How this kerf spacing calculator works
Kerf bending works by cutting a series of parallel saw slots (kerfs) part-way through a board on the concave face, leaving a thin hinge of wood at the convex face. When you bend the board, each hinge flexes slightly and the kerf gaps close up, letting a straight board follow a curve without steaming or laminating.
- Number of cuts: for the kerfs to close evenly across your whole sweep angle, the calculator works out how many cuts are needed based on wood thickness, kerf width and sweep angle.
- Cut spacing: the total board length (either the outside arc length, or the straight point-to-point span, depending on your layout reference) is divided evenly across the cuts to give centre-to-centre spacing.
- Wood between cuts: spacing minus kerf width gives the solid wood left between each cut — this is what you're actually measuring and marking on the board.
Example: a 300 mm outside radius curve over a 90° sweep, in 20 mm thick timber with a 2 mm saw kerf and a 3 mm hinge, needs 16 cuts at roughly 31 mm centres, leaving about 29 mm of solid wood between each cut.
Choosing your minimum thickness and kerf width
The remaining hinge thickness can't be calculated exactly — it depends on the timber species, grain direction and how tight the curve is. As a starting point, 10–15% of the total wood thickness is a reasonable hinge for most Australian softwoods and mid-density hardwoods. Always cut a test piece from scrap before committing to your final board — if the hinge snaps, increase the minimum thickness slightly; if the curve won't close smoothly, reduce it.
Kerf width is simply your saw blade's cut width — most circular saw blades cut a 2–3 mm kerf, thin-kerf blades closer to 1.5–2 mm. If you're using a tapered router bit instead of a saw, use the router bit calculator above to work out the effective kerf width at your cut depth.
Indoor uses for kerf-bent timber
- Curved skirting and cornice — following a bay window, curved wall or rounded archway without joining lots of short mitred segments.
- Curved furniture parts — chair backs, curved shelf fronts, bed heads and other joinery pieces that need a smooth radius.
- Arched doorway and window trim — architrave that follows an arched opening rather than a series of straight, angled cuts.
- Curved stair stringers and handrail brackets — small-radius curved details in staircases and balustrading.
For painted finishes, MDF kerf-bends cleanly and holds paint well once filled — fill the kerf cuts on the concave face with flexible filler before priming. For a clear-finished look, choose a straight-grained timber; interlocked or figured grain is more likely to splinter along the hinge.
Kerf spacing calculator — frequently asked questions
What is kerf bending?
Kerf bending (also called kerf cutting or kerf spacing) is a technique for bending solid timber without steam-bending or laminating. A series of parallel saw cuts are made part-way through the board on the concave face, leaving a thin hinge of wood intact on the convex face. When bent, the hinges flex and the saw cuts close up, allowing the board to follow a curve.
How thick should the remaining wood be after each kerf cut?
There's no exact formula — it depends on timber species, grain and how tight the curve is. As a starting point, aim for a hinge around 10–15% of the total board thickness, and always test on a scrap offcut of the same timber before cutting your final piece.
What kerf width should I use for a circular saw?
Most standard circular saw blades cut a kerf of 2–3 mm. Thin-kerf blades cut closer to 1.5–2 mm. Check your specific blade's kerf width, or measure a test cut with calipers.
Does kerf-bent MDF hold paint well?
Yes — MDF is one of the easiest materials to kerf bend for a painted finish. Fill the kerf cuts on the concave face with a flexible, paintable filler once bent, sand smooth, then prime and paint as normal. Solid timber intended for a clear finish should be straight-grained to avoid splintering along the hinge.
What's the difference between "longer board" and "end to end" layout reference?
"Longer board" spaces your cuts based on the outside curve's arc length — use this when you're working to a specific board length. "End to end" spaces cuts based on the straight-line distance between the two ends of the finished curve — use this when the finished piece needs to span a fixed opening, like an arched doorway width.