Skip to content 
A machining tolerances chart shows the acceptable dimensional variation for manufactured parts. Engineers and designers use tolerance charts to balance accuracy, cost, and manufacturability. This guide provides clear CNC machining tolerance charts and explains how to apply them correctly in real production environments.
This machining tolerances chart is used by engineers to quickly reference acceptable dimensional limits during CNC production. A clear machining tolerances chart helps reduce design errors and improves communication between design and manufacturing teams.
General Machining Tolerances Chart
General machining tolerances apply when no specific tolerance is defined on an engineering drawing. These tolerances are commonly used for non critical features where exact precision is not required.
Typical general machining tolerance ranges include:
Linear dimensions: ±0.005 in or ±0.13 mm
Hole diameters: ±0.005 in
Shaft diameters: ±0.005 in
Flatness and straightness: 0.005 in per 12 in
General tolerances reduce programming time, inspection effort, and overall machining cost. They are suitable for brackets, housings, and structural components.
CNC Machining Tolerance Chart
CNC machining provides higher accuracy and repeatability compared to manual machining. Modern CNC machines can consistently hold tighter tolerances when processes are controlled.
Common CNC machining tolerance ranges include:
Standard CNC machining: ±0.005 in
Precision CNC machining: ±0.002 in
Tight tolerance CNC machining: ±0.001 in
Ultra precision machining: ±0.0005 in
The actual tolerance achieved depends on material type, part geometry, machine condition, and tooling quality. Longer parts and thin features typically require looser tolerances.
Standard vs Tight Machining Tolerances
Standard tolerances are used for most machined parts where dimensional variation does not affect function. They allow faster machining speeds and minimal inspection.
Tight tolerances are required for mating parts, press fits, and precision assemblies. These tolerances demand slower cutting speeds, stable setups, and additional quality control.
Using tight tolerances where they are not functionally required increases production cost without improving performance.
How to Use a Machining Tolerance Chart
Machining tolerance charts should be used early in the design process. Proper application improves manufacturability and reduces production issues.
Identify functional features first.
Apply general tolerances to non critical dimensions.
Specify tight tolerances only on mating or moving features.
Confirm tolerance feasibility with the machine shop before finalizing drawings.
Clear tolerance planning reduces rework, scrap, and lead time.
Why Machining Tolerances Matter in Production
Machining tolerances directly affect part fit, performance, and cost. Loose tolerances reduce machining time and inspection effort but may result in poor assembly alignment. Tight tolerances improve precision but increase cycle time and tooling wear.
In production environments, tolerance decisions influence machine selection, fixturing methods, and inspection strategy. Poor tolerance planning often causes delays, rework, and unexpected cost increases.
Understanding tolerance charts helps engineers balance functional requirements with efficient manufacturing.
ISO General Tolerances Reference
ISO 2768 is a widely used standard for defining general machining tolerances. It simplifies drawings by applying tolerance classes instead of specifying limits on every dimension.
ISO 2768 f: Fine
ISO 2768 m: Medium
ISO 2768 c: Coarse
ISO 2768 v: Very coarse
ISO tolerance standards reduce ambiguity between designers and machine shops, especially in global manufacturing environments.
Well defined tolerances also improve communication between design and manufacturing teams. Clear limits reduce interpretation errors on the shop floor. This leads to consistent part quality, predictable inspection results, and smoother production workflows across multiple machining batches.
Frequently Asked Questions
What is a machining tolerance chart ?
It is a reference that defines acceptable dimensional variation for machined parts.
What is a standard CNC machining tolerance ?
A common standard tolerance is ±0.005 in for general CNC machining.
Can CNC machines hold ±0.001 in ?
Yes. Most modern CNC machines can achieve ±0.001 in under controlled conditions.
Do tighter tolerances increase cost ?
Yes. Tighter tolerances require slower machining, additional inspection, and higher process control.
For detailed explanations and real examples, see our guide on CNC machining tolerances or visit us.
