How to specify a special purpose machine: the brief a machine builder needs

1. 01The partDrawing, material, weight and every variant the machine must take. Send real samples if you can — including the awkward ones from the edge of the tolerance.
2. 02What the machine must doThe operations in order: load, locate, clamp, press, assemble, test, mark, unload. Say what is done to the part, not how you imagine the machine doing it.
3. 03What makes a part good or badMeasurable acceptance criteria — a force window, a pressure drop limit, a dimension, presence of a component. “Properly assembled” cannot be built into a PLC; “pin pressed to 12 ± 0.2 mm at no more than 4 kN” can.
4. 04OutputParts per shift, shifts per day and the cycle time you need. Include the time the operator spends loading and unloading — it is usually most of the cycle.
5. 05Loading and peopleManual loading or automatic, one operator or two, sitting or standing. Where the parts come from and where they go next.
6. 06ChangeoverHow many part variants, how often you switch between them, and how long a changeover may take.
7. 07Utilities and spaceCompressed air pressure available at the point of use, electrical supply, floor space, and anything the machine must fit under, beside or into.
8. 08Control standardYour plant's PLC and HMI make, if you have one, and safety requirements: guarding, light curtains, two-hand start, the standards your customers audit against.
9. 09Data and traceabilityDo results need to be stored? Against a part serial, a barcode, a batch? Does anything need to reach a SCADA, MES or ERP system?
10. 10Documents and trainingWhat you need handed over: drawings, PLC and HMI source, manuals, spares list, and who needs training — operators, maintenance, or both.
11. 11AcceptanceHow the machine will be accepted at the builder's end and again at yours: how many parts, at what cycle time, with which master good and bad parts.
12. 12Budget and dateA budget range and the date the machine has to be producing. Both shape the concept; neither commits you to anything.

Specifying the solution instead of the problem

“Use a servo press” locks the builder into an answer before anyone has looked at the part. Describe the force, the stroke and how a good press is recognised, and let the concept propose the mechanism.

No bad parts to test with

A machine that checks quality must be shown what failure looks like. Keep master bad parts — a missing component, a leak at the limit, an oversize pin — for the trial and for routine checks.

Forgetting the operator

Loading height, reach, where the start buttons are, how a rejected part is taken away. A machine that is awkward to load runs slower than the cycle time on paper.

Leaving acceptance until the end

If nobody wrote down what “accepted” means, the trial becomes a negotiation. Agree the number of parts, the cycle time and the master parts before the build starts.

Not asking for the source

Without the PLC and HMI source and the drawings, every small change needs the builder. Make them part of the delivery — and check they open.

• Questions back on anything unclear — usually acceptance criteria and part variation.
• A concept: layout sketch, sequence of operation, cycle-time estimate, main components and a budget range.
• A quotation with a scope, a schedule and acceptance criteria once the concept is agreed.

Our own process, step by step, is on the special purpose machines page.