CNC Machining Services for Prototypes in 2025

The first question on a prototype quote is not price. It is how many setups the part needs. A bracket with holes on two faces runs on a 3-axis mill with one or two re-clamps. A housing with angled ports, blended ribs, and a curved sealing face usually cannot be reached from three directions, and forcing it means extra fixtures, extra re-clamps, and stack-up error that no inspection report can fix.

Simultaneous 5-axis work earns its place when the part has undercuts, deep pockets with drafted walls, or features that must stay concentric across faces. Cutting in one setup holds those relationships far better than re-fixturing three times. GreatLight runs 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers, so the setup plan is chosen for the part rather than for whatever machine happens to be free.

Size decides the machine too. Large frames and long shafts go up to a 4,000 mm processing envelope, with travel of 4,000 × 400 × 150 mm on the biggest platform. Medium parts fit 750 × 1,150 × 550 mm or 600 × 600 × 600 mm. Compact parts land on 500 × 500 × 450 mm or 500 × 310 × 200 mm tables, and round parts with radial features can use a Ø400 mm rotary table.

One warning. A part that is 5-axis capable is not automatically cheaper on 5-axis. On simple geometry the extra programming and setup time shows up in the quote. Ask the supplier which operations actually need simultaneous motion and which ones do not.

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  Best for 5-axisUndercuts, drafted deep pockets, concentric features on multiple faces
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  Best for 3-axisPlate work, open pockets, holes on one or two faces
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  Best for mill-turnShafts, bushings, parts with turned and milled features

Prototypes exist to answer a question. If the question is fit, then 6061 aluminium or ABS will do, and they machine fast and cheap. If the question is wear, then the alloy matters and soft material will give you a false answer. Decide what the part has to prove before you pick the stock.

Aluminium is the default for most functional prototypes. The shop stocks 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075, and ADC12. Use 7075 when you need strength close to steel at a third of the weight. Use 6061-T6 when you need a stable, weldable, anodisable part. Use 2024 when fatigue behaviour matters more than corrosion resistance.

Stainless comes up whenever the part touches water, chemicals, or a cleanroom. Grades 303, 304, 316, 316L, 420, 430, 431, 440C, and 17-4PH (SUS630) are all available. Grade 303 machines the easiest and is fine for a fit check. Grade 316L is the one for medical and marine exposure. Grade 17-4PH can be aged to a higher strength after machining, which matters on load-bearing brackets.

Steel grades 1018, 1045, 4130, 4140, 4340, A36, and tool steel cover most structural and wear parts. Copper alloys C101, C103, C110, beryllium copper, C27400, C28000, and C36000 are used for busbars, RF housings, and thermal parts. Titanium TA1, TA2, and TC4 (Ti-6Al-4V), plus Inconel and magnesium AZ31B / AZ91D, are options when weight or temperature rules out everything else. Plastics include ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE, and carbon fibre.

Two practical notes. Titanium and Inconel cut slowly and wear tooling, so a prototype in those materials costs more and takes longer than the same part in aluminium. PEEK and carbon fibre need sharp tooling and controlled feeds to avoid delamination or melted edges. Neither is a reason to avoid the material, but both should show up in the timeline.

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  Fit check only6061-T6 aluminium, ABS, POM
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  Wear or load7075, 4140, 17-4PH, TC4
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  Corrosion or cleanroom316L, 316, 304
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  Thermal or electricalC110 copper, C36000 brass, aluminium 6063

Anodising adds a coating that grows the part. Hardcoat anodising grows it more than clear anodising. If a bore is machined to the final number and then anodised, the bore gets smaller and the pin no longer fits. Tell the shop which surfaces are cosmetic and which are functional, and mask the functional ones.

Plating behaves the same way. Electroless nickel, zinc, silver, and gold plating all add thickness, and the amount varies by process. Silver and gold are usually chosen for conductivity or solderability, not for wear, so thickness is small but still worth calling out on a tight connector face.

Powder coating and black oxide are the two finishes that most often surprise people. Powder coating can be 50 μm or more and will round off a sharp edge. Black oxide adds almost nothing and keeps the edge, which is why it is common on tooling and fixtures. Bead blasting, tumbling, brushing, and polishing are cosmetic or surface-prep steps and remove material rather than add it, so they should be listed before final inspection, not after.

Laser marking and engraving is the last step. Minimum character height is 1.5 mm. Put part numbers, revision letters, and serial marks on a flat, reachable face. Marking inside a deep pocket or on a curved surface can be done but the legibility drops, and it is worth confirming the location on a drawing rather than in an email.

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  Dimension-critical surfacesMask before anodising or plating
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  Sharp edges to keepChoose black oxide over powder coating
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  Cosmetic coversBead blast or brush after machining

A prototype is a measurement exercise as much as a manufacturing one. The report should tell you which dimensions were checked, what instrument was used, and what the actual reading was against the nominal. A single line that says "within tolerance" is not a report.

GreatLight inspects 100% of parts before shipment, with a raw material check, in-process monitoring, and a final inspection. Reports are available on request. For a first article, ask for the critical dimensions by name: the bore that carries the bearing, the hole pattern that bolts to the frame, the face that seals. Those are the numbers that decide whether the second version needs a design change or just a tolerance change.

Tolerances on prototypes run to ±0.005 mm (±0.0002 in) where the feature needs it. That number is achievable on a rigid setup with the right tooling, but it is not free. Reserving it for two or three features instead of the whole drawing keeps both cost and lead time realistic.

Quality systems matter when the prototype is a step toward production. GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. For automotive and medical programmes, that means the prototype records and the process controls carry forward instead of being rebuilt from scratch at the production stage. Uploads are secure and confidential, and an NDA is available on request.

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  Ask forDimension list, instrument, actual reading vs nominal
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  Keep looseNon-functional profiles, internal clearances
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  Keep tightBearing seats, bolt patterns, sealing faces