Chennai CNC machining excellence: what to check before you place a PO

A shop that only runs three-axis mills will quote your part, then fight it. Undercuts, angled ports, deep pockets on five faces, and thin walls that deflect under load all push work toward multi-axis machines. In Chennai, many suppliers run three-axis and four-axis mills with a rotary table. That handles a lot of automotive brackets and pump housings. It does not handle a turbine blade profile or a surgical instrument with compound curves.

The practical test is whether the shop owns simultaneous five-axis centers or only 3+2 positioning. Simultaneous five-axis moves all axes at once, so a single setup can finish a contoured surface without re-fixturing. Every re-fixture adds a datum error. If a part has three faces of critical features, that error stacks.

We run 16 simultaneous five-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. Maximum processing size reaches 4,000 mm, with travels of 4,000 × 400 × 150 mm on the large frame and 750 × 1,150 × 550 mm on medium frames. The Ø400 mm rotary table covers a lot of round work. That mix matters because it keeps us from forcing a part onto the wrong machine.

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  Simultaneous five-axisOne setup finishes contoured surfaces; fewer datum shifts, tighter true position.
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  3+2 positioningGood for angled holes and faces; still needs re-fixturing for curved profiles.
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  Mill-turnShafts and bushings come off one machine with concentricity held in one chucking.
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  Large travelsUp to 4,000 mm parts; anything longer needs a different process.

A tolerance callout is a promise about the whole process, not just the cutter. ±0.005 mm (±0.0002 in) is achievable on rigid setups in aluminium and brass, and on smaller stainless and titanium features when the toolpath is planned for it. It is not realistic on a 900 mm long thin aluminium extrusion with a 2 mm wall, because thermal drift and clamping force move the part between passes.

Surface finish follows the same logic. As-machined finishes land around Ra 1.6–3.2 μm. A high-quality finish of Ra 0.8–1.6 μm is normal for sealing faces and bearing bores. Fine finishes of Ra 0.2–0.8 μm need slower feed rates, sharper tools, and often a finishing pass with a smaller stepover. That costs cycle time. Engineers should only call it where a seal, an O-ring, or a sliding fit requires it.

Geometry drives the decision more than the tolerance number. A deep pocket with a 4:1 depth-to-diameter ratio needs a long tool, and long tools chatter. A sharp internal corner cannot be cut by a round end mill. Design the corner radius at least 1.2 times the tool radius and the part gets cheaper and straighter.

We inspect 100% of parts before shipment. That covers raw material check, in-process monitoring, and final inspection, with reports available on request. Historical qualification rate is 99.99%. Those numbers come from measuring the part, not from trusting the machine.

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  ±0.005 mmHold it on rigid, well-supported features; not on long flexible walls.
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  Ra 0.2–0.8 μmReserve for seals and sliding fits; adds finishing cycle time.
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  Corner radiusKeep at 1.2 × tool radius minimum to avoid slow, weak small tools.
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  Depth-to-diameterPast 4:1, expect chatter and step-downs; redesign or accept cost.

Aluminium is the default for prototypes and low-volume housings. The 6061 and 7075 grades machine fast and hold tolerance well. 7075 gives higher strength but is less weldable and more prone to stress cracking if the part sees sustained load. For marine or wet environments, 5052 and 5083 resist corrosion better and machine a little gummier.

Stainless grades split into free-machining and corrosion-resistant families. 303 cuts cleanly but has lower corrosion resistance. 304 and 316L are the workhorses for medical and food equipment. 17-4PH (SUS630) can be heat treated to high strength after machining, which suits aerospace fittings. It also moves during heat treatment, so leave stock and plan a finish pass after.

Titanium and Inconel are where process control shows. Ti-6Al-4V (TC4) and TA1/TA2 generate heat at the cutting edge and work-harden if the tool rubs. Inconel is worse. Both need sharp tools, rigid setups, and conservative feeds. We machine these on the five-axis centers to reduce setups, because every extra clamping operation on titanium risks a scrapped part.

Engineering plastics behave differently again. PEEK and POM move with temperature, so rough machine, let the part rest, then finish. ABS and PC are fine for fixtures and covers. Carbon fibre machines well with diamond-coated tools but the dust needs extraction, and edges can delaminate if the feed is too aggressive.

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  Aluminium 6061 / 7075Fast, stable, good for housings and brackets; 7075 for strength.
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  Stainless 304 / 316L / 17-4PHCorrosion and medical use; 17-4PH moves after heat treat.
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  Titanium / InconelHeat and work-hardening; five-axis cuts setups and scrap risk.
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  PEEK / POM / carbon fibreThermal movement; rough, rest, finish. Extract carbon dust.

A design review does not care where the machine sits. It cares whether the supplier can read the drawing, flag a problem, and hold the tolerance. The quote and free DFM analysis come back within 12 hours. Production can start within 24 hours once the drawing and material are confirmed. Parts ship in 3–5 days for most jobs. Historical late-delivery probability is below 2%.

That timing changes the sourcing decision. For a one-off fixture needed tomorrow, a Chennai shop with a three-axis mill is the right call. For a 500-piece run of five-axis parts with a ±0.005 mm callout and an IATF 16949 paper trail, the machine list and the inspection process matter more than the pin code.

Consolidating operations also cuts time. When five-axis milling, turning, finishing, and inspection sit under one roof, there are no inter-supplier handovers and no re-qualification of datums. We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. For medical and automotive programs, those certificates are not decoration. They are the reason a customer can audit the process.

There is no minimum order quantity. One prototype and a 10,000+ part run both go through the same first-article check. Uploads stay secure and confidential, and an NDA is available on request. If the part is not a good fit for our machines, say so early. A clear no is cheaper than a scrapped batch.

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  12 hoursQuote and DFM analysis after drawing and material are clear.
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  24 hoursProduction start once the order and first article are approved.
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  3–5 daysTypical shipment window for standard machined parts.
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  No MOQOne prototype to 10,000+ parts on the same inspection flow.