1. A written requirement and design specification
Ask for the design to start from a document you can sign off, not from a verbal brief. It should state the intended use of the equipment, the functional requirements, the operating conditions at the site, the performance parameters the structure has to hold, and the cost target you are working to. When the design later behaves differently from what you expected, this document is the reference both sides return to.
A supplier that develops equipment products from concept to production normally produces this requirement analysis and technical proposal as the first output. Request it as a separate item so you can review it before engineering work begins.
2. 3D model and 2D production drawings
Specify the model format you need (STEP, for example) and whether you want the native CAD files or only neutral exports. A 3D model lets your own team check clearances, assembly order and service access. It is also what your second-source fabricator will ask for.
For fabrication, 2D drawings are the ones that carry tolerances, weld and surface finish notes, material grade and part numbers. Ask for the full set: whole-machine assembly drawings, sheet-metal and frame details, transmission and moving-platform details, and piping or layout drawings where the machine has fluid circuits. Drawings without a revision history are unusable; require a revision block and a drawing index.
On PowerDe's engineering services page, the deliverable list for an engineering project explicitly runs from the requirement document through 3D structure diagrams and 2D processing drawings, and continues into electrical schematics, PLC/HMI programs, BOM, prototype, test report, assembly process documents, factory inspection standards and a production introduction plan. Use that list as a starting checklist and cut what does not apply to your scope.
3. Interface documents, not just part geometry
Mechanical structures rarely fail on their own; they fail where they meet the electrical, control and fluid systems. Request the electrical schematic, the sensor and actuator mounting arrangements, the cable routing paths, and the control panel layout that was assumed in the mechanical design. If these are not documented, whoever assembles the machine will invent them, and the invention will not match the drawings.
4. A BOM you can actually price and buy against
A bill of materials should separate custom-fabricated parts from purchased items. For purchased items, ask for manufacturer and model, not just a description. For fabricated parts, the BOM line should point to a drawing number. Flag long-lead items so you can order them early.
Ask the supplier to state which design decisions were driven by cost and which by manufacturability. A structure that is right on paper but needs five non-standard fixtures to assemble is a cost problem you will pay for on every unit.
5. Prototype build records and test evidence
A prototype is not a deliverable on its own; the evidence around it is. Agree in advance which tests the prototype has to pass, and require written records: functional checks, performance measurements under real operating conditions, continuous running and repeated start-stop runs, safety checks such as earthing, leakage and emergency stop, and any sealing or high-temperature protection verification. Hardware testing services of this kind usually output a test plan, test record forms, a problem list, fault cause analysis, and optimisation suggestions — all of which you should receive, not just a pass or fail summary.
Ask for a retest record as well. A problem list without a retest confirmation tells you what was found but not what was fixed.
6. Assembly, inspection and handover documents
If you intend to build or maintain the equipment, request the assembly process documents, the torque and fitting notes for critical joints, the factory inspection items, the pass/fail criteria, and the inspection record form that ships with each unit. These documents are what make the design transferable to another workshop. Without them, the know-how stays with the supplier's fitters.
7. Change control and ownership
Put three items in the contract: who issues drawing revisions and how you are notified; which files are delivered at each milestone; and who owns the design data once you have paid for it. Then match your payment schedule to document acceptance, not to calendar dates. A supplier who will not commit to file delivery at milestones is signalling that the data will be hard to get later.
A short acceptance checklist
- Requirement and design specification, signed off before engineering starts
- 3D model in an agreed format, plus indexed 2D drawings with revision history
- Electrical schematics and mechanical-electrical interface notes
- Priced BOM with drawing numbers and purchased-item part numbers
- Test plan, raw test records, problem list and retest confirmation
- Assembly process documents and factory inspection standard with record form
- Written change-control process and ownership of the design data
Compare two suppliers on this checklist rather than on their quoted engineering hours. The one who agrees to deliver the records up front usually costs less over the life of the machine, because you are buying equipment you can rebuild, upgrade and inspect — not a design you have to call them about every time something changes.
