Webinar Recording - Trimming Costs, Keeping Quality: Smart Design Tips for CNC Machining

CNC machining is known for its precision, speed, and ability to produce complex parts with tight tolerances. However, the cost of CNC machining can quickly rise if the design process overlooks key manufacturability principles. That’s why smart design is not just about making a part that works—it's about making a part that’s cost-efficient, easy to produce, and maintains the necessary quality. In a recent webinar titled “Trimming Costs, Keeping Quality: Smart Design Tips for CNC Machining”, manufacturing experts discussed practical, actionable ways to optimize part design without compromising performance. The insights shared are essential for engineers, product designers, and procurement teams looking to make the most of their CNC machining projects.

The webinar focused on identifying common cost drivers in CNC machining and how early design decisions can eliminate unnecessary complexity. Here’s a comprehensive breakdown of the major takeaways.

1. Simplicity is Powerful in CNC Design

One of the key points in the webinar was the value of simplicity. The more intricate a part is, the more time and tools are required to machine it. This often translates to higher production costs. By simplifying the geometry wherever possible—without sacrificing functionality—you reduce the overall machining time and tool wear.

Avoid unnecessary features such as deep pockets, undercuts, or tight internal radii unless absolutely needed. Not only are these features more challenging to machine, but they may also require specialized tooling or multi-axis setups, increasing both complexity and cost.

2. Choose the Right Materials Wisely

Material selection has a huge impact on both the machinability and cost of your part. The webinar highlighted that some designers automatically choose exotic metals or high-strength alloys without considering whether a lower-cost alternative could achieve the same results.

For example, aluminum is lightweight, corrosion-resistant, and easy to machine, making it ideal for many components. Stainless steel is harder to machine and takes more time, so it should be chosen only when necessary for strength or corrosion resistance. Using readily available, machinable materials helps lower costs and speeds up turnaround times.

3. Tolerances: Don’t Overtighten the Specs

Holding tight tolerances can significantly increase machining costs because they require more precise cutting, slower feed rates, and sometimes multiple setups or finishing passes. The speakers emphasized that unless a specific tolerance is essential for the part's function, it's best to allow for standard tolerances.

It’s common for designers to default to tighter tolerances than necessary, thinking it ensures better quality. In reality, this often leads to overengineering. Tolerances should be driven by function. Communicate critical dimensions clearly on your drawing and let the machinist know which tolerances can be relaxed.

4. Minimize Tool Changes and Setup Times

Every time a tool is changed or the machine setup is adjusted, it adds cost. One of the key design tips from the webinar was to consolidate features that can be machined using the same tool or within the same setup. This not only reduces machine downtime but also improves consistency across parts.

For instance, parts with symmetrical features can often be flipped or rotated rather than requiring a complex 5-axis machining approach. Design with fixturing in mind, making sure your part can be securely clamped without requiring custom jigs.

5. Avoid Thin Walls and Deep Cavities

Thin walls and deep cavities are known for creating problems during CNC machining. Thin walls are prone to vibration and deflection, leading to poor surface finish or even breakage. Deep cavities often require long tools, which are more flexible and can introduce chatter, poor accuracy, or slower machining speeds.

The experts in the webinar recommended maintaining wall thicknesses of at least 1 mm for metals and slightly more for plastics. For cavities, consider the maximum tool length-to-diameter ratio, and avoid designing features that exceed it. If a deep pocket is required, breaking it up into shallower levels can make it easier to machine.

6. Design for Standard Tooling

CNC machines use a variety of standard cutting tools, and designing parts that align with these tools can help reduce costs. For example, using standard hole sizes (like 6 mm, 8 mm, or 10 mm) allows machinists to use off-the-shelf drill bits and end mills rather than custom tools.

Similarly, radii on internal corners should match standard cutter sizes. If you design a tight internal corner with a 1 mm radius, the machinist may need to perform additional passes or use a smaller, more fragile tool. Designing with common tool diameters in mind helps ensure a quicker, more economical production process.

7. Understand Machine Capabilities

Another important point raised during the webinar was the value of understanding the capabilities of CNC equipment. Not all CNC machines are the same. Some shops may have 3-axis machines, while others specialize in 5-axis machining or Swiss turning.

Designers should collaborate with their manufacturing partners to understand what their equipment can handle. For example, if a feature can only be machined with a 5-axis machine, but a simpler alternative exists that works with 3-axis, the cost savings could be significant. Matching your design to the strengths of the available machines is a smart way to trim costs.

8. Use Fillets to Your Advantage

Sharp internal corners are difficult to machine and require small diameter tools that increase machining time and risk tool wear or breakage. Adding fillets—rounded transitions—wherever possible helps tools move more efficiently and reduces stress concentrations in the final part.

In the webinar, the experts recommended using generous fillets on internal corners unless square geometry is absolutely necessary. This tip not only improves machinability but also extends tool life and enhances the mechanical strength of the part.

9. Consider Secondary Operations

Sometimes, achieving the final shape or finish of a part requires more than just CNC machining. Post-machining operations like anodizing, heat treating, or grinding can add value but also introduce delays and additional costs.

During the design phase, try to minimize the need for such operations. If surface finish is critical, specify only the areas where it’s required. If threads are needed, design them for standard sizes and use thread inserts if needed to avoid tap breakage or rework.

10. Prototype Early, Iterate Often

Finally, the webinar stressed the importance of prototyping. A physical prototype reveals design flaws or machining challenges that are hard to spot in CAD. Rapid CNC prototyping allows for iterative improvements while still keeping costs manageable.

Early prototyping can validate tolerances, surface finishes, assembly fit, and overall design logic. This reduces the risk of costly redesigns once mass production begins.

Conclusion

The “Trimming Costs, Keeping Quality” webinar delivered a wealth of valuable advice for designers and engineers looking to optimize CNC machining projects. Smart design choices can have a massive impact on cost, efficiency, and product quality. By simplifying geometries, selecting the right materials, using standard tooling, and collaborating closely with machinists, designers can reduce waste, improve lead times, and maintain exceptional part performance.

Design for manufacturability isn’t about compromising innovation—it’s about making that innovation practical, affordable, and scalable. Whether you're working on aerospace components, automotive parts, or custom enclosures, applying these principles will help you stay competitive and deliver top-quality results every time.