Automotive CNC Machining: Parts, Tolerances and PPAP Requirements汽车零件 CNC 加工：零件族、公差与 PPAP 要求全指南

Automotive CNC machining is the production of vehicle components — powertrain parts, transmission components, chassis brackets, braking hardware, EV housings, sensor housings — by controlled material removal on 3-axis, 4-axis and 5-axis machining centres, delivered with the quality evidence an automotive programme requires. That last clause is what separates automotive CNC machining from general precision machining. The dimensions are only half the deliverable; the other half is the documentation trail that proves the process can hold those dimensions again next month.

We are an IATF 16949 certified CNC machine shop in Dongguan, China, running 200+ machining centres and serving automotive Tier 1 suppliers, EV developers and engineering teams across North America and Europe. This guide is not a capacity brochure. It is the decision framework we walk a buyer through when they send us a drawing — process selection, CTQ tolerances, heat treatment, PPAP evidence by programme stage, and the cost structure behind the number on the quote.

In one sentence: automotive CNC machining is the controlled removal of metal on 3-, 4- and 5-axis machining centres to produce vehicle components, delivered with the quality evidence an automotive programme requires.

If you are still at the concept stage, read this together with our DFM analysis guide, because roughly a third of the cost of an automotive part is locked in before the first chip is cut.

What automotive CNC machining actually covers

A vehicle contains somewhere between 20,000 and 30,000 parts, and a few hundred of them are machined metal. Automotive CNC machining sits in the gap between two extremes: parts too complex or too low-volume for stamping and die casting, and parts too critical to trust to a process with no dimensional feedback loop.

That gap is wider than most people assume, and it is where most automotive CNC machining work actually lives. It covers:

• Anything in a prototype or validation build, where volumes are 1–50 units and tooling amortisation is impossible
• Anything with three-dimensional geometry — angled faces, contoured sealing surfaces, intersecting bores
• Anything with tight CTQ features — bearing fits, sealing faces, press-fit diameters, runout on a rotating assembly
• Anything safety-critical in low volume — braking hardware, steering components, restraint system fittings
• Anything where a post-machining process is already required — heat treatment, hard turning, precision grinding

The four questions every RFQ has to answer

When we open an automotive RFQ, four things determine whether the quote is straightforward or needs an engineering conversation:

1. Which features are CTQ, and how is each one measured? A tolerance with no measurement method is not a tolerance, it is a wish. A 0.02 mm flatness callout measured with a surface plate and a dial indicator is a different job from the same callout measured on a CMM with a scanning head.
2. What is the annual volume and the ramp curve? 200 parts a year and 200,000 parts a year are not the same part, even with identical drawings. The first wants multi-axis machining; the second wants a different process entirely.
3. What does the finished part have to survive? Temperature cycling, vibration, salt spray, pressurised fluid, repeated assembly and disassembly. This decides material, heat treatment and coating — in that order.
4. What documentation is required at each milestone? FAI at prototype, control plan and capability study at pilot, PPAP Level 3 at SOP. Say it in the RFQ, not three weeks before launch.

Prototype, pilot and SOP are three different jobs

A European engineering team once asked us to quote 30 transmission housings a year on the same terms as their 30,000-a-year production part. The drawing was identical, the price expectation was a tenth of the pilot quote, and the gap was not profit margin — it was that the two numbers describe two completely different jobs. A European engineering team once asked us to quote 30 transmission housings a year on the same terms as their 30,000-a-year production part. The drawing was identical, the price expectation was a tenth of the pilot quote, and the gap was not profit margin — it was that the two numbers describe two completely different jobs. The single most expensive misunderstanding in automotive sourcing is treating prototype production as a small version of serial production.

The geometry can be identical across all four rows. The *evidence* is not. If you quote a China supplier on a prototype price and then expect PPAP at SOP, you will get a surprise; if you specify PPAP from day one on a prototype, you will pay for documentation you cannot yet generate meaningfully.

Seven automotive part families we machine

CNC machined car parts are usually grouped by the vehicle system they belong to, because the system determines load case, material and tolerance regime. These seven families account for the overwhelming majority of the automotive CNC machining work we quote.

Powertrain and engine

Engine brackets and mounts, valve bodies, pump housings, throttle body inserts, sensor bosses, camshaft position sensor rings. Materials are dominated by 42CrMo, 20CrMnTi, S45C and, where weight matters, 6061-T6 and 7075-T6 aluminium. Tolerances are driven by bore fits and sealing faces. Our dedicated guide to engine components machining covers the tolerance stack in detail.

Typical CTQ: bore roundness, face flatness, position of bolt patterns relative to the primary datum.

Transmission and driveline

Shafts, synchroniser rings, shift forks, differential pins, clutch actuator components, transmission housing connectors. Mostly turned parts, frequently with milled features added — which makes turn-mill, not turning, the right machine class. Surface and concentricity control matter more than absolute size. See our transmission shaft machining guide for the process chain and the seven tolerances that decide whether a shaft survives.

Typical CTQ: runout, coaxiality, cylindricity, spline or keyway position, journal Ra.

Chassis, steering and suspension

Chassis work is where automotive CNC machining most often competes with forging and casting, because the load case is severe and the geometry is genuinely three-dimensional. Control arm inserts, steering knuckle bosses, subframe brackets, suspension mounts, tie rod adapters. These are load paths, so fatigue life dominates design. Sharp internal corners are the enemy; generous radii, shot peening and correct heat treatment extend life more than an extra tolerance band ever will.

Typical CTQ: hole position, boss height, thread depth, surface integrity at high-stress radii.

Braking and safety

These are the parts where automotive CNC machining is chosen for traceability rather than for geometry: a machined part can be tied to a material heat number in a way a casting often cannot. Caliper guide pins, ABS sensor rings and housings, brake actuator components, safety fasteners. These are the parts where 100% inspection on critical features is normal rather than optional, and where traceability is not negotiable.

Typical CTQ: 100% on guide pin diameter and runout, ring concentricity, thread functional gauge.

EV battery, motor and thermal

Battery module interconnects, busbar components, motor housings and stator alignment pins, cooling plate manifolds, e-axle housing inserts, high-voltage connector bodies. This is the fastest-growing family and it brings new requirements: copper and lead-free brass, RoHS compliance, IP-rated sealing faces, and thermal management surfaces. Our EV motor housing guide covers the tolerance and finish regime specific to motor housings.

Typical CTQ: coaxiality ≤ 0.005 mm TIR on stator alignment, sealing face Ra ≤ 0.8 µm, press-fit diameters to H7/p6.

ADAS sensors and electronics housings

ECU enclosures, sensor housings, radar and lidar mounting brackets, heat sinks, connector shells. Environmental sealing and thermal paths dominate. Aluminium 6061 and ADC12 pressure-cast billets machined to final form are common.

Typical CTQ: gasket groove depth and width, sealing surface flatness, position of mounting holes relative to the optical or radar axis.

Interior hardware, tooling, fixtures and gauges

High-aesthetic knobs, bezels, trim inserts, plus the assembly fixtures, inspection fixtures and gauge bodies that a production line consumes. These parts often carry cosmetic specifications that no functional requirement justifies — and that is where the money goes if nobody pushes back.

Process selection: CNC vs stamping vs die casting vs sheet metal

We quote a lot of parts we would rather not machine. A flat steel bracket at 80,000 pieces a year does not belong on a machining centre, and saying so early is worth more to a buyer than a low first-article price on a process that will lose money at volume. We quote a lot of parts we would rather not machine. A flat steel bracket at 80,000 pieces a year does not belong on a machining centre, and saying so early is worth more to a buyer than a low first-article price on a process that will lose money at volume. This is the decision that most often gets made wrong, because it gets made on unit price alone for a single volume.

The honest framing is that CNC machining wins where complexity, tolerance or volume flexibility matter, and loses on unit cost once volume is high enough to amortise tooling. The crossover points below are the ones we see across automotive programmes; treat them as planning numbers, not commitments.

Two rules sit above the table.

First rule: below about 5,000 parts a year, tooling never pays back within a realistic programme window. A progressive die that costs the equivalent of six months of engineering attention has to run for years to justify itself, and it cannot be revised when the design changes — which, on an EV programme, it will.

Second rule: above about 50,000 parts a year for a simple flat part, CNC machining is the wrong answer — and automotive CNC machining is no exception. If the geometry is genuinely two-dimensional, stamping will beat machining on unit cost by a wide margin once the die exists. We say this even though we would rather machine the part. Both of these comparisons are worked through in more depth in metal stamping vs CNC and CNC machining vs sheet metal.

Where multi-axis changes the answer

Multi-axis capability moves the crossover point, and not only by making cycle times shorter.

• 5-axis simultaneous machining removes setups. Every re-clamp is a new datum error, so a part with features on five faces cut in one setup holds position far better than the same part machined in four operations. Our five-axis CNC machining guide covers which geometry actually benefits.
• Turn-mill eliminates the second operation on rotational parts with milled features. On a transmission shaft with cross-drillings and a milled flat, this can remove two fixtures and a full day of queue time.
• Deep hole drilling is a specialist capability that is often assumed rather than verified. A 20:1 depth-to-diameter oil gallery is not a drilling operation, it is a process with its own tooling, coolant pressure and straightness control. See deep hole drilling for the limits.

Materials for automotive CNC parts

Material choice in automotive work is driven by four things in order: load case, operating temperature, corrosion exposure, and weight target. Cost runs fifth, and appearance last.

Aluminium: the default for weight-driven parts

Aluminium is the default material for automotive CNC machining that has a weight target attached, and 6061-T6 is the workhorse. It machines cleanly, anodizes predictably, welds, and carries enough strength for most brackets and housings. 7075-T6 gives roughly 60% more yield strength at the cost of machinability and slightly worse corrosion behaviour — anodizing is strongly recommended rather than optional. Our aluminium CNC machining guide covers the alloy trade-offs and the anodizing interaction.

One warning that costs people real money: do not mix aluminium heats on cosmetic parts without controlling the anodizing process. Silicon and iron content vary slightly between heats, and Type II anodizing amplifies that variation into a visible colour difference. On one audio programme we inherited, two batches came back visibly different under showroom lighting, and the root cause was exactly this. The fix was a controlled glass-bead pre-treatment, a locked alloy source, and a documented dye concentration.

Steels: where heat treatment enters the route

42CrMo4 and 20CrMnTi are the classic automotive alloy steels. 20CrMnTi is a case-hardening grade — it takes a hard, wear-resistant surface over a tough core, which is exactly the profile a gear or a splined shaft wants. 42CrMo4 is a through-hardening grade used where the whole section must carry load.

The machining consequence is the same in both cases: heat treatment comes after rough machining and before finish machining. Rough out with 0.3–0.5 mm of stock left, treat, then finish to size. Trying to machine to final size first and then heat treat guarantees distortion problems you cannot fix without scrap. The full sequence and the distortion-control techniques are in our heat treated CNC parts guide.

Stainless, copper alloys and the specialties

Stainless 303 is the free-machining grade and the right answer for most fittings and sensor bodies. 304 and 316 are chosen for corrosion resistance, not machinability; 316 in particular work-hardens aggressively and needs positive feed and rigid tooling. Our stainless steel machining guide covers the cutting parameters.

Copper and brass appear wherever current flows or low friction is required. Note that RoHS restricts leaded brass in many automotive applications, which pushes designs toward lead-free grades that machine differently and need adjusted parameters. Titanium is a motorsport material in practice — the strength-to-weight ratio is excellent, the tool life is not.

Tolerances and CTQ: what to put on the drawing

A North American EV customer sent us a housing with 47 dimensions, 41 of them at ±0.05 mm. We asked which six mattered; the answer was three bores, a sealing face and two bolt patterns. Loosening the other 41 cut the quote by roughly a quarter and changed nothing about how the part performs. A North American EV customer sent us a housing with 47 dimensions, 41 of them at ±0.05 mm. We asked which six mattered; the answer was three bores, a sealing face and two bolt patterns. Loosening the other 41 cut the quote by roughly a quarter and changed nothing about how the part performs. The most useful thing an automotive buyer can do before sending an RFQ is to separate the drawing into "dimensions that matter" and "dimensions that exist". Cost scales with the *number* of tight tolerances far faster than it scales with the *value* of any single one.

Per-family CTQ thresholds

Two principles sit behind this table.

The decision between 100% inspection and sampling is driven by feature risk and process stability, not by habit. Critical mating interfaces and safety-critical dimensions get 100% verification. Stable structural features on a proven process move to statistically controlled sampling once capability is demonstrated.

Measurement method must be fixed before production, not after. A flatness value measured on a surface plate and the same value measured by CMM scanning will not agree, because they are measuring different physical things. Agree the method in the control plan and use the same instrument, fixture, datum and technique at every interval — otherwise SPC data reflects measurement drift rather than process behaviour.

GD&T callouts that decide fitment

Five callouts do most of the work on automotive drawings:

1. Position with a datum reference frame — defines the tolerance zone relative to the assembly datums, not to whatever surface the operator felt like clamping.
2. Profile of a surface — the only callout that controls a contoured sealing or mating surface in both form and location.
3. Perpendicularity or parallelism to a datum — controls the relationship that actually causes assembly failure.
4. Total runout — for rotating parts, this is the callout that decides whether the assembly vibrates. It is stronger than circular runout and usually the correct choice.
5. Maximum material condition (MMC) modifiers — allow bonus tolerance as a hole departs from MMC, which is a legitimate cost reduction when it matches the functional requirement. Use it when it is real, not as a default.

The tolerance you should not specify

Every shop has seen a drawing where a non-functional cosmetic surface carries a ±0.05 mm tolerance and a functional bore carries ±0.1 mm. Correcting that is often worth 10–20% of the part price with no functional loss. If a dimension controls nothing, loosen it. Our CNC machining tolerance guide walks through how tolerance count and value translate into cost.

Heat treatment and surface finishing in the automotive route

Heat treatment and finishing are where the sequence matters more than the individual process. Get the order wrong and you either destroy the surface you just paid for, or you distort a part you already finished.

Three practical notes.

For automotive CNC machining, heat treatment is not an optional add-on — it is usually the step that determines whether the part meets its service life. Hardness targets, not process names, belong on the drawing. "Harden to 58–62 HRC" is a specification; "carburise" is a method. Specify the outcome and let the shop choose the route, unless the method is functionally constrained.

Coating thickness is a dimensional change. A 20 µm anodic layer grows roughly 10 µm outward and penetrates roughly 10 µm. A 60–150 µm powder coat will close small holes and destroy thread fits. Either mask the critical features or widen their tolerance deliberately. Our CNC parts finishing guide covers the dimensional math process by process.

Passivate every machined stainless part. Machining embeds free iron from tooling into the surface; without passivation, even correct 304 or 316 shows rust in service.

IATF 16949: what it changes on the shop floor

The word buyers use most often about PPAP is 'pain'. It is also the word they use about an uncontrolled supplier. The word buyers use most often about PPAP is 'pain'. It is also the word they use about an uncontrolled supplier. IATF 16949 is not ISO 9001 with a different cover. It adds automotive-specific requirements on top of ISO 9001:2015, and the operational core of it is five tools that a certified shop uses continuously rather than assembling at audit time.

The five core tools

• APQP — Advanced Product Quality Planning. The framework that takes a part from concept to serial production in five phases, each with defined deliverables and a gate.
• PPAP — Production Part Approval Process. The evidence package proving the production process can repeatedly make parts to the drawing.
• FMEA — Failure Mode and Effects Analysis. Process risk assessment. Since the 2019 AIAG-VDA handbook, most OEMs require Action Priority (AP) rather than a raw RPN number, with severity weighted first.
• SPC — Statistical Process Control on CTQ features, with capability measured against a customer-defined target, commonly Cpk ≥ 1.33 and 1.67 for safety-critical characteristics.
• MSA — Measurement System Analysis. Gage R&R on the instruments used for CTQ measurement, typically required below 30% and preferably below 10% of tolerance.

The tool that catches most first-time buyers off guard is MSA. It is entirely possible to have a process holding ±0.01 mm while the gauge used to verify it contributes most of the observed variation — in which case the capability study measures the gauge, not the process.

What PPAP looks like at each programme stage

PPAP Level 3 requires 18 elements, but not all of them are meaningful at every stage. This is the staged map we work to with buyers:

The most common PPAP mistakes we see are not missing documents. They are procedural:

• A capability study run on 10 parts. Statistically, an initial process study needs 30 or more parts from a production run to mean anything.
• A process FMEA copied from a similar part and never reviewed against the actual geometry and fixtures.
• A control plan that does not line up with the FMEA's high-priority failure modes.
• Gage R&R above 30% on a critical dimension, quietly accepted.
• Measuring only the CTQ features and skipping reference dimensions on the layout.
• Sample parts that are the best parts off the machine rather than randomly selected production parts.

Documents we include with every automotive order

Beyond the programme-stage package, every shipment carries:

Engineering changes without mixed revisions

An engineering change notice in the middle of a production run is one of the most reliable ways to ship a defective batch, because the failure mode is silent: a mixed shipment of two revisions that both pass their own inspection.

The controls that prevent it are simple and non-negotiable:

1. Quarantine existing stock at the old revision the moment the ECN is confirmed. Physically separate it; do not rely on labels in a shared bin.
2. Confirm the change scope in writing — which features move, which processes are affected, whether the fixture or program changes.
3. Update the program and the inspection plan together. A new toolpath with the old CMM routine is worse than not changing anything.
4. Re-run FAI before resuming production, and document the changeover point — the serial number or date after which all parts are the new revision.
5. Never mix revisions in a single shipment. Each lot ships at one confirmed revision with traceability back to the changeover.

Cost structure and lead time

Unit price in automotive CNC machining is the sum of five things, and knowing their relative weight tells you where to negotiate.

Where the money goes

The same six cost elements appear in every automotive CNC machining quote, and their relative weight changes more with volume than with geometry.

The pattern to notice is that tolerance count and inspection frequency can outweigh material choice. A part in expensive alloy with two CTQ features and sampling inspection is frequently cheaper than the same part in mild steel with twelve tight tolerances and 100% CMM.

The twelve inputs that make custom automotive CNC parts quotable in 24 hours

We turn most quotes for custom automotive CNC parts around in 24 hours. What makes that possible is not a database — it is a complete input set:

1. 3D model (STEP or IGES preferred) plus a dimensioned 2D drawing
2. Drawing revision number
3. Material grade and specification
4. Heat treatment requirement, specified as hardness or property outcome
5. Surface finish requirement per surface, with masked areas identified
6. CTQ feature list, or the drawing callouts that identify them
7. GD&T datum reference frame
8. Annual volume and the first-order quantity
9. Target programme dates for prototype, pilot and SOP
10. Required documentation per stage (FAI only, or full PPAP Level 3)
11. Packaging and shipping requirements
12. Any customer-specific requirements — OEM CSR, IMDS, RoHS or REACH declarations

Missing items 6, 7 or 10 account for most of the delay on automotive RFQs.

Lead time

In automotive prototype machining, low-volume parts typically ship in 3–7 days from drawing sign-off. Pilot quantities with dedicated fixtures run 2–3 weeks. Serial production with full PPAP adds documentation and capability-study time on top of production time — plan for the documentation, not around it. Our CNC prototyping guide covers the prototype-to-production transition; low volume CNC machining covers the programme sizes in between.

How to qualify a supplier for IATF 16949 CNC machining

For IATF 16949 CNC machining, certification is a starting filter, not a conclusion. Ten things to verify beyond the certificate:

1. Certificate scope. Does the certification cover the processes you are buying — machining only, or machining plus heat treatment plus finishing?
2. In-house versus outsourced finishing. Outsourced heat treatment and anodizing add a supplier to the traceability chain. Ask who controls it and how the thickness and hardness are verified.
3. Inspection equipment list. CMM, roughness tester, roundness tester, thread gauges, hardness tester, spectrometer. If they own it, they use it.
4. Capability data, not claims. Ask for Cpk on a comparable CTQ feature from a real production run.
5. Traceability chain. Can they walk a finished part back to a material heat number and a machine record?
6. Machine list with axis count and work envelope. Not "200 machines" — which machines, what envelope, what tolerance class.
7. Process for handling an ECN mid-production. The answer tells you whether revision control is real.
8. Reaction plan. What happens when a CTQ feature drifts below target mid-run? A shop without an answer is hoping, not controlling.
9. Engineering presence. Can they push back on a tolerance that does not serve the function? A shop that quotes exactly what you drew without comment is not adding value.
10. Communication cadence. Who is your contact, in what time zone, and how fast do DFM questions come back? Our choosing a CNC supplier guide covers the commercial and cultural dimensions of this.

Why a Dongguan IATF 16949 shop for automotive CNC parts

Dongguan is one of the densest precision-manufacturing clusters in the world. For automotive work, three advantages are structural rather than promotional.

Supply chain depth. Material, heat treatment, anodizing, plating and metrology all sit within a short drive. That matters because automotive parts rarely stop at machining — a programme that needs carburising, hard turning and passivation routed within one cluster keeps lead time and quality control in a single accountable chain.

Equipment density at the right price point. Multi-axis machining capacity per unit of capital is higher here than in most Western markets, which is what makes low-volume and pilot automotive work economically viable without compromising on 5-axis capability.

Familiarity with Western documentation expectations. A shop that routinely produces PPAP Level 3 packages, IMDS submissions and EN 10204 3.1 material certificates for European and North American customers does not need to be taught what a PSW is.

Our own position in automotive CNC machining: IATF 16949 certified, ISO 9001:2015 certified, ISO 13485 certified for medical-adjacent work, 23+ years of precision manufacturing, 200+ machining centres including 3, 4 and 5-axis, holding ±0.01 mm on automotive work with tighter capability on selected features. We run prototype, pilot and serial production for automotive CNC machining programmes, with in-house access to anodizing lines and a qualified heat-treatment network. Related reading: automotive bracket CNC machining, CNC turning services, CNC milling services and automotive metal bearings. Related reading: automotive bracket CNC machining, CNC turning services, CNC milling services and automotive metal bearings.

A representative example: an automotive Tier 1 supplier came to us with a metal bearing for an engine auxiliary and transmission assembly. The challenges were dimensional control on the running surfaces, surface quality variation between batches, and a prototype cycle that had stretched to 12 days. We replaced the existing route with a turning plus precision grinding combination, added defined roughness control on the functional surfaces, and brought heat treatment and protective finishing into one controlled sequence. Prototype lead time dropped from 12 days to 5, dimensional acceptance ran above 99.5%, and on-time delivery of serial batches held at 100%. Their engineering contact put it simply: *"Their machining consistency and quality control give us great confidence in mass production."*

FAQ about automotive CNC machining

What tolerances can you hold in automotive CNC machining? ±0.01 mm is our standard automotive machining tolerance, with ±0.005 mm achievable on selected features where geometry, material and fixturing allow. The practical limit depends far more on the feature than on the machine — a bearing bore in a rigid steel part is easier than a thin-wall aluminium housing.

Do you provide PPAP documentation? Yes. We provide PPAP Level 3 packages including dimensional results on all ballooned characteristics, material and performance test results, process flow diagram, PFMEA, control plan, MSA studies, initial process study data, sample parts and a signed Part Submission Warrant. Tell us the required submission level in the RFQ so the documentation can be planned into the programme schedule rather than added at the end.

How long does an automotive CNC quote take? We return most quotes within 24 hours when the RFQ includes a 3D model, a dimensioned drawing, the CTQ list, volumes and the required documentation level. Incomplete input on CTQ features and documentation is the usual cause of delay.

Can you handle both prototype and serial production? Yes, and that is deliberate. Running prototype, pilot and SOP quantities with the same process logic means the capability data generated at pilot actually predicts serial performance. Our CNC prototyping guide explains how the transition is managed.

What materials do you machine for automotive parts? Aluminium 6061-T6, 7075-T6, 6063, 5052 and 3003; alloy steels 42CrMo, 20CrMnTi, 40Cr and S45C; stainless 303, 304, 316 and 430; brass, phosphor bronze and copper; titanium Grade 5; and engineering plastics including POM and PEEK. Our CNC machining materials guide covers selection logic.

Do you offer heat treatment and surface finishing? Yes. Carburising, through hardening, tempering and stress relieving are available through qualified partners, and we operate adjacent anodizing capacity. Finishing options include anodizing, electroplating, electroless nickel, powder coating, passivation, shot peening, laser marking and screen printing.

How do you handle an engineering change mid-production? We quarantine existing stock at the old revision, confirm the change scope in writing, update the program and inspection plan together, re-run FAI, and document the changeover point. We do not mix drawing revisions in a single shipment — each lot ships at one confirmed revision with full traceability.

Do you support low-volume automotive CNC machining, not just high volume? Yes. Much of our automotive work is prototypes, engineering validation builds and pilot runs in the 1–2,000 part range, where a 5-axis multi-axis approach avoids tooling investment entirely. Our low volume CNC machining guide covers the economics.

Conclusion: buy the process, not the part

Automotive CNC machining rewards buyers who treat the drawing and the documentation as one deliverable. The geometry is usually the easy part — a competent shop with multi-axis capacity can hit ±0.01 mm. What separates suppliers is whether they can tell you, before production starts, which features are critical, how each will be measured, what evidence will exist at each programme stage, and what happens when the design changes.

If you have an automotive part in development, send us the model, the drawing and the CTQ list. For a broader view of sourcing, see choosing a CNC supplier, CNC machining cost drivers and precision fasteners. For a broader view of sourcing, see choosing a CNC supplier, CNC machining cost drivers and precision fasteners. Upload your CAD files for a DFM review and a quotation within 24 hours, and we will tell you which process route fits your volume — including when that route is not CNC machining at all.