Best Practices for Designing for Router Sheet Cutting Parts

CNC router cut arcade game designed in Fusion 360

Designing router-cut sheet parts is a critical step in ensuring that the machining process is efficient, precise, and cost-effective. These design-focused best practices will help you create parts that are optimized for CNC router cutting, minimize material waste, and simplify assembly.

1. Select the Appropriate Material

Choosing the right material is the foundation of a successful design. Each material has unique properties that influence its machinability and suitability for specific applications. Common options include:

• Plywood and MDF: These are affordable, widely available, and easy to machine. They are ideal for prototyping, furniture production, and architectural models. However, they are less durable and not suitable for outdoor applications unless treated.

• Acrylic and Polycarbonate: These plastics are perfect for creating signage, display parts, and decorative components. Acrylic offers excellent clarity and a smooth finish, while polycarbonate provides greater impact resistance.

• Aluminum: Lightweight, corrosion-resistant, and strong, aluminum is widely used for industrial components, enclosures, and fixtures. Ensure the router has the right tooling and cooling setup for effective aluminum cutting.

• HDPE, Delrin, Acetal, and UHMW: These durable, low-friction plastics are ideal for mechanical and industrial components like gears, bearings, and guides. UHMW (Ultra-High Molecular Weight Polyethylene) is especially suited for wear-resistant applications.

When selecting a material, consider factors such as strength, finish, environmental conditions, and machining requirements. Always source high-quality, flat sheets to ensure accuracy. Review material certifications and test for compatibility with your specific router settings.

2. Plan for Efficient Nesting

Efficient nesting is crucial to maximize material usage and reduce waste. Use dedicated nesting software or manual methods to arrange parts strategically on the sheet. Best practices include:

• Grain Direction: For materials like plywood, ensure parts are aligned to maximize strength or achieve the desired aesthetic.

• Spacing: Leave enough space between parts to accommodate the kerf and reduce the risk of heat buildup.

• Tabs and Bridges: Add small connectors to keep parts secure during machining and prevent them from shifting or ejecting.

• Common-Line Cutting: For simple geometries, use shared edges between parts to minimize toolpath length and material waste.

• Sheet Utilization Metrics: Track material usage efficiency using CAD software metrics to improve future nesting layouts.

Proper nesting saves costs, reduces environmental impact, and simplifies cleanup.

3. Incorporate Kerf Allowances

This example demonstrates proper spacing between adjacent parts to account for kerf compensation, ensuring the router bit can pass through without cutting into the parts and preventing undersizing

Kerf width is the amount of material removed by the cutting tool. Ignoring kerf can result in loose fits or out-of-tolerance parts. To account for kerf:

• Measure the kerf width of your specific tool and material combination.

• Adjust your CAD design to ensure the final dimensions match your requirements.

• For tight tolerances, perform test cuts and fine-tune dimensions before full production.

• Include Kerf Data in Design Notes: Clearly document kerf adjustments to ensure consistency across revisions and multiple operators.

4. Simplify Geometries

This CNC router dust shoe was designed in Fusion 360 and machined from HDPE for durability and effective dust collection.

Simplified designs are faster to machine, reduce tool wear, and improve reliability. To streamline your design:

• Minimize Nodes: Reduce the number of points in curves and shapes to create smoother toolpaths.

• Use Fillets: Replace sharp internal corners with fillets that match the tool radius to avoid additional finishing work.

• Consolidate Features: Combine similar features to reduce tool changes and setup time.

• Avoid Over-Complex Designs: Overly intricate details can lead to higher machining costs and increased risk of errors.

5. Design for Strength

This part is for a dust boot for a small CNC Router. Notice how internal corners have rounded transitions, long narrow slots are supported adequately on each side with thicker wall material.

Thin or fragile features can lead to breakage during machining or assembly. To ensure structural integrity:

• Avoid Long, Narrow Slots Near Edges: These slots can weaken the material, especially when placed too close to the part's edge. Maintain at least 3x the slot width as a buffer between the slot and the edge.

• Minimize Sharp Transitions: Use gradual transitions and rounded corners to reduce stress concentrations.

• Ensure Sufficient Support: For thin sections, include localized reinforcements, such as tabs or thicker areas, to prevent flexing during use.

• Include Breakage Tests in Prototyping: Test designs under expected loads to verify strength and performance.

• Balance Weight and Rigidity: Design lightweight parts without compromising structural stability, using honeycomb patterns or ribbing when possible.

6. Plan for Assembly Joinery

These are aluminum router-cut robotic components. Notice the holes in the internal corners of the tabs and slots—these are designed to remove excess material, allowing mating parts to sit flush for precise assembly.

Router bits are circular and cannot create sharp internal corners. Adding dog-bone fillets (small circular cutouts) ensures:

• Flush Assembly: Mating parts fit together without interference.

• Reduced Post-Processing: Avoids the need for manual corner adjustments.

• Improved Fit for Joinery: Especially useful for wooden joints, ensuring precision in interlocking designs.

For assembled slots and joinery, ensure that the slots are slightly larger than the material thickness of the mating piece. This extra clearance accounts for material variation and ensures easier assembly without compromising fit.

Dog-bone fillets are particularly useful for wooden joinery and interlocking designs. Ensure the fillet size matches the tool diameter for optimal fit.

Please Note: For materials thickness 1/2” and under - dog bone fillets should be sized .13” diameter. Materials thicker than 1/2” should have a dog bone filled sized at .26” diameter. This allows for material removal slightly larger than the diameter of the tool which will reduce tooling forces and produce cleaner cuts.

7. Label Parts for Assembly

This labeled drawing specifies the designated locations for part tagging in the post-production process, ensuring proper identification and traceability.

Engraving part numbers or labels directly onto components simplifies organization and assembly. Consider the following:

• Engraving Depth: Use a shallow depth to maintain part strength and avoid excessive machining time.

• Positioning: Place labels in non-visible areas to preserve aesthetics.

• Readable Fonts: Use clear, simple fonts for easy identification.

• Use QR Codes for Complex Assemblies: QR codes can link to assembly guides or instructions for enhanced usability.

8. Prototype Before Production

CNC Router cut arcade game prototype made from MDF.

Prototyping is an essential step to validate your design and identify potential issues. Benefits include:

• Fit Testing: Ensure parts assemble correctly and fit within the intended application.

• Toolpath Verification: Confirm that toolpaths are efficient and free of errors.

• Material Assessment: Test different materials to find the best option for your design.

• Evaluate Post-Machining Requirements: Check for areas needing additional sanding, finishing, or adjustments.

Start with small-scale prototypes or use scrap material for initial tests. Incorporate lessons learned into final designs to optimize production.

Conclusion

By focusing on design best practices, you can create parts that are not only aesthetically pleasing but also optimized for CNC router machining. Thoughtful design reduces errors, improves efficiency, and enhances the overall quality of your projects. Whether you’re designing for furniture, signage, or industrial components, these principles will help you achieve success. Continuously test, refine, and improve your designs to master the art of router-cut parts.