Conventional material extrusion additive manufacturing is capable of building complex structures. Overhanging features require the use of support structures. Printing the support structure requires additional time and material. Conventional processes need time to remove support material and may lead to degraded surface finish. The use of support structures can be avoided by dynamically reorienting the build-platform. This paper presents a novel approach to build accurate thin shell parts using supportless extrusion-based additive manufacturing. We describe the layer slicing algorithm, the tool-path planning algorithm, and the neural network-based compensated trajectory generation scheme to use a 3 degree of freedom build-platform and a 3 degree of freedom extrusion tool to build accurate thin shell parts using two manipulators. Such thin shell parts cannot be built without supports by previous supportless AM processes. We illustrate the usefulness of our algorithms by building several thin shell parts.