Drill bit and system for drilling a borehole
A drill bit for drilling a borehole in an object, the drill bit having a central longitudinal axis and comprising a bit body provided with a central shank for connecting the drill bit to a drilling system. The drill bit further comprises at least one cutting arm, each cutting arm being provided with a set of cutters for cutting the object and being coupled to the bit body allowing the cutting arm to pivot between a radially retracted position and a radially expanded position.
1. A drill bit for drilling a borehole in an object, the drill bit having a central longitudinal axis and comprising a bit body provided with a central shank for connecting the drill bit to a drilling system, the drill bit further comprising at least one cutting arm, each cutting arm being provided with a set of cutters for cutting the object and being coupled to the bit body via pivot means allowing the cutting arm to pivot between a radially retracted position and a radially expanded position, the drill bit being provided with support means for supporting the at least one cutting arm in the radially expanded position thereof, wherein the support means is arranged to transmit at least a portion of the rotational torque generated during drilling from the at least one cutting arm to the bit body so as to reduce or prevent transmission of said rotational torque via the pivot means, wherein the support means is arranged to transmit axial loads from the cutting arm to the bit body when the at least one cutting arm is in the radially expanded position, wherein the support means comprises an axial end surface on the bit body, for transmitting said axial loads from the at least one cutting arm to the bit body, and said axial end surface includes a profile configured to transmit a portion of said rotational torgue from the cutting arm to the bit body.
2. The drill bit of claim 1 , wherein the support means is further arranged to transmit an axial compressive load from the at least one cutting arm to the bit body.
3. The drill bit of claim 1 , wherein the support means is further arranged to support a radial compressive load from the at least one cutting arm to the bit body.
4. The drill bit of claim 1 , wherein the support means is arranged to transmit a majority of the rotational torque, preferably essentially the full rotational torque, from the at least one cutting arm to the bit body.
5. The drill bit of claim 1 , further comprising a pilot section provided with pilot cutters arranged for pre-cutting a pilot borehole ahead of the at least one cutting arm.
6. The drill bit of claim 5 , wherein the pilot section is axially movable with respect to the shank whereby the at least one cutting arm is coupled to the pilot section for controlling the pivoting of the at least one cutting arm.
7. The drill bit of claim 6 , wherein the pilot section is coupled to a hydraulic system for controlling said axial movability.
8. The drill bit of claim 1 wherein the drill bit is a drill bit for drilling a borehole in an earth formation.
9. The drill bit of claim 1 wherein said profile includes teeth.
10. The drill bit of claim 1 wherein said profile includes a stepped profile.
11. The drill bit of claim 1 wherein said cutting arm does not engage said profile when said cutting arm is not in said radially expanded position.