China CNC Machining Parts

How do you audit what a parts manufacturer can actually make?

A "manufacturer" is a claim until it is a machine list. The capability section of the checklist tests three things in order: which materials the shop runs, which processes are in-house, and which tolerances it can hold — with measurement to back each one. A trading desk repeats the same generic catalog to every buyer; a real manufacturer names its machines and shows the report.

The test below is what this factory answers. It is offered here not as marketing, but as the checklist you run before trusting a supplier with a drawing.

The order of the test matters. Material first, because if the shop cannot source and verify the alloy, nothing else saves the part. Process second, because the machine determines the geometry it can reach. Tolerance third, because tolerance is only meaningful against the process that holds it. A shop that can answer all three with evidence is a manufacturer; a shop that answers with a catalog is a desk.

Which materials does the shop actually machine?

The material range matters because it tells you whether the shop is a specialist or a generalist, and whether it can say no honestly. This factory machines the alloys buyers actually specify on drawings, and verifies every incoming lot before it reaches a machine.

Material family	Grades run	What it is for
Aluminum	6061, 6063, 6082, 7075, 2014	Prototypes and production where weight, thermal, or cost matter; anodizes well
Stainless steel	303, 304, 316, 316L, 17-4PH	Corrosion and hygiene; 303 for free-machining, 17-4PH for strength
Carbon / alloy steel	1018, 1045, 4140, 4340, 12L14	Structural and wear parts; carburizing or nitriding available
Brass / copper	C360, H62, C110	Electrical and thermal conductivity
Titanium	TA2, TC4 (Grade 2 / 5)	Strength-to-weight; stress relief above 500 °C outsourced to a qualified partner
Plastics	ABS, POM, nylon, PTFE, PEEK	Non-metal prototypes and insulators

Material audit point: incoming lots are XRF-checked against the mill certificate. A substitution is caught at the door, not at the customer's dock — the single most important material-control you can ask for.

The grade list is what separates a machining shop from a price-list. A shop that names 6061-T6, 316, 4140, and TC4 is telling you it has cut those alloys before and knows how each one behaves under the tool. A shop that answers "we machine aluminum and steel" has not, and the first time a grade does something unexpected, you pay for the lesson.

What tolerances can the parts actually hold?

A tolerance on paper means nothing without the measurement to prove it. This factory ties tolerance to process and proves every critical dimension on a CMM rather than taking it on faith.

Process	Held tolerance	Typical part
CNC milling	±0.003 mm	Housings, brackets, prismatic parts
CNC turning	±0.002 mm	Shafts, pins, bushings, round parts
Precision grinding	±0.002 mm	Bearing seats, roundness-critical surfaces

These are held to process capability, not to a best-case claim. On a representative length characteristic of 76.1–76.5 mm, SPC shows Cpk = 1.851 (one characteristic on one part, not a blanket capability claim) against an initial-study target of Ppk ≥ 1.67. If a print calls for a dimension the shop cannot reliably hit, it is flagged during the design-for-manufacturing review — before cutting, not after.

Read the tolerance band before you read the index. Cpk is a ratio of the tolerance band to the process spread, not an absolute measure of accuracy. The figure above was recorded on a length characteristic with a 0.4 mm band (76.1–76.5 mm) — wide by design. Hold the same process spread against a ±0.005 mm feature and it fails outright. Ask for the band, the subgroup count and the sampling window on every capability number a supplier quotes.

Tolerance also scales with size: a ±0.002 mm band is ordinary on a small turned pin and demanding on a large milled housing, because thermal drift and tool deflection grow with the workpiece. The honest shop states the tolerance against the size and the process, not as a single number that sounds good on every part.

Which processes run in-house?

In-house processes mean one accountable supplier and a shorter lead time, because parts do not wait on a truck between operations. The floor covers the full metal-cutting range.

Process	Capacity	Max workpiece
3-axis milling	50+ centers	1300 × 700 × 600 mm (milling)
4-axis milling	20+ centers
5-axis milling	20+ centers
CNC turning	25+ lathes	Ø720 × 1280 mm
Mill-turn	Multi-task centers (Mazak / Brother class)	Single-setup complex geometry
Grinding	7+ (surface / centerless / cylindrical)	±0.002 mm finishes

The workpiece limits are part of the audit because they tell you whether the shop can reach your part at all. A housing inside 1300 × 700 × 600 mm and a shaft under Ø720 × 1280 mm fit the floor; anything beyond is a quote the shop should decline, not stretch to. The honest answer to an oversized part is "no," and that honesty is itself a capability signal.

How are the parts verified before they ship?

A part is only as good as the measurement that confirms it. The inspection bench here is the same class of equipment a buyer would use to audit the shop, and the results are documented, not just the pass/fail.

• Hexagon GLOBAL S CMMs (2) plus a gear measuring center and vision measuring machines for dimensional verification.
• KEYENCE VK-X3000 laser microscope and SURFCOM 1800D for surface finish and profile.
• XRF (iCHEQ) spectrometer for incoming material composition checks.
• HVS-1000A micro-Vickers hardness tester, Fischer coating thickness gauge, salt spray and tensile testers.
• SPC control charts on key characteristics, with Ppk ≥ 1.67 at the initial study on critical characteristics and Cpk ≥ 1.33 in production on general characteristics.

The point of listing the instruments is not the brand names — it is the coverage. Dimensions, surface finish, material composition, hardness, coating, and corrosion each have an instrument, so no part leaves on a claim that was not measured. The inspection bench is the second half of the tolerance claim, and it is the half you should insist on seeing.

Which secondary operations can be bundled?

Finished parts, not machined blanks, are what a buyer actually needs. Secondary operations run in parallel or through named, qualified partners so there is one invoice and one accountable supplier.

• Surface finishing: standard and hard anodizing, zinc / nickel / silver / gold / chrome plating, powder coating, painting, brushing, mirror polishing.
• Heat treatment: vacuum, bright, carburizing, nitriding, and stress-relief aging. In-house ovens reach 500 °C; titanium stress relief above that goes to a qualified partner.
• Deburring, tapping, laser marking, assembly: included as the print requires.

The bundle is the difference between receiving a part and receiving a finished part. A buyer that ships a machined blank to a second supplier for anodizing has taken on a second audit, a second lead time, and a second point of failure. The bundle collapses that to one invoice and one owner, which is exactly what the audit is trying to establish.

What should you check before trusting a parts manufacturer?

Whether the order goes here or elsewhere, these checks separate a manufacturer from a reseller, and you should run them on any supplier, including this one.

Send a drawing and every check above is run for you, in writing, before a commitment is asked.

Which part geometries does each process produce best?

Every CNC process has a geometry it does well and a geometry it does poorly, and the cheapest part is the one routed to the right machine. If you know the map, you can read a quote and spot a shop that is selling the wrong process for the part.

Part geometry	Best process	Example parts
Prismatic — flat faces, pockets, holes	3-axis milling	Brackets, plates, housings, covers
Compound angles, deep reach	4/5-axis milling	Robotics housings, aerospace geometry
Round — diameters, threads, grooves	CNC turning	Shafts, pins, bushings, spacers
Round with milled features	Mill-turn	Parts that would need two machines otherwise
Bearing seats, sliding surfaces	Grinding	Seats, spindles, roundness-critical faces

The routing is an audit answer in itself. A shaft quoted on a milling center, or a bracket quoted on a 5-axis, tells you the shop is not reading the geometry, or is reading it and pricing the wrong machine. The honest shop routes the part to the process that matches it and can say why.

What should a parts spec include before you send it?

The quality of the quote you get back is set by the quality of the spec you send out. A complete spec names five things, and a quote that matches it is a quote you can hold a supplier to; a spec that skips them is a spec that leaves the supplier guessing, and charging for the guess.

• The 3D model — STEP or IGES, so the geometry is unambiguous.
• The 2D drawing — with the tolerance band on each critical dimension, not just "tight."
• The material grade — 6061-T6, not "aluminum"; 316, not "stainless."
• The surface finish — the Ra call-out where it matters, so the finishing step is priced and planned.
• The quantity and finishing — prototype count, production count, and any anodizing, plating, or heat treatment.

Send all five and the DFM review comes back against the real drawing; send two and the review comes back against an assumption. The spec is your half of the audit, and it is the half most buyers under-invest in.

What this shop actually runs

Capability evidence should come as specifics, not slogans. Behind this guide is a 6,800 m2 plant in Dongguan, China running 100+ CNC machines with 100+ staff. The machine list by category:

• 5-axis machining centres (10+) - Mazak VARIAXIS I-600 (510/910/510 mm travel, 12,000 rpm, 22 kW, 71.6 N·m, 30-tool BT40) and Mazak INTEGREX I-250H S (B-axis 0.0001°, 24 kW, 124 N·m, 38-tool HSK-A63). Made for compound-angle parts, single-setup multi-face prismatic work, and aerospace fittings where datum transfer loss is unacceptable.
• 3-axis / 4-axis machining centres (50+) - Brother SPEEDIO S500Z2N / S700Z2N (10,000 rpm, 14/21-tool ATC, 0.7 s tool-to-tool, Z-axis 2.2 G) and Mazak VCE-430A L / VCE-570C L (10,000 rpm, 118 N·m, 24-tool ATC). Made for prismatic parts, plates, brackets, housings.
• Swiss-type turning centres (10+) - Citizen Cincom A20-3F7 (Φ20 mm, 10,000 rpm), TSUGAMI B0206-III / B0205-III (Φ20 mm, 0.1 µm), STAR SR-32JII / SR-32J Type N (Φ32 mm, 8,000 rpm). Made for long, slender rotational parts at ±0.002 mm.
• CNC turning centres (20+) - HEADMAN T70M/1250 (720 mm swing, 117 mm bore, 3,000 rpm, BMT75 12-station turret). Made for shafts, bushings, flanges up to ±0.002 mm.
• Wire EDM (5+) - Sodick AQ535L (550/350/300 mm travel, ±20° taper, 800 kg workpiece). Made for hardened tool steel, internal splines, sharp internal corners that milling cannot reach.
• Inspection: Hexagon CMM + 20+ gauges - Hexagon CMM for coordinate measurement, plus vision system, profilometer, hardness tester, coating thickness gauge, XRF for material verification. The 10:1 rule (gauge 10x more accurate than the band) is applied to every feature.
• Machine highlights - VARIAXIS I-600: one-setup multi-face 5-axis + MAZA-CHECK auto-calibration; INTEGREX I-250H S: DONE-IN-ONE mill-turn, B-axis 0.0001° + Ai thermal shield; SPEEDIO S500Z2N / S700Z2N: Z-axis 2.2 G + 0.7 s ATC; Swiss-type: guide-bush switchable + 0.1 µm resolution.

Tolerance: ±0.003 mm CNC milling / ±0.002 mm CNC turning / ±0.002 mm grinding and wire EDM. Capability: Ppk >= 1.67 initial on key characteristics, Cpk >= 1.33 ongoing.

Certificates: ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, with design clause 8.3 excluded, stated openly) and ISO 14001:2015 (116024/B/0001/UK/En), issued to Dongguan Zhuohang Ltd, registration 91441900MA4UWT6X39, founded 2005.

Where we ship: Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa — plus other countries and regions worldwide, shipped from our base in Dongguan, China.

Contact: Felipe Iglesias, [email protected], +86 13126536955.

Frequently Asked Questions

Standards referenced on this page

• ASTM B211/B211M-19 — Standard Specification for Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire
• ASTM A276/A276M-17 — Standard Specification for Stainless Steel Bars and Shapes
• ISO 9001 — Quality management systems — Requirements