An underreamer for connection with a rotary pipe string includes inner and outer body sections which form a body structure to provide a fluid flow path therethrough for communicating with piston and cylinder means formed between the body sections for receiving drilling fluid to effect telescopic movement between the body sections permitting engagement of cutter arms and support of said cutter arms on the outer body of the underreamer utilizing a slideable, non-pivoting stop block. Cutter arms are pivotally mounted on the inner body section and, upon engagement of the cutter arms to effect underreaming are fully supported on the outer body section thereby minimizing damage from vibration and repeated use on the threaded inner body sections.

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application incorporates U.S. Pat. No. 4,614,242 herein by reference as background information for this application. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC OR AS A TEXT FILE VIA THE OFFICE ELECTRONIC FILING SYSTEM (EFS-WEB) 
     Not Applicable. 
     STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     (1) Field of Invention 
     This invention relates to a hole enlargement arrangement and method of use; more specifically to an underreamer that provides a cutter arm assembly supported, upon extension, by a slideable, non-pivoting stop block which passes all shocks absorbed by the cutter arm to the outer body of the tool. 
     (2) Description of Related Art including information disclosed under 37 CFR 1.97 and 1.98 
     Various types of hole enlargement arrangements have been heretofore employed and are currently in use. In the devices with which applicant is familiar, a body structure formed of inner and outer body sections has cutter arms pivotally secured on the outer body section and a piston and cylinder means defined between the inner and outer body sections receives hydraulic fluid to effect telescopic movement of the body sections in one relative direction whereupon a cam surface mechanically engages and forces cutter arms out to an underreaming or bore hole enlarging position. This arrangement is more clearly shown in U.S. Pat. No. 4,614,242, which is incorporated herein by reference as background information for this application. 
     After the underreaming operation is completed, the cutter arms of the prior art devices are generally then retracted by reducing the pump pressure and raising the operating string on which the body structure is supported so that the expanded or projecting arms engage the shoulder formed at the point of commencement of the underreaming. Continued raising of the operating string exerts a force on the extended cutter arms to move the arms inwardly to a retracted position relative to the body structure. 
     When the arms of the underreamer are extended during hole enlarging operations to underream or drill an enlarged portion in a bore hole, there are various forces that act upon the cutter arms, such as an upwardly directed force on the outer projecting end of the arm due to the weight of the operating string during underreaming reacting with the well bore. 
     In the prior art devices, these forces are transmitted from the cutter arms to the pivot arrangement of the cutter arms on the body structure and to the cam surface which is relied upon to move and maintain the cutter arms in an extended cutting position, then to the yoke and threads connecting the inner tube elements. These forces may be substantial and, in some instances, repeated use will damage or break components of the underreamer where the inner body was threaded to the yoke assembly. Wear from continued use of the device causes vibration of the arm and underreamer in extension, causing or accelerating further wear, damage or failure of these types of tools. 
     The present invention provides an arrangement that assists in overcoming the above problems by transferring all mechanical forces acting on the cutter arm to the slideable, non-pivoting stop block and the outer body. The solidity of the stop block seated against the outer body of the underreamer also provides additional strength to deformation from the lateral forces acting upon the underreamer in contact with the well bore. As an additional benefit, the improved underreamer arm assembly can retrofit an existing underreamer body with these new components. 
     The inner body structure and a cooperative support arrangement move the stop block and arms into position on the outer body section. This cooperative support to yoke arrangement moves the cutter arms to the extended cutter position. The cooperating support arrangement is relieved of supporting the extended arms. Because the stop block and outer body fully support and assist in distributing the loads and forces employed during the bore hole enlarging operation, the support provided by the stop block and outer body also increase the mechanical advantage tending to maintain the cutter arms in an expanded position during underreaming. The shape of the stop block accommodates a full metal-to-metal contact between the base of the cutter arm and outer body and thereby avoids passing these large shock loads on to the threaded or weaker internal components of the underreamer device. 
     BRIEF SUMMARY OF THE INVENTION 
     An improved underreamer cutter arm assembly provides a cutter arm with a lateral slot on at least one lateral side of the cutter arm and one or more cutter elements on a distal end of the cutter arm; a moveable yoke assembly engaging an interior surface of an underreamer pinned to a proximal end of the cutter arm, and a stop block slideably engaged on an interior surface of the underreamer positioned between the cutter arm and an outer surface of the underreamer; whereby the stop block abuts the outer body of the underreamer upon full extension of the cutter arm from the underreamer, transferring all mechanical forces acting on the cutter arm to the stop block and the outer body. 
     This improved cutter arm can support a variety of cutter means frequently used on underreamers in the art. For example, the cutter means can be either roller cone cutters, hardened cutter elements, such as tungsten carbide buttons, or polycrystalline diamond cutters (PDC) without deviating from the spirit or intent of this invention, positioned on the distal end of said arm, depending on the type of formation in which the tool is to be used. 
     The disclosed embodiment permits the assembly of an improved underreamer having a fluid flow path comprising a body structure including an inner and an outer telescopic body section having circumferentially spaced, longitudinal slots for receiving the cutter arms; one or more moveable cutter arms pivotally supported on a distal end of the inner telescopic body section; a yoke on the inner body section slideably engaging one or more stop blocks and pivotally connected to the one or more moveable cutter arms; longitudinally extending grooves on at least one lateral side of the one or more moveable cutter arms cooperatively engaged with a projection for selective movement of the cutter arms in the outer body section to pivotally support the cutter arms in the longitudinal slots of the outer body section; and, a fluid actuated piston to move the inner body section, moving the one or more cutter arms between the projections and the grooves to expand the cutter arms outwardly of the outer body section and to seat the stop block against the outer body. 
     This improved underreamer also thereby provides the additional feature permitting a plurality of field-replaceable stop blocks adjustably limiting the telescopic movement of the body sections, allowing a range of hole enlargement diameters that may be attained with the same underreamer body. The cutter arm provides the ability to interchange the stop block; lengthening the block to shorten the extension of the cutter arm from the lateral surface of the underreamer, or shortening the block to increase the extension of the cutter arm from the lateral surface of the underreamer. 
     The longitudinally extending grooves on at least one side of the cutter arms extend diagonally relative to the longitudinal axis of the cutter arms and, with a resilient member move the inner body section to retract the cutter arms in the longitudinal slots in the outer body section. 
     Other objects and advantages of the present invention will become apparent from a consideration of the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view illustrating a preferred embodiment of the bore hole enlarger with the cutter arms in retracted position. 
         FIG. 2  is a sectional view of the tool with the cutter arm in the extended position. 
         FIG. 3  is a sectional view on the line  3 - 3  of  FIG. 1  to better illustrate certain structural details. 
         FIG. 4  is a sectional view on the line  4 - 4  of  FIG. 1  to illustrate an embodiment of the cooperative means on the outer body section and the cutter arms. 
         FIG. 5  is a sectional view on the line  5 - 5  of  FIG. 1  to illustrate an embodiment of the cooperative means on the outer body section and the cutter arms. 
         FIG. 6  is an end view of the stop block; 
         FIG. 7  is a perspective side view of the stop block showing the inner railed slot; and, 
         FIG. 8  is a top perspective view of the stop block. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the underreamer of the present invention in the closed or relaxed position.  FIG. 2  shows the underreamer of the present application in the energized position with the cutter arm engaging a well bore WB. 
     Directing our attention to the underreamer shown in  FIG. 1 , the upper tubular body  10  provides a bore  14  allowing hydraulic communication through the upper body  10  from a drillstring (not shown) which is threaded to the upper male threads  12  of upper body  10 . Upper body  10  also provides a counterbore section  16  into which is fitted upper tube assembly  26  providing a set of hydraulic seals  44  to provide a dynamic seal on the tube in the counter-bored section  16  of the upper body  10 . 
       FIG. 1  also shows a threaded connection means  12  on upper body  10  allowing connection in a drill string (not shown) and permitting the flow of drilling fluid through the upper tube assembly  26  through longitudinal passage  14 . Upper body  10  is counter-bored  16  to provide a means for inner body, shown generally at  9 , to move longitudinally in the upper body  10  and lower body  20  in the following manner. 
     The upper piston of the tube assembly  26  engages an interior wall of an annular sleeve  29  inserted in an upper threaded throat  27  of the lower body  20 . This sleeve  29  portion is held in a fixed position in the lower body  20  by set screw  29   a . Counterbore  16  also provides chamber  18  with fluid passage  22 , enclosing a spring  23  which provides resistance to the extension movement of the inner body when pump pressure is increased and fills the space  28  through the port  24  to move the cutter arm  32  into engagement with the well bore for underreaming. 
     Tube assembly  26  provides a passage  24  to chamber  28  to provide hydraulic pressure from a longitudinal passage  14  to move the piston assembly connected to yoke  30  and cutter arm  32 . Yoke  30  provides a rail permitting movement of stop block  34 . Stop block  34  has a complementary slot for relative movement on yoke  30 . Yoke  30  is threadedly connected to tube assembly  26  by threaded connection  38  and is prevented from loosening by set screw  40 . Dynamic seals  42 ,  44 , and  46  are provided between the hydraulically sealed tubes  26 ,  36  to seal the tube assembly within the assembled underreamer body  10 ,  20 . The cutter arm assembly  32  has a slot  48  into which is assembled a cam  50  retained in the body by pin or other means  52  to thereby permit relative lateral cutter arm  32  movement thereby engaging the cutter elements  54  on a distal end outward of the body  20  on a wellbore (not shown in  FIG. 1 ). Lower tube assembly  36  is seated on shoulder  35  onto which is placed upper tube  26  which are then affixed to the yoke assembly  30  by set screw  40  to prevent disengagement of the inner body assembly  9 . Seal bushing assembly  46  is mounted in the distal end to support the dynamic sealing elements and is retained thereon by a snap ring  47  or other device, all in a manner well known in this art. 
     As further shown in  FIG. 1 , inner body  9  comprised of an assembly providing a bore  17  communicating from the interior diameter  14  of an underreamer, comprised of an upper body  10  connected to lower body  20 , providing a jetting nozzle  100  in a manner well known in this art and providing hydraulic pressure on the drill bit or motor which are normally found on the distal end of the drill string. 
       FIG. 2  is another view of the improved underreamer of the present application showing the cutter arm in extension after pump pressure has moved the inner body up and caused each arm to move outwardly of the body. All of the structure shown in  FIGS. 1 and 2  are described in U.S. Pat. No. 4,614,242, with the exception of the cooperating stop block  34  with the upper body  10  connected with lower body  20  to form the outer body of the underreamer. As shown in  FIG. 2 , an increase in pump pressure moves the piston arrangement, i.e. the top  26  of the inner body or tube assembly  9  providing a dynamic seal  45   a  between the outer diameter of the inner body  9  and the inner diameter of the sleeve portion  29 , having lower seal  45 . 
     As may be readily appreciated, increased pump pressure moves drilling mud from the inner longitudinal bore  17  through port  24  into the space  28  moving the piston upward and compressing resilient member  23 . This action moves yoke  30  drawing the stop block  34  across the unencumbered space  62 , as seen in  FIG. 1 , into engagement with the shoulder  60  of lower body  20  which together with upper body  10  forms the outer body of the underreamer.  FIG. 2  also shows the relative movement of the pin  66  from the relaxed or unextended position and pin  68  of the extended position of the cutter arm  32  yoke assembly  30 . 
       FIG. 3  is a cross-sectional view of the stop blocks  34 , shown on  FIG. 1  at line  3 - 3 , showing lower tube  36  providing passage  17 ′ and yoke  30  on which each stop block  34  is slideably engaged.  FIG. 3  also more clearly shows the relative distribution of the stop block assemblies  34  on each rail of the yoke assembly  30 . 
       FIG. 4  is a cross-sectional perspective through the view, shown in  FIG. 1  at line  4 - 4 , providing a view of the relative location of the cams  50  in grooves on each cutter arm  32  fitting around the central passage  36  to permit relative outward movement of the cutter arm assembly  32 . Each side of the cam  50  is either provided with a pin  50   a  for engaging the underrreamer body  20  or another method of fixing of said cam in said groove by means well known in the trade at  52 . 
       FIG. 5  is a cross-sectional view of the pivot pin  66  and stop block  34  connection through the line  5 - 5  shown in  FIG. 1  detailing the eccentric screws  70  which retain the pivot pins  66  in each cutter arm assembly  32 . Each screw  70  is retained in the body with a snap ring  72 . Tube  36  provides a fluid passageway  17 ′ through the yoke assembly  30 . 
       FIG. 6  is an end view of the stop block assembly  34  of the present embodiment showing the slot  600  running through the body  34  permitting slideable engagement with a rail on each portion of the yoke (not shown) and providing a shoulder  608  for engaging the yoke (not shown) and the stop block  34  in slideable engagement. The narrow portion of yoke  30  is affixed to the stop block  34  through the passageway  606 . Stop block  34  also provides an upper surface  602  having a bevel  604  for conformity of the circular profile of the underreamer body  20 . 
       FIG. 7  is a side view of the stop block assembly  34  of the present embodiment showing the arcuate shaped lower end  614 . The figure shows a side view of the stop block  34  having a lower surface profile  614  which accommodates the end of cutter arm (not shown) and which, upon movement of the stop block  34  in the lower body (not shown, but shown as  20  in  FIGS. 1 and 2 ), engages the upper end  612  with the body (not shown, but shown as  20  in  FIGS. 1 and 2 ). Lower profile  614  is designed to fully support the end of cutter arm (not shown, but more fully shown as  32  in  FIGS. 1 and 2 ) in its extended position upon movement of the stop block  34  into contact with the outer body (not shown, but shown as  10  and  20  in  FIGS. 1 and 2 ) at face  612  on the upper end of the stop block  34 . Bevels  610  are provided on the upper end of stop block  34  to allow movement of the stop block  34  into full flush engagement with the upper body  20  shoulder at  60 , as shown in  FIGS. 1 and 2 . The stop block is shaped to accommodate the pivot pin assembly (not shown in this view, but shown as  66  and  68  in  FIGS. 1 and 2 ) and the movement of the cutter arm (not shown) outward from the body  20  to hold the cutter arm in full engagement with the well bore (not shown). 
     The flattened, shaved or beveled  604  exterior surface  602  allows the stop block  34  to conform with the circular profile of the underreamer body (not shown). The inner slot shown in the dashed area  600 ,  606  engages a rail (not shown) on the yoke assembly to slideably move and retain the stop block during operation within the underreamer body as previously described. 
       FIG. 8  is a top view of the stop block assembly  34  of the present embodiment showing in the dashed areas, the inner rail slot location  600   a ,  606   a  cut through the stop block  34  and slideably engaging the rail on the yoke assembly as previously described.  FIG. 8  also shows the upper surface  602 , the bevels  610  on the upper surface  612  as previously described and the lower surface  614  for engagement of the end of the cutter arms, all as previously described. 
     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.