This paper seeks to increase the knowledge surrounding the Filament Deposition Modelling (FDM) process by eliciting the variability in mechanical properties of printed parts. These findings are then applied in a manner that would permit the design and manufacture of parts with reliable properties. In doing this, this paper first indentifies the need to better understand the FDM manufacturing process and then defines and contextualises the work with respect to the democratisation of design and trans-disciplinary engineering. It then reviews existing literature that covers the mechanical properties of parts manufactured via FDM. Results from tensile tests showed a large variation (17%) in Ultimate Tensile Stength (UTS) of identical parts. Given this variation the paper explores whether relationships exist between mechanical properties and other part properties as a means to non-destructively determine a manufactured part's UTS. As a consequence of null hypothesis regarding the aforementioned relationships, fluctuations in extruder temperature are identified as a possible cause for the high variability and subsequently characterised via thermal imaging. This characterisation reveals a correlation between variation in UTS and temperature fluctuations that is found to be consistent with existing literature. Correspondingly, data from the tensile tests is presented as a statistical model that can be used to predict confidence in manufacturing a part with acceptable mechanical properties.