Precision CNC Machining for Sale: How to Pick a Supplier

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  Key takeaways
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  What to Compare Before You Buy
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  Start With Tolerance and Part Geometry
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  Match Material and Finish to the Service
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  Lead Time, Order Size, and What You Actually Pay For
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  Check Certifications Against Your Industry
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  From One Prototype to a Production Run
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  How to Run the Supplier Check

Tolerance is the first filter. A shop that quotes ±0.05 mm as standard cannot hold a bearing bore or a mating face on a gearbox housing. Ask what the machine can hold across the full part, not just on a clean test coupon. GreatLight works to ±0.005 mm (±0.0002 in) on 16 simultaneous 5-axis centers, with 12 four-axis mills and 27 three-axis machines covering simpler work.

Geometry decides the machine. A part with undercuts, deep pockets, or five-sided access to one setup belongs on a 5-axis center. A shaft with a cross-hole and a thread on both ends usually runs better on a mill-turn center, where one chuck holds the part through turning and milling. That avoids a second setup and the stack-up error that comes with it.

Size sets the floor. GreatLight handles parts up to 4,000 mm, with travels of 4,000 × 400 × 150 mm on the large frame and 750 × 1,150 × 550 mm or 600 × 600 × 600 mm on medium frames. Compact work goes on 500 × 500 × 450 mm and 500 × 310 × 200 mm machines, with a Ø400 mm rotary table for round parts.

If your print calls for a true position of 0.01 mm across a 600 mm casting, say so in the RFQ. A shop that quotes without reading that callout will either pad the price or miss the feature.

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  5-axisComplex pockets, undercuts, one-setup five-sided work
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  Mill-turnShafts and bushings with cross-features
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  3-axisPrismatic parts with open faces

Material availability changes both price and lead time. Aluminum 6061-T6 and 7075 machine fast and hold tight tolerances. Stainless 316L and 17-4PH move more slowly and wear tooling faster, so a quote that treats them like aluminum will not survive contact with the shop floor. Titanium TC4 (Ti-6Al-4V) and Inconel add another step: heat and tool wear must be managed or the finish and tolerance drift.

Plastics behave differently again. POM and PEEK hold dimension well after machining; ABS and PP flex under clamping pressure and need lighter cuts. If your part is a fixture or a housing, that difference decides wall thickness and fastener torque.

Finishing is where handoffs hurt. Anodizing, electroless nickel, zinc, silver, and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing, and polishing all change the surface. If the shop sends parts out for each step, the parts travel, get re-packed, and pick up marks. GreatLight keeps these steps in house, with laser marking down to 1.5 mm character height.

Surface finish is a number, not a mood. Ra 0.2–0.8 μm is a fine finish for sealing faces and sliding surfaces. Ra 0.8–1.6 μm covers most functional mating faces. Ra 1.6–3.2 μm is a normal as-machined finish for brackets and covers.

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  Aluminum6061, 2024, 5052, 5083, 6063, 6082, 7075, ADC12
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  Stainless303, 304, 316L, 420, 440C, 17-4PH
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  Titanium and specialTA1, TA2, TC4, Inconel, magnesium AZ31B / AZ91D
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  PlasticsABS, PC, PMMA, POM, PA, PEEK, PP, HDPE, carbon fibre

Lead time is a schedule input, not a slogan. A shop that quotes in 12 hours and starts production within 24 hours gives you room to react when a design changes. Parts that ship in 3–5 days keep a prototype loop short. Ask for the historical late-delivery rate; GreatLight tracks below 2%.

Order size should follow the program. A supplier that demands 1,000 pieces before it will quote forces you to commit to a design that may still change. No minimum order quantity means you can buy one prototype, test it, revise the drawing, and only then move to a 10,000+ part run with the same shop and the same process.

Price is built from material, machine time, setup, finishing, and inspection. If a quote arrives as one lump sum, you cannot tell whether the shop understood the part. A line-item quote lets you compare two suppliers on the same basis and spot the number that looks wrong.

Freight and duty are separate. A low unit price with slow consolidation can cost more than a higher unit price that ships when promised. Ask what ships, when, and from where. GreatLight runs from Dongguan, China and a Singapore factory at No.3 Joo Koon Circle.

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  QuoteWithin 12 hours, with free DFM analysis
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  StartProduction can begin within 24 hours
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  ShipParts ship in 3–5 days
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  VolumeOne prototype to 10,000+ parts

Certifications are not interchangeable. ISO 9001:2015 covers a general quality system and fits industrial machinery, robotics, and electronics work. IATF 16949:2016 is the automotive and engine hardware standard, and it carries the traceability and change-control rules that vehicle programs expect. ISO 13485:2016 is the medical device standard. ISO 27001:2022 covers information security, which matters when you send CAD files and process data to an outside shop.

Ask for the certificate scope, not just the logo. A certificate that covers machining but not heat treat or plating does not cover those steps if they are outsourced. Match the scope to the actual operations your part needs.

Inspection is where the tolerance claim is tested. Raw material check, in-process monitoring, and final inspection before shipment are the three points that catch problems while they are still fixable. 100% inspection before shipment is a stronger position than sampling, and reports should be available on request.

A shop with a 99.99% qualification rate still has to show how it gets there. Ask what happens when a dimension drifts out of tolerance mid-run: is the operator allowed to stop the machine, and who signs off on the rework?

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  ISO 9001:2015General quality system
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  IATF 16949:2016Automotive and engine hardware
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  ISO 13485:2016Medical devices
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  ISO 27001:2022Information security

Many programs stall at the handoff between prototype and production. The prototype shop cannot scale, so the work moves to a second supplier that re-quotes, re-programs, and sometimes changes the process. The part then needs re-qualification.

Keeping both phases with one shop removes that risk. The same fixturing, tool paths, and inspection plan carry over from the first article to the production run. Revisions are tracked against one drawing set.

Rapid prototyping, 5-axis machining, CNC milling and turning, sheet metal fabrication, 3D printing, die casting, vacuum casting, and surface finishing under one roof mean fewer suppliers to manage. That matters most when a program needs a machined housing and a cast bracket in the same build.

For parts that will be cast later, die casting and vacuum casting give a path from machined prototype to tooled production without leaving the supply chain.

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  One shop, two phasesSame fixturing and inspection plan
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  Fewer handoffsMachining, casting, and finishing in house
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  ConfidentialitySecure uploads, NDA available on request