In this paper, the optimization of the anchor points of a cable driven parallel robot (CDPR) for 3D printing is proposed in order to maximize the rigidity. Indeed, in the context of 3D printing, robot stiffness should guarantee a high level of tool path following accuracy. The optimized platform showed a rigidity improvement in simulation, but also experimentally with a first study of vibration modes. In the same time, this study illustrates the influence of preload in cables on the platform rigidity.