Our top 4 Tips for Designing for Manufacturing
Designing for CNC machining requires precision and foresight to ensure components are not only manufacturable but also optimised for performance, durability, and cost-effectiveness. Key factors such as internal radii, hole design, wall thickness, and tolerance specifications play a crucial role in achieving high-quality, efficient CNC production.
In this blog, we explore four essential design strategies that enhance CNC machining efficiency, reduce production costs, and improve overall component quality.
1. Include Sufficient Radii for Internal Corners
Why It Matters
Internal radii are fundamental to CNC part design, yet they are often overlooked. Their inclusion directly impacts manufacturability, tool life, and structural integrity.
Improved Machinability
Sharp internal corners create machining difficulties, increasing tool wear and the risk of breakage. Introducing sufficient radii allows for smoother tool paths, reducing stress on cutting tools, extending their lifespan, and improving machining speed and efficiency.
Enhanced Structural Integrity
Sharp corners can create stress concentration points, weakening the part. Adequate radii help distribute stress more evenly, reducing the risk of premature failure or deformation and increasing the part’s longevity.
Better Surface Finish
Parts with well-designed radii achieve a smoother surface finish, reducing the need for post-processing. This is particularly important for visible components or those with strict aesthetic requirements.
General Guideline
For best results, maintain an internal radii-to-pocket depth ratio of 1:8. This ensures structural stability while improving manufacturability.
2. Design Holes for Efficient Machining
Use Standard Drill Sizes
Where possible, opt for standard drill sizes to simplify the manufacturing process. Standard tooling minimises machining time, reduces costs, and ensures greater accuracy. Additionally, aligning all holes, fasteners, and screw threads within a part reduces tool changes, further optimising production efficiency.
Optimise Hole Placement and Size
Holes positioned too close to edges risk creating cosmetic defects or structural weaknesses. Threaded holes, in particular, should be strategically placed to maintain part strength. Additionally, keep in mind that most of a thread’s load-bearing capacity comes from the first few pitches, making excessive thread depth unnecessary.
For best results:
- Avoid holes smaller than Ø3mm as these are prone to breakage.
- Maintain a minimum distance of 12mm between the drill centre and adjacent walls.
Consider Hole Depth
Deep holes present machining challenges, increasing tool deflection and breakage risks. A general recommendation is to limit hole depth to 8–12 times the drill diameter. When designing blind holes, account for the drill point at the base, ensuring sufficient clearance for chips to escape and prevent clogging.
3. Maintain Proper Wall Thickness
Wall Design Considerations
Thin walls can reduce part weight and material costs but present machining challenges. As a guideline, aim for a minimum wall thickness of 0.75mm (0.030”) unless specific design constraints allow otherwise. The feasibility of thinner walls depends on material properties, geometry, and machining techniques—consult with an expert if needed.
Effects of Thin Walls
Excessively thin walls are susceptible to vibrations (or chatter) during machining. This can lead to cosmetic defects or dimensional inaccuracies, compromising the part’s performance and quality. Maintaining appropriate wall thickness mitigates these issues, ensuring stability throughout the machining process.
4. Avoid Overly Tight Tolerances
The Impact of Over-Tolerancing
Unnecessarily tight tolerances increase machining complexity, prolong production time, and drive up costs. Specialised tooling and secondary processes may be required to achieve extreme precision, leading to higher scrap rates and potential rework.
Guidelines for Cost-Effective Tolerancing
- The standard shop tolerance at Quickparts is ±0.125mm (0.005”).
- Tighter tolerances, such as ±0.025mm (0.001”), are possible but may increase lead times and costs.
- Consider using Geometric Dimensioning and Tolerancing (GD&T) for critical features, such as flatness, cylindricity, and concentricity, to improve part consistency without overcomplicating production.
Conclusion
Smart design choices are key to successful CNC machining. By incorporating appropriate internal radii, optimising hole design, maintaining sufficient wall thickness, and specifying practical tolerances, manufacturers can achieve superior part quality, improved efficiency, and reduced costs.
