Designing for CNC Machining: Best Practices for Engineers

CNC machining is one of the most versatile and accurate manufacturing methods available, but achieving optimal results requires careful consideration during the design phase. By incorporating best practices, you can enhance manufacturability, reduce costs, and ensure the quality of your parts.

Here, are some essential tips for designing parts that are CNC-friendly.

Understand the Machining Process

CNC machining involves removing material using computer-controlled machine tools. This subtractive process has inherent limitations, such as tool accessibility and cutting tool geometry. Designing with these constraints in mind is key to creating manufacturable parts.

Tips

• Familiarise yourself with the capabilities of CNC mills and lathes – if in doubt, ask us!
• Consider tool accessibility when designing deep pockets or internal features.

Simplify Geometries

Complex features often require additional machining steps, specialised tooling, or multi-axis setups, increasing cost and production time. Simplifying geometries can make parts easier and more economical to produce.

Tips

• Minimise non-essential features, such as intricate patterns or excessive details.
• Break down complex designs into multiple simpler components that can be assembled.

Use Standard Dimensions and Features

Parts with non-standard dimensions or features often require custom tooling, leading to longer setup times and higher costs.

Tips

• Use standard hole sizes and thread pitches (e.g., M6, M8).
• Align features with standard material thicknesses and dimensions.

Optimise Wall Thickness

Walls that are too thin can lead to vibrations during machining, causing defects, while overly thick walls may increase material costs unnecessarily.

Tips

• Maintain a minimum wall thickness of 1mm for metals and 1.5mm for plastics.
• Ensure uniform wall thickness where possible to prevent warping.

Design for Fewer Setups

Every time a part needs to be repositioned during machining, it increases production time and introduces the risk of alignment errors.

Tips

• Consolidate features on fewer faces to reduce the need for multiple setups.
• Design parts that can be machined using 3-axis tools, or 5-axis tools, depending on your needs, when feasible.

Incorporate Fillets for Internal Corners

Sharp internal corners are difficult to machine and require small tools, which increase machining time and tool wear.

Tips

• Add fillets to internal corners, with a radius equal to or larger than the cutting tool’s radius.
• Use standard radii, such as 3mm or 6mm, to simplify tool selection.

Specify Tolerances Thoughtfully

Overly tight tolerances increase machining time and cost, and may not be necessary for the part’s function.

Tips

• Apply tight tolerances only to critical dimensions.
• Use general tolerances (e.g., ±0.1mm) for non-critical features.

Select the Right Material

Material choice affects machinability, cost, and part performance. Some materials are easier to machine than others, while harder materials may require slower cutting speeds and more frequent tool changes.

Tips

Choose materials that balance machinability with the required mechanical properties.

Consult with your machining partner to identify cost-effective options.

Conclusion

Designing for CNC machining is about striking the right balance between functionality, manufacturability, and cost. By following these best practices, you can create parts that are not only easier to machine but also meet your performance requirements.

We work closely with engineers and designers to optimise parts for CNC machining. Whether you need advice on material selection, tolerances, or design features, our team is here to help. Get in touch with us today to streamline your design-to-production process.

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Contact us on 01763 249760 to discuss your requirements.

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