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How to Scallop Board Edge With CNC Router: Guide

Scalloping the edge of a board is a decorative woodworking technique that adds an elegant, wavy profile to furniture, trim, or cabinetry. Using a CNC router for this task ensures precision, repeatability, and efficiency compared to manual methods. In this guide, we’ll walk through the step-by-step process of creating scalloped edges with a CNC router, including design considerations, tool selection, and machining best practices. We’ll also briefly discuss how similar techniques can be applied when machining tool steel for industrial applications.
 
How to Scallop Board Edge With CNC Router

Understanding Scalloped Edges
A scalloped edge consists of a series of concave curves (or semi-circles) cut along the perimeter of a board. This design is commonly used for decorative moldings, table edges, and cabinet doors. The key to achieving a professional finish lies in consistent spacing, smooth transitions, and proper toolpath optimization.

Step 1: Designing the Scallop Pattern
Before machining, you’ll need a digital design. CAD (Computer-Aided Design) software such as AutoCAD, Fusion 360, or Vectric Aspire is essential for creating the scallop profile.
  1. Define the Board Dimensions – Input the exact length, width, and thickness of your workpiece.
  2. Create the Scallop Profile – Use the arc or spline tool to draw evenly spaced concave curves along the edge.
  3. Adjust Spacing and Depth – Ensure the scallops are symmetrical and proportional to the board’s dimensions.
    Once the design is complete, export it as a DXF or SVG file for CAM (Computer-Aided Manufacturing) processing.

Step 2: Selecting the Right Router Bit
The choice of router bit significantly impacts the final finish. For scalloping, consider the following:
  1. Ball-Nose End Mill – Ideal for smooth, rounded cuts. A ¼” or ½” diameter works well for most wood applications.
  2. Spiral Upcut Bit – Helps clear chips efficiently, reducing tear-out in softer woods.
  3. Compression Bit – Useful for materials prone to fraying, as it cuts cleanly on both the up and downstroke.
For harder materials like machining tool steel, carbide-tipped or solid carbide bits with appropriate coatings (e.g., TiAlN) are necessary to withstand high cutting forces and heat.
 
Selecting the Right Router Bit

Step 3: Setting Up the CNC Router
  • Secure the Workpiece – Use clamps or a vacuum table to prevent movement during cutting.
  • Install the Router Bit – Ensure it is firmly seated and runout is minimized.
  • Set Zero Points – Calibrate the X, Y, and Z axes to match your material’s position.

Step 4: Generating the Toolpath
In CAM software (such as Mach3, UGS, or Fusion 360 CAM), configure the following settings:
  • Cutting Strategy – Use a profiling or 2D contour toolpath.
  • Stepover and Step Depth – For wood, a stepover of 10-20% of the bit diameter ensures a smooth finish. Deeper scallops may require multiple passes.
  • Feed Rate and RPM – Adjust based on material hardness. For hardwood, 12,000-18,000 RPM with a feed rate of 100-200 IPM is typical.
*Note: When machining tool steel, significantly lower feed rates (10-30 IPM) and RPM (1,500-3,000) are required to avoid excessive tool wear.*

Step 5: Running the CNC Job
  1. Perform a Dry Run – Verify the toolpath by running the program without cutting.
  2. Begin Machining – Start with a shallow initial pass, especially for deep scallops.
  3. Monitor the Process – Check for chip evacuation and adjust coolant (if applicable) to prevent overheating.

    Running the CNC Job

Step 6: Finishing the Scalloped Edge
After cutting, sand the edges lightly to remove any tool marks. A fine-grit sandpaper (220+ grit) or a handheld router with a rounding-over bit can enhance the profile.

Advanced Tips for Precision
  • Climb vs. Conventional Cutting – Climb milling (moving with the rotation of the bit) produces cleaner edges in wood but may cause chatter in harder materials.
  • Dust Collection – Proper chip removal prevents re-cutting and extends tool life.
  • Material Considerations – Softer woods like pine cut easily but may require sharper bits to avoid tear-out. Hardwoods like oak or maple demand slower feeds and sharper tooling.

Machining Tool Steel: A Brief Insight
While this guide focuses on wood, similar CNC techniques apply to machining tool steel—a much harder material used in industrial applications. Tool steel requires rigid setups, slower speeds, and specialized carbide or diamond-coated cutters. Coolant is often necessary to dissipate heat and prolong tool life. The principles of precise toolpath planning remain critical, but cutting parameters must be adjusted to account for the material’s toughness.

Scalloping a board edge with a CNC router is an efficient way to achieve decorative, repeatable results. By carefully designing the pattern, selecting the right bit, and optimizing toolpaths, you can produce professional-quality workpieces. Whether working with wood or tougher materials like tool steel, understanding the fundamentals of CNC machining ensures success in any project.

For best results, always test cuts on scrap material and refine your approach based on the specific material and machine capabilities. Happy machining!
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