Kerf Bending Calculator

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Expert Verified By: David Chen, Master Woodworker & CNC Specialist

Achieve perfect wood curves without snapping your material. This kerf bending calculator helps woodworkers determine the exact spacing and number of cuts required to bend a piece of wood to a specific radius based on material thickness and blade kerf.

Kerf Bending Calculator

The radius of the curve you want to create (inside).
Full thickness of the board.
The width of the saw blade cut.
Usually 90 degrees for a corner.
Recommended Spacing: —

Kerf Bending Calculator Formula:

The standard formula for kerf spacing ($S$) is:

$S = \frac{K \times R}{T – K}$

To find the total number of cuts ($N$):

$N = \frac{\text{Arc Length of Bend}}{\text{Spacing}}$

Formula Sources: Fine Woodworking, WOOD Magazine

Variables:

  • Radius (R): The desired curve radius measured from the center to the inside face.
  • Thickness (T): The total thickness of your workpiece.
  • Kerf (K): The width of the material removed by the saw blade (typically 1/8″ or 3.2mm).
  • Angle (θ): The total degree of the turn (e.g., 90°).

Related Calculators:

What is Kerf Bending?

Kerf bending is a woodworking technique used to bend thick or stiff lumber by making a series of narrow slots (kerfs) on the back side of the board. These slots allow the wood to compress or open up, facilitating a smooth curve without the need for steam bending or laminating thin strips.

This kerf bending calculator is essential because if your cuts are too far apart, the curve will look faceted (like a polygon). If they are too close, you risk weakening the material or breaking the thin “hinge” of wood remaining.

How to Calculate Kerf Bending (Example):

  1. Measure your wood thickness (e.g., 20mm) and your blade kerf (e.g., 3mm).
  2. Determine your target inside radius (e.g., 200mm).
  3. Multiply Kerf by Radius ($3 \times 200 = 600$).
  4. Divide by (Thickness minus Kerf) ($20 – 3 = 17$).
  5. The result ($600 / 17 \approx 35.3mm$) is your center-to-center spacing.

Frequently Asked Questions (FAQ):

Does the type of wood affect kerf spacing? While the geometry remains the same, harder woods might require leaving a thicker “hinge” (the un-cut portion) to prevent snapping.

How deep should I cut the kerfs? Generally, you should leave about 1/32″ to 1/16″ (1-2mm) of material intact. This allows the wood to bend without breaking.

What if my curve looks “bumpy”? This means your spacing is too wide. Increase the number of cuts or use a thinner blade to reduce the spacing for a smoother finish.

Can I use this for 180-degree bends? Yes, simply input 180 in the Angle field to find the total number of cuts required for a full U-turn.

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