A machining system includes a tool head having a yoke, a housing pivotally mounted to the yoke and a collet rotatable in the housing. The collet includes a tool head rocker driven by fluid to allow rocking of a tool relative to the collet in a plane normal to the housing pivotal axis in the yoke. The machining system also includes a source of constant liquid pressure and a source of constant gas pressure. The collet has pressure chambers in communication with the sources of constant pressures to bias the rockable collet assembly. The collet/tool axis is arranged to trail in the direction of relative motion when the contour of the work is moving away from the tool head and to lead when the contour of the work is approaching the tool head.