Tight tolerance CNC machining. ±0.002mm. Proven.
Holding ±0.002mm is half the job. The other half is proving it with data. Every critical feature gets CMM-verified with actual vs. nominal deviation documented — not a pass/fail stamp. Free DFM tolerance review on every quote.
- CMM verified every feature
- Cpk ≥ 1.67 at volume
- Free DFM tolerance review
- ISO 9001 certified
Tightest achievable tolerance
±0.002
mm · dedicated 5-axis setup + climate control
Standard 3-axis tolerance：± 0.050 mm
Precision setup tolerance：± 0.002 mm
Surface finish Ra：0.1 μm achievable
CMM accuracy MPE：± 0.0008 mm
Measurement room temp.：20°C ± 0.5°C
Cpk (production)：≥ 1.67
±0.002mm
Tightest tolerance
±0.0008mm
CMM accuracy MPE
Cpk≥1.67
Process capability
100%
Critical dims verified
Certifications
ISO 9001:2015 IATF 16949 — Cpk ≥1.67 Zeiss / Renishaw CMM CMM report every order Free tolerance DFM Quote in 2 hours
Tight Tolerance CNC — The 5 Tiers
Every tolerance claim means something different. Here’s what each tier costs in terms of process, setup, and verification.
± 0.1 mm
Caliper
Standard 3-axis
Gauge
± 0.01 mm
Precision setup
CMM batch
± 0.005 mm
5-axis dedicated
CMM 100%
± 0.002 mm
Climate-ctrl.
Thermal comp.
INSPECTION COST MULTIPLIER BY TOLERANCE
1×
CMM adds time
1.6×
Dedicated setup
2.4×
Climate-controlled measurement
4×+
Multiplier applies to inspection cost per feature — not the whole part. A single tight bore on a loose part costs far less than calling out ±0.002mm everywhere.
± 0.002 mm = ± 2 microns
1/35th of a human hair. A 100mm aluminium bar expands 2.36μm per °C of temperature change. At this tolerance, measurement room temperature is not optional — it’s part of the process. Parts are stabilised for minimum 2 hours at 20°C ±0.5°C before measurement.
Tolerance Capability — Quick Reference
| Tolerance | Al 6061 | SS 316L | Ti-6Al-4V | Inspection |
|---|---|---|---|---|
| ± 0.1 mm | ✓ Easy | ✓ Easy | ✓ Easy | Caliper |
| ± 0.05 mm | ✓ Standard | ✓ Standard | ✓ Standard | Gauge |
| ± 0.01 mm | ✓ Achievable | ✓ Achievable | △ With care | CMM batch |
| ± 0.005 mm | △ Precision setup | △ Precision setup | △ Specialist | CMM 100% |
| ± 0.002 mm | △ Climate-ctrl. | △ Challenging | ✗ Not standard | CMM + thermal |
GD&T Callout Guide — What We Measure and How
Every GD&T symbol specifies a different measurement method. Understanding which callout to use prevents the most common drawing errors we see in DFM review.
True Position
Location · critical for mating parts
Controls hole / boss / slot location relative to datums. Measured as a cylindrical tolerance zone — more efficient than bilateral ±x/±y. Most common callout on precision mating parts.
Achievable: ⌀0.010mm at MMC on Al · ⌀0.020mm on steel. Always specify datum references — we flag missing datums in DFM.
Flatness
Form · no datum reference required
Peak-to-valley deviation across a surface. No datum needed. Measured by best-fit plane on CMM. Critical for sealing faces, optical mounts, and precision assembly interfaces.
Achievable: 0.005mm on 100×100mm Al · 0.010mm on stainless. Tighter than 0.003mm typically needs grinding.
Cylindricity
Form · bore & shaft quality
Combines roundness, straightness, and taper into a single zone tolerance. Gold standard for precision bores and shafts in hydraulic and bearing applications.
Achievable: 0.005mm on turned Al bore · 0.003mm on precision-bored SS. Tighter than 0.002mm requires honing.
Perpendicularity
Orientation · datum referenced
Controls squareness of a surface, axis, or plane to a datum. Most common orientation callout on prismatic parts. Specified as a zone width (surface) or diameter (axis).
Achievable: 0.010mm/100mm on machined surface · 0.020mm on bore axis. Degrades with depth-to-diameter ratio.
Profile of a Surface
Profile · freeform & complex surfaces
Controls any surface form — the most flexible GD&T callout. Used for complex 3D surfaces and freeform geometry. Requires 5-axis CMM capability. Measured by point-cloud comparison to nominal.
Achievable: 0.050mm bilateral on 5-axis milled surfaces · 0.020mm on precision prismatic faces.
Circular Runout
Runout · rotational parts
Combined effect of all errors in a rotating part — concentricity, roundness, and wobble — measured in a single cross-section. Most practical runout callout for turned parts in service.
Achievable: 0.010mm on precision-turned Al shaft · 0.005mm with ground datum reference.
Missing GD&T datums or unclear tolerance stack?
Our DFM review flags every incomplete or ambiguous callout before machining starts.
Cpk & SPC — How We Prove Process Capability
A single part within tolerance proves nothing. Cpk quantifies whether your process is consistently capable — and by how much.
Cpk <1.00
>2,700 PPM defects
Incapable — defects certain
Process spread exceeds tolerance. Some parts will fail even with a centred process. Not acceptable for any precision application.
1.00–1.33
66–2,700 PPM
Marginal — monitoring required
Technically capable but minimal margin. Any drift causes immediate defects. Continuous SPC mandatory.
1.33–1.67
6–66 PPM
Capable — ISO 9001 minimum
Adequate margin for normal variation. Acceptable for most commercial precision applications.
Cpk ≥1.67
<1 PPM defects
Our guarantee — IATF 16949 standard
±5σ margin between process mean and nearest spec limit. Required for automotive and aerospace production. We deliver this — documented — at 100+ piece volumes.
How SPC Works in Our Facility
n=25
Subgroup size for SPC measurement
Every 25 parts, 5 are pulled for measurement. X-bar and R charts updated. Any out-of-control signal triggers immediate work-stop before the process drifts further.
Cp vs Cpk
Process spread vs centring
Cp measures spread relative to tolerance. Cpk accounts for centring. A perfectly centred process has Cp = Cpk. We report both — Cpk is the governing value. Mean is targeted to nominal, not the midpoint.
8 rules
Nelson rules applied to all SPC charts
All 8 Nelson rules detect non-random patterns — not just points outside control limits. Rule violations trigger investigation even when all parts pass tolerance — because patterns predict drift before defects appear.
PPK
Short-run vs long-term capability
At PPAP sign-off, we report Ppk ≥1.67 using data from the full production run. Both Cpk (short-term) and Ppk (long-term) are included in the capability study — not just the last 25 parts.
SPC included when:
Standard on runs of 100+ pieces for any critical dimension. Available at lower quantities on request. Per-feature Cpk reported when tolerance is ≤±0.010mm. PPAP Level 3 includes initial process capability study (Ppk ≥1.67).
Material × Process × Tolerance Capability
Not every material reaches every tolerance tier equally. Here’s our honest capability matrix — what’s achievable, what requires specialist setup, and what needs a different process.
| Material | ± 0.05 mm | ± 0.01 mm | ± 0.005 mm | ± 0.002 mm | Ra 0.4μm | Ra 0.1μm |
|---|---|---|---|---|---|---|
| Al 6061-T6 | ✓ Standard | ✓ Achievable | △ Precision setup | △ Climate-ctrl. | ✓ Standard | ✓ Fine passes |
| Al 7075-T651 | ✓ Standard | ✓ Achievable | △ Precision setup | △ Challenging | ✓ Standard | ✓ Fine passes |
| SS 316L | ✓ Standard | ✓ Achievable | △ With care | △ Demanding | ✓ Standard | △ More time |
| 17-4 PH SS | ✓ Standard | ✓ Achievable | ✓ Achievable | △ Specialist | ✓ Standard | △ With care |
| Ti-6Al-4V | ✓ Standard | ✓ Achievable | △ With care | △ Very demanding | ✓ Standard | △ More time |
| Inconel 718 | ✓ Achievable | △ With care | △ Specialist | ✗ Not standard | △ With care | △ Very difficult |
| PEEK Optima | ✓ Standard | ✓ Achievable | △ Moisture drift | △ Very demanding | ✓ Standard | △ Possible |
✓ Standard — standard 3-axis setup△ With care — precision setup, more time△ Demanding — specialist setup, confirm in DFM✗ Not standard — alternative process recommended
6 Tight Tolerance Mistakes We Catch in DFM Review
These are the tolerance drawing errors that consistently add cost without adding value — and that our free DFM review catches before metal is cut.
Blanket ±0.005mm on Every Feature
The single most common unnecessary cost driver. Calling out ±0.005mm on clearance holes, cosmetic pockets, and non-mating faces adds CMM time to features that don’t need it — and raises scrap risk without functional benefit.
Fix: Apply ±0.005mm only where a mating part, sealing requirement, or functional spec demands it. Use ±0.05mm as the general tolerance and tighten only 2–3 critical features. Our DFM identifies which is which.
Typical wasted cost: 25–40% of inspection budget
Function-Driven Tolerance Specification
Assign tolerances based on functional requirements: what does this feature mate with? What is the maximum permissible variation? Everything else gets the general tolerance.
Example: A bracket with a ±H7 bearing bore (±0.010mm), two M6 clearance holes (±0.1mm), and four tapped holes (±0.1mm) performs identically to the same bracket with ±0.010mm on everything — at 30–40% less cost.
Typical saving: 20–35% per part
Ignoring Thermal Expansion at ±0.002mm
A 200mm aluminum part expands ~4.7μm per °C. At ±0.002mm, a 1°C room temperature difference during incoming inspection can cause a false rejection on a perfectly good part.
Fix: For tolerances tighter than ±0.010mm, specify measurement temperature (20°C per ISO 1) on the drawing. Ensure your incoming inspection environment matches our measurement room conditions.
Risk: false rejects at incoming inspection
Missing or Incomplete Datum References
A true position callout without datum references is ambiguous — different suppliers interpret it differently. Parts “pass” on one CMM but fail at mating assembly. Also technically invalid under ASME Y14.5.
Fix: Define datum A (largest flat surface — eliminates most degrees of freedom), then B and C. Ensure your inspection fixture replicates the actual assembly datum scheme, not just what’s convenient to fixture.
Risk: assembly failures despite passing inspection
Tight Tolerance on Deep Narrow Pockets
A ±0.005mm width tolerance on a 1mm-wide × 10mm-deep slot means a 1mm end mill at 10× L/D ratio. At that aspect ratio, tool deflection under cutting force limits achievable tolerance to ±0.05mm.
Fix: For deep narrow slots, tolerance must match what’s achievable at that depth-to-width ratio. Our DFM calculates this for each feature and either relaxes the tolerance or suggests redesigning the pocket geometry.
Risk: 100% scrap rate on deep-pocket features
No Surface Roughness Callout at Tight Tolerance
At ±0.002mm, residual stress and heat from aggressive machining can cause the part to “spring” after fixture release — measured within tolerance on the machine, out of tolerance on your CMM.
Fix: For critical tight-tolerance features, specify a maximum Ra value alongside the dimensional tolerance. Higher Ra values indicate aggressive parameters that risk thermal damage. Our DFM recommends Ra limits for each tight feature.
Risk: dimensional drift post-inspection
What Drives Tight Tolerance Cost
Five variables explain 95% of tight tolerance pricing differences.
Number of tight-tolerance features
Each feature under ±0.010mm requires 5–15 minutes of dedicated CMM time. Two tight features vs twenty is a 10× inspection cost difference. CMM time often exceeds the machining premium at extreme tolerances.
- Highest cost driver
Tolerance tier — the ±0.002mm premium
Going from ±0.010mm to ±0.005mm roughly doubles inspection cost. Going from ±0.005mm to ±0.002mm multiplies it by 3–4× and adds temperature stabilisation and thermal compensation. The cost jump between tiers is non-linear.
- Extreme at ±0.002mm
Material machinability and thermal stability
Aluminium’s high CTE (23.6 μm/m·°C) makes it more sensitive to temperature than titanium (8.6 μm/m·°C). This affects stabilisation time. Harder materials need slower finishing passes to avoid deflection — extending cycle time.
- Material-dependent
Quantity — inspection overhead at low volume
At 1 piece, full CMM plan runs on one part — all overhead absorbed. At 50+ pieces, the overhead amortises. SPC becomes meaningful above 25 pieces. Per-piece inspection cost drops significantly from 1 to 50.
- Scales with quantity
Standard precision (1–5 pcs)
From $18 / pc
Al 6061 · 3-axis · ±0.010mm on 2–3 features · gauge inspection · 2–4 day lead
High precision (1–5 pcs)
From $45 / pc
Al 6061 · 5-axis · ±0.005mm on critical features · CMM report · 3–5 day lead
Maximum precision ±0.002mm (1–3 pcs)
From $120 / pc
Dedicated setup · climate-controlled measurement · CMM 100% · Cpk documented · 5–8 day lead
Production run with Cpk (50–500 pcs)
Volume pricing + Cpk ≥1.67
SPC monitoring · X-bar/R charts · dimensional report per lot · PPAP available
Free Tolerance DFM — Every Quote
Our engineer maps every tight-tolerance feature against process capability, flags unnecessary tightness, and quantifies cost savings from tolerance relaxation. Written report included at no charge. Average savings: 20–40% on inspection cost.
Tight Tolerance CNC Supplier Comparison
| Requirement | Baosheng | Platform | Local job shop |
|---|---|---|---|
| Tolerance to ±0.002mm | ✓ In-house, 5-axis | Via 3rd-party shops | Rare capability |
| CMM inspection report | ✓ Every critical feature | Extra charge | Spot check only |
| Cpk ≥1.67 at volume | ✓ Documented, IATF 16949 | Not standard | Rarely available |
| Free DFM tolerance review | ✓ Written, every quote | Limited / automated | Verbal only |
| SPC charts (100+ pcs) | ✓ X-bar/R, Nelson rules | Not standard | Not standard |
| Climate-controlled measurement | ✓ 20°C ±0.5°C | Supplier-dependent | Rarely available |
| Direct engineer contact | ✓ Assigned engineer | Sales rep / platform | Yes |
| Quote turnaround | ✓ 2 hours | Instant (algorithm) | 1–3 days |
Tight Tolerance CNC Machining — Questions Answered
What is the tightest CNC machining tolerance you can hold?
On dedicated 5-axis setups with climate-controlled measurement, we hold ±0.002mm on specific features. This requires part temperature stabilisation for minimum 2 hours at 20°C ±0.5°C and a CMM accuracy of ±0.0008mm MPE. It’s not achievable on every feature — our DFM review confirms feasibility for your specific geometry and material before quoting.
What is your standard CNC machining tolerance?
Standard tolerance is ±0.05mm for general features — achieved on 3-axis machines with no premium. For precision applications, ±0.010mm is achievable with standard CMM verification. ±0.005mm and ±0.002mm require specialist setups. Specifying ±0.002mm on features that only need ±0.05mm approximately doubles your inspection cost per feature — our DFM review identifies where tight tolerance is actually needed.
Do you provide CMM inspection reports?
Yes — CMM inspection on Zeiss Contura and Renishaw CMMs. Reports show actual vs. nominal with deviation values and pass/fail status for every GD&T callout. Available as per-part reports for tight-tolerance work, or batch statistical reports for production runs. Our CMM accuracy (MPE) is ±0.0008mm — 4× more accurate than ±0.002mm tolerance.
What is Cpk and why does it matter?
Cpk (process capability index) measures how consistently the process produces parts within tolerance — accounting for both spread and centring. Cpk ≥1.67 (our guarantee on 100+ piece runs) means <1 PPM defect rate and ±5σ margin from the specification limit. A single part within tolerance proves nothing about the process — Cpk proves the process is consistently capable.
Why does ±0.002mm cost so much more than ±0.010mm?
Three reasons: (1) Dedicated precision setup — lighter finishing passes, slower feeds, specialised tooling. (2) Temperature management — part stabilised 2+ hours in climate-controlled room; thermal compensation applied. (3) CMM time — extended measurement at each feature with higher probe qualification requirements. Total overhead at ±0.002mm is typically 4–6× the cost vs ±0.010mm per tight-tolerance feature.
Can you achieve tight tolerance on aluminium?
Yes — aluminium is actually the easiest material to machine to tight tolerances because low cutting forces minimise tool deflection. The challenge at ±0.002mm is its high CTE (23.6 μm/m·°C) — a 100mm part expands 2.36μm per degree. Climate-controlled measurement and temperature stabilisation are essential, not optional, at this tolerance level on aluminium.
Do you offer SPC for production runs?
Yes — SPC is standard on production runs of 100+ pieces for any critical dimension. We apply X-bar/R charts with all 8 Nelson rules to detect process drift before defects occur. SPC data is included in the inspection report. For IATF 16949 customers, we additionally report Ppk (long-term capability) using data from the full production run.
What is the difference between IT grade and ±mm tolerance?
ISO 286 IT (International Tolerance) grades define standardised bands relative to nominal size: IT6 on 25mm bore = ±0.013mm; IT5 = ±0.009mm; IT4 = ±0.006mm. We machine to both IT-grade callouts (H7, g6, etc.) and direct ±mm callouts. Always include the nominal dimension alongside the fit class — we calculate the corresponding band and verify on CMM.
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Tight tolerance. CMM verified. Cpk documented.
Upload your drawing with tolerance callouts. Free DFM review identifies which features actually need tight tolerance — and which don’t. Itemised quote in 2 hours.
✓ Free tolerance DFM | ✓ CMM report included | ✓ Cpk ≥1.67 at volume | ✓ ±0.002mm capable | ✓ ISO 9001 certified | ✓ Quote in 2 hours