Generating CNC (Computer Numerical Control) code for a layer additive process is fundamentally different from a subtractive process. In a subtractive process, tool paths and tool changes are computed to remove material from a billet leaving behind the specified shape. In a layer additive process tool paths and tool changes need to fulfill the opposite goal of building a part in empty space. In the case of Electron Beam Free Form Fabrication (EBF3) another degree of freedom exists, which is changing the tool ‘on-the-fly'. The electron beam parameters can change while the deposition moves along the tool path. The need for changing EBF3 parameters along the tool path arise from three requirements. First, EBF3 parameters may need to change to ensure a uniform deposit as the positioning systems accelerate and decelerate along their axes of motion. Second, parameters may need to change to correct geometry errors from previous deposits such as slight variations in planned versus actual build layer heights (variations will occur without a closed loop control system). Third, parameters may need to change to facilitate a functional gradient in either geometry or material properties. This presentation will summarize effort that has been made in two functional areas: tool path generation and parameter variation along the tool path.