The promise of robotic fabrication as an enabler for mass-customization in Architecture has been hindered by the intricate workflow required to go from parametric modelling to CNC fabrication. The lack of integration between highly-specialized proprietary software, normally required to operate the machines, and most of the design tools constitutes a major limitation. One way to tackle this constraint is by developing simple tools that directly link parametric modelling to robotic coding. Accordingly, "Fisac Variations" develops an uninterrupted digital workflow from form-generation to robotic fabrication. This innovative approach to Computer Aided Design and Manufacturing was tested by studying and reengineering a specific historic construction system - Miguel Fisac's Bones System was used as a case study - and by enabling it to address problems of contemporary architectural agenda such as flexibility, variability and mass-customization. The proposed workflow threads form-finding, structural analysis, geometric definition, CNC code generation and digital fabrication within the same open-source computational environment. In this way, this innovative procedure aims to increase design freedom while ensuring fabrication feasibility. This paper describes background research, concept, form-finding, construction process, methodology, results and conclusions.