JO1906B1 - System for in situreplacment of cutting means for aground drill - Google Patents

Abstract

A retractable drill bit system 10 comprises a drive sub 18 which is adapted A retractable drill bit system 10 comprises a drive sub 18 which is adapted for connection ‎to a lower end of a drill 12, a tool 20 for installing and retracting drill bit segments 22 ‎from the drive sub 18, and an insert 24 for selectively locking the bit segments 22 to an ‎end of the drive sub 18 and releasing the bit segments 22 to and end of the drive sub 18 ‎and releasing the bit segments 22.‎ A plurality of recesses 5B are formed about, an inner circumferential wall at one end of ‎the drive sub 18 and a landing seat 32 formed about the inner wall upstream of the ‎recesses 58, the area of the interior wall between the landing seat 32 and recesses 58 ‎profiled with a series of tapered and level surfaces,‎ The tool 20 includes a slidable cradle 176 extending from one end about which the bit ‎segments 22 are held during installation and retrieval, the bit segments 22 being held in ‎place about the cradle by an elastic band 198. the insert 24 is provided at one end with a ‎series of keyways 218 which located over the bit segments 22 when the bit segments are ‎locked to the drive sub 18, the insert 24 is always retained within the drive sub 18,‎ Bit segments 22 are carried by the tool 20 to the drive sub 18 and locked in place by the ‎insert 24 the tool 20 can then be withdrawn the drill 12 operated in the normal manner, to ‎retrieve the bit segment 22, the tool 20 is relowered into the drill and then withdrawn a ‎short distance to retract the insert 24 to so that the bit segments 22 collapse back onto the ‎cradle 176 and can then be withdrawn from the drill 12.‎