Sub-assembly
Assembly of machined parts, bearings, guides, drives and fasteners to drawing, with tightening torques, thread locking and clearance checks, for prototypes or series.
Expertise
Mechanical engineering and assembly subcontracting
Sub-assembly, machine integration, commissioning and maintenance: compare offers from mechanical engineers and integrators.
- Free, account created only when you publish
- Verified businesses (company number checked)
- Drawings visible to members only
A machine, a piece of equipment or a mechanical product is more than a list of parts: they have to be assembled, fitted, connected, adjusted and tested. This is the job of mechanical assembly workshops and integrators, who handle machined parts, off-the-shelf components, fasteners, and pneumatic or hydraulic elements, then deliver a working assembly.
Needs are varied: assembling sub-assemblies in series for a manufacturer, building a special-purpose machine from drawings, integrating components into a frame, refurbishing or upgrading existing equipment (retrofit), or providing industrial maintenance for a fleet of machines. Companies that outsource these tasks gain flexibility: they draw on skills and on lifting and testing equipment that they do not need permanently.
Choosing an assembly supplier means defining the level of responsibility you hand over: simple assembly to a drawing, or taking charge of sourcing, wiring and commissioning. This page covers the services, the usual components, price factors, safety requirements (CE marking, authorisations) and the information to provide in order to get comparable quotes.
Common services
Special machine integration
Building a complete machine from drawings: frame, mechanical elements, pneumatics, hydraulics, sensors and control cabinet, adjusted and tested before delivery.
Wiring and connections
Electrical, pneumatic and hydraulic connection of components, cable and hose labelling, integration of PLCs and sensors in conjunction with an industrial electrician.
Commissioning and testing
Adjustments, no-load and on-load tests, parameter tuning, operator training and acceptance reports, in the workshop or at the client’s site.
Preventive and corrective maintenance
Scheduled visits, breakdown repair, replacement of wear parts and tracking of interventions, under contract or on demand.
Machine retrofit and refurbishment
Upgrading older equipment: replacing obsolete components, bringing safety up to standard, modernising the controls.
Kitting and packing
Preparing part kits for final assembly at the client’s premises, labelling, packing and dispatching sub-assemblies.
Materials worked
Fasteners and fixings (grades 8.8, 10.9 and 12.9, A2 and A4 stainless steel)Bearings, linear guides and ball screwsGeared motors, motors and drivesCylinders, valves and pneumatic componentsPumps, rams, hoses and hydraulic componentsAluminium profiles and welded framesBelts, chains, sprockets and couplingsSensors, PLCs and control cabinetsStructural adhesives, thread lockers and seals
Common applications
- Special-purpose machine and automated line builders
- Manufacturers of industrial and agricultural equipment
- Production of sub-assemblies for the automotive and rail industries
- Maintenance of machine fleets in factories
- Integration of equipment for laboratories and cleanrooms
- Refurbishment of machine tools and presses
- Test benches and test equipment for quality control
- Mechanical systems for robotics and mobility
What affects the price
-
1
Assembly and adjustment hours
Skilled labour is the biggest cost item: number of components, precision of fits, accessibility, fine adjustments. The workshop’s experience with this type of machine speeds up assembly.
-
2
Supply of components
Depending on whether you supply the parts or the supplier buys them, the scope and the price change. Lead times for specific components also affect the schedule.
-
3
Documentation and drawings
A complete file (general arrangement drawings, bill of materials, assembly instructions) reduces errors and design time. Without documentation, the workshop has to make up for it with analysis time.
-
4
Testing, inspection and acceptance
On-load tests, test bench, acceptance procedure, inspection report: the higher the level of requirement, the more time and resources the job takes.
-
5
On-site work
Travel, accommodation, lifting, specific tooling and safety formalities (prevention plan, authorisations) add to a job carried out at the client’s premises.
-
6
Quantity and recurrence
Repeated assembly in series allows tooling and the process to be optimised, and the unit price to fall. A regular maintenance contract is generally cheaper than one-off emergency call-outs.
Tips for a successful request
Post a request- Attach the general arrangement drawing, the detail drawings, the bill of materials with references and quantities, and if possible an exploded 3D view.
- State clearly what you supply (parts, components, tooling) and what the supplier must buy.
- Specify the tightening torques, the fits, the greasing instructions and the acceptance criteria for the assembly.
- Describe the environment: clean workshop, cleanroom, outdoors, corrosive or explosive atmosphere, safety constraints.
- For maintenance, list the machine fleet, its age, make, breakdown history and the availability expected.
- Mention the authorisations required (electrical, lifting, working at height) and the access rules for your site.
Sub-assemblies and special machines: defining the scope properly
The first issue with outsourced assembly is a clear scope. A workshop may simply assemble parts that you deliver to it according to a drawing, or build a complete machine, taking care of design, sourcing, assembly, wiring and testing. Between these two extremes there are many variants: specify who designs, who buys, who assembles, who wires, who adjusts and who signs off.
A good assembly file contains the general arrangement drawing, the detail drawings, the bill of materials with manufacturers’ references, the tightening torques, the greasing and thread-locking instructions, and the assembly tolerances (clearance, parallelism, flatness, coaxiality). Off-the-shelf components come with manufacturer recommendations that must be followed. A prototype assembled in the workshop often reveals design adjustments to be made before launching a series: allow for this improvement phase, possibly with a design office.
The assembled parts often come from several trades: machining, sheet metal work, welding and fabrication. A supplier who coordinates everything simplifies follow-up, but you lose the direct relationship with each supplier: decide with your eyes open. Electronics and automation often form a second chain to synchronise with the mechanics.
Machines, CE marking and safety: responsibilities to clarify
A machine placed on the European market must meet essential health and safety requirements. Directive 2006/42/EC covers this today; Regulation (EU) 2023/1230, which replaces it, applies from 20 January 2027. Under this framework, the manufacturer is whoever designs, or has designed, the machine and places it on the market under their own name: they carry out the risk assessment (standard NF EN ISO 12100), compile the technical file, write the instructions, affix the CE marking and sign the declaration of conformity.
When you entrust assembly to a supplier, the question to settle is who takes on this role. In the case of simple assembly to your drawings, responsibility generally stays with you. If the supplier designs and assembles, it may become the manufacturer. Put it in writing in the quote or contract, with the deliverables expected (risk assessment, electrical diagrams, instructions).
For work at your premises, a serious supplier complies with your rules: prevention plan, lock-out of energy sources before work, electrical authorisations (standard NF C 18-510 in France), authorisations to operate lifting equipment. Well-run maintenance follows a visit schedule, logs each intervention and keeps the list of parts replaced. For acceptance measurements and tests, turn to the laboratories on the inspection and metrology page.
Industrial maintenance and retrofit: outsourcing without losing control
Outsourced maintenance takes several forms: preventive visit contract, on-demand repair, on-call cover, spare parts management. Before choosing, measure the impact of a machine stoppage on your production: if a breakdown is costly, a contract with a guaranteed response time is better than looking for a supplier when the problem arises.
Retrofit, meaning the upgrade of an existing machine, is an alternative to buying new when the mechanics are sound but the controls are obsolete or safety is no longer compliant. It requires a prior diagnosis: condition of the mechanical components, availability of parts, existing diagrams. A reverse-engineering or drawing-update service may then precede the work.
To prepare the request, gather the machine’s rating plate, photos, drawings and manuals, the breakdown history and downtime constraints. In a Meaflow request, attach the rating plate and a few photos of the machine: mechanical engineers and integrators can then ask the right questions, and quote for an intervention, a contract or a retrofit. You compare their references and response times, with the help of our guide to choosing an industrial subcontractor. Describe your requirement once your file is ready.
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.
How to choose an industrial subcontractor: 10 criteria
Skills, capacity, quality, proximity, responsiveness, references, financial strength, communication, price and contract: 10 criteria and a comparison grid.
From prototype to series production: the stages of industrialisation
Mock-up, functional prototype, pre-series, tooling, qualification: how to structure the move from a single unit to repeatable production, and choose the right processes for your volumes.
Related expertise
CNC machining
Milling, turning, 3- to 5-axis machining centres
Electronics
PCBs, wiring, board assembly, electrical cabinets
Welding & boilermaking
TIG, MIG, structures, tanks, metalwork
Design office & CAD
Design, drawings, 3D modelling, calculations
Frequently asked questions
A question not answered here? Visit the help centre or write to us.
How much does it cost to assemble a mechanical sub-assembly?
The price depends on the number of components, the precision of the fits, the adjustments and tests, and whether or not you supply the parts. For a single unit, it includes process planning; in series, this cost is spread. A general arrangement drawing, a bill of materials and a description of the tests expected allow suppliers to quote precisely.
Can a subcontractor build a special machine for me?
Yes, integrators design and assemble special machines from a specification. State the functional need, the throughput, the environmental constraints and the safety level. Also clarify who becomes the manufacturer under machinery regulations, because that determines who is responsible for CE marking and documentation.
What lead time should I allow for mechanical assembly?
A simple sub-assembly can be put together in a few days if the parts are available. A complete machine takes several weeks, even several months, depending on design, sourcing of specific components, testing and acceptance. The availability of those components is often the most uncertain factor. In your request, distinguish the mandatory deadline from the one that is merely desirable.
Can a supplier work at my site?
Yes, many suppliers travel for commissioning, maintenance or breakdown repair. Allow for travel costs, your site’s safety rules, the prevention plan and the authorisations required. In the request, state the address, access conditions, permitted time slots and lifting equipment available.
What is machine retrofit?
Retrofit means modernising an existing machine by replacing obsolete components, updating the controls and bringing safety up to standard, while keeping the frame. It makes sense when the mechanics are still sound. A prior diagnosis lets you compare its cost with that of a new machine, with no commitment on the integrator’s part.
Need help with mechanics & assembly?
Describe your project for free and compare price quotes from workshops.
Are you a mechanics & assembly workshop?
Create your profile for free and respond to requests that match your expertise.