CNC machining and subcontract manufacturing to your drawing

CNC milling produces prismatic parts, pockets, faces and complex 3D surfaces; multi-axis machines reach several faces in one set-up, which improves accuracy between features. CNC turning makes round parts such as shafts, bushes and threaded components, and mill-turn centres combine both. Laser cutting profiles flat sheet and plate quickly, and press brakes bend it into brackets and enclosures. Welding and fabrication join parts into assemblies.

3D printing is useful for prototypes, fixtures and complex low-volume parts, but the material properties differ from machined stock. If a printed prototype will be replaced by a machined production part, test the machined version before you commit.

Tell the supplier which processes you expect, but stay open to its suggestions. A shop may propose turning a part from bar instead of milling it from block, or laser cutting and folding instead of machining from solid, and save you a lot.

The basis is a dimensioned 2D drawing plus a 3D model, usually as a STEP file. The model defines the geometry; the drawing defines what matters: critical dimensions, tolerances, geometric tolerances, surface finish, threads, and any heat treatment, plating or anodising. Many UK engineering businesses work to BS 8888 for technical product specification.

Tolerances drive price more than almost anything else. A general tolerance class such as ISO 2768 for non-critical dimensions, with tight tolerances only where parts mate or seal, lets the shop use sensible machining times and inspection. Specifying tight tolerances everywhere means slower cutting, more inspection and more scrap, and you pay for all of it.

Quantities matter too. A prototype, a batch and an annual call-off schedule are priced differently because set-up and programming are spread over more parts. Give realistic volumes and say whether repeat orders are likely.

• drawing and 3D model at the current revision
• material grade and form, and whether you supply material
• quantity per batch and expected annual volume
• finishing, heat treatment and coating requirements
• inspection level and paperwork required
• packaging, delivery address and target date

ISO 9001 certification shows that a supplier runs a documented quality management system: drawing revision control, calibrated gauges, traceability, handling of non-conforming parts. It does not prove that every part is right, but it tells you there is a system for finding out. Ask for the certificate and check that it was issued by a certification body accredited by UKAS or an equivalent accreditation body, and that the scope covers machining.

For material, ask for mill certificates. In metals, inspection documents are defined by BS EN 10204, and a type 3.1 inspection certificate traces a batch to its chemical and mechanical test results. If traceability matters to your customer, say so at quotation stage, because certified material and the paperwork cost more and must be ordered that way from the start.

For the first batch, a first article inspection report, often with coordinate measuring machine results against the drawing, is a reasonable request. Agree how rejected parts are handled, who pays for remakes and how quickly.

Your drawing is your intellectual property. Before sending detailed drawings, it is common to put a non-disclosure agreement in place, especially for a new product. The NDA should cover drawings, models and samples, restrict use to quoting and making your parts, and require return or deletion at the end.

Also settle ownership of what the job creates: CNC programmes, fixtures and dedicated tooling. If you pay for a fixture, agree that it belongs to you and that you can collect it if you move the work. Without that, changing supplier later can mean paying for everything twice.

A machining quote is built from programming, set-up, cycle time per part, material, finishing, inspection and delivery. For one-offs, programming and set-up dominate; for large batches, cycle time and material do. Ask the supplier to separate one-off costs, such as programming and fixtures, from the price per part, so you can see what repeat orders will cost.

Lead time depends on material availability, the shop's workload and outside processes such as plating or heat treatment, which are often subcontracted and add days or weeks. Confirm the delivery date in the order, not just in an email.

In the form you choose the processes, the material, the quantity and whether drawings exist. Once you have confirmed your phone number with a code sent by text message and your email address through a link, we offer the job, without your name or contact details, to machining businesses in your region. It is sold to one company only; that company pays Offrano and the service is free to you.

Before that business gets your contact details, we email you who it is, with address and phone number. Share drawings only after you have spoken and, if needed, signed an NDA. There is no guarantee that a machine shop takes the job, and the request lapses after 21 days if none does. Offrano checks registration, not capability, so ask for the ISO certificate and examples of similar work.