Patent ID: 8113302

Claim:
A drilling tool including a drill shaft for transmitting axial load, said drill shaft comprising a series of coaxial ring members connected together such that adjacent ring members are flexible in an axial plane relative to each other; wherein: each ring member is connected to an adjacent ring member by a connecting member arranged to transmit torque therebetween; axial supports extend between the adjacent ring members so as to transmit the axial load therebetween the connecting member and the axial supports allow the adjacent ring members to bend in one axial plane while remaining stiff in another axial plane offset by up to 90°; and the connecting member and the axial supports are constituted by separate physical structures, the axial support comprising at least two axial links extending between circumferentially aligned points on the adjacent ring members, and the connecting member comprising inter-engaging teeth projecting from the adjacent ring members.