. A simple optimization program was created in Excel to optimize the beam dimensions given a load, a safety factor, and a beam wall thickness. From this optimization routine a five-inch square steel beam was chosen with the yield strength of steel as 50,000 psi, a safety factor of 1.5, a wall thickness of 0.188 inches and a vertical load of 4,500 pounds. If other design considerations are applicable, a similar optimization could be used to create a satisfactory design for those conditions. 
     The winch  44  and pulleys  42  were then chosen to be able to lift the weight of the pipe  28  and more, but both of these components have a lower capacity than the beam  26 . The goal was to ensure that there would never be any failure of the lifting structure. A hand winch with a 3,500 pound first layer capacity (and an 1849 pound full drum capacity) was selected as the winch  44 . The selected winch has an enclosed gear for protection from the harsh environments of drilling, and it has an automatic brake, which means that it cannot move unless an operator is rotating the handle even with tension in the wire rope. Furthermore, at its maximum capacity the operator only has to apply 19.4 pounds of force to the end of the winch handle to move the load. 
     The pulleys  42  were selected to match the lifting capabilities of the winch  44  as closely as possible; however, the pulleys  42  were also constrained in size by the inside dimension of the beam  26 . Stainless steel pulleys with a 4.25-inch diameter and plain bronze bearings were selected. These pulleys have an operating capacity of 3,000 pounds. 
     One major advantage that the structure shown in  FIG. 1  and described above is the ability to apply upward force to the drill pipe  28  while drilling. This is a result of having a structure that is always in place over the hole. The upward pressure prevents the drill bit from becoming lodged in soil at the bottom of the borehole. This ultimately results in a smaller average torque applied to the pipe  28 . This structure also allows the winch  44  to impart a constant vertical force while raising or lowering the pipe instead of a force that decreases as the pipe  28  approaches the top of the structure as in a design with a block and tackle pulling from two sides. 
     Assembly of the wheel support  14  to the structure  12  is shown in  FIGS. 6-7 . The wheel support  14  is made of several three-inch by two-inch rectangular steel tubing sections that are welded together to make a platform  50  on one end that a lazy Susan bearing and the wheel  16  can rest on (see  FIG. 6 ). The other end  52  has sections of tubing spaced wide enough to fit over the vertical columns  22 ,  24  of the structure  12 . Two parallel long sections  54  slide around both columns  22 ,  24  and are bolted in place. Two smaller short sections  56  six inches above the long sections  54  slide around the second vertical column  24  only and are bolted in place. Bolting the wheel support  14  to the columns  22 ,  24  in this manner and as shown in  FIG. 7  provides more structural stability to the structure  12  and the wheel support  14 . 
     The platform  50  end is approximately forty-five inches from the ground, which will make it ergonomically ideal for an average height operator to turn the wheel. The platform  50  is twelve inches wide with ample space in the middle for the Kelly bar  46  and pipe  28  to slide through. Essentially, the only load that will be seen by the wheel support  14  is the weight of the wheel  16  itself. 
     This wheel support  14  is advantageous in that it allows unimpeded access to the drill pipe  28  that is beneath the wheel  16 . In other designs, cross braces that provided structural stability to the table or platform that supported the wheel restricted access to the pipe  28  and made adding or removing pipe sections difficult. Also, this wheel support  14  offers more strength and stability because it is attached to a rigid structure  12  with a wide base  20 . 
       FIGS. 9-14  show assembly of the wheel  16 . The wheel  16  is made up of a central hub  60  and eight spokes  62  (see  FIG. 13 ). The hub  60  has eight inch-long sections of three-inch by two-inch rectangular steel tubing that are spaced evenly in a circular or octagonal pattern with open ends facing outward. These form sleeves  64  into which the spokes  62  are inserted. The sleeves  64  are sandwiched between two ¼-inch-thick octagonal plates  66  that are twelve inches wide. The plates  66  have 4.1 inch square holes  68  in the middle that are aligned for the Kelly bar  46  to slide through. All components of the hub  60  are strongly welded together for robustness. A small piece of metal is welded to the inside bottom lip of each of the sleeves  64  of the hub  60  to prevent the spokes  62  from sagging. The wheel hub  60  is then attached to the wheel support  14  by a thrust bearing allowing the wheel  16  to spin freely. 
     The spokes  62  are three-foot long 1.5 inch by 2.5 inch rectangular tubing sections. One end of each spoke  62  fits into one of the sleeves  64  of the hub  60  and is pinned in place. The other end of each spoke  62  has an 11.5 inch long and 1.25-inch diameter solid steel rod  70  going through the middle perpendicular to the main axis of the spoke  62 . A 1.25-inch diameter is ergonomically optimal for a power grip. Each rod  70  serves as a handle and is centered on the spoke  62  with five inches protruding both above and below the spoke  62 . This accommodates people of different heights working on the drill  10 . The outside end of the spoke  62  is closed and deburred for safety. For additional support of the wheel spokes  62 , a 2 foot piece of one inch by one inch angle iron is pinned as a cross brace  72  between all adjacent spokes  62 . 
     The six-foot diameter of the wheel  16  provides enough torque to drill efficiently in all soil types while still maintaining its portability. The spokes  62  are not permanently attached to the hub  60  so that the wheel  16  may easily be assembled and taken apart for transportation. Additionally, the weight of the wheel  16 , especially the solid steel rods  70  serving as handles at the end of the spokes  62 , provides enough inertia for the wheel  16  to maintain a continuous motion and act as a flywheel. 
     With the wheel  16  applying a constant torque to the drill pipe  28 , it is possible that some angle of twist will develop through the length of the drill pipe  28  (within the borehole). This can cause unwanted wind-up that could potentially be dangerous if the wheel  16  were suddenly released. Therefore, calculations were performed to determine the twist angle with 250 feet of pipe  28  and a maximum torque of 1,000 foot-pounds, which corresponds to three operators exerting 111 pounds of force at the edge of the wheel. In the limiting case where the drill bit is held stationary, forty-nine degrees of twist will develop in the pipe. This would result in the wheel unwinding approximately ⅛ of a turn, which means that at most one spoke  62  will pass by the operator. In addition, with use of the winch  44  and the subsequent upward force that can be applied to the pipe  28 , the situation in which the drill bit is held stationary can be avoided. 
     This wheel design holds many advantages over other possible designs. While testing with a wooden wheel prototype, it became apparent that moving six-foot diameter wheel was cumbersome and problematic. In order to begin the drilling process, the heavy wheel had to be slid over the top of the Kelly bar. Adjustment and placement of the wheel was also difficult because the operators had to work from three feet away. With the illustrated design of the wheel  16 , the Kelly bar  46  is slid through the permanent hub  60 . There are no awkward or heavy pieces to lift overhead and transport. Additionally the wheel  16  is able to be disassembled for transport and it can easily fit with in the required space (six feet by ten feet) with all of the other components. 
     The change-over process is facilitated by using three-foot sections of the pipe  28 . The Kelly bar  46  has a square cross section slightly smaller than the diameter of the square hole  68  of the hub  60  and has a length of approximately 3 and ⅔ feet. Of course, the Kelly bar  46  and the hole  68  can be formed of any appropriate cross-section and corresponding shape that permits the transfer of torque from the wheel  16  to the Kelly bar  46  and thence to the pipe string. Regardless, this length of the Kelley bar  46  allows a quicker changeover and more manageable parts for manual labor. 
     When drilling starts, the Kelly bar  46  is almost completely above the wheel  16 . As the drill cuts, the Kelly bar  46  and pipe  28  will lower until the top of the Kelly bar  46  is level with the top of the wheel hub  60 . Then the winch operator lifts the pipe  28  until the slip plate  38  can fit under a coupler  80  between sections of pipe  28  and over the legs  36  of the base  20  (see  FIG. 24 ). After unthreading the Kelly bar  46  from the drill pipe  28 , the Kelly bar  46  is raised until it reaches the top of the cantilever beam  26 . Then a new three-foot pipe section of pipe  28  can fit between the Kelly bar  46  and the top of the previous section of pipe  28  (see  FIG. 26 ). The new section is threaded onto the pipe  28  using the coupler  80 , and then onto the Kelly bar  46 . This is done under the wheel  16  by one operator holding the pipe  28  with a pipe wrench  82  and the other operators tightening the Kelly bar  46  by turning the wheel  16  (as the drill  10  runs, the pipe sections will fully tighten). A wrench stop  84  has also been welded to the base  20  so that the operator does not have to supply the resistance to loosen or tighten the pipe  28  (See  FIG. 25 ). Then the pipe  28  is lifted slightly until the slip plate  38  can be removed. Drilling can then continue. A more detailed explanation of the process is provided below. 
     The major advantage of the change-over process came with the decision to use pipe segments that are three feet long instead of pipe segments that are longer, thus allowing the Kelly bar  46  to never be removed completely. Likewise a pump hose  90  and a swivel  92  never need to be removed. The pump hose  90  rests on hose hooks  94  attached to the beam  26 . The small pipe sections are also easy to lift and handle, and there is plenty of space to comfortably work on the changeover under the wheel  16 . Since there is no need to completely remove the Kelly bar  46  and raise and lower the pipe string, this process is much faster and easier than if longer pipe sections were used. 
     The final design of the drilling rig may optionally include a human powered pump. For example, a treadle pump system may be used. Regardless, in order to operate an effective mud rotary drill, a drilling fluid must be utilized that can remove the cuttings from the borehole. This process occurs by pumping a viscous slurry down the hole through the center of the drill pipe. The slurry then returns through the annulus between the borehole wall and the pipe with the cuttings created by the drill bit. This process can remove any type of cuttings by adjusting the viscosity of the slurry. As one example, a slurry additive called bentonite may be mixed with water to change the viscosity of the slurry. Since the cuttings are typically denser than the slurry, a combination of fluid pressure and shear stress act on the cuttings to propel them to the surface. 
     This results in pump requirements that can provide the necessary flow rate and fluid pressure, as is known in the art. A flow rate of fifty to one hundred gallons per minute is sufficient to create the necessary shear stresses on the cuttings and remove the cuttings at a quick enough rate. In order to provide adequate pressure, the pump needs to provide one foot of pressure head for every foot of depth of the borehole. This equates to a pressure of approximately 100 psi at a depth of 250 feet. Using these pump specifications, a table of pump power requirements can be calculated to determine pump needs, including the feasibility of operating a pump or pumps with human power. 
     Prototype Testing Results: 
     The final design was generated by proving many different concepts in preliminary prototypes. The first concept that was proved through testing was the ability to turn the pipe by walking in circles around the pipe. The test was very simple. A drill bit was spot welded to a pipe, and using pipe wrenches, the pipe was gripped and turned. During this test, one inch of depth was drilled in ten minutes. Originally, a system that would have the workers walk around the pipe twisting it as they walked in circles was envisioned. However, while testing this primitive prototype the idea that it would be much easier to be stationary and pass the wrench around was developed. This idea was selected as a part of the first fully functional prototype. 
     The first fully functional prototype was made of wood. This was done to reduce cost and decrease manufacturing time. A six-foot wooden wheel was used to harness human power to turn the pipe. This wheel had vertical handles and was pushed along by up to six workers that could stand around it in a circle. This design could be both operated with minimal effort and apply large amounts of torque to the drill pipe. This prototype was first tested in a small hole to ensure its feasibility. It met all expectations. The inertia of the wheel was able to keep the drill spinning in between pushes. This made for a smooth operation. The diameter of the wheel was a good size to operate and it would easily enable operators to apply enough torque. 
     After the two proof of concept tests, the fully functional wooden prototype was finished. The next test location was selected because of ease of access to water and clay soil conditions. Parts of the design that were being proved were the pumping system, the wheel, and the amount of downward pressure needed to drill. Through twenty-four minutes of continuous drilling a hole twenty-nine inches deep was drilled. This corresponded to an average drilling rate of one inch per minute. From this test, it was evident that one human-powered treadle pump as then being tested could not provide enough flow to lift all of the cuttings out of the hole. This caused the drill to get stuck easily and increased the effort required by the operators to turn the wheel. When extra downward pressure was added the drill dug a little faster at first but then the bit became stuck. It was determined that the ability to remove the cuttings needed to be improved by adding a second treadle pump before the next test. 
     The next two tests were located where the soil contained rocks varying in diameter from one-half inch to four inches. This condition is known as cobblestone. These tests were performed on two separate days using the wooden prototype. In these tests a second pump was added and bentonite was used to thicken the drilling mud. This was done in hopes that the cuttings would be removed more effectively. However, during the second test both treadle pumps broke because they could not generate the pressure needed to move the thick slurry. During the second test a mud pump was rented to enable the rest of the prototype to be tested. 
     The first four feet went just as the test in clay, but then the cobblestones were encountered. The cobblestones made the drilling slow and arduous and it became difficult to measure progress. Since there was no way to lift the drill bit off of the bottom of the borehole, the cobblestones were simply moved around instead of being cut through. Despite the slow progress the prototype was able to drill through rock and pull up the cuttings with a mud pump. From the borehole a rock was pulled that had the profile of the drill bit carved in, and the settling pond had shovels full gravel as proof that the drill had drilled through and removed rock. During these tests it became apparent that the design made it hard to access under and around the table to add and remove pipe. This resulted in modifications to the design. 
     The final design needed to include a way to remove the wheel to provide greater access in and around the pipe interchange area. Also, a hoist that would always be in place so that the pipe could be lifted and lowered while drilling. At this point it was decided that the initial implementation of the drilling rig would use a gas-powered pump to pump the drilling slurry. Although this uses a consumable fuel, it will use drastically less fuel than a conventional rig. 
     The final test with the final steel prototype was performed in sandy soil conditions. In all, twenty-seven feet were drilled in one and one-half hours. The actual time the drill was spinning was twenty-one minutes. The average time for adding a new pipe was two and one-half minutes. Extrapolating from this data it is calculated that it would take approximately eleven hours to drill 250 feet. This number may be optimistic because it assumes that no problems will be encountered with increased depth that have not already been encountered; however, a professional driller present at the test stated that there is no reason to believe that it becomes harder to dig with increased depth. This makes the 11 hour estimate more feasible. 
     The ability to raise and lower the pipe while drilling was an important part of this success. When the drill&#39;s full weight was resting in the hole the drill would dig too fast and the wheel would become very hard to turn. The winch was used to control the rate of penetration. This made the drill easy to keep at an approximately constant thirty rotations per minute. Being able to keep a constant rhythm while spinning the wheel greatly increases its sustainability. 
     Before this test, the process of adding new pipe had only been tested once. The procedure was very difficult, dangerous and took an entire team to perform. One of the main purposes of the final test was to test the modified pipe changing procedure. In the final design, the pipe sections were made smaller, for easy handling, and cleared out space to work underneath the wheel. During the testing it was very easy to change the pipe with only two people. Overall the results were very pleasing. More than a dozen boreholes fitted with functioning hand pumps have been completed using embodiments of the drill  10 . 
     Through testing, it was determined that the illustrated design is capable of drilling in several soil types including clay, sand and cobblestones. Although at times the progress may be slow, the drill  10  remains effective. The drill  10  is also easily transportable and robust. 
     Although not specifically illustrated in the drawings, several possible modifications to the design have been contemplated as a result of the testing process. As a whole the manufacturing of the device is accomplished with simple operations; however, there are a few components that are manufactured using mills. Ways to eliminate the need for these more complex operations could be sought. The drill  10  also contains many exposed moving parts, which might be better shielded to prevent the possible pinching of operators&#39; body parts. Finally, ways to reduce the overall cost of the device could be sought. Any such changes are embraced by the various embodiments of the invention. 
     In addition, tool joints might be used at every pipe connection to improve change-over and prevent over-tightening of joints. Also, a second slip plate  38  could be added to introduce redundancy to better prevent the pipe  28  from falling down the borehole during the removal of pipe sections. A sealed thrust bearing could be used between the wheel hub  60  and the wheel support  14  to protect against corrosion and to improve the performance of the wheel  16 . Finally, the wheel  16  could be provided with a unidirectional mechanism that can prevent the wheel  16  from being spun in the wrong direction and employing a method of stopping the wheel  16  while it is turning. Any of these changes are also embraced by the various embodiments of the invention. 
     Instructions for Use: 
     To further assist in understanding the illustrated embodiment of the invention, the following paragraphs provide instructions for using the drill  10 . First, an appropriate location to drill, directly above an aquifer, is located. An appropriate water source is also located to be used to pump down the drill pipe  28  while drilling. A flat, level location of appropriate size is then selected. 
     As is illustrated in  FIG. 2 , a six-inch pilot hole  100  is then dug to a depth of approximately one foot. A trench  102  that is approximately four inches wide, six inches deep, and eight feet long is dug extending out one side of the pilot hole. At the other end of the trench, two large three-foot square by two-foot deep basins  104  are dug connected by another short trench  102 . During the drilling process, silt and cuttings may need to be removed periodically from the trenches  102  and basins  104 . 
     The structure  12 , wheel support  14  and wheel  16  may be assembled at the same time as the slurry pump is set up. The slurry pump (not shown) is set up by placing the pump near the second basin  104  (that most distant from the pilot hole  100 ) and by feeding the pump inlet hose (also not shown) into the second basin  104 . It should be ensured that a filter is in place to avoid clogging the pump with small pebbles. At the beginning, the outlet hose (not shown) is placed inside the pilot hole  100 . 
     The trenches  102  and basin holes  104  are lined with Bentonite and all holes are filled with water until about three inches from ground level. The Bentonite will seal the trench and borehole walls reducing seepage and lowering the risk of down-the-hole cave-in. While the pump is running, cycling the water through the trench and basins, Bentonite is mixed in near the pump inlet hose, with vigorous stirring with a shovel. This is continued until the slurry is almost as thick as runny yogurt. Additional water or Bentonite may need to be added throughout the process to keep a proper slurry mixture. 
     Meanwhile, as shown in  FIG. 3 , the base  20  is placed to align a square opening of the legs  36  over the pilot hole  100 . The base  20  is positioned at an angle so that the trench  102  runs under cross braces and not the main uprights. Dirt may be filled in or removed as needed under portions of the base  20  until the base is level in all directions. 
     As shown in  FIG. 4 , both vertical columns  22 ,  24  are then inserted into the base  20 . The vertical columns  22 ,  24  are not yet bolted to the base  20  to allow for flexibility in positioning the various components of the structure  12 . Then, as shown in  FIG. 5 , the beam  26  (with its associated components) is placed on top of the vertical columns  22 ,  24 . Again, bolts are not yet inserted. Next, as shown in  FIG. 6 , the wheel support  14  is positioned at its appropriate position on the vertical columns  22 ,  24  and is bolted to the vertical columns  22 ,  24  as shown in  FIG. 7 . At this point, the vertical columns  22 ,  24  may be bolted to the base  20  and to the beam  26  as shown in  FIG. 8 , and the structure  12  and wheel support  14  are checked to ensure that the entire assembly is secure and solid. 
     Next, as illustrated in  FIGS. 9-14 , the wheel  16  is assembled. First, as shown in  FIG. 9 , the spokes  62  are inserted into the wheel hub and are secured as shown in  FIG. 10 . The cross braces  72  are then attached as shown in  FIGS. 11-13  to complete the wheel  16 . The wheel  16  is then checked to ensure it turns freely without interference or loose parts. When assembly of the wheel  16  is complete, the drill will appear as shown in  FIG. 14 . 
     As is shown in  FIG. 15 , the swivel  92  is threaded onto the Kelly bar  46 . The winch hook is then attached to the top of the swivel  92  as shown in  FIG. 16  and the winch  44  is used to raise the Kelly bar  46  to its maximum height. The bottom of the Kelly bar  46  is then placed inside the square hole  68  of the wheel  16  while being kept at or near its maximum height. As shown in  FIG. 17 , the first segment  110  of the pipe string is assembled by ensuring that the first section of pipe  28  is securely connected to a drill bit  112  by one of the couplers  80 . Another coupler  80  is then attached atop the section of the pipe  28 . 
     The first segment  110  of the pipe string is placed down into the pilot hole and is aligned underneath the Kelly bar as shown in  FIG. 18 . The Kelly bar and coupler  80  are then connected by first ensuring that the threads are engaged and then turning the wheel  16  clockwise while holding the drill pipe in place with the pipe wrench  82 , as shown in  FIG. 19 . The winch  44  is used to slowly lower the Kelly bar while this is done. The pump hose  90  is then attached to the swivel  92  using the proper hose connections and while the pump is not running, as illustrated in  FIG. 20 . The pump hose  90  is rested on the hose hooks  94  as shown in  FIG. 21 . The drill  10  is then ready to be staffed by four workers as shown in  FIG. 22 , with one worker operating the winch  44  and three workers operating the wheel  16 . Additional workers may operate the slurry pump, clear the trenches  102  and basins  104 , and may ensure that sufficient slurry is prepared and available. The workers may rotate through their positions from time to time as drilling proceeds for rest purposes. 
     The slurry pump should always be running before beginning to spin the wheel  16  to drill. Thus, the pump is run and the worker ensures that slurry comes out the bottom of the drill bit  112 . At later stages, the worker ensures that slurry is rising in the borehole. Any leaks in the hose connections are fixed, then the wheel  16  is spun clockwise at a comfortable rate, such as thirty rotations per minute. Safety is ensured by keeping hands and arms out of the path of the spokes  52  and rods  70 . Meanwhile, the operator of the winch  44  uses it to slowly lower the pipe string at a rate that allows the wheel  16  to continue to spin freely from the inertia of the wheel  16 . 
     Controlling the descent of the pipe string helps ensure efficient drilling: if the wheel  16  stops immediately after being released, the pipe string should be pulled up using the winch  44  until the wheel  16  spins freely again. When the descent rate is too quick, the drill bit  112  becomes buried in the bottom of the borehole and will become difficult to turn, while a proper slow rate allows the slurry to flush excavated material away so the drill bit  112  does not become buried at the bottom of the borehole. If rock or harder soil is encountered, it may be necessary to allow the drill bit  112  to fully rest on the bottom to grind away the rock or harder soil, and the wheel  16  will become harder to turn. 
     Drilling continues until the top of the Kelly bar  46  is approximately flush with the top of the wheel hub  60  as shown in  FIG. 23 . In loose soil, this may take approximately two minutes. The winch  44  is then used to raise the pipe string slightly, until the slip plate  38  will fit under the bottom coupler  80  as shown in  FIG. 24 . The slurry pump is then run for another three to five minutes without spinning the wheel  16  to flush out all cuttings. 
     After the cuttings are flushed, the slurry pump is stopped, and the pipe wrench  82  is snugged around the coupler  80  as shown in  FIG. 25 . The assembly is turned until the wrench  82  rests against the wrench stop  84  as shown, then the wheel  16  is turned counterclockwise to unthread the Kelly bar  46  from the coupler  80  and pipe string in the hole. The wheel  16  may be harder to turn than when drilling, and the winch  44  can be used to slowly raise the Kelly bar  46  as it unthreads. Once unthreading is complete, the winch  44  is used to raise the Kelly bar  46  to its maximum height as shown in  FIG. 26 . 
     A new segment of pipe  28  is prepared by attaching a coupler  80  to one end and by generously spreading thread grease on the open threads of the pipe  28  and inside the coupler  80  as indicated in  FIG. 27 . The new segment of pipe  28  is inserted into the coupler  80  resting on the slip plate  38 , and the new segment of pipe  28  is gently threaded into the coupler by hand, ensuring that the threads align, as shown in  FIG. 28 . The winch  44  is then used to lower the Kelly bar until it rests on top of the newly added segment of pipe  28 , as shown in  FIG. 29 . The wheel  16  is then carefully (to avoid stripping the threads) turned clockwise while slowly lowering the Kelly bar  46  with the winch to thread the Kelly bar into the coupler  80  of the new segment of pipe  28 . Then, as shown in  FIG. 30 , the wrench  82  and slip plate  38  are removed (the winch  44  may be used to raise the pipe string slightly if necessary), the slurry pump is reengaged and the flow of slurry checked, and drilling can continue as before. 
     When the desired borehole depth is reached (measured by the number of segments of pipe  28  that have been added to the pipe string multiplied by the segment length), the pump is left running for ten to fifteen minutes to flush all cuttings from the borehole. Then, the slurry pump is no longer needed, and the pipe string can be removed from the borehole as will be illustrated in  FIGS. 31-42 . As all components referred to in  FIGS. 31-42  have been previously labeled and discussed, they are not shown in  FIGS. 31-42 . 
     The pipe string removal process occurs first by using the winch  44  to lift the pipe string until the slip plate  38  and wrench  82  can be positioned as shown in  FIG. 31 . Then the pump hose  90  is removed from the swivel  92  and hose hooks  94  as shown in  FIG. 32 . The Kelly bar  46  is unthreaded from the pipe string by turning the wheel  16  counterclockwise, then the winch  44  is used to raise the Kelly bar  46  to its maximum height as shown in  FIG. 33 . The Kelly bar is then removed as shown in  FIG. 34 . As shown in  FIGS. 35-37 , the cross braces  72 , spokes  62 , and wheel support  14  are subsequently removed (or can be removed together if the weight is not excessive compared to the available manpower). 
     A hook  114  is then threaded into the remaining top coupler  80  by hand, securing the pipe string with the pipe wrench  82 , as shown in  FIG. 38 . The winch rope is attached to the hook  114 , and the winch  44  is used to raise the pipe string, sliding through the slip plate  38  for safety, as shown in  FIG. 39 . Throughout the process, care should be taken to ensure that the slip plate  38  remains in place as much as possible to prevent loss of the pipe string down the borehole, and two slip plates  38  may optionally be used to ensure that one slip plate  38  always secures the pipe string. Once two pipe segments have been raised up as shown in  FIG. 40 , the slip plate  38  is repositioned to secure the lowermost visible coupler. Two pipe wrenches  82  are then used as shown in  FIG. 41  to untighten the two pipe segments from the lower coupler  80 . The two pipe segments are then removed as shown in  FIG. 42 , and the process repeats from  FIG. 38  until the entire pipe string has been removed. 
     Once the entire pipe string has been removed, the slurry is removed from around the borehole, such as by using a bailer or other method, and a plastic or metal casing is inserted the length of the borehole. Gravel is then packed around the outside of the casing, and the pump and connecting pipe is lowered to the bottom of the hole. The Bentonite slurry used to drill the hole is flushed out, and the ground surface around the casing is sealed with cement or with another method. Then a water wheel or pump is installed at ground level to draw up the water. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Summary:
A human-powered borehole drill bridges the gap between large drilling rigs and the other less-effective manual methods. Intended mainly for developing countries, the design is affordable and also extremely simple, as very little product support or spare parts will be needed. The drill uses conventional drill pipe and drill bits allowing the drill system to mimic more conventional methods of drilling and existing hardware to maintain uniformity in drilling and easier access to more drilling products.