When selecting CNC machine tools, “machining accuracy” is one of the most important indicators for most customers. However, many people only focus on nominal values such as “±0.01 mm”, while ignoring an important fact:

Machine accuracy is not a single parameter, but a comprehensive result determined by multiple systems working together.

1. Position Accuracy

Position accuracy refers to the deviation between the target position commanded by the CNC system and the actual position reached by each motion axis.

For example:
If the system commands the X-axis to move 100 mm, the actual movement may be 100.008 mm or 99.995 mm. This deviation is called positioning error.

2. Repeatability (Repeat Positioning Accuracy)

Repeatability refers to the consistency of the machine when repeatedly executing the same positioning command.

For example:
If the same position is processed 10 times, how consistent are the results each time?

In actual production, this indicator is more important than absolute positioning accuracy, because:

In mass production, customers care more about “stability and consistency” rather than single-point accuracy.

If repeatability is unstable, even if single positioning accuracy is high, it may still lead to:

• Dimensional variation in batch parts
• Increased assembly defects
• Poor product consistency

3. Machining Accuracy

Machining accuracy is the indicator closest to the final product quality. It refers to the deviation between the actual finished part dimensions and the design drawings.

It is not only affected by the machine itself, but also by various external factors, such as:

• Tool wear condition
• Cutting parameter settings (speed, feed rate)
• Material hardness variation
• Coolant and chip removal conditions
• Operation and programming strategy

Common Machine Accuracy Levels (Industry Reference)

In the actual market, different grades of machines typically correspond to the following accuracy ranges:

Standard machine: ±0.02 mm
Suitable for general machining, structural parts, and non-precision components

Precision machine: ±0.01 mm
Suitable for mold processing and medium-precision parts

High-precision machine: ±0.005 mm or better
Suitable for aerospace, precision molds, and high-end fitting components

Important Note (Common Misunderstanding)

The accuracy data published by machine tool manufacturers is usually measured under ideal conditions, such as:

• Constant temperature environment (standard 20°C)
• No external vibration interference
• Standard test workpiece
• New machine condition (not used for long-term production)

However, in real production environments, accuracy is affected by thermal deformation, cutting load, and long-term wear. Therefore:

Nominal accuracy ≠ long-term stable accuracy in real production

A truly excellent machine tool is defined not only by its factory test data, but more importantly by its ability to maintain stability during long-term operation.