Our commitment to quality is evident in our standard machining tolerances in mm of 0.005 mm, inches of ±0.0002 inches (5μm). This level of accuracy is ideal for applications requiring tight tolerances, such as medical devices, automotive components, and scientific instruments. Explore more machining tolerance standards for your project in the CNC tolerance chart below.
A CNC machining tolerance chart is a quick reference that shows the acceptable variation between your part’s design dimensions and the actual machined result. It lists dimensions on one side and the allowed tolerance range (plus/minus values) on the other. This helps engineers and machinists stay on the same page when it comes to dimensional accuracy.
We know that CNC tolerance standards like ISO, ANSI, and ASME set important guidelines, but they’re not identical across the board. A tolerance class that’s acceptable in one industry might not be acceptable in another. For example, aerospace and medical parts often follow stricter tolerance charts compared to general industrial components. That’s why machinist always make sure to match my tolerance requirements to the specific guidelines of the client’s industry. Below, I’ll share several machining tolerance charts of different standards.
This tolerance class is used for parts where precise dimensional limits are required but not necessarily to the tightest possible standards (fine tolerances). The tolerance values (±0.05, ±0.1, etc.) are appropriate for parts in industries like automotive or general manufacturing, where tight tolerance is not as critical as it is in more precise fields like aerospace or medical. This chart is generally aligned with industry standards, especially for fine tolerances used in general manufacturing. If you’re working with highly critical parts (like in aerospace), you might need stricter tolerance charts. | |
| Permissible deviations in mm for ranges in nominal lengths | Tolerance Class Designation (Description) |
| f (fine) | |
| 0.5 up to 3 | +/- 0.05 |
| over 3 up to 6 | +/- 0.05 |
| over 6 up to 30 | +/- 0.1 |
| over 30 up to 120 | +/- 0.15 |
| over 120 up to 400 | +/- 0.2 |
| over 400 up to 1000 | +/- 0.3 |
| over 1000 up to 2000 | +/- 0.5 |
| over 2000 up to 4000 | |
For nominal sizes below 0.5 mm, the deviat ons shall be indicated ad acent to the relevant nominal size(s). | |
Tolerances for plastic parts are typically wider than those for metals, as plastics can have more variability in their properties and behaviors, such as thermal expansion and shrinkage. | |
Permissible deviations in mm for ranges in nominal lengths | Tolerance Class Designation (Description) |
m (medium) | |
0.5 up to 3 | +/- 0.1 |
ov er 3 u p to 6 | +/- 0.2 |
over 6 up to 30 | +/- 0.3 |
over 30 up to 120 | +/- 0.5 |
over 120 up to 400 | +/- 0.8 |
over 400 up to 10 00 | +/- 1 2 |
over 1000 up to 2000 | +/- 2.0 |
over 2000 up to 4000 |
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For nominal sizes below 0.5 mm, the deviations shall be indicated adjacent to the relevant nominal size(s) | |
Tolerance of Metal (mm) The tolerances for metal parts are very precise and are in line with industry standards for high-precision machining. These tolerances are suitable for industries like aerospace, automotive, and medical devices where high precision is required. | Tolerance of Plastic (mm) The tolerances for plastic parts are also within typical industry standards for general plastic manufacturing. They are looser compared to metal tolerances, which is expected due to the material properties of plastics (such as shrinkage and thermal expansion during molding). | |
Linear Dimensions | +/- 0.01 | +/- 0.05 |
Diameter | +/- 0.005 | +/- 0.02 |
Precise Hole | +/- 0.002 | +/- 0.02 |
Chamfer Heights | +/- 0.02 | +/- 0.05 |
Angular Dimensions | +/- 0°5′ | +/- 10 |
Straightness | +/- 0.003 | +/- 0.02 |
Flatness | +/- 0.003 | +/- 0.02 |
Perpendicularity | +/- 0.003 | +/- 0.02 |
Symmetry | +/- 0.003 | +/- 0.02 |
Concentricity | +/- 0.003 | +/- 0.005 |
Parallelism | +/- 0.003 | +/- 0.01 |
CNC tolerance standards like ISO, ANSI, and ASME set guidelines, but they’re not identical across the board. A tolerance class acceptable in one industry might not be acceptable in another. For example, aerospace and medical parts often follow stricter tolerance charts compared to general industrial components. Always match your tolerance requirements to your specific industry’s guidelines. Learn the basic generic machining tolerance standards knowledge below.
| Description | General Tolerance |
| Distance Dimensions | For features of size (Length, width, height, diameter) and location (position, concentricity, symmetry) +/-0.005″ |
| Orientation and Form Dimensions | 0-12″+/-0.005″,Angularity 1/2 degree. For 24″and beyond please consult Xometry’s Manufacturing Standards. |
| Edge Condition | By default, sharp edges will be broken and deburred. If reserved, please check with contact to ensure that the specified key edge must be kept sharp. |
| Standards | Definition | CNC Milling | CNC Turning |
| Part Size | Maximum and Minimum Part Size define the physical size limits of the workpiece, serving as guidelines for machine tool workspace and fixture design. | Maximum 4000×1500×600 mm 157.5×59.1×23.6 in. | Maximum 200×500 mm 7.9×19.7 in. |
| Minimum 4×4 mm 0.1×0.1 in. | Minimum 2×2 mm 0.079×0.079 in. | ||
| Minimum Feature Size: The smallest detail that can be machined, such as hole diameter or slot width, related to tool selection and machining processes. | Φ 0.50 mm | Φ 0.50 mm | |
| Φ 0.00197 in. | Φ 0.00197 in. | ||
| Tolerances and Precision | Standard Tolerances: Allowable deviations specified to ensure part interchangeability and functionality. | Φ 0.50 mm | Φ 0.50 mm |
| Φ 0.00197 in. | Φ 0.00197 in. | ||
| Linear Dimension: Dimensions in the linear direction of a part, affecting the mating accuracy. | +/- 0.025 mm | +/- 0.025 mm | |
| +/- 0.001 in. | +/- 0.001 in. | ||
| Holes, Shafts, and Other Features | Hole Diameter (Not Reamed): Common dimension for drilled holes. | +/- 0.025 mm | +/- 0.025 mm |
| +/- 0.001 in. | +/- 0.001 in. | ||
| Shaft Diameter: Important for mating with holes. | +/- 0.025 mm | +/- 0.025 mm | |
| +/- 0.001 in. | +/- 0.001 in. | ||
| Edge Condition: Specifies rounding or chamfering of edges. | Chamfer or radius must be specified on engineering drawings. | ||
| Threads and Tapped Holes: Key dimensions for connecting parts. | Diameter: Φ 1.5-5 mm, depth: 3×diameter | Diameter: Φ 1.5-5 mm, depth: 3×diameter | |
| Diameter: Φ 5 mm or more, depth: 4-6×diameter | Diameter: Φ 5 mm or more, depth: 4-6×diameter | ||
CNC machining tolerances define the allowable variation in a machined part’s dimensions from its intended design. In manufacturing, no process can produce parts with absolute perfection, so tolerances set the acceptable limits to ensure the part still functions as intended. The tighter the tolerance, the closer the part will be to the exact nominal measurement.
In CNC machining, tolerances are typically classified into several types:
The selection of proper machining tolerances plays a critical role in product quality. Overly tight tolerances can increase production time, require specialized tooling, and raise costs dramatically, while overly loose tolerances may affect performance, assembly, or part life span. Achieving the right balance ensures reliable functionality, improves fit and finish, and keeps manufacturing economical.
Reading a CNC machining tolerance chart isn’t complicated once you know what to look for. The chart shows the nominal dimension alongside the allowable deviation, usually written as “±” a specific value. For example, a shaft diameter of 20.00 mm ±0.02 mm means it can be anywhere between 19.98 mm and 20.02 mm and still meet specifications.
When choosing tolerances, think about:
The key is balancing precision with what’s practical to manufacture. In U.S. job shops, many non-critical dimensions use standard CNC machining tolerances such as ±0.005″ (0.127 mm) for metals and ±0.010″ (0.254 mm) for plastics. Critical features get tighter specs only where they matter.
At Chiheng, we follow this same principle. We work directly with clients to review their tolerance charts before starting production. One example was a U.S. aerospace order where the original design called for ±0.001″ across the board. Instead of over-engineering every feature, we identified the few points where that tight range was essential, relaxed other dimensions, and cut machining time by 20% without sacrificing function. This keeps parts precise, costs under control, and delivery on schedule.
Tighter tolerances always mean better quality
A lot of people think that the tighter the tolerance, the better the part. That’s not always true. A tolerance that’s tighter than needed can drive up machining costs, slow production, and even make parts harder to assemble. The “best” tolerance is one that meets the functional need of the part without adding unnecessary expense or complexity.
Industry standards are the same everywhere
CNC tolerance standards like ISO, ANSI, and ASME set guidelines, but they’re not identical across the board. A tolerance class acceptable in one industry might not be acceptable in another. For example, aerospace and medical parts often follow stricter tolerance charts compared to general industrial components. Always match your tolerance requirements to your specific industry’s guidelines.
Design specs always match machining capabilities
It’s common for design teams to set tolerances that look fine on paper but are hard—or even impossible—for a machine to achieve consistently. A CNC shop’s equipment type, tooling, material selection, and environmental factors all play a role in real-world precision. This is why engineers and machinists need to work together early in the process to align design intent with the machine’s actual capability.
At Chiheng, we focus on hitting the right balance between tight CNC machining tolerances and practical manufacturing. We know U.S. customers often need parts that meet strict quality standards without pushing costs through the roof, so our process is set up to deliver both precision and value.
Advanced Equipment and In-House Control
We use high-precision CNC machines, including 3-axis, 4-axis, and 5-axis setups, paired with calibrated measuring tools. Every job goes through an in-house quality check where we track CNC machining dimensional accuracy against the required tolerance chart. By controlling the process start to finish, we can achieve tolerance classes in line with ISO and ANSI standards for metals, plastics, and custom projects.
Working Closely With Clients
Before production starts, our engineers talk directly with customers to nail down the most realistic CNC machining design tolerances based on the part’s function, material, and budget. We help avoid over-specifying ultra-tight tolerances that can drive costs up without improving performance.
Proven Results From Past Projects
By combining advanced CNC machining precision, strict tolerance control, and tight customer collaboration, we’re able to consistently hit the industrial tolerance standards global. buyers count on.
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