If you’re an SME manufacturer making high-tech devices in small batches, you already know that time disappears in the gaps. A drawing is updated, a part arrives late, the only calibrated test rig is booked all afternoon, and suddenly, a believable delivery date turns into a ‘hope for the best.’
Capacity requirement planning, or CRP, is simply a way to turn that chaos into a plan you can stand over. It looks at the real work that needs to be done at each work centre and asks a practical question: do we actually have enough hours, by day and by workstation or bench, to hit the dates we’ve promised our customers?
What is CRP?
Think of CRP as the detailed version of production planning. Rather than assuming every bench and piece of equipment is available whenever you need it, CRP tallies up the time needed for each operation on each job and places those hours against the places where the work really happens: the assembly bench, the inspection area, the functional test rig.
It counts setup time, the actual task time, the checks, and the inevitable waiting between stages. For small teams, that last bit matters. One person called into a meeting or a test rig needing recalibrated can wipe out a morning.
You may have heard of RCCP, rough-cut capacity planning. RCCP is the quick sense-check you do early on, by broad resource family such as ‘assembly’ or ‘test.’ It tells you whether a week looks feasible in principle. CRP is where you roll up your sleeves and schedule at work-centre level, using the actual routing times you run the shop with.
For quoting and early promises, RCCP is useful. For setting dates you can hit, you need CRP.
Small Business? Why the textbook versions often miss the mark
Most online guidance assumes large plants, long runs and stable routings and it’s part of the reason why so many small manufacturers think CRP doesn’t apply to them. But a better grasp of deliverability isn’t just for large enterprise manufacturers.
Small device makers live a different life to large firms, sure. Jobs are custom or semi-custom, batch sizes are smaller, and changeovers are frequent. You have named skills and approvals to respect. First-article inspection is not a formality. The test rig needs to be in calibration and especially if you’re a manufacturer of scientific instruments or medical devices, your customer may want the calibration number on the record. Labels have to be correct.
All of that is real work, and if it isn’t in the plan, you will be late even when the spreadsheet says you have hours to spare.
So CRP for a small device shop needs three honest habits:
- Put the admin that protects quality into the routing. Serial capture, inspection sign-offs, device history entries. They take minutes but minutes add up.
- Treat the test rig as a real constraint with a real calendar. If it is usable six hours a day, plan for six, not eight.
- Expect change. Engineering changes, small rework loops and supplier slips happen. A sensible buffer is not waste. It is professionalism.
A practical example
Imagine a three-person team. Two on bench assembly, one on inspection, plus a functional test rig that is realistically available for six hours a day once you allow for warm-up, calibration checks and the odd hiccup. You have two jobs due in ten working days. Job A is engineered-to-order, twelve units. Job B is make-to-order, eight units. The assembly on A takes about an hour and a quarter per unit, B is closer to an hour and a half. Inspection is a third of an hour for A and just under half an hour for B. Tests take roughly an hour each, a bit less on A, a bit more on B. Because both are new or changed, you will run a first-article on the first unit of each.
If you only look at the week totals, it doesn’t seem too bad. Assembly is easily within the two people’s week. Inspection isn’t close to full either. The test rig totals about a working day and a bit for A, and another day for B, plus a little buffer for first-articles and the odd re-test. Across a week you’d say there is space.
But small teams don’t live by week totals. Sequence matters. Two afternoons on the rig can vanish to first-articles and a tricky diagnosis on one unit, and suddenly the remainder pile up. CRP forces the detail. You schedule the test operations in the same way you schedule assembly, count the real availability of the rig, include the first-article time, and model a little rework where it is sensible.
When you do that, you can see Wednesday getting tight and Friday becoming wishful thinking. Better to know on Monday and make a small adjustment than scramble at the end.
What sort of adjustment? Often it is as simple as resequencing so Job A’s first units reach test earlier, or pushing a few units of Job B into the following week, or cross-skilling so the inspector can support basic test prep and free the rig for the work that truly needs it. Sometimes the answer is to subcontract a handful of test cycles. The point is not to be clever. It is to choose calmly while you still have choices.
Queues, changeovers and batch size
Queues are not mysterious. If your bottleneck runs close to full, there will be a queue. For small device manufacturing teams, the safer target is to run the constrained centre at roughly 75 to 85 percent. That leaves room for variance and avoids starving the next step. Likewise with batch size. Huge batches create long changeovers and long waits. Tiny batches drown you in setup. CRP helps you find the middle ground that keeps the bottleneck flowing.
Bringing dates and capacity together
Sales will always ask for believable dates. That is reasonable. Capable-to-promise, or CTP, is just the discipline of giving dates that reflect two realities at once: do we have the materials, and do we have the hours on the benches and rigs at the right time. When you run CRP, you can press a button and tell the truth. If an engineering change lands mid-build, re-run the plan and re-promise quickly. Most customers accept a clear, early update. Few forgive a surprise at the end.
Subcontractors and suppliers are part of capacity
In a small device shop, outside steps often matter as much as the internal work. PCB assembly, machining, coatings and specialist calibration can all be the true limiter. Treat those as capacity calendars in the plan, not as a single fixed lead time. If your coater shuts for a week in August, put that into the calendar now. It stops pretend dates sneaking into quotes.
What to track
A handful of measures tell you whether the plan is working:
- On-time promise against on-time ship. If the first is honest, the second improves.
- First-pass yield. If this climbs, queues shorten all by themselves.
- Utilisation of the constrained centre, commonly the test rig.
- Average queue time at that constraint.
- Hours lost to rework from non-conformances.
None of these require a big-company dashboard. A simple weekly view is enough.
Putting CRP to work in Flowlens
Start by defining your work centres and calendars as they really are. If the test rig is only reliable for six hours a day, write six. Load realistic routing times, including the small but vital quality tasks and first-article steps. Generate a weekly load view and check the next fortnight for pinch points. At the end of the month, compare planned times against actuals and nudge the standards. Ten minutes here and there make a difference when your whole week is under forty hours per person.
A closing word
CRP is not about fancy algorithms. It is about respect for the way small teams actually work. When you include the quality work, honour the constraints, and accept that change happens, you get calmer weeks and happier customers. More importantly, you can say yes to orders with a straight face.
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