Abstract: In this paper, the systematic study and analysis are presented on the diamond tool geometry and cutting process variables in ultraprecision machining of freeform surfaces using slow tool servo (STS) technology. Furthermore, the guidelines for design of diamond tooling geometry are presented particularly against the stringent requirement in ultraprecision diamond turning using STS. By using Nanotech 250 ULv2 diamond turning machine and UG simulations, the cutting tool paths and the layout of cutting tool positioning points are investigated through ultraprecison machining trials and simulations. It concludes that the optimal design and analysis of appropriate cutting direction, cutting tool paths and positioning points layout and process parameters are essentially important in enabling ultraprecision machining of free-form surfaces using STS in a highly efficient and effective industrial manner.