What is the reasonable range of CNC machining tolerances?

The tolerance range of CNC (computer numerical control) processing technology depends on factors such as processing equipment accuracy, material properties, process parameters and workpiece size. The following are typical tolerance ranges and key influencing factors in different processing scenarios:

Typical tolerance range

(1). General machining

General tolerance	±0.05mm to ±0.2mm	(depending on the equipment and process)
High-precision machining	±0.01mm to ±0.05mm	(such as precision molds, aerospace parts).
Ultra-precision machining	±0.001mm to ±0.005mm	(such as optical devices, medical implants)

(2). Tolerances of different materials and processes

Metal materials (such as aluminum, steel):

• General milling/turning: ±0.05mm ~ ±0.1mm.
• High-precision machining (such as five-axis linkage): ±0.01mm ～ ±0.02mm.

Plastic materials (such as PEEK, nylon):

• General processing: ±0.1mm ~ ±0.2mm.
• Composite materials (such as carbon fiber):
  The tolerance is relatively large, usually ±0.1mm ~ ±0.3mm.
• Precision processing: ±0.05mm ~ ±0.1mm.

(3) Tolerances of different processing methods

Milling:	Turning:	Drilling:
Plane milling: ±0.05mm ~ ±0.1mm.	External cylindrical turning: ±0.01mm ~ ±0.05mm.	General drilling: ±0.1mm to ±0.2mm.
Complex surface milling: ±0.1mm ~ ±0.2mm.	Internal hole turning: ±0.02mm ~ ±0.08mm.	Precision drilling : ±0.01mm ~ ±0.05mm (such as deep hole drilling for aviation)

Key factors affecting tolerance

(1) Equipment accuracy

Machine tool type:

• Ordinary CNC machine tools: tolerance is usually ±0.05mm ~ ±0.1mm.

• High-precision machine tools (such as five-axis CNC Machine, slow wire cutting): tolerance can reach ±0.005mm ~ ±0.01mm.

Spindle accuracy:

• Spindle radial runout and axial runout will affect processing accuracy.

Guide rail accuracy:

• Guide rail straightness error will be directly reflected in the workpiece size.

(2) Process parameters

Cutting speed:

• Excessive or low cutting speed may cause tool wear or vibration, increasing tolerance.

Feed rate:

• Excessive feed rate will increase surface roughness and affect dimensional accuracy.

Cutting depth:

• Excessive cutting depth may cause workpiece deformation, especially thin-walled parts.

(3) Material properties

Material hardness:

• Tools wear faster and tolerances increase when machining hard materials (such as hardened steel).

Material deformation:

• Heat treatment or cutting heat may cause material deformation, affecting tolerances.

Material uniformity:

• Castings or composite materials may have internal stress or non-uniformity, resulting in machining errors.

(4) Workpiece size and shape

Size effect:

• The larger the workpiece, the larger the absolute value of the tolerance (e.g., the tolerance of a 1-meter-long workpiece may be ±0.1mm, while the tolerance of a 10-centimeter-long workpiece is ±0.02mm).

Shape complexity:

• The tolerance of complex curved surfaces or deep cavity structures is generally larger than that of simple flat or cylindrical structures.

(5) Temperature change

Thermal expansion:

• The different thermal expansion coefficients of the machine tool, tool, and workpiece can lead to dimensional deviations.

For example, aluminum has a high thermal expansion coefficient, and temperature compensation must be considered during machining.

Tolerance control in practical applications

(1) General scenarios

• General industrial parts: ±0.05mm to ±0.1mm (such as mechanical equipment housings, brackets).
• Precision parts: ±0.01mm to ±0.05mm (such as automobile engine parts, molds).
• Ultra-precision parts: ±0.001mm to ±0.005mm (such as optical lenses, medical implants).

(2) Special scenarios

Aerospace:
Tolerances are usually controlled at ±0.01mm ～ ±0.05mm.

Medical devices:
Tolerances are ±0.005mm ～ ±0.02mm (such as artificial joints, dental implants).

Electronics industry:
Tolerances are ±0.01mm ～ ±0.05mm (such as mobile phone housings, connectors).

Summary

Typical tolerance range:

• General CNC machining: ±0.05mm～ ±0.2mm.
• High-precision machining: ±0.01mm ～ ±0.05mm.
• Ultra-precision machining: ±0.001mm ～ ±0.005mm.

Key factors affecting tolerance:

Equipment accuracy, process parameters, material properties, workpiece size, temperature control.

Ways to improve accuracy:

• Use high-precision machine tools and cutting tools.
• Optimize cutting parameters (such as cutting speed, feed rate).
• Perform temperature compensation and aging treatment.
• Use precision detection tools (such as three-coordinate measuring machines) for real-time monitoring.

According to specific needs and process conditions, choosing the right equipment and parameters can find the best balance between cost and accuracy.