Widespread interest has arisen in the use of dynamic geometry software as a constructivist learning tool. However, the software has been accused of contributing to an empirical, data-collecting approach to geometry, where students have little or no understanding of deductive reasoning. Mechanical linkages which occur in many common household items, as well as in ‘mathematical machines’ from the past, offer a wealth of geometry appropriate for secondary school mathematics. Dynamic geometry models of these linkages form an interface between the concrete and the theoretical, and create a visually rich environment for students to explore, conjecture and construct geometric proofs.