Sussex CNC Processing Service Guide: 6 Checks Before You Order

• 1
  Key takeaways
• 2
  Which shop fits which job
• 3
  Start with the tolerance your feature actually needs
• 4
  Read the quote, not just the price
• 5
  MOQ, lead time and what changes them
• 6
  Certifications and paperwork
• 7
  Materials and finishes that fit the process
• 8
  Capacity tells you what the shop can reach
• 9
  Six steps to pick a supplier

Most buyers send a drawing and ask for a price. The better move is to mark the features that matter. A housing with one bore at ±0.005 mm and everything else at ±0.1 mm should not be quoted as if the whole part were tight. Tolerance drives machine choice, fixturing and inspection time, and it drives the price more than material does.

We hold ±0.005 mm (±0.0002 in) on critical features when the geometry allows it. That number only means something if the shop can measure it. Ask what instrument is used and whether the report comes with the parts. A CMM report on the tight features costs little and settles arguments later.

Some features cannot hold that tolerance. A deep narrow slot, a thin wall under 0.5 mm, or a bore far from any locating surface will move during cutting. In those cases the honest answer is a looser callout or a second operation, not a promise.

Rule of thumb: if the tolerance is tighter than one third of the natural process variation, expect extra cost. For milling, that line sits near ±0.01 mm on most aluminum parts.

A quote built for a Sussex CNC processing service should carry four things: unit price at your quantity, setup and tooling cost, material grade and finish, and a lead time with a start date. If any of those are missing, the number is not comparable to another supplier's number.

The DFM note matters more than the price line. It tells you whether an engineer looked at the part. Common notes cover an undercut that needs a 5-axis setup, a hole that should be drilled before heat treat, or a corner radius that is smaller than the cutter can reach. Each note is a cost you would otherwise find out at first article.

Beware of quotes that arrive in an hour with no questions. Either the part is simple, or nobody opened the file.

At GreatLight, quotation and free DFM analysis come back within 12 hours.

No minimum order quantity sounds like a sales line, but it changes how you plan. A shop that runs one prototype and a 10,000+ part run on the same floor can carry your design from validation to production without a second supplier qualification. That saves weeks of paperwork.

Lead time has three parts: material, machining and finishing. Standard aluminum plate is easy. Titanium and Inconel often add days before the spindle turns. Anodizing and plating run in batches, so a small order may wait for a full rack. Ask which step is the long pole.

Production can start within 24 hours of a confirmed order and released drawing. Parts ship in 3–5 days for typical jobs. Historical late-delivery probability is below 2%, but treat any date as a plan, not a contract.

If your schedule is fixed, say so at RFQ. It is easier to quote a realistic date than to recover a missed one.

ISO 9001:2015 covers quality management and satisfies most industrial buyers. IATF 16949:2016 is the one automotive programs ask for. Medical device work usually needs ISO 13485:2016. If you handle other people's designs, ISO 27001:2022 covers information security.

Ask for the certificate scope, not just the logo. A certificate that covers machining but not finishing does not cover your anodized part. Check the expiry date and the site address. A group certificate from another plant is not the same as the plant making your parts.

Material certificates, dimensional reports and first article inspection reports should be named in the purchase order. Reports are available on request. Ask before the run, because pulling data after shipment is slower and sometimes impossible.

Uploads are kept secure and confidential, and an NDA is available on request.

Aluminum 6061-T6 is the default for prototypes and fixtures: good machinability, stable, easy to anodize. 7075 gives higher strength for aerospace brackets but costs more and cuts slower. 2024 machines well and is common in aircraft work.

Stainless 303 is free-machining and good for shafts and fittings. 304 and 316/316L resist corrosion and are common in medical and food equipment, though they work-harden. 17-4PH (SUS630) takes heat treatment and holds strength at temperature. Tool steel and 4140 appear in molds and high-load parts.

Titanium TC4 (Ti-6Al-4V) and Inconel are used where weight or heat rules out steel. Both are slow to cut and hard on tooling, so budget more time. Magnesium AZ31B and AZ91D cut fast and light but need careful chip handling.

On finishing: anodizing (clear, color, hardcoat, conductive), electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing. Laser marking holds a minimum character height of 1.5 mm.

Machine count is a weak signal on its own. What matters is whether the shop has the right machine for your geometry. A part with features on five faces needs a 5-axis center, or three setups on a 3-axis mill with added error and fixturing cost.

GreatLight runs 127 high-precision CNC machines: 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Maximum processing size is 4,000 mm, with travels of 4,000 × 400 × 150 mm on the large platform and 750 × 1,150 × 550 mm on the medium one.

Mill-turn centers handle parts that need turning and milling without a second setup. A Ø400 mm rotary table covers ring-shaped and flange parts. If your part is longer than 4,000 mm or heavier than the table allows, say so early.

Ask how the shop fixtures your part. A good answer names a vise, a custom soft jaw or a vacuum plate. A vague answer means the setup is being invented during the quote.