This paper presents the design and the optimization of a parallel machine-tool composed of (i) an actuated parallel 3-dof mechanism (a linear Delta) and (ii) a measuring 6-dof mechanism (a Gough platform)). The interest to use a measuring device independent of the actuation device is shown and the modeling of both devices used for the optimization is explained. Then, the optimization is presented; it is performed to obtain the best resolution for the measuring system evaluated at the tool level.