Taper thread in drill retrieving device - has asymmetric profile with support flank at 86 to 98 degrees to diametric plane

摘要

The conical screw thread connection has an a-symmetric thread profile of which the support flank of the thread is at an angle of which 86 deg. to 98 deg. to a plane at right angles to the centre line. This screw connection may be used in a device for retrieving the drilling tool from a bore in an emergency, in which device an element (1) is connected with a co-axial hollow internal rod (2). The end of the rod (2), is, in that case, secured to a co-axial conical internal bush (3) with external conical thread whilst the element (1) contains an external conical bush (4) with corresponding internal conical thread. The support flank of the thread profile is at an angle of 88 deg.30' to 89 deg.40' to a plane at right angles to the centre line. The bush (4) is preferably thin-walled and leaves an annular chamber (c) between itself and the element (1) over the full length of the thread.