Kerf Bending CalculatorSaw Cut Spacing for Curved Work
Work out the saw cut spacing, depth and count needed to bend plywood or MDF to a given radius — with the skin thickness that decides whether it curves or snaps.
Why this calculation matters
Kerf bending is how a flat sheet becomes a curve without a press or a vacuum bag. Get the spacing wrong and the outside of the curve either shows the cuts as facets or the skin snaps part-way round — and both are only discovered after the piece is on the former.
Kerf Bending Calculator
Saw Cut Spacing for Curved Work
Plywood, MDF or solid stock.
Uncut material left as the hinge. 10-20% of thickness.
Auto-set by saw type; adjust if known.
Radius to the kerfed face.
Used for the kerf void area.
| Metric | Value | Detail |
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About Kerf Bending Calculator
Kerf bending removes material from the face that will become the inside of a curve, so the remaining thin skin acts as a continuous hinge. Each saw cut closes as the piece bends, and the angle it absorbs is fixed by the width of the cut and how deep it goes — not by the radius. The radius decides how far apart the cuts sit, which is why a tighter curve needs the same cuts closer together rather than deeper ones.
Where Is This Used?
Formulas Used
Kerf depth d = stock thickness - remaining skinAngle per kerf = 2 x atan((kerf width / 2) / d)Kerfs = bend angle / angle per kerfSpacing = (inside radius + d) x angle per kerfHow the calculation works
Each saw cut is a wedge that closes as the piece bends, and the angle it can absorb depends only on how wide the cut is and how deep it goes — not on the radius. The radius decides how far apart the cuts sit. That is why a tighter curve needs the same cuts placed closer together rather than deeper ones.
Show the formula
Kerf depth d = stock thickness - remaining skin. Angle absorbed per kerf a = 2 x atan((kerf width / 2) / d). Number of kerfs = ceil(bend angle / a). Kerf spacing = (inside radius + d) x a, measured at the hinge line. Arc length at the hinge = (inside radius + d) x bend angle in radians.Exact geometry for a kerf that closes fully. It assumes even spacing and a constant depth, which is what a depth stop gives you. Springback is not modelled: a kerfed panel relaxes when released, so fix it to a former rather than expecting it to hold the radius.
References and what each one provides
- USDA Wood Handbook (FPL GTR-190)USDA Forest Products LaboratorySpecies bending behaviour and the grain properties that govern whether the skin holds.
Unverified values are marked as such rather than presented as sourced.
Limitations of this calculation
Calculates cut geometry from the dimensions entered. It does not account for grain direction in the outer ply, glue or filler in the kerfs, springback after release, or the reduced strength of a kerfed panel — a kerfed piece is a skin and is far weaker than the stock it was cut from.
Do not use this for Structural or load-bearing curved members, or any bent component that carries load. A kerfed panel is a facing, not a beam.
Figures are engineering estimates from the inputs and assumptions shown. Verify against the actual material and, where the result affects structure or safety, against a qualified professional.
- Kerf bending geometry — derived from the closing-wedge relation, not a published table
- Angle per kerf = 2 x atan((kerf width / 2) / kerf depth); spacing = (inside radius + depth) x that angle
- Checked numerically: kerfs x spacing reproduces the arc length at the hinge line
Formula checked against the sources above by an automated regression test (tests/test-calculators.js) that derives each expected value independently of this page. Last reviewed .
How to use this tool
- Enter the stock thickness and how much skin to leave uncut. Ten to twenty per cent of thickness is the usual working range.
- Pick your saw type, or enter the kerf width directly if you know it.
- Enter the inside radius, measured to the face being cut, and the total angle of the bend.
- Press Calculate. Set the saw depth stop to the kerf depth shown, then mark out at the spacing given.
Worked example
Common mistakes to avoid
- Cutting to the radius rather than to the skin. The depth stop is what matters: too deep and the skin snaps, too shallow and the cuts will not close.
- Spacing the cuts by eye. Uneven spacing shows as flats and kinks on the outside of the curve, and it cannot be sanded out once the piece is glued.
- Kerfing along the face grain on plywood. Cut so the kerfs run across the grain of the outer ply, or the skin has nothing holding it together.
- Forgetting springback. A kerfed panel relaxes when released, so fix it to the former rather than expecting it to hold the radius on its own.
Frequently Asked Questions
Wood species data
Density, hardness and movement for 60 timbers