¿De verdad necesitas una tolerancia de ±0,01 mm? El coste oculto de exigir una precisión excesiva

Tighter tolerances are not always better.

In CNC machining, specifying a tolerance of ±0.01 mm instead of ±0.1 mm can significantly increase manufacturing cost — even when the tighter tolerance makes no meaningful difference to the part's function.

The key question is not:

How precise can this part be?

It's:

How precise does this part actually need to be?

Why do tighter tolerances cost more?

1. More demanding machining processes

Tight CNC machining tolerances require greater control over tool wear, cutting forces, thermal expansion, workholding, and machine conditions.

Depending on the material and part geometry, achieving a tighter tolerance may require additional finishing operations or more carefully controlled machining parameters.

2. More inspection and quality control

When dimensional tolerances become tighter, inspection becomes more demanding.

Manufacturers may need more suitable measuring equipment, more frequent measurements, and additional checks to verify dimensional accuracy.

The closer a dimension is to the process capability limit, the more difficult it can be to maintain consistently across a production batch.

3. Higher scrap and rework risk

A part that meets a ±0.1 mm requirement may be perfectly functional, while the same part could fail an unnecessarily strict ±0.01 mm requirement.

If the tighter tolerance does not improve fit, function, alignment, or performance, the extra manufacturing effort may add cost without adding real value.

How should engineers specify tolerances?

Here are three practical principles to consider when preparing a design for CNC machining.

1. Apply tighter tolerances only where function requires them

For example, bearing seats, locating features, and precision mating surfaces may need tighter dimensional control than non-critical external profiles.

The correct tolerance depends on the actual fit, loading, operating conditions, and design requirements.

2. Use GD&T when geometric relationships matter

Dimensional tolerances alone do not always communicate how a part must fit or function in an assembly.

Geometric Dimensioning and Tolerancing (GD&T) can define requirements for features such as position, flatness, perpendicularity, and runout when those characteristics are important to the design.

3. Review critical dimensions before requesting a quote

If a drawing applies tight tolerances to every dimension, ask whether each requirement is functionally necessary.

A manufacturing review can help identify which dimensions need tighter control and which can use more practical tolerances.

This does not mean compromising quality. It means defining quality according to the part's actual requirements.

The takeaway

Good precision engineering is not about making every dimension as tight as possible.

It's about applying the right tolerance to the right feature — so the part performs as intended without unnecessary manufacturing cost.

At AluCarbon Tech, we believe manufacturability should be considered alongside design intent when evaluating custom CNC-machined components.

When reviewing a new part, do you define tolerances based on functional requirements, or do you tend to apply tighter tolerances as a precaution?