CNC Machining Tolerances Guide
Standard, tight and precision tolerances for CNC milling, turning, grinding and EDM. Understand what tolerances cost, when to specify them, and how to write them correctly on your drawings.
Tolerance by Process — Reference Table
All tolerances shown are for metallic parts at nominal dimensions of 10–250 mm. Tolerances may be tighter for small features or looser for very large parts.
| Process | Standard Tolerance | Tight Tolerance | Precision Tolerance | Surface Finish (Ra) | Relative Cost | Notes |
|---|---|---|---|---|---|---|
| CNC Milling | ±0.1 mm | ±0.025 mm | ±0.010 mm | Ra 1.6–3.2 µm | Standard for most machined parts | |
| CNC Turning | ±0.05 mm | ±0.013 mm | ±0.005 mm | Ra 0.8–1.6 µm | Turned diameters naturally tighter than milling | |
| 5-Axis Milling | ±0.05 mm | ±0.015 mm | ±0.008 mm | Ra 0.8–2.0 µm | Complex geometry in fewer setups | |
| Cylindrical Grinding | ±0.013 mm | ±0.005 mm | ±0.002 mm | Ra 0.1–0.4 µm | Shafts, bores, bearing seats | |
| Surface Grinding | ±0.025 mm | ±0.008 mm | ±0.002 mm | Ra 0.2–0.8 µm | Flat reference surfaces, gauge blocks | |
| Wire EDM | ±0.025 mm | ±0.010 mm | ±0.005 mm | Ra 0.4–1.6 µm | Complex profiles, hardened material | |
| Sinker EDM | ±0.05 mm | ±0.013 mm | ±0.005 mm | Ra 0.4–2.0 µm | Cavities, blind slots, hardened steel | |
| Sheet Metal Bending | ±0.5 mm | ±0.25 mm | ±0.1 mm | — | Springback affects angle — design with compensated angles | |
| 3D Printing (SLA) | ±0.15 mm | ±0.05 mm | — | Ra 1.0–3.0 µm | Post-curing may affect dimensions |
How Survi Verifies Your Tolerances
Tolerances are only meaningful if they are measured. At Survi Engineering, our quality workflow for tight-tolerance parts includes: CMM (coordinate measuring machine) inspection on first-off parts, in-process gauging during production runs, and final 100% inspection on features tighter than ±0.025 mm. All inspection data is recorded and supplied with your shipment on request.
Our Zeiss CMM and calibrated gauge sets are traceable to NABL-accredited standards — the Indian equivalent of ISO/IEC 17025. This gives US and European clients the same calibration traceability they would expect from a domestic supplier.
Submit Your DrawingISO 2768 — General Tolerances Reference
ISO 2768 defines general linear tolerances for machined parts without individual dimension callouts. Specify the class in your drawing title block to save time. The four classes:
| ISO 2768 Class | 0.5–3 mm | 3–30 mm | 30–120 mm | 120–400 mm | 400–1000 mm | Typical Use |
|---|---|---|---|---|---|---|
| f (Fine) | ±0.05 | ±0.05 | ±0.08 | ±0.12 | ±0.2 | Precision instruments |
| m (Medium) ★ | ±0.1 | ±0.1 | ±0.15 | ±0.2 | ±0.3 | Standard CNC machined parts |
| c (Coarse) | ±0.2 | ±0.3 | ±0.5 | ±0.8 | ±1.2 | Structural, welded assemblies |
| v (Very Coarse) | — | ±0.5 | ±1.0 | ±1.5 | ±2.5 | Castings, forgings |
ISO 2768-m in your drawing title block. Add individual tolerance callouts only for features where tighter or looser tolerances are functionally required. This reduces drawing errors and is what most CNC shops default to.
Hole & Shaft Fit Tolerances
For mating parts (shaft in bore), fits are defined by ISO 286. Common fits for CNC machined parts:
| Fit Type | ISO Class (Hole/Shaft) | Clearance | Typical Application |
|---|---|---|---|
| Loose Clearance | H11/c11 | +0.06 to +0.35 mm | Structural assemblies, non-precision location |
| Easy Running | H9/d9 | +0.025 to +0.105 mm | Shafts in plain bearings, generous clearance |
| Close Running | H8/f7 | +0.006 to +0.050 mm | Precision shafts, spindles |
| Sliding | H7/g6 | +0.002 to +0.025 mm | Pistons, precision slides |
| Location Clearance | H7/h6 | 0 to +0.025 mm | Accurate location, removable assembly |
| Location Transition | H7/k6 | -0.006 to +0.021 mm | Moderate press, accurate location |
| Location Interference | H7/p6 | -0.015 to +0.006 mm | Light press fit, permanent assembly |
| Force Fit | H7/s6 | -0.027 to -0.007 mm | Heavy press, structural joints |
GD&T — Common Geometric Tolerances
GD&T (Geometric Dimensioning and Tolerancing) per ASME Y14.5 or ISO 1101 specifies the form, orientation and position of features, not just their size. Typical achievable values at Survi Engineering:
⊥ Perpendicularity
Standard: 0.1 mm | Tight: 0.025 mm | Requires datum setup
∥ Parallelism
Standard: 0.05 mm | Tight: 0.013 mm | Grinding may be required for tight values
⌀ True Position
Standard: ⌀0.2 mm | Tight: ⌀0.05 mm | CMM verified — include in QC requirement
○ Roundness (Circularity)
CNC Turning: 0.01–0.025 mm | Grinding: 0.002–0.005 mm
— Flatness
Standard: 0.05 mm | Ground: 0.005–0.01 mm | Distortion risk after thin-wall milling
◎ Concentricity / Runout
CNC Turning: 0.02–0.05 mm TIR | Grinding: 0.005–0.010 mm TIR
Tight Tolerances Cost Money — Here's Why
Standard CNC milling holds ±0.1 mm comfortably without any extra effort. When you specify ±0.025 mm, the machinist must take a finishing pass, use a different cutter, and slow down the feed rate — typically adding 20–40% to the cycle time. At ±0.010 mm or tighter, additional processes like grinding or lapping are often required, plus dedicated fixturing and 100% CMM inspection of every feature.
The business case: before specifying tight tolerances across your entire drawing, identify which features are functionally critical (bearing seats, press-fit bores, alignment pins) and specify tight tolerances only there. For everything else, ISO 2768-m in the title block is sufficient and saves real money at both prototype and production scale.
10 Tolerance Design Tips (DFM)
Only tolerance what matters
Every tight tolerance adds cost. Identify the 2–3 features that are functionally critical and specify tight tolerances only there.
Use ISO 2768-m as your baseline
Specify it in the title block and only call out exceptions. This avoids over-constraining every dimension.
Account for finish thickness
Anodizing (Type III) adds up to 150 µm. Powder coat adds 60–100 µm. Tight bore tolerances must be pre-compensated or masked.
Design bores for standard drill sizes
Specify holes as standard drill sizes where possible. Non-standard diameters require boring, adding time and cost.
Thin walls distort
Walls thinner than 0.5 mm in aluminium or 1.0 mm in steel can spring and deflect during machining. Tight flatness or position tolerances on thin walls are difficult to achieve.
Request CMM reports for critical features
For ±0.025 mm or tighter, always request a CMM inspection report. It verifies compliance and catches tool wear early.
Get a Quote with Your Tolerance Requirements
Upload your drawing or CAD file. Our engineers review tolerance callouts and confirm feasibility before you're charged — no surprises.
Frequently Asked Questions
We understand that choosing a manufacturing partner requires clarity and confidence. Our FAQs address common queries about pricing, quality, delivery timelines, quotations, and service support. Whether you're exploring our cost-effective solutions or need details on our processes, you'll find the answers here.
How does Survi offer pricing that is 75% lower than the U.S. and Chinese market?
At Survi, we optimize costs through efficient manufacturing processes, strategic sourcing, and lean operations. By leveraging advanced automation and minimizing overhead, we provide high-quality parts at a fraction of the typical market price—without compromising on precision or durability.
How does Survi ensure high-quality parts?
Quality is at the core of everything we do. We use cutting-edge technology, rigorous quality control processes, and skilled craftsmanship to meet and exceed industry standards. Every part undergoes thorough inspection to ensure precision, durability, and compliance with your specifications.
What is your typical lead time for orders?
Lead times vary based on the complexity and volume of the order, but we prioritize timely delivery. Most projects are completed within a few days to a couple of weeks. We work closely with our clients to ensure deadlines are met without compromising quality.
How quickly can I get a quotation?
We provide fast and accurate quotations, typically within 24 hours of receiving your request. For complex projects, we may require additional details, but we always strive for a quick turnaround.
What support do you offer after an order is placed?
We provide comprehensive service support before, during, and after production. Our team is available to address any concerns, assist with technical queries, and ensure a seamless experience from order placement to final delivery.
Which industries do you serve?
We cater to a wide range of industries, including automotive, aerospace, medical, robotics, and consumer electronics. Whether you need prototyping or high-volume production, we have the expertise to deliver top-notch solutions.
Can you handle custom manufacturing requests?
Absolutely! We specialize in custom machining, sheet metal fabrication, 3D printing, injection molding, and more. Share your design requirements with us, and we'll create a tailored solution to meet your needs.