Setup time is the interval between the last good part of one job and the first good part of the next. Measuring from 'machine stops' to 'machine starts' flatters the number and hides the part that usually costs the most: everything that happens before the operator reaches the machine.
6 min read · Last reviewed 21 September 2026 · All resources
Last good part to first good part is the definition worth using, because it includes the first-off inspection and any adjustment that follows it. Those are real, they are variable, and they are where a surprising share of the time goes.
A baseline measured any other way will be contradicted the first time someone on the shop floor disagrees with it, and the improvement project loses credibility before it starts.
Internal work can only happen while the machine is stopped. External work could happen while it is still running — finding tooling, pre-setting, fetching the fixture, locating the programme and the drawing.
The largest and cheapest gains usually come from moving work from internal to external, not from doing internal work faster. That requires no new equipment, only preparation.
A single timed changeover measures one operator on one day, usually while being watched. Several, across shifts and operators, show the spread — and the spread is often more informative than the average.
Where one operator is consistently faster, the reason is worth capturing. It is frequently a small piece of preparation nobody wrote down.
Tooling and workholding address a specific part of the problem: repeatable location, pre-settable tools, clamping that does not need dialling in. Where a changeover is dominated by adjustment and re-checking, that is often exactly the constraint.
Where it is dominated by searching, waiting and paperwork, new tooling will not help much. It is worth knowing which situation you are in before spending money, and an honest supplier will ask.
A baseline is more useful when it records conditions: which part, which machine, which operator, which shift, over how many changeovers. That way an improvement can be compared like for like rather than argued about.
It also protects the result. An improvement measured against a vague baseline tends to be discounted by whoever is paying for it.
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There is no universal figure — it depends on the part, the machine and the batch size. The useful comparison is against your own baseline on the same job, not against a number quoted for someone else's operation.
Self-timing is convenient but tends to omit waiting and searching, because those do not feel like part of the job. An observer records them more reliably, provided it is clear the process is being studied and not the person.
Enough varies with the starting point that any stated percentage is marketing rather than engineering. Establish the baseline, identify the largest contributor, and size the opportunity from that.
Usually after the study, not before. Once you know which steps dominate, it is clear whether the answer is tooling, workholding, preparation or scheduling.
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