Tapping head

A tapping head having at least two groups of indexable chasers of different pitches, arranged over a circumferential array and radially extending thereto, comprising a block in the form of a hollow cylinder block, radial grooves in said cylinder block for slidably receiving therein said chasers, the chasers of a first of said groups having each a groove on a side thereof facing one end of said cylinder block and the chasers of a second of said groups having each a second groove on an opposite side thereof facing a first ring nut coaxially arranged near said one end of said hollow cylinder block and circumferentially slidable therein, said first ring nut having cam means in the form of an arcuated rib projecting from a surface thereof facing said side of the chasers of said first group thereof and engaging said grooves thereof to radially shift said first group chasers during rotation of said first ring nut, said first ring nut having transverse indexing notches on an outside peripheral surface thereof for positioning said first ring nut in operative positions thereof defined by said notches and first locking means on said cylinder block, for locking said first ring nut in a selected operative position, said first locking means comprising a first click member hinged on said cylinder block and first spring means urging said first click member in selective engagement with one of said first notches when the selected first notch is brought in the reach of said first click member during indexing of said first ring nut and a first threaded adjustment dowel for exact angular positioning of said first ring nut, a shaped cover ring superposed on said first ring nut independently thereof and fixed on said cylinder block, said shaped cover ring and said first ring nut defining an arcuated cavity therebetween, spring means within said arcuated cavity and having one end thereof rigid with said first ring nut an another end thereof rigid with said cover ring to urge said first ring nut in a rest position thereof, a second ring nut concentric with said hollow cylinder block and arranged slidably thereon remote from said first ring nut, said second ring nut having second cam means in the form of an arcuated rib projecting from a surface thereof facing said opposite side of the second group chasers and engaging said second grooves thereof to radially shift said second group chasers during rotation of said second ring nut, said second ring nut having second transverse indexing notches on an outside peripheral surface thereof for positioning said second ring nut in operative position thereof defined by said second notches and second locking means on said cylinder block remote from said first locking means for locking said second ring nut in a selected operative position thereof, said second locking means comprising a second spring biased click member hinged on said cylinder block and urged in selective engagement with one of said second notches when the selected second notch is brought in the reach of said second click member during indexing of said second ring nut, a circumferential recess at the inside periphery of said second ring nut member, a second spring means within said circumferential cavity and having one end thereof rigid with said second ring nut and the other end thereof rigid with said hollow cylinder block to urge said second ring nut member in a rest position thereof, self centering guide and support devices for the pipe to be worked while cutting the thread therein and devices for rotating the cylinder block to impart cutting motion to the chasers.