In recent years, additive manufacturing (AM) techniques have transcended their typical rapid prototyping role and become viable methods to directly manufacture end products in a highly versatile manner. Due to its low cost and relative ease of use, fused deposition modeling (FDM) has become the most universally applied AM technology. Nonetheless, skilled operators are often still required to perform maintenance, diagnostic, and repair tasks. Such operators need to be adequately trained. Here, Augmented reality (AR) technology could be used to automate this training and help to promptly provide new operators with the necessary skills to perform specific tasks as required. However, the most effective approach to designing such AR-based assistance systems has not yet been fully explored. Consequently, we address this need by reporting on how to design such guiding systems using well-known design engineering methodologies. We then further assess the applicability of our approach through a user study with domain experts. In addition, we complete our assessment with heuristical verification of system expressiveness to reason about the influence of cognitively important components of the AR interface on the operators.