Maintaining Close Tolerances when CNC Machining

Maintaining tight tolerances is one of the most critical — and challenging — aspects of CNC machining, especially when working with complex geometries or difficult materials. At XRC Engineering, we specialize in high-precision CNC machining and understand how small variations can have a big impact on part performance and quality.

In this article, we’ll break down key best practices for maintaining tight tolerances in CNC machining, covering everything from material selection and fixturing to process optimization. Whether you're designing for aerospace, robotics, or high-end mechanical systems, these principles will help ensure your parts meet specification every time.

1. Choose the Right Material for Dimensional Stability

Material selection plays a foundational role in tolerance control. Some materials are naturally more dimensionally stable than others during and after machining.

• Metals like aluminum and steel tend to hold tolerances well due to their rigidity and predictable machining behavior.

• Plastics and composites, on the other hand, can warp or deform due to thermal expansion, residual stresses, or cutting forces.

For high-precision applications, it’s best to use materials with:

• A uniform grain structure

• Low internal stress

• Good machinability ratings

Material certification and traceability can also help ensure consistency across production runs.

2. Precision Fixturing and Workholding Techniques

A part is only as accurate as how it’s held. Proper fixturing is essential to avoid movement, distortion, or vibration during machining — all of which can lead to out-of-spec parts.

Key fixturing practices include:

• Using even clamping pressure to prevent distortion

• Employing custom soft jaws or vacuum fixtures for delicate or complex parts

• Minimizing overhang and unsupported surfaces

• Designing fixtures that locate parts consistently and repeatably between setups

At XRC Engineering, we often develop custom fixtures in-house to meet the unique requirements of each project.

3. Optimize Machining Parameters for Accuracy

Tight tolerances demand more than just the right toolpath — they require refined process parameters. The following considerations help reduce dimensional error:

• Tool selection: Use high-quality, sharp tools with coatings suited to the material

• Feed rate and spindle speed: Dialed in for minimal deflection and thermal distortion

• Depth of cut and step-over: Optimized to prevent tool chatter and surface variation

We also recommend:

• Machining in stages (roughing and finishing separately)

• Allowing parts to cool or stress-relieve between operations

• Regular machine calibration to maintain axis accuracy

In-process inspection — including probing and gauging — helps catch deviations early, before they become scrap.

4. Continuous Monitoring and Inspection

Advanced tolerance control doesn’t end at the toolpath. Quality assurance is an ongoing process throughout the machining cycle:

• In-process measurement with Renishaw probes

• Post-process inspection with CMM or precision metrology tools

• Documented quality checks and traceable inspection reports

For parts that require tolerances in the microns, environmental factors like temperature and vibration can also be managed with climate-controlled machining environments.

Delivering Precision at XRC Engineering

At XRC Engineering, we understand that precision is more than just numbers on a drawing — it's a promise to our customers. From prototyping to production, we apply rigorous process control, precision tooling, and careful planning to deliver parts that meet the most demanding tolerance requirements.

Need help with your next high-precision machining project?

Reach out to our engineering team for a quote or technical consultation — we’re here to help you get it right the first time.