GB766242A - Rotary expansible well drill bits - Google Patents

Abstract

766,242. Borehole drill bit. KAMMERER, A. W. March 23,1955, No. 8462/55. Class 85. A rotary expandable well drilling bit for enlarging boreholes has a body, carrying expandable cutters, slidably splined and centralized on a mandrel connectable to a drill string and has hydraulic means to move said body axially of said mandrel to expand the cutters, the force expanding said cutters decreasing or remaining substantially constant as the cutters expand. The upper end of the mandrel 13 is connected to the drill string B and the lower end has flattened sides 83, Fig. 5, to allow the body 14 to slide axially on but not rotate relative to the mandrel. Arms 23 carrying roller cutters 27 are pivoted by pins 25 in slots in the bottom of the body 14. To expand the arms 23 fluid is pumped down the drill string B when the back pressure caused by the restriction 49 is transmitted through passages 77 to the under side of a shoulder 70 attached to the body 14 causing the body 14 to slide upwards relative to the mandrel 13 until the tapered bottom 18 of the body contacts the tapered end 17 of the mandrel so centralizing the body relative to the mandrel. During this movement an expander 38 on a tubular member 47, extending from the mandrel, co-operates with curved surfaces 30 on the arms 23 to expand them when they are held expanded by surfaces 32 on them contacting a surface 39 on the expander. The surface 30 is so curved that a common tangent 91 at the point of contact 90 of the surface 30 and the expander 38 makes a decreasing angle with the plane normal to the axis of the mandrel as the arms expand: When pumping stops and the string B and mandrel 13 are raised a shoulder 96 on the expander 38 contacts shoulders 97 on the arms 23 to contract them. If due to sand &c. in the annular space 22 below the shoulder 70 the arms 23 do not contract the mandrel is raised until the arms 23 contact a shoe F on the well casing D when sufficient upward force will cause snap rings 20,65,75 to contract in their V-shaped grooves and allow the shoulder 70 and a head 63 thereabove together with the sand to move upwards relative to-the body 14 allowing the arms to contract.