MachineCalcs

Kerf Bending Calculator

Lay out kerf cuts for a woodworking bend from inside radius, bend angle, stock thickness, saw kerf, remaining web and target cut spacing.

Materials 7 inputs 10 results
Used in Woodworking 25

Calculator

Inputs

View results
Finished inside radius of the bend.
in
Included bend angle through the curved section.
°
Actual thickness of the board, plywood, MDF or panel.
in
Width removed by one saw cut.
in
Uncut material left at the outside face after the kerf cut.
in
Maximum preferred center-to-center distance between kerf cuts along the bend layout.
in
Uncut margin before the first kerf and after the last kerf within the bend zone.
in

Results

Default result
Edit inputs
Kerf cuts(N)
21kerfs
Pass

Count is driven by the target spacing.

Also computed

Center spacing(s)Pass0.4752in

Measured center to center along the bend layout line.

Bend layout length(L_layout)0.8754ft

Measure along the uncut web/outer-side hinge line.

Cut depth(d_cut)Pass0.625in

Stock thickness minus remaining web.

Remaining web(w)0.125in

Thin webs bend easier but split easier.

Closure per kerf(c)0.05142in

Required inside shortening divided by kerf count.

Inside gap after bend(g)0.07358in

Slots are not expected to close fully at the inside face.

Kerf layout and bend preview Shows 21 of 21 kerfs when the count is dense; dashed line is remaining web. 21 kerfs spacing 12.1 mm cut depth 15.9 mm gap after bend 1.9 mm
Method notes 3 notes
  • The layout length is measured along an approximate hinge line in the remaining web: L = theta x (inside radius + stock thickness - web/2).
  • The required inside shortening is the difference between that hinge-line arc and the inside radius arc; each kerf can close by roughly the saw kerf width.
  • This is a shop-layout screen only. Kerf bending success depends on material, grain direction, veneer orientation, moisture, glue, cut quality, springback and scrap testing.

Kerf bending uses closely spaced saw cuts to shorten the inside face of a bend while a thin outside web stays continuous. This calculator estimates the hinge-line layout length, required inside shortening, kerf count, center spacing, cut depth, closure per kerf and remaining inside gap from bend radius, bend angle, stock thickness, saw kerf and web thickness.

Continue workflow

All Materials
Workflow placement Woodworking Stage 3: Check behavior and finish
Next 1 Build cut list Pack straight rails, slats or trim pieces before marking the curved kerf-bend section. Next 2 Check wood movement Check moisture movement separately when a bent part also needs tight reveals or seasonal clearance. Next 3 Estimate board feet Convert the selected stock dimensions and quantity into board-foot and lumber cost. Chart Use reference data Decimal to fraction chart

How to use this calculator

  1. Enter bend geometry. Set the finished inside bend radius and bend angle for the curved section.
  2. Enter stock and saw data. Use actual stock thickness, saw kerf width and the remaining web you plan to leave uncut.
  3. Set spacing and margin. Choose the target center spacing between kerfs and the uncut end margin at each end of the bend zone.
  4. Mark and test. Mark the bend layout length, cut the listed kerf count at the calculated spacing, and test the bend on scrap before cutting the finished part.

How it works

The calculator treats the uncut outer web as the approximate hinge line. With bend angle theta, inside radius R_i, stock thickness t and remaining web w, the bend layout length is:

L_layout = theta x (R_i + t - w / 2)

The finished inside arc is shorter:

L_inside = theta x R_i

The difference is the inside shortening the kerfs must absorb. Each slot can close by roughly the saw kerf width, so the closure-driven count is:

N_closure = ceiling((L_layout - L_inside) / kerf width)

The spacing-driven count comes from the usable layout length and your target spacing. The calculator uses the larger count, then reports the actual center spacing and remaining inside gap.

Worked example

Verified against the live calculator

For a 3/4 in panel bent 90 deg around a 6 in inside radius with a 1/8 in saw kerf, 1/8 in remaining web, 1/2 in target spacing and 1/2 in end margins, the layout length is about 10.5 in. The spacing target drives the layout to about 21 kerfs at roughly 0.475 in center spacing, with a cut depth of 0.625 in.

Frequently asked questions

How many kerfs do I need for a bend?

Use the larger of the count needed to meet your target spacing and the count needed to provide enough inside-face shortening. This calculator shows which requirement is driving the kerf count.

How deep should kerf cuts be?

Kerf cuts usually stop short of the outside face, leaving a thin web to bend. This calculator uses stock thickness minus remaining web as the cut depth, but the exact value should be tested on scrap.

Why are the kerfs not always fully closed after bending?

If you use many closely spaced kerfs for a smoother curve, each slot only needs to close partway. The inside gap after bend output estimates the remaining slot opening.

Does this account for wood species or springback?

No. It is a layout screen. Kerf bending behavior depends on material, grain, veneer orientation, moisture content, glue, cut quality, remaining web and clamping, so test the exact stock before a finished part.

Method & assumptions

  • The hinge line is approximated halfway through the remaining uncut web.
  • Kerf closure is treated as linear shortening at the inside face.
  • Kerf count is the larger of spacing demand and closure demand.
  • Cut depth is stock thickness minus remaining web.
  • The SVG is a layout preview, not a printable template or material test.
  • Does not model cracking, springback, glue-up, species flexibility, veneer orientation, grain direction, blade runout or saw setup error.
  • For exact kerf search paths, use the kerf calculator or the kerf width calculator for straight saw loss.
  • For adjacent woodworking planning, use the cut list calculator, wood movement calculator and board feet calculator.
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