Risks

One person cannot keep up with two presses

Risk	On a part with more cutting, parts pile up at the table and the belt stands stopped while the press keeps running.
Early sign	The belt is stopped with a full table more than a few times per shift.
Mitigation	Time the hand work first, and pair only presses whose hand work fits inside one cycle.
Impact	The saving at that pair, about $36,900 per year.

Risk	The second person stays near the pair, or overtime is worked as before, so nothing is saved in cash.
Early sign	Overtime hours per week do not fall after the first pair is fitted.
Mitigation	Name the work the freed person moves to before the belts are bought.
Impact	All of the saving: the freed hours stay operator time.

Risk	One person now looks at the parts of two presses, and a bad part is easier to miss.
Early sign	More parts from these two jobs are rejected at the final check or by a customer.
Mitigation	Keep the look at each part inside the hand work that is timed, and check the first box of each shift.
Impact	Rejected parts and a customer complaint, which can outweigh the hours saved.