Machine tools

A machine tool comprising a frame arranged to be secured to and to be rotatable upon a work piece, the frame including bearing means located adjacent each end of the frame, each bearing means comprising an outer bearing attached to and rotatable with the frame, the outer bearings being formed in two parts pivotably attached together and having clamping means to hold the two parts together, and an inner bearing having clamping means arranged to attach each inner bearing to a work piece at spaced apart locations, said inner bearings being split into at least two parts, and driving means arranged to drive the frame relative to the work piece, the frame including at least one cutting tool support means including a rotatable shaft, at least one rotatable milling cutting tool being mounted on the rotatable shaft which is eccentrically mounted in two housings, the shaft being arranged to be driven by drive means, including an air motor, through a reduction gear box attached to one of said housings, the cutting tool also having feed means to adjust the position of the cutting tool relative to the work piece in at least a radial sense, the frame drive means and the cutting tool drive means being operable to cause the cutting tool support means to rotate about the work piece and for the rotating cutting tool to machine a surface of revolution of the work piece.