What is the simile for clockwork?

It's not really possible to have a simile *for* clockwork because similes compare one thing to another. Clockwork itself is often used as a comparison, meaning something is very precise, predictable, and mechanical.

Here are some examples of similes *using* clockwork:

* The machine ran like clockwork. (comparing the machine's smooth operation to the predictable movement of clockwork)

* Her life was as predictable as a clockwork toy. (comparing the predictability of someone's life to the set movements of a clockwork toy)

Instead of a simile *for* clockwork, you could consider these options:

* Metaphor: "His daily routine was a well-oiled machine." (directly comparing his routine to the smooth function of a machine)

* Other similes: "The plan worked like a charm." (comparing the plan's success to the flawless operation of a magical device)

* Descriptive language: "The process was perfectly timed and executed." (avoiding a simile altogether and focusing on the precise and mechanical aspects)

Ultimately, the best way to express the concept of clockwork depends on the context and what you want to emphasize.