3D modelling and printing are becoming increasingly popular. However, beginners often face high barriers of entry when trying to use existing 3D modelling tools, even for creating simple objects. This is further complicated on mobile devices by the lack of direct manipulation in the Z dimension. In this paper, we explore the possibility of using foldable mobile devices for modelling simple objects by constructing a 2.5D display and interaction space with folded touch screens. We present a set of novel interaction techniques - AngleCAD, which allows users to view and navigate a 3D space through folded screens, and to modify the 3D object using the physical support of touchscreens and folding angles. The design of these techniques was inspired by woodworking practices to support surface-based operations that allow users to cut, snap and taper objects directly with the touch screen, and extrude and drill them according to the physical fold angle. A preliminary study identified the benefits of this approach and the key design factors that affect the user experience.