This paper examines the import of figurative language (specifically of conceptual and grammatical metaphors) in the discourse of engineering patents, a genre hardly researched for stylistic and pedagogical purposes and traditionally regarded as highly impersonal. To that end, a corpus of over 300 US electro-mechanical patents has been analysed with the aid of a concordancing tool and applying a threefold convergent framework that gathers the metafunctions of Systemic Functional Linguistics (Halliday, 1978, 1985), the Applied Linguistic Approach to Metaphor (Low, 2008) and the Metadiscursive Approach (Hyland, 2000, 2005). Findings reveal a complex network of metaphorical schemata, most non-deliberate, which constitute a tripartite choice dependent on the legal culture, the discipline and, to a lesser extent, on the authorial voice. It also binds patent writers into a community of practice (Wenger, 1998) sharing a phraseological repertoire basically acquired by imitation and whose creative and confident use requires explicit instruction.