3D mechanical design
Defining parts and assemblies from a functional need: choice of technical solutions, modelling, validation of clearances and assemblies, associated bill of materials.
Expertise
Design office and CAD subcontracting
3D design, manufacturing drawings, calculations and reverse engineering: compare quotes from design offices and independent designers.
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A mechanical design office turns a need into a product that a workshop can make: 3D model, dimensioned drawings, bill of materials, calculations, manufacturing file. Many companies do not need a full-time designer, or face peaks in activity that exceed their team’s capacity. Design subcontracting covers these cases: occasional extra capacity, a complete project, or specific expertise such as a structural calculation or the drawing up of an existing part.
Typical requests revolve around the design of parts and assemblies from a specification, the drawing up of existing parts or 3D models, the reverse engineering of an object with no documentation, finite element simulations and optimisation for manufacture (DFM). Suppliers are design offices, independent engineers, draughtspeople and design technicians, and sometimes workshops that offer design work ahead of manufacturing.
A successful design project depends as much on the quality of the brief as on the designer’s talent. This page reviews the services, the deliverables to demand, the software and formats to know about, the management of rights over drawings and how to write a request that makes quotes genuinely comparable.
Common services
Drawing up and manufacturing files
Dimensioned drawings with tolerances, surface finishes and materials, assembly drawings and bills of materials, ready to send to a machining, sheet metal or moulding workshop.
Calculations and simulation
Strength of materials, finite elements, thermal, fatigue and buckling: calculation validates a design or optimises the amount of material required.
Reverse engineering
From a physical part, a set of measurements or a 3D scan, the design office rebuilds a CAD model and a drawing so that an undocumented item can be remade or improved.
Design for manufacture
Adapting a design to a specific process: machining, cutting and bending, injection moulding, casting, welding. It lowers cost by simplifying shapes and aligning tolerances.
Machine and tooling design
Special machines, inspection gauges, assembly and welding fixtures, test equipment: bespoke design work for your production.
Industrial design and ergonomics
Shaping the product, choosing user interfaces, mock-ups and 3D renderings to validate the appearance before the technical phase.
Materials worked
SolidWorks, Inventor, Fusion, Creo, CATIA, Solid EdgeAutoCAD and DraftSight for 2D drawingsFreeCAD and Onshape for collaborative projectsFinite element simulation softwareSTEP, IGES and Parasolid exchange formatsPDF and DXF drawings for manufacturing3D scanning and point clouds for reverse engineeringTechnical drawing and tolerancing standards (ISO 1101, ISO 2768)
Common applications
- Designing a new product for a start-up or an SME
- Drawing up existing parts in order to place a manufacturing order
- Renovating an obsolete part with no drawing
- Design of special machines and production tooling
- Structural or mechanical strength calculation for an assembly
- Optimising a part to reduce its manufacturing cost
- Adapting a product to a new market or a new standard
- Temporary reinforcement of an in-house design office at peak times
What affects the price
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1
Nature and complexity of the project
A simple part, a mechanical assembly or a complete machine do not require the same duration or level of expertise. Functional complexity matters more than the number of parts.
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2
Precision of the specification
A clear brief, with constraints, environment and acceptance criteria, avoids iterations. A vague brief leads to back-and-forth that translates into billed hours.
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3
Billing method
Design work is billed at a fixed price for a defined deliverable, or on a time-and-materials basis. A fixed price gives visibility; time and materials suits projects that evolve.
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4
Calculations and validation
Simulations, compliance justifications and validation tests add time. They are essential for safety-critical parts or load-bearing structures.
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5
Deliverables required
Native and neutral models, detail drawings, bills of materials, instructions, supporting file: the longer the list, the higher the price. Specify the formats expected from the quote stage.
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6
Lead time and responsiveness
A tight schedule puts one person on the job as a priority. Conversely, a planned project lets the designer’s workload be smoothed out and costs limited.
Tips for a successful request
Post a request- Write a functional specification: function, constraints, environment, loads, service life, standards, target cost.
- Specify the processes and suppliers envisaged for manufacture so that the design takes them into account from the start.
- State the software and formats expected: native model, STEP, PDF and DXF drawings, depending on how you will use them afterwards.
- Attach any existing documentation: drawings, photos, original parts, manuals and references of the components to be integrated.
- Define validation milestones (sketch, design review, manufacturing drawings) rather than a single final delivery.
- Specify ownership of the drawings, the confidentiality expected and the assignment of rights from the outset.
Specification and deliverables: what to define
A design project starts with a specification. It describes the product’s function (what must it do?), its constraints (size, loads, temperature, humidity, standards), its operating environment, its service life, its production volumes and its target cost. The more precise it is, the more comparable the quotes will be, and the less drift there will be along the way. Writing such a document is covered in our guide to the manufacturing specification.
The deliverables must be listed from the request stage: native 3D model and neutral STEP format, detail and assembly drawings, bill of materials, assembly instructions, calculation note, manufacturing file. Drawings must follow technical drawing rules and show general tolerances (for example ISO 2768) as well as geometric tolerancing (ISO 1101) for functional dimensions. A poorly drawn plan is costly in manufacturing: machining and sheet metal workshops are the first to suffer.
Plan intermediate reviews: validation of the sketch or concept, then a design review before the drawings are produced. They let you correct errors early, when they cost far less than after a first production run. You can also ask for a validation prototype, see the prototyping page, before freezing the design.
Rights, confidentiality and ownership of drawings
The question of who owns the drawings is often addressed too late. Under French law, copyright in a creation belongs in principle to its author, and any assignment must be expressly in writing. For commissioned design work, state in the quote or contract the assignment of exploitation rights over the drawings, models and documents delivered, the scope of that assignment (use, duration, territory) and its price. Without this, you could be limited in exploiting your own product.
Also provide for a confidentiality undertaking (non-disclosure agreement, or NDA) before passing on sensitive information. Our guide to drawing confidentiality and NDAs in subcontracting details these precautions. In the other direction, a designer may wish to reuse their generic solutions for other clients: clarify what remains exclusive and what is reusable.
Finally, make sure you receive all the source files needed to modify your drawings later. A model delivered only as a PDF or STEP greatly limits changes. Ask for the native format or, failing that, a structured STEP with an assembly tree. Check that the supplier holds professional indemnity insurance suited to the nature of the work, particularly for safety calculations.
Reverse engineering and optimisation: giving a part a second life
Reverse engineering addresses a frequent case: a broken or obsolete part, no drawing, a supplier that has disappeared. The designer takes dimensions with callipers or on a measuring machine, 3D-scans the part if its shape is complex, then rebuilds a usable CAD model. They will generally suggest improving the design: changing material, reinforcing a weak area, simplifying shapes to cut cost. They deliver a drawing from which any workshop can produce.
Optimisation for manufacture follows the same logic: a part machined from solid block can sometimes be replaced by a bent sheet metal part, a moulded part or a 3D-printed part. An experienced designer asks these questions, because they know the constraints of each process. To compare, see the 3D printing and plastics processing pages.
There is no need to freeze everything before you consult: a Meaflow request can start from a need that is still open, which design offices and independent designers help you refine by messaging before proposing a fixed price or a day rate. You compare approaches, references and deliverables side by side. Describe your design requirement to receive their replies.
Suppliers: design office & CAD
Guides to go further
Writing a manufacturing specification: method and template
What a workshop needs to know to quote and make your part: a method in a few points, a ready-to-copy template and common mistakes to avoid.
Protecting your drawings in subcontracting: NDAs, ownership and good practice
Typical content of a confidentiality agreement, trade secrets, ownership of drawings and tooling, scope of the 1975 French law and sharing habits: how to entrust your drawings with confidence.
STEP, DXF, STL… which files should you send your manufacturer?
STEP, IGES, Parasolid, DXF, STL, 3MF, dimensioned PDF, Gerber: the right file for each manufacturing process, a summary table and good practice for sending files.
Related expertise
Prototyping
Functional prototypes, pre-series, models
CNC machining
Milling, turning, 3- to 5-axis machining centres
3D printing
FDM, SLA, SLS, metal, prototypes and small runs
Mechanics & assembly
Assembly, integration, machine maintenance
Frequently asked questions
A question not answered here? Visit the help centre or write to us.
How much does a mechanical design project cost?
The cost depends on complexity, the level of detail required, calculations, deliverables and the billing method, fixed price or time and materials. A simple drawing-up job bears no comparison with the design of a machine. A precise specification allows design offices to give a firm price; otherwise they quote a range of hours to be adjusted.
What documents should I provide to request a design project?
A functional specification (function, constraints, environment, standards), sketches or photos, existing drawings and models, references of the components to be integrated and your cost and quantity targets. State the deliverables and formats expected. The clearer the request, the more precise the quotes.
Can a part with no drawing be modelled in 3D?
Yes, that is reverse engineering: the designer measures the part, scans it if necessary, then rebuilds a 3D model and a dimensioned drawing. If possible, supply the original part or, failing that, photos, dimensions and information on its use. The material and tolerances often have to be determined or confirmed with you.
Who owns the drawings produced by a design office?
Without a written clause, copyright stays in principle with the author of the drawings. To be able to use the work freely, include an assignment of rights in the quote or contract, with its scope. Also ask for the source files. A confidentiality clause usefully complements this arrangement.
What is the lead time for a design project?
A simple drawing-up job is done in a few days. Designing a complete product, with calculations and prototypes, takes several weeks or months, as a guide. The lead time depends mainly on how precise the brief is, the number of reviews and the designer’s availability. Set delivery milestones rather than waiting for the final deliverable.
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