METHOD OF PRODUCING TIGHT THREADED JOINTS OF OILFIELD PIPES Russian patent published in 2010 - IPC B23G1/22 

FIELD: process engineering.

SUBSTANCE: proposed method comprises radial facing, rough and final turning of bearing taper surfaces, turning cone for tapping, pipe tapping and radial facing, boring inner chamfer, boring cone for tapping, rough and final boring of bearing taper surfaces, and tapping the coupling. To increase precision and quality, radial facing, rough turning of outer bearing taper surfaces and turning cone for pipe thread are performed in one combined pass by two cutting plates without clearance angle and with feed f=0.8-1.4 mm/rev. Cutting outer thread is made in four passes by cutting plate with three crests, constant cutting depth and thread length L_eff+2P, where L_eff is effective length of thread, P is thread pitch, while cutting inner thread of the coupling or pipe is made in five passes by cutting plate with two crests, constant cutting depth and thread length L_eff+P. Note here that final running and boring of bearing taper surfaces are made after tapping.

EFFECT: higher thread precision and quality.