Precision Is Not a Coincidence — It Is the Result of a System
CNC precision is not determined by a single factor but by the interaction of many variables. Even the best CNC machine cannot produce precise parts when tools are worn, the workpiece is poorly clamped or room temperature fluctuates.
In this article, we systematically analyse the most important influencing factors.
Machine-Related Factors
Machine Accuracy
The basic accuracy of the CNC machine sets the theoretical limit:
- Positioning accuracy: Typically ±0.005 mm for modern machining centres
- Repeat accuracy: Often ±0.003 mm — the ability to consistently reach the same position
- Thermal stability: Temperature changes cause machine deformation — modern machines compensate in real time
Spindle Quality
The spindle is the heart of every CNC machine. Its runout, stiffness and thermal behaviour directly determine machining quality. Spindle bearings have a limited service life; regular monitoring of vibration values is essential.
Tool-Related Factors
Tool Quality and Condition
A worn tool is the most common cause of dimensional deviations in practice:
- Cutting edge wear: Increases cutting forces and can cause deviations of >0.05 mm
- Tool deflection: Long, thin tools bend under cutting forces
- Tool runout: Asymmetric runout leads to oversized bores
More on the correct tool choice in our article Tool Materials and Coatings.
Tool Clamping
The tool holder is the link between machine and tool. Shrink-fit chucks achieve runout values of <0.003 mm and are the standard for precision manufacturing. Collet chucks (ER) are good for standard applications but with less precision.
Workpiece-Related Factors
Material Properties
Each material behaves differently under cutting forces:
- Internal stresses: Releasing material stresses can lead to distortion after machining
- Thermal expansion: The workpiece heats up during machining and changes dimensions
- Material hardness: Varying hardness in the blank causes irregular chip formation
Workpiece Clamping
The clamping strategy directly affects achievable accuracy:
- Clamping forces: Too much pressure deforms thin-walled parts
- Clamping points: The clamping must support the workpiece where cutting forces act
- Re-clamping: Every re-clamping introduces positioning errors — minimise re-clamps
Environmental Factors
Temperature
Temperature is the most underestimated factor for precision. A temperature change of 1°C causes a steel workpiece of 500 mm length to change by approx. 6 µm. For µm accuracy, climate-controlled workshops (20°C ±1°C) are essential.
Vibrations
External vibrations (forklift trucks, adjacent machines, road traffic) can significantly impair precision. Sensitive machines require vibration-isolated foundations. More on vibrations in our detailed article.
Frequently Asked Questions (FAQ)
What accuracy can CNC machining achieve?
Under optimal conditions, modern CNC machines achieve tolerances of ±0.005 mm and better. Standard production typically achieves ±0.01–0.02 mm reliably and reproducibly.
How does batch size affect precision?
In series production, tool wear must be compensated. Good manufacturers use automatic tool correction or integrated measurement to maintain constant quality across all parts.
Conclusion: Precision Is System Performance
Achieving CNC precision is not a question of a single factor but entire system performance — machine, tool, workpiece and environment must work together harmoniously.
Need precisely manufactured parts? Contact us — we guarantee process-safe precision.