1. A computer-implemented method of generating a three-dimensional CAD solid model, comprising: configuring a plurality of computer processors, said plurality of computer processors being instructed to perform the steps of Computer-Aided Design (CAD) computer processing and generate the three-dimensional CAD solid design suitable for a 3D printer, said steps comprising: accepting a user's input comprising a primary curve of data points; determining a first rail curve of data points and a second rail curve of data points based on said primary curve of data points; performing a sweep operation function of CAD utilizing said first rail curve of data points and said second rail curve of data points to generate a tubular surface shape of data points; generating two end caps of data points using said tubular surface shape of data points; and generating a solid tubular three-dimensional CAD model utilizing said tubular surface shape of data points and said two end caps of data points, wherein said solid tubular three-dimensional CAD model is used for 3D printing.