Face turning of optical surfaces on precision lathes needs high precision tool height adjustment, which may be a difficult and time-consuming task. In this paper we present a new tool adjustment mechanism based on varying the bearing gap height of the hydrostatic bearings present in precision lathe slides. Slide height variation is realised by influencing the flow to the bearing chambers. This is obtained by adding adjustable restrictions into the oil supply tubes. The bearing stiffness change is limited and stays high in comparison with other machine elements. The realised system has a fine adjustment range of 20 urn, a resolution better than 0.1 µm and a repeatability error lower than 0.1 µm.