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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 61/271,414 filed Jul. 21, 2009 by Alan L. Nackerud, which is incorporated by reference herein. 
     
    
     BACKGROUND AND FIELD OF INVENTION 
       [0002]    This invention generally relates to bore hole tools, including, but not limited to underreamers, section mills, casing cutters, casing scrapers and drill string centralizers, hereinafter collectively referred to as Bore Hole Tool(s). Most conventional Bore Hole Tools which expand in diameter when operating have expandable blades or cutters which are opened by pump pressure and returned to a closed position by a spring or other mechanical retraction device when not in use. However, some Bore Hole Tools do not have a spring or other mechanical retraction device for said blades but rather are free to rotate on their axis at any time, and are activated or opened when fluid is pumped and expelled through the blades and/or rotation of the drill string is applied. In a vertical well bore the Bore Hole Tool blades close by gravity upon cessation of pumping and cessation of rotation which allows the drill string to be advanced or retracted within the bore hole without the blade or blades catching the side walls of the well bore. One problem with said tools without a mechanical retraction device is that in a horizontal or angled well bore they do not always readily close or remain in a closed position when desired due to gravity pulling the rotatable downward blade against the well bore sidewall. Advancement or retraction of the drill string in a non-operating mode can thereby be problematic. The present invention is an improvement to said Bore Hole Tools and alleviates this problem by having one or more retention magnets positioned in the body or blades such to keep the blades in a closed position when fluid is not being pumped through the drill string and the drill string is not being rotated. At least one full slow rotation of the drill string allows the blade or blades to close into the body whereby the retention magnets keep the blades retracted in the body in a non-operating mode. The retention magnets are of a predetermined sufficient strength to keep the blades in a closed position when fluid is not being pumped through the drill string and the drill string is not being rotated, however said magnets are of a predetermined limited strength which allows the blades to open upon sufficient pumping or rotation. The present invention thereby allows the drill string and Bore Hole Tool to advance or retract within the bore hole when in a non-operating mode. 
       SUMMARY OF THE INVENTION 
       [0003]    The above and other advantages and features will become more readily appreciated and understood from a consideration of the following detailed description of different embodiments when taken together with the accompanying drawings in which: 
     
    
     
       DRAWINGS-FIGURES 
         [0004]      FIG. 1  is a side view of assembled tool in closed position; 
           [0005]      FIG. 2  is a side view of assembled tool in closed position rotated 90 degrees; 
           [0006]      FIG. 3  is a section view of assembled tool through the magnetic retention device with blades in a closed position; 
           [0007]      FIG. 4  is a side view of assembled tool in an open position; 
       
    
    
     DRAWINGS-REFERENCE NUMERALS 
       [0000]    
       
           10 . body 
           11 . blade one 
           12 . blade two 
           13 . blade one magnet 
           14 . blade one magnet opening 
           15 . blade one magnet encasement material 
           16 . blade two magnet 
           17 . blade two magnet opening 
           18 . blade two magnet encasement material 
           19 . blade cutters 
           20 . blade fluid ports 
           21 . blades slot 
           22 . blades main fluid bores 
           23 . body main fluid bores 
       
     
       DETAILED DESCRIPTION 
       [0022]    Referring to the drawings, there is illustrated in 
         [0023]      FIGS. 1 through 4  one form of the present invention being an improved Bore Hole Tool with magnets  13 ,  16  for steel blades  11 ,  12  retention in the body  10  when the Bore Hole Tool is in a closed position and in a non-operating mode. In  FIG. 1  the Bore Hole Tool has a top threaded connection and a bottom threaded connection to allow connection to a drill string. The Bore Hole Tool has a bore through the top threaded connection. Said bore intersects angled bores in the body  10  which lead to and intersect body main fluid bores  23  which run down both sides of the body  10  which then intersect angled bores back into a bore leading out the bottom threaded connection and into the preceding drill string and any preceding bottom hole assembly. The Bore Hole Tool body main fluid bores  23  also intersect bores into blades  11 ,  12  and main fluid blade bores  22  whereby fluid can travel into and through blades  11 ,  12  and expel out blade fluid ports  20  which assist the Bore Hole Tool opening. The blades  11 ,  12  are free to move on their pin or bearing axis near the top of the Bore Hole Tool whereby rotation of the drill string allows centrifugal force to also assist opening of the Bore Hole Tool blades  11 ,  12 . When the Bore Hole Tool is in a non-operating mode, retraction of the blades  11 ,  12  back into the Bore Hole Tool body  10  is caused by cessation of pumping fluid and cessation of rotation of the drill string whereby gravity causes the blades to close by gravity in a vertical well bore. In an angled or horizontal well bore, closure of the blades  11 ,  12  is assisted by one or more slow rotations of the drill string whereby gravity cause the blades  11 ,  12  to retract into the body  10 . The blades remain in a closed or retracted position by one or more magnets  13 ,  16  which are placed in the magnet openings  14 ,  17  in the body  10 . This is especially helpful when the Bore Hole Tool is working in an angled or horizontal well bore where gravity would otherwise pull the blade able to rotate downward to an open position whereby it may catch the side wall of the well bore. The magnets  13 ,  16  could also be positioned in the blades  11 ,  12  rather than the body  10  with the same result of blade retention. The magnets  13 ,  16  are retained in the magnet openings  14 ,  17  by encasement material  15 ,  18  being an epoxy or other encasement material means or mechanical suspension means such as pins. The magnets  13 ,  16  can be in a plate form or cylindrical or other shape. The magnets  13 ,  16  are suspended in the slot within the encasement material  15  such that direct contact with the metallic Bore Hole Tool body  10  is not made or minimized whereby the magnetic force is maintained. The magnets  13 ,  16  are positioned to make contact, or near contact with the blades  11 ,  12  when said blades  11 ,  12  are in a closed position. The magnets  13 ,  16  are of sufficient size, shape and magnetic strength and positioned such in the body  10  to allow retention of the blades  11 ,  12  in a closed position. The magnets  13 ,  16  are however of a limited size, shape and magnetic strength and positioned such in the body  10  to allow opening of the blades  11 ,  12  when adequate fluid is pumped through the Bore Hole Tool or adequate rotation of the drill string is made to actuate the Bore Hole Tool. 
         [0024]    It is therefore to be understood that even though numerous characteristics and advantages of the present embodiment have been set forth in the foregoing description, together with the details of the structure and function of the embodiment, the disclosure is illustrative only, and changes may be made within the principles of the embodiment to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed and reasonable equivalents thereof.

Summary:
A bore hole tool which uses magnetic means to retain the tool in a closed or collapsed position when in a non-operating mode while able to release from the magnetic retention to an open or enlarged position when said tool is in an operating mode when rotation is applied or fluid is pumped through said tool.