Cutting a round edge on wood, often referred to as rounding over or creating a radius, is a fundamental woodworking technique that serves both aesthetic and functional purposes. A rounded edge can soften the look of a piece, prevent splintering, and improve safety by removing sharp corners. While seemingly simple, achieving a smooth, consistent, and professional-looking radius requires the right tools, careful technique, and attention to detail.
I. 🛠️ Essential Tools and Terminology
Before diving into the process, it’s crucial to understand the tools of the trade. The most common and effective method for cutting a radius on an edge involves using a router.
A. The Router
The router is a power tool that uses a revolving cutting bit to hollow out an area or shape an edge.
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Fixed-Base Router: The cutting depth is set and remains fixed. Excellent for sustained routing operations.
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Plunge Router: Allows the bit to be lowered (plunged) into the wood while the motor is running. Useful for starting a cut mid-board, but often used for edge work as well.
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Trim Router (Palm Router): Smaller, lighter, and easier to handle for lighter-duty edge work on smaller pieces.
B. Router Bits for Rounding
The shape of the round edge is determined by the router bit used.
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Round-Over Bit: This is the primary tool for this task. It features a concave cutting profile and a pilot bearing. The bearing rides along the edge of the wood, ensuring a consistent cut depth and radius.
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Radius ($r$): The size of the bit is defined by the radius it cuts (e.g., $1/4″$ radius, $1/2″$ radius). The greater the radius, the more the corner is rounded.
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Beading Bit: Similar to the round-over bit, but it includes a small cove or fillet at the top of the curve, adding a decorative shoulder.
C. Other Necessary Equipment
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Clamps: To securely fasten the workpiece to the bench.
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Safety Gear: Safety glasses and hearing protection are non-negotiable.
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Straightedge/Square: For initial setup and marking.
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Sandpaper: For finishing (various grits).
II. 📐 Preparation and Setup
Proper preparation is the key to a successful routing operation.
A. Prepare the Workpiece
The edge to be rounded must be smooth and square. Any nicks, bumps, or inconsistencies on the edge will be transferred and amplified during the routing process, as the router bit’s bearing will follow these imperfections. Use a planer or jointer to ensure the edge is perfectly flat and perpendicular to the face.
B. Select and Install the Bit
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Select the Radius: Choose a round-over bit with the desired radius. A smaller radius (e.g., $1/8″$) offers a subtle softening, while a larger radius (e.g., $1/2″$) creates a more dramatic, pronounced curve.
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Install the Bit: Unplug the router. Insert the shank of the bit into the collet and tighten it securely. The bit should be inserted deep enough to ensure a strong grip but should not bottom out in the collet.
C. Set the Depth of Cut
This is the most critical setup step. The bearing of the round-over bit must be aligned perfectly with the existing corner of the wood.
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Place the router on the workpiece.
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Lower or raise the bit until the bearing is flush with the vertical edge and the top cutter is just slightly above the surface of the wood.
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Lock the router base at this depth. This setting ensures the full radius is cut, resulting in a smooth, continuous curve that meets the face of the board tangentially.
III. 🏃 The Routing Procedure
Executing the cut requires a steady hand and adherence to safety guidelines.
A. Secure the Wood
The workpiece must be immovably secured to the workbench using reliable clamps. It’s unsafe and bad practice to try and hand-hold wood while routing. Ensure the clamps do not obstruct the path of the router base.
B. Determine the Direction of Feed (Climb vs. Conventional)
The router must always be moved in the correct direction relative to the rotation of the bit. Looking down at the router, the bit spins clockwise.
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Conventional Cut (Standard): The bit’s rotation pushes the router against the direction of travel. This is the safest and most controlled direction.
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For an edge facing you, move the router from left to right.
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Climb Cut (Opposite to Conventional): The bit’s rotation pulls the router with the direction of travel. This can lead to the router “running away” (kickback) and should be strictly avoided for handheld edge work unless necessary for complex grain patterns or to reduce tear-out in specific scenarios, and only by experienced woodworkers.
C. Making the Pass
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Start the Router: Hold the router firmly with two hands and start the motor to reach full speed before contacting the wood.
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Begin the Cut: Gently bring the router bit’s bearing against the corner of the wood.
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Feed Rate: Move the router along the edge at a consistent, moderate speed.
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Too slow can burn the wood.
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Too fast can strain the motor, leave an uneven finish, and cause tear-out (where wood fibers are ripped out at the end of the grain). Listen to the motor; if the sound deepens significantly, you are pushing too fast.
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Complete the Pass: Maintain contact with the bearing until the entire edge is routed. Keep the router base flat on the wood surface at all times.
D. Dealing with End Grain
When rounding an entire frame or piece, always rout the end grain first. End grain is highly prone to tear-out, especially when the bit exits the wood. By routing the end grain first, any minor tear-out at the corners will be removed when you rout the long grain sides, resulting in clean, sharp corners.
IV. 🧐 Troubleshooting and Advanced Techniques
A. Tear-Out and Grain Direction
Tear-out is the most common issue. If you encounter significant tear-out, especially on highly figured or soft wood:
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Multiple Passes: Instead of cutting the full radius in one go, set the depth to cut a small bevel first, and then reset the depth for the full radius. This is especially useful for larger radii (e.g., $3/4″$).
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Climb Cut on the Last Inch: Carefully perform a very light climb cut for the last inch of the cut to prevent the fibers from blowing out. This requires extreme control.
B. Rounding Thick Edges (Double Pass)
For very thick pieces, the router base might not fully contact the wood when the bit is set for the full radius, causing instability. To solve this, you can:
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Rout the edge with the desired bit.
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Flip the board over and rout the opposite side with the same bit, making sure the passes overlap perfectly in the center to create a full, smooth half-circle profile.
V. ✨ Finishing the Edge
Even the cleanest routed edge will benefit from sanding to achieve a truly professional feel.
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Hand Sanding: Use a sanding block or simply your fingers to press the sandpaper into the curve. Start with the grit you last used on the flat surface (e.g., 120-grit) and progress to a finer grit (e.g., 180 or 220).
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Avoid Flattening: Be careful not to sand off the crisp line where the curve meets the face of the board. Over-sanding this area will “flatten” the radius and undo the precise work of the router.
Conclusion
Cutting a round edge on wood transforms a piece from being merely functional to having a crafted, finished quality. The process is a combination of precise tool setup and a smooth, controlled feed rate. By consistently following the steps—ensuring a square edge, correctly setting the router depth, and respecting the conventional direction of cut—woodworkers can reliably achieve flawless radii that are both beautiful and durable. Mastering this simple technique is an important milestone in any woodworker’s journey toward producing high-quality furniture and joinery.
