Wire Arc Additive Manufacturing (WAAM) is a rapid and cost effective approach that is suited to the production of large components. Machining of these parts is difficult due to variations in surface roughness and part distortions and therefore specialised techniques have recently been developed. In order to use these methods reliably, an enhanced understanding of the residual stress generated (& relieved) by these approaches is required. In this study time of flight neutron diffraction will be performed to map lattice strain variation in 3D within a Ti-6Al-4V WAAM part before and after machining. These results will be used to optimise existing models of production and will be used to tailor machining parameters. Such insights are critically required in order to validate these new processing routines and facilitate reliable industrial use of this highly promising production methodology.