Dimensional accuracy of threads manufactured by fused deposition modeling

For parts manufactured by fused deposition modeling (FDM), helical threads drawn in accordance with normal standards (e.g. ISO 68-1), tend to end up deformed when manufactured. These dimensional imperfections typically include violation of radial tolerances and often distorted thread profile. Therefore, making successful threaded connections using FDM would often require looser tolerances than standard ones, unless the nominal threaded sections are in the very loose end of their tolerance band. As a proof-of-concept, this paper aims to characterize such dimensional inaccuracies through image analysis. It also investigates the implications of the defects and partially compensate for the defects by using a strategy of narrowing the thread profiles. In addition, an analytical model for defects on printed inclined planes is presented and verified experimentally by manufacturing three M10x1.5 screws using layer heights corresponding to approximately 10, 8 and 5 layers per pitch. The results show that a lower layer height significantly reduces the defects. However, there is a significant nominal targeting error independent of layer height. On most performance measures, the results show that narrowing the thread profiles with 1/16th of the pitch has only an effect on specimens modelled with 10 layers per pitch. The coarser samples did show improvement in some measures, yet leaving others unchanged. In addition to the quantitative results, key points for investigating threads by microscopy is highlighted in this study.