A mechanical clock, such as a pendulum clock, uses an escapement to couple the motion of an oscillator to regulate the motion of another degree of freedom (a "hand") driven by an external force. Clocks built after this principle can yield high precision at low energetic cost. They provide a counterexample to the thermodynamic uncertainty relation, which is thus shown not to hold for systems undergoing driven Brownian diffusion with inertia. Considering a thermodynamically consistent, discrete model for an escapement mechanism, we first show that the oscillations of an underdamped harmonic oscillator in thermal equilibrium are sufficient to break the thermodynamic uncertainty relation. We then show that this is also the case in simulations of a fully continuous underdamped system with a potential landscape that mimics an escaped pendulum.