The term CNC stands for “computer numerical control,” and CNC is a subtractive manufacturing process that typically employs computer controls and machine tools to remove layers of material from a blank and produce custom-designed parts.

CNC machining is widely used in the fields of machinery manufacturing, aerospace, automotive industry and medical equipment. It has high-precision and high-efficiency processing capabilities, can achieve large-scale parts processing, and improve the accuracy and consistency of processing.

Many engineers and product designers are familiar with CNC machining. In order to create the best possible part, there are several rules to follow when designing your CNC Machining part.

1. Tool Geometry: Cutting tools have cylindrical shapes, limiting the geometries that can be produced. For example, internal vertical corners will always have a radius.

2. Tool Access: Features like internal hidden geometries or deep undercuts are not feasible due to tool limitations.

3. Workpiece Stiffness: Thin walls or tall features can deform or vibrate, affecting accuracy.

4. Tool Stiffness: Long, thin tools are prone to deflection, which can loosen tolerances and break tools.

5. Work Holding: The way parts are clamped affects both cost and accuracy, especially with multiple setups.

1. Cavity Depths

• Limit cavity depths to 3–4 times their diameter or a maximum of 25mm to reduce deflection and vibrations.
• Keep cavity width proportional to depth for better machining quality.

2. Internal Edges

• Corner radius should be at least ⅓ of cavity depth. Larger radii improve tool performance and surface finish.
• For sharp corners, consider adding a T-bone undercut instead of reducing radius sizes

3. Thin Walls

• Minimum wall thickness: 0.8mm for metals, 1.5mm for plastics. Thin walls increase vibration and reduce accuracy, especially in plastics prone to warping. And the metal walls are designed to be less than half a millimeter thick — leading to warping and part failure.

4. Holes and Threads

• Use standard drill bit sizes for holes and limit their depth to 4x diameter. Deeper holes require specialized tools.
• Thread lengths should not exceed 3x diameter, as this doesn’t improve strength and complicates machining.

5. Tall Features

• Maintain a height-to-width ratio of 4:1 to reduce vibrations and improve accuracy.

6. Tolerances and Part Sizes

• Standard tolerance: ±0.125mm unless specified. Over-tolerancing can increase costs unnecessarily.
• Maximum part size: 400mm x 250mm x 150mm for milling; larger sizes require specialized machines.

7. Undercuts

• Use standard dimensions for undercuts (e.g., widths in whole mm increments) to avoid custom tooling.
• Keep undercut depth less than 2x width and ensure sufficient clearance for tool access.

During the end-to-end production cycle of a product, different manufacturing technologies may be used to create early prototypes, mechanical prototypes, and end-use parts. For example, 3D printing may be used for concept prototypes of a part, while CNC machining may be used for production.

A common mistake designers make is failing to adequately plan for this transition between technologies during the design phase. If a 3D printed prototype is required, it may be necessary to abandon certain CNC design rules in favor of additive-friendly practices. Conversely, when a final CNC part is required, the design rules for CNC must be reverted.

By understanding design restrictions, you can save time, reduce costs, and create parts with precision and efficiency. And by applying these recommendations, you can reduce machining challenges and achieve better results with your CNC projects.

If you want to 3D Printing or CNC Machining and bring new impetus and opportunities to your industry, or you want to find a reliable and affordable parts and prototype manufacturer, you can consult our experts online or email to info@protosoon.com, we will contact you as soon as possible.