How to prepare the specification for a special-purpose machine

A special-purpose machine is built exactly once — for one process, one product and one shop floor. That is why the specification for a special-purpose machine matters more than when buying a catalogue machine: there is no product datasheet to fall back on. Anything the builder does not receive in writing, they have to assume themselves — and every assumption is a risk built into the price, the deadline or the acceptance.

This article shows what data to gather before sending an enquiry: the product, the process, the environment, the people, and safety. You will get a checklist and a table showing what the lack of a specific piece of information leads to. If you are still deciding whether to build a dedicated machine at all, start with special-purpose machine or off-the-shelf workstation.

Why the specification decides the quote and the deadline

Quoting a special-purpose machine is in practice a quick, preliminary concept design. The design engineer has to settle: how the part gets into the machine, how many stations are needed, which drives, which control system, how many engineering hours the design, assembly and commissioning will take. Every one of these decisions is made on the basis of the client's data.

When data is missing, two things happen. First, the builder adds a margin for uncertainty — you pay for risk, not for the machine. Second, the missing information surfaces during the project and triggers changes: a redesigned feeder, a different gripper, an extra station. A change made at the specification stage costs hours; the same change at the assembly stage costs weeks. That is the shortest explanation of why two enquiries for a "similar" machine can differ in price by tens of percent.

The product: what the machine will machine or assemble

The starting point is the part or product. The builder needs:

• drawings or 3D models of all the variants the machine is supposed to handle,
• limit dimensions: the smallest and largest variant, weight, material,
• manufacturing tolerances of the incoming part — because they determine how it can be located and fed,
• surface condition: oily, burred, washed, delicate paintwork,
• information on how the part is delivered: loose in a container, in a blister, on a pallet, oriented or not.

The last point tends to be underestimated, yet it often decides half the cost of the machine. For illustration: feeding an oriented part from a tray is a simple manipulator, while the same part delivered loose may require a vibratory feeder or a vision system. It is also worth sending physical part samples straight away — including defective ones, because the machine has to detect them or at least survive them being fed in.

The process: cycle time, operations and sequence

The second group of data describes what the machine is supposed to do and how fast:

• the required output: parts per hour or cycle time in seconds, plus the target number of shifts,
• the list of operations in sequence: feeding, locating, assembly, welding, inspection, unloading,
• the critical parameters of each operation: press-in force, tightening torque, dosing time,
• what the inspection results in: a signal only, rejection into an NOK container, a measurement report,
• the planned annual volume and production horizon — this determines how heavily to equip the machine.

If the process runs manually today, describe it the way it really looks, including the "unofficial" steps: bending into place, wiping, checking by eye. These are what most often overturn an automation concept. How to put a process in order before automation is covered in more detail in how to prepare a process for automation.

The environment: utilities, space and line integration

The machine has to fit into your shop floor physically and at signal level:

• available utilities: supply voltage, connected load, compressed air (pressure and flow rate), possibly water or extraction,
• installation space: footprint dimensions, hall height, floor load capacity, the transport route to the installation site,
• environmental conditions: dust, oil mist, temperature, zones requiring increased protection,
• integration: does the machine work standalone or in a line — where the part comes from, where it goes, what signals it exchanges with neighbouring stations,
• IT requirements: a controller from a preferred manufacturer, communication with a supervisory system, traceability.

State your control-system standard already in the enquiry. If your maintenance team knows one system, a machine with a different controller will be cheaper to buy but more expensive over its whole life cycle.

The people: operation and qualifications

Even an automatic machine is operated by someone. Define who will work at the machine: a dedicated operator or one covering several stations, what qualifications they have, what language the interface should be in. Clarify what belongs to the operator (loading, container changes, clearing faults) and what belongs to maintenance. From this follows the level of diagnostic automation, the design of the loading points and how detailed the messages on the panel must be. Well-designed automation takes people into account from the first sketch, not after commissioning.

For illustration: if the machine is to run three shifts and maintenance is only available on the first, the diagnostics must lead the operator by the hand — from an unambiguous message on the panel to instructions for clearing a typical fault. Written into the specification, such a requirement costs little; added after deployment, it means rebuilding the program and the screens.

Safety and acceptance

The last group of requirements is the formal one. Agree with the builder:

• safety requirements: fixed guards or light curtains, service mode, plant standards,
• the documents the machine must come with at acceptance: technical documentation, a manual in the language of the country of use, the declaration of conformity and CE marking — details in CE marking for a special-purpose machine,
• acceptance criteria: how you count output, on what sample, what availability and what reject rate is acceptable,
• the acceptance sequence: tests at the builder's site (FAT), tests after installation (SAT), a period of supervised production.

Acceptance criteria written into the specification protect both sides — the client knows what they are paying for, and the builder knows when they are done.

Missing data vs project risk

The table below collects the most common gaps in specifications and their typical consequences:

What refining the specification with the builder looks like

You do not have to have a complete specification straight away. In practice it works like this: you send a process description and product data, the builder comes back with a list of questions, and ideally with a proposal for a meeting or a site visit. On this basis a joint requirements document is created — known in German-speaking industry as a Lastenheft — which becomes an annex to the contract and the reference point at acceptance.

A good builder of special-purpose machines challenges the requirements at this stage instead of merely writing them down: they ask whether the cycle time really follows from demand, whether one of the variants can be excluded, whether some operations should stay manual. As a guide, it is worth reserving one or two working meetings for this stage — these are the cheapest hours in the whole project.

Afterwards, treat the requirements document as a living annex to the contract. If a change appears during the project — a new product variant, a different installation location, an additional inspection function — it should go into the document as an amendment with an assessment of its impact on price and deadline. That way both sides know at any moment exactly what the contract covers, and settling changes does not rely on the memory of meeting participants.

Summary

The specification for a special-purpose machine covers five areas: product, process, environment, people, and safety with acceptance criteria. A complete set of this data shortens the quoting, makes the deadline realistic and removes the uncertainty margin from the price. Gaps do not block the conversation — but the earlier they surface, the cheaper they are to fill.

Do you have a process you want to automate with a dedicated machine? Describe it via the contact form — we will reply with clarifying questions and a quote within 48 hours.