Discover how CNC Design Choices Impact Your Budget

When designing a part for CNC machining, the choices you make in the design phase can significantly influence the cost, lead time, and overall manufacturability. We often see designs that could be optimised to reduce unnecessary expenses while still achieving the desired functionality and aesthetics.

In this article, we explore key factors that drive CNC machining costs and share practical tips for designing parts with manufacturability in mind.

Number of Setups

Each time a part needs to be repositioned (or “flipped”) during machining, it adds to the overall cost. Complex designs requiring multiple setups to access all surfaces increase machining time and may introduce alignment challenges. Of course, 5-axis machines may mitigate this, however, the added complexity of programming for 5-axis may increase an element of cost or time, especially if it is for very low quantities.

Design for Manufacture

Design parts that can be machined from one or two setups. Consolidate features on as few faces as possible to reduce reorientations. Think about, undercuts, square corners, minimum radius in corners and of course the depth of cut vs the radius size, i.e. length of cutters available (see below for more).

Inside Corners and Sharp Edges

Sharp inside corners require the use of small tools, which take longer to machine and can increase tool wear. Achieving perfectly sharp edges is often impossible with standard tools, and attempting to do so can add significant costs.

Design for Manufacture

Use fillets for internal corners. A radius that matches standard tool sizes (e.g., 3mm, 6mm) is ideal.

Avoid specifying sharp edges unless absolutely necessary for functionality.

Tool Changes and Non-Standard Features

Every tool change increases machining time. Additionally, parts that require custom tooling or unconventional features (e.g., sculpted surfaces or intricate patterns) demand extra preparation and often involve specialised operations.

Design for Manufacture

Minimise the number of different tools needed by standardising hole sizes and features.

Avoid intricate surface detailing unless it’s critical to the part’s purpose.

Tolerances and Finishes

While tight tolerances and high-quality finishes may be essential for certain parts, over-specifying them for non-critical areas unnecessarily increases costs. Achieving a polished finish, for example, requires additional passes and polishing steps.

Design for Manufacture

Define tolerances only where they are critical to the function or assembly of the part.

Clearly specify which areas require high-quality finishes and which can remain in their as-machined state.

Trapped Cavities and Undercuts

Features such as internal cavities, undercuts, or other hard-to-reach areas often necessitate specialised tools or multi-axis machining, both of which add to the cost.

Design for Manufacture

Avoid internal features that can’t be accessed directly by standard tools. Consider alternative designs, such as splitting the part into two simpler components that can be assembled.

Material Selection

Different materials vary in machinability, which directly impacts machining time and tool wear. Harder materials, such as stainless steel or titanium, often require slower cutting speeds and more frequent tool changes, increasing the cost.

Design for Manufacture

Select materials that balance performance and machinability. Please note that while we can advise if a material is easy or hard to machine, we cannot offer guidance on material choices based on your application.

Key point: Collaboration with Your Machinist Early

Engaging with your machining partner (such as Prototype Projects) early in the design process can save both time and money. Machinists can provide valuable insights into optimising your design for the machining process.

Design for Manufacture

Share your design files and discuss any challenging features with your machining partner before finalising the design. We accept 2D drawings with GD&T information, providing precise guidance on critical features.

Conclusion

Designing for CNC machining is about finding the balance between functionality and manufacturability. By applying the tips above, you can reduce costs, shorten lead times, and create parts that are easier to machine without sacrificing quality.

We have extensive experience in CNC machining, and are here to help optimise your designs for production. Whether you need advice on material selection, tolerances, or design adjustments, our team is ready to assist.

Contact us today to learn how we can bring your designs to life efficiently and cost-effectively.

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Contact us on 01763 249760 to discuss your requirements.

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