Patent ID: 7891442

Claim:
A drilling tool including a drill shaft for transmitting an 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 connects to an adjacent ring member by a connecting member arranged to transmit torque therebetween; a plurality of axial supports extend between adjacent ring members so as to transmit axial loads therebetween; the connecting member and said plurality of axial supports allow adjacent ring members to transmit axial loads therebetween; the connecting member and said plurality of axial supports comprise separate physical structures; the plurality of axial supports comprises at least two axial links extending between circumferentially aligned points on adjacent ring members; and the connecting member comprises pairs of links, each of said pairs of links extending between a connection point connection point on one ring member to a plurality of connection points on an adjacent ring member circumferentially offset by up to 90°, such that each connection point is connected by one of said pairs of inclined links to the adjacent ring.