CNC Design Guidelines (Design Advice for Customers)
Reasonable part design is the key to improving CNC machining efficiency, reducing production costs, and ensuring product quality and stability. Unreasonable design may lead to machining difficulties, part deformation, defects, or increased production costs. To help you design parts that are more suitable for CNC machining, we have sorted out key design guidelines, focusing on minimum wall thickness, minimum hole diameter, fillet design, sharp corner avoidance, and drawing format requirements, with detailed specifications and suggestions.
1. Minimum Wall Thickness
The minimum wall thickness of CNC machined parts is limited by the material’s hardness, toughness, machining method (milling, turning, etc.), and the overall size of the part. Too thin a wall will lead to insufficient structural strength, easy deformation during machining (caused by cutting force, cutting heat, and clamping force), and even part scrapping. The following are the recommended minimum wall thickness standards for common materials:
| Material Type | Recommended Minimum Wall Thickness | Notes |
|---|---|---|
| Aluminum (6061, 7075, 5052) | 0.8 – 1.0mm | If the wall height exceeds 5 times the thickness, add reinforcing ribs to prevent deformation |
| Stainless Steel (304, 316) | 1.0 – 1.2mm | Harder material, thinner walls are more prone to vibration and deformation during machining |
| Carbon Steel (45#, 1045) | 1.0 – 1.2mm | Suitable for medium thickness; too thin will affect structural strength |
| Engineering Plastics (PEEK, POM, PPS) | 0.6 – 0.8mm | Good toughness, but avoid excessive thinness to prevent breakage during assembly |
Design Tip: When designing, try to make the wall thickness uniform. Uneven wall thickness will cause uneven heat distribution during machining, leading to part deformation. If thin walls are unavoidable, increase the fillet transition and add reinforcing ribs appropriately.
2. Minimum Hole Diameter
The minimum hole diameter of CNC machined parts is determined by the length of the hole (depth-diameter ratio), material, and machining tool. Too small a hole diameter or too large a depth-diameter ratio will lead to difficulty in tool processing, tool breakage, and inability to guarantee hole accuracy. The following are the recommended minimum hole diameter standards (for through holes; blind holes need to be increased by 0.2-0.3mm):
| Hole Depth-Diameter Ratio (Depth/Diameter) | Recommended Minimum Diameter (Metal Materials) | Recommended Minimum Diameter (Plastic Materials) |
|---|---|---|
| ≤ 3:1 | 1.0mm | 0.8mm |
| 3:1 – 5:1 | 1.5mm | 1.2mm |
| 5:1 – 10:1 | 2.0mm | 1.5mm |
| > 10:1 (deep hole) | ≥ 3.0mm | ≥ 2.5mm |
Design Tip: For blind holes, the bottom should be designed with a fillet (radius ≥ 0.5mm) to avoid the tool being stuck or broken; for threaded holes, the minimum diameter should be 0.2mm larger than the standard thread diameter to ensure smooth tapping and avoid thread slipping.
3. Fillet Design
Fillet design is an essential part of CNC machining design. Adding fillets at the corners of parts can not only improve the structural strength of the part (avoid stress concentration, prevent part cracking) but also facilitate machining, reduce tool wear, and improve machining efficiency. The specific design guidelines are as follows:
- General Fillet Radius: For most parts, the fillet radius is recommended to be ≥ 0.5mm; for parts with larger size or higher strength requirements, the fillet radius is recommended to be 1.0-2.0mm.
- Fillet Matching: The fillet radius should match the size of the cutting tool. The minimum fillet radius should not be smaller than the radius of the machining tool (usually 0.2-0.5mm for end mills), otherwise, the tool cannot process the fillet completely, resulting in residual sharp corners.
- Functional Fillets: For parts that need to be assembled, the fillet at the assembly position should be designed according to the assembly space to avoid affecting the fit of the parts; for parts subject to large force, increasing the fillet radius can effectively disperse stress and extend the service life of the part.
4. Avoid Sharp Corners
Sharp corners (angle = 90° or smaller) should be avoided as much as possible in CNC machining design. Sharp corners not only have potential safety hazards (easy to scratch operators or other parts) but also bring many difficulties to machining and affect part performance. The reasons and improvement suggestions are as follows:
- Machining Difficulty: The cutting tool has a certain radius, and it is impossible to process absolute sharp corners. Residual material will remain at the sharp corners, requiring secondary manual trimming, which increases production costs and affects efficiency.
- Stress Concentration: Sharp corners are prone to stress concentration during use, especially for parts subject to impact, vibration, or high pressure, which may lead to cracks or even breakage at the sharp corners.
- Improvement Suggestions: Replace sharp corners with fillets (radius ≥ 0.5mm) or chamfers (angle 45°, width 0.5-1.0mm). For parts that must have sharp corners due to functional requirements, please note in the drawing, and we will use special tools for precision machining to minimize residual material.
5. Recommended Drawing Formats
Clear and standard drawing files are the basis for ensuring machining accuracy. We recommend the following drawing formats to avoid errors caused by file incompatibility or unclear dimensions. The priority of drawing formats is as follows (from highest to lowest):
2. IGES Format (.iges, .igs): Another universal 3D model format, widely used in cross-software file transfer, suitable for parts with complex curved surfaces (such as aerospace parts, medical parts), and can well retain the curved surface data.
3. DWG Format (.dwg): A common 2D drawing format, suitable for parts with simple structures. It is recommended to attach detailed dimension annotations, tolerance requirements, and surface roughness requirements when providing DWG files.
4. PDF Format (.pdf): Suitable for providing 2D drawing drawings or 3D model preview files. It is not recommended as the only drawing format (cannot be edited), but can be used as an auxiliary file to clarify design requirements and annotations.
Important Note: When providing drawing files, please clearly mark the dimensional tolerance, surface roughness, material, and special requirements (such as surface treatment, assembly requirements) to avoid misunderstanding and ensure that the machined parts meet your design expectations.
6. Supplementary Design Advice
- Try to simplify the part structure and avoid overly complex internal cavities or deep and narrow grooves, which can reduce machining difficulty and production costs.
- When designing threaded holes, use standard thread specifications (Metric or UNC) to avoid custom threads, which can reduce the cost of tapping tools and improve machining efficiency.
- If the part has multiple matching surfaces, clearly mark the reference surface to ensure the assembly accuracy of each surface.
- Before finalizing the design, you can consult our engineering team to confirm whether the design is suitable for CNC machining, avoiding subsequent design modifications and cost increases.