I got to thinking about maŝino — machine — and wondering whether maŝini is the appropriate Esperanto word for "to machine" (tr) as when one machines a metal part using (say) a metal lathe. And is the person who does that a maŝinisto?

I know that in English a person who works on machines is not a machinist but a mechanic. Esperanto has mekaniko for mechanics and thus mekanikisto is a mechanic. Mechanics is also a branch of physics, but the specialist in mechanics (in physics) would be fizikisto, of course. Mekanikisto would be the trade or the practice use of mekanikaj devices, I presume.

But I'm wondering about machining metal: does Li maŝinas la parton make sense? Is the person doing that a maŝinisto, or is a maŝinisto one who works on maŝinoj?

When you are talking about lathes in specific, I think the correct words would be torni, tornilo or tornmasxino and tornisto. In my understanding all tornistoj are masxinistoj.

For a more general term, maybe masxine labori/produkti/formi could do the trick. Or at a moment, when nobody is looking, you just coin the word masxinumi and run with it.

In my understanding a masxinisto operates machines and gives day to day maintenance, while a mehxanikisto is called when the machine breaks down and you have to dismantle it in order to fix it or in order to foul it up completely.

maŝinisto is any worker using a machine,
maŝinestro is a chief of such workers.
maŝinizi is use more machines