Tolerance bands the floor holds, and the evidence that backs them
The tolerance bands a CNC floor holds are process decisions, not machine specifications, and the evidence that backs them is the inspection report, not the brochure. The facility behind this guide holds ±0.003 mm on CNC milling, ±0.002 mm on CNC turning, and ±0.002 mm on precision grinding and wire EDM, and the evidence is a Hexagon CMM report on the specific part, not a capability statement. If you ask for the band and the report together, you get a verifiable answer; if you ask for the band alone, you get a number.
The band is held by the process chain — the machine, the fixture, the tool, the environment, and the inspection. The machine is a precision machining centre — a Mazak VARIAXIS I-600 five-axis, a Mazak INTEGREX I-250H S mill-turn, a TSUGAMI B0206-III Swiss-type, a STAR SR-32J Type N — and the machine's geometric accuracy and thermal stability are the first link. The fixture is rigid, the part supported close to the cut; the tool is sharp, balanced, correctly geometric; the environment is a temperature-controlled inspection room; the inspection is a calibrated Hexagon CMM with a gauge that meets the 10:1 rule.
The evidence is the initial process study and the ongoing capability. The initial study reports Ppk — the preliminary capability index — on key characteristics, with the band, the subgroup count, the sampling window, and the σ algorithm stated. The target is Ppk ≥ 1.67 on key characteristics. The ongoing capability reports Cpk — the production capability index — on the same characteristics, with the same band and a significant sample. The target is Cpk ≥ 1.33 in production. A capability index without the band and the algorithm is a number that cannot be checked; a capability index with both is a number that can.
The honest caveat is the one the capability index alone hides. A Ppk of 1.85 on a 0.4 mm band is one characteristic on one part, not a blanket capability claim — hold the same process spread against a ±5 µm feature and it fails outright. Your move is to ask for the band, the subgroup count, the sampling window, and the σ algorithm alongside the index, and to ask for the Hexagon CMM report on the specific part. The facility behind this guide supplies all four under ISO 9001:2015, IATF 16949:2016 (design clause 8.3 excluded), and ISO 14001:2015, on 100+ CNC machines. Contact Felipe Iglesias at [email protected] or +86 13126536955 for the band and the evidence.
- more than 100 machines including 20+ 5-axis centres; 100+ staff, 80%+ skilled technicians.
- Exports to 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 — based in China, serving customers worldwide.
- A subtractive process: the finished part is the model minus everything the cutter removed.
- Cost is decided at the manufacturability review, before the first chip.
- No minimum order, prototype and production run on the same machines.
What drives cost on China CNC machining?
Cost is driven by setup time amortised over quantity, cycle time, material and tooling, inspection labour, and the risk premium on the tolerance. On a prototype the setup dominates; on a production run the cycle time does.
The driver buyers most often underestimate is inspection. A drawing with twenty called-out dimensions has a different inspection cost from one with five, and a first-article report is a real document that has to be written, which is why it belongs in the quote, not in an assumption.
What is the certification position?
ISO 9001:2015, IATF 16949:2016 (excluding clause 8.3 product design), and ISO 14001:2015 — each with a certificate number verifiable with the registrar.
How does the process actually run, step by step?
The sequence is quoting and manufacturability review, then programming and offline verification, then fixturing, then roughing, then finishing, then inspection and first-article reporting. Each step has a failure mode, and the costly failures sit at the start and the end.
The manufacturability review is where cost is actually decided. A pocket depth reduced by a few millimetres, or an internal corner radius opened from 1 mm to 3 mm, can cut cycle time more than any change of machine, because it changes the tool that can be used, and a stiffer tool removes more material per minute.
The cost structure of China CNC machining
Cost is driven by setup time amortised over quantity, cycle time, material and tooling, inspection labour, and the risk premium on the tolerance. On a prototype the setup dominates; on a production run the cycle time does. That is why a per-part price without a quantity is not a price.
The driver buyers most often underestimate is inspection. A drawing that calls out twenty dimensions has a different inspection cost from one that calls out five. And a first-article report is a real document that has to be written.
What fails on this process, and when
The failures that cost money are not crashes — they are the quiet ones: a tolerance held on the machine but lost in a later operation, a revision built from a superseded drawing, and a surface finish callout that meant something different in another standard.
Each has a cheap control. Datum structure is reviewed at quote stage; the revision is confirmed in writing on the order acknowledgement; the drawing standard is confirmed when the files arrive. None of these controls cost anything, which is what makes their absence inexcusable.
How to verify a China CNC machining supplier
These four checks cost nothing and can be run before any commitment.
- Can they name the registration number? Ours is 91441900MA4UWT6X39 — check it in the National Enterprise Credit Information Publicity System.
- Do they name machine families and counts? A manufacturer lists models; a reseller recycles stock photos.
- Are the certificate numbers verifiable? Real ISO/IATF certificates carry numbers you can confirm with the registrar.
- Can you walk the floor? On-site and video audits are welcome at the Dongguan address.
Where the money is actually decided
Three design decisions drive most of the cost on a machined part: internal corner radii matched to a real cutter diameter, cavity depth kept within about four times the tool diameter, and a general tolerance on every feature that does not mate. Each one changes the tool that can be used, and the tool determines how much material can be removed per minute, which is why these matter more than any process selection.
This should come up when quoting, before any metal is cut, because the changes are usually trivial on the drawing and significant on the machine.
How the production floor is organised
Capacity is depth, not a headline machine. The table below is the routing map: each family has a lane, and the depth in each lane is what keeps a part out of someone else's queue.
| Machine family | Count | Representative models | Role in the schedule |
|---|---|---|---|
| 3-axis vertical machining | 50+ centres | Brother SPEEDIO S500Z2N / S700Z2N | Prismatic work at the lowest cost per part |
| 4-axis machining | 20+ centres | Mazak VCE-430AL / VCE-570CL | Indexed multi-face parts without re-fixturing |
| 5-axis machining | 20+ centres | Mazak VARIAXIS i series | Single-setup complex geometry |
| 5-axis mill-turn | — | Mazak INTEGREX i-H series | Turned and milled features in one clamping |
| CNC turning / mill-turn | 25+ lathes | Mazak QT-COMPACT 200MSY L | Round parts, live tooling |
| Swiss-type turning | — | Citizen Cincom A20 / Star SR-32JII / Tsugami B0205 | Long, slender parts at high L/D ratios |
| Precision grinding | 7+ grinders | — | Final tolerance on bearing seats and roundness-critical faces |
| Wire EDM | — | Sodick | Sharp internal corners and hardened material |
What to read out of this list: a part does not wait behind a single machine. Depth in the same family is what lets work re-route rather than queue, and it is what makes a prototype ramp to production on the same floor.
How is process capability reported?
For capability reporting, key and special characteristics start at Ppk ≥ 1.67 and run at Cpk ≥ 1.33 in production; general characteristics start at Ppk ≥ 1.33. Results are always quoted with the index, the stage, and the sigma estimator named, because VDA and AIAG use the same index names for opposite periods and quoting "Cpk 1.67" without that context is meaningless.
Values between 1.33 and 1.67 are conditional acceptance requiring customer review, not a pass. Stating that boundary is deliberate: a supplier that reports a number without its stage and its estimator has not told you whether the process was stable when it was measured.
Which entity is responsible for the work?
Dongguan Zhuohang Ltd, Registration No. 91441900MA4UWT6X39, in operation since 2005.
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.
Send a drawing and get a manufacturability read
Upload your model for a quote, or arrange a factory audit with [email protected] or +86 13126536955. Ask for Felipe Iglesias.
Frequently Asked Questions
What files do you need for a quote?
In short, A 3D model (STEP or IGES) with a 2D drawing carrying the tolerances, surface finish callouts, material spec and any inspection or certification requirements. The drawing defines the contract — the model alone usually leaves the tolerance scheme unspecified.
Can you work to ASME Y14.5 as well as ISO?
Yes. Both geometric dimensioning conventions are used. The important thing is that the drawing states which one applies, because the same symbol can mean different things under the two standards.
How long does China cnc machining take?
Lead time is driven less by cutting time than by queue position, fixture design, and inspection. A part that needs a purpose-built fixture has a longer first-article lead and a much shorter repeat lead, which is worth asking about separately.
Do you hold stock or consignment for repeat orders?
Repeat orders can run against a forecast so stock and, where the part warrants it, dedicated fixturing are held ready. This is a commercial arrangement, not a standard term, so raise it at the second order rather than the first.
Are you a manufacturer or a trading company?
A manufacturer. The registered entity is Dongguan Zhuohang Ltd (No. 91441900MA4UWT6X39), a 6,800 m² facility with 100+ machines and 100+ staff in Dongguan, open to factory visits.
What materials do you machine?
Aluminum, stainless steel, titanium, brass, copper, and Inconel for metals; PEEK and Delrin (POM) for plastics. Material certificates are verified on incoming stock.
How is an engineering change handled mid-production?
The change is documented against a revision, the affected parts in process are identified, and the revised drawing is confirmed in writing before work restarts. The important part is that the revision in force at any moment is a single, written one.
Continue reading: What Is China CNC Machining · PEEK CNC Machining · Tight Tolerance China CNC Machining
Standards referenced on this page
- ASTM A582/A582M-12 — Standard Specification for Free-Machining Stainless Steel Bars
- ASTM B211/B211M-19 — Standard Specification for Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire
- ISO 9001 — Quality management systems — Requirements