CNC Machining Services Basingstoke: How to Pick a Supplier

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  What matters most when you compare suppliers
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  Supplier comparison: what to check before you commit
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  Start with the geometry, not the price
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  Tolerance, finish and the cost curve
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  Lead time, MOQ and what a quote should contain
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  Red flags in a machining quote
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  How to run the supplier selection, step by step

Send a part with a deep pocket, a thin wall and a tight true-position callout, and the supplier's machine list matters more than their hourly rate. A three-axis mill can cut the same shape, but it needs more setups, more fixtures and more chances to lose the datum. Every extra setup adds stack-up error and inspection time. That cost lands in your quote even if the shop never explains it.

Ask how many setups the part needs before you ask for a number. A housing with features on five faces is a natural fit for a simultaneous 5-axis center. The tool reaches the part at an angle, so you skip the re-fixturing. GreatLight runs 16 simultaneous 5-axis machining centers, plus 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers, so the setup plan is chosen per part rather than per shop habit.

Size sets the machine too. The largest travel we quote is 4,000 × 400 × 150 mm, with common envelopes at 750 × 1,150 × 550 mm, 600 × 600 × 600 mm, 500 × 500 × 450 mm and 500 × 310 × 200 mm. A Ø400 mm rotary table covers round parts that need indexing. If your part does not fit those envelopes in one setup, say so early. A split design might be cheaper than a special fixture.

Basingstoke sits close to a lot of small-batch design work: instrument enclosures, lab fixtures, motor housings. Those parts are usually aluminium or stainless, quantities under 200, and the schedule is driven by a build or a test date. That profile rewards a shop that can quote fast and hold tolerance without a long setup study.

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  Complex geometryFive faces of features, angled holes or undercuts: 5-axis is usually cheaper than a fixture set.
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  Simple turned partsShafts and bushings belong on a mill-turn center; do not pay for 5-axis time.
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  Thin wallsUnder 1 mm in aluminium, plan light finishing passes and expect to pay for them.

Tolerance is not a single shop-wide number. It is a per-feature decision. A ±0.005 mm bore costs far more than a ±0.05 mm mounting hole on the same part, because it needs a controlled environment, a warm-up cycle and probing. Mark only the features that carry function. Everything else can sit at general tolerance and save you money without hurting the assembly.

Surface finish follows the same logic. Ra 1.6–3.2 μm is a normal as-machined result on aluminium and steel. Ra 0.8–1.6 μm needs a finishing pass and sometimes a different insert. Ra 0.2–0.8 μm is a specialist operation and should be reserved for sealing faces, bearing bores or optical seats. If you call out a fine finish across the whole part, you are paying for cosmetic work.

Materials behave differently at the same tolerance. Aluminium 6061 and 7075 cut clean and hold size well. Stainless 316 and 17-4PH work-harden, so feeds and speeds need care and the toolpath changes. Titanium TC4 and Inconel move more under heat and take longer. Plastics like POM and PEEK deflect during clamping, so a ±0.005 mm callout on a long plastic part is often unrealistic.

A useful habit: send the drawing with the tolerance and finish callouts highlighted, and ask the supplier to flag any that they consider risky. GreatLight returns a free DFM analysis with the quote, usually within 12 hours, and that is where tolerance problems surface before the chips fly.

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  Tight only where it countsReserve ±0.005 mm for fits, bores and datums.
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  Finish is a separate cost lineRa 0.2–0.8 μm belongs on functional faces, not on every surface.
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  Material changes the planWork-hardening stainless and titanium need different feeds, not the same program.

Lead time on a machined part is mostly queue time, not cutting time. A shop with spare capacity can start within 24 hours and ship in 3–5 days on standard work. A busy shop may hold your job behind a large run. Ask when the machine will actually be free, not just how long machining takes. Historical late-delivery probability below 2% is the kind of number worth asking about.

Minimum order quantity is the other lever. Some suppliers set a floor at 500 pieces because setup is expensive for them. That is a business choice, not a technical limit. A shop that runs one prototype and a 10,000-part run on the same floor can take your single unit without inflating the price to discourage you.

Read the quote as a document. It should list material grade, blank size, machine and setup count, tolerance on critical features, finish, inspection method, lead time and the price break at each quantity. If any of those are missing, you will find out later, usually after the parts arrive. A quote without a material grade is not a quote.

Certification belongs in the same conversation. ISO 9001:2015 covers general quality management. IATF 16949:2016 is what automotive and EV programs expect. ISO 13485:2016 is the medical device standard. ISO 27001:2022 covers information security, which matters when you send proprietary drawings. Match the certificate to your sector, not to the supplier's marketing page.

Payment terms, shipping method and Incoterms sit outside the technical review but affect your landed cost. Agree them before the first order, especially on air freight from Asia. A cheap part price with unclear shipping terms is not a cheap part.

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  Ask for the start dateQueue position tells you more than an average lead time.
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  No MOQ is a real optionSingle prototypes and 10,000+ runs can sit on the same floor.
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  Demand a full quoteMaterial grade, setup count, tolerance, finish, inspection and price breaks.

The first red flag is a price that arrives in minutes with no questions. Machining quotes need a setup decision and a tool list. A number that fast usually means someone guessed, and the guess gets corrected after you place the order. A short DFM note with the quote is a better sign than a fast number.

The second is a tolerance promise that ignores geometry. If a supplier says they hold ±0.005 mm on everything, ask how they measure it and on which machine. Real answers mention CMM, temperature and probe cycles. Vague answers mention experience.

The third is certification without scope. A certificate that does not name the process or the site tells you little. Ask which plant will run the job and whether that plant holds the certificate. When a supplier runs several sites, the certificate may cover only one of them.

The fourth is silence on inspection. A supplier who cannot describe their first-article process or their sampling plan is a risk on any regulated program. 100% inspection before shipment, with raw material check, in-process monitoring and a final report on request, is a clear answer. Anything less specific deserves a follow-up question.

Finally, watch for a quote that changes after the PO. Material price moves, but a setup count or a tolerance class should not. If the revision appears without a drawing change on your side, treat it as a warning about how the next order will go.

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  Too fast, too vagueA quote with no DFM note is a guess, not an offer.
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  Blanket tolerance claimsAsk which machine and which measuring method back the number.
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  Certificate without scopeConfirm the site and the process the certificate actually covers.