Positioning assembly and method

A positioning assembly for positioning a rotary part having at least a first surface to be machined, comprising:

• a machining fixture having a positioning support member defining a center axis, the rotary part concentrically mountable to the machining fixture about the center axis to expose the first surface;
• a positioning device having an elastically-deformable diaphragm, concentrically mounted to the machining fixture about the positioning support member and defining an annular loading zone thereon, and a plurality of circumferentially-spaced engaging segments fixed to the diaphragm and extending away therefrom, at least some of said engaging segments having a contact member which is displace radially to frictionally engage a circumferential surface of the rotary part when the annular loading zone receives an axial force applied thereon substantially parallel with the center axis;
• and
• an actuating member having a force applicator displaceable relative to the machining fixture about the center axis, the actuating member having a proximal surface and a distal surface for engaging the loading zone of the diaphragm, and a force provider having an application surface engaging with the proximal surface of the force applicator to provide the axial force thereto.