A method of machining the bore of a two-lobe stator for a progressive cavity machine, said bore having a desired profile along a longitudinal axis of the bore comprising a minor (R 0) and a major diameter and an helically varying radial axis (C 1,C 2) along said longitudinal axis and defining a helix pitch, said profile being defined, at any axial position along said longitudinal axis, by the area swept by a circle of diameter equal to said minor diameter being translated along said radial axis by an equal displacement amount on either side of said longitudinal axis, said method comprising the steps of: a) providing a tubular stator body with a cylindrical bore centred on said longitudinal axis and of diameter not less than said minor diameter (R 0), and first and second machining devices (100a,b) that are each a close sliding fit on said minor diameter, wherein b) the first device comprises a milling head on the end of a shaft, the milling head mounting a rotary cutter arranged for rotation about an axis transverse said longitudinal axis by a drive mechanism along the shaft; c) the second device comprises a cutting head on the end of a shaft, the cutting head comprising a journal member for mounting a whirling cutter for rotation about an axis substantially parallel to said longitudinal axis but offset therefrom by a selectively variable degree between a minimal and maximal separation of the whirling cutter axis from the longitudinal axis; d) driving the first device through the bore so that said rotary cutter follows a helical path with said helix pitch, in the process milling a groove along said path in the stator bore using a sufficiently small diameter rotary cutter that the torque necessary to drive the cutter remains within the capacity of the drive mechanism; e) angularly offsetting (A,B,C) the rotation axis of the rotary cutter of the first device with respect to the radial axis (120, 130) and again driving the first device through the bore along said helical path, milling a further helical groove (30b,c,d) in the stator bore, also using a sufficiently small diameter rotary cutter that the torque necessary to drive the cutter remains within the capacity of the drive mechanism; f) extending the depth of cut of the rotary cutter (30e,h) of the first device and repeating steps d) and e) without over cutting the desired profile; g) driving said second device through the bore so that the whirling cutter follows said helical path with the rotation axis of said whirling cutter intersecting said radial axis (30, 120) and cutting elements of the whirling cutter milling the stator bore to a diameter (R 0) equal said minor diameter, wherein said cutting head is translated along said radial axis (30, 120) by said displacement amount along said longitudinal axis. a) providing a tubular stator body with a cylindrical bore centred on said longitudinal axis and of diameter not less than said minor diameter (R 0), and first and second machining devices (100a,b) that are each a close sliding fit on said minor diameter, wherein b) the first device comprises a milling head on the end of a shaft, the milling head mounting a rotary cutter arranged for rotation about an axis transverse said longitudinal axis by a drive mechanism along the shaft; c) the second device comprises a cutting head on the end of a shaft, the cutting head comprising a journal member for mounting a whirling cutter for rotation about an axis substantially parallel to said longitudinal axis but offset therefrom by a selectively variable degree between a minimal and maximal separation of the whirling cutter axis from the longitudinal axis; d) driving the first device through the bore so that said rotary cutter follows a helical path with said helix pitch, in the process milling a groove along said path in the stator bore using a sufficiently small diameter rotary cutter that the torque necessary to drive the cutter remains within the capacity of the drive mechanism; e) angularly offsetting (A,B,C) the rotation axis of the rotary cutter of the first device with respect to the radial axis (120, 130) and again driving the first device through the bore along said helical path, milling a further helical groove (30b,c,d) in the stator bore, also using a sufficiently small diameter rotary cutter that the torque necessary to drive the cutter remains within the capacity of the drive mechanism; f) extending the depth of cut of the rotary cutter (30e,h) of the first device and repeating steps d) and e) without over cutting the desired profile; g) driving said second device through the bore so that the whirling cutter follows said helical path with the rotation axis of said whirling cutter intersecting said radial axis (30, 120) and cutting elements of the whirling cutter milling the stator bore to a diameter (R 0) equal said minor diameter, wherein said cutting head is translated along said radial axis (30, 120) by said displacement amount along said longitudinal axis.