Engineering
CNC machining tolerances explained
Understanding where precision matters can help control cost while maintaining the performance of the final part.
Introduction
No machining process produces a dimension with zero variation.
A tolerance establishes the acceptable range around a specified dimension and gives the manufacturer a measurable target for production and inspection.
What is a machining tolerance?
If a drawing specifies a dimension of 25.00 mm with a ±0.05 mm tolerance, the acceptable range is:
24.95 mm to 25.05 mm
The tighter the tolerance, the more controlled the manufacturing process generally needs to be.
Where tighter tolerances matter
Tight tolerances may be important for:
Bearing locations
Mating components
Shafts and bores
Sealing surfaces
Precision alignment features
Critical assemblies
Where standard tolerances may be enough
Other features may not require extremely tight control.
For example:
Non-functional outer dimensions
Clearance areas
Cosmetic features
General mounting surfaces
Using practical tolerances where possible can make production more efficient.
Conclusion
The goal is not to make every dimension as tight as possible. The goal is to specify the level of accuracy required for the part to perform correctly.
