How to Kerf Bend Wood: A Guide to Making Curved Parts
Adding curves to a woodworking project can create a dramatic change in its appearance. But making curved parts often requires specialized techniques, such as steam bending or laminating thin strips of wood around a form.
Kerf bending offers a much simpler way to bend wood and plywood. By cutting a series of closely spaced slots, or kerfs, into one face of a board, you can make an otherwise rigid workpiece flexible enough to form a smooth curve.
The process requires little more than a table saw, a miter gauge, and a simple indexing jig. With the right kerf depth and spacing, you can create curved cabinet panels, arched tops, decorative details, and other woodworking components.
There are a few important details to understand before getting started, however. The type of material, depth of the cuts, and distance between kerfs all affect how tightly the board can bend and how strong the finished piece will be.
What Is Kerf Bending?
Kerf bending is a woodworking technique that uses a series of closely spaced saw cuts to make a board flexible.
The kerfs are cut into one face of the workpiece, leaving a thin layer of material intact on the opposite face.
This remaining material, called the web, acts as a flexible connection between the thicker sections of wood, known as ribs.
As the board bends, the webs flex and the kerfs begin to close. The ribs eventually contact one another, helping support the curved shape.
The result is a curved workpiece that retains more substance than a thin sheet of veneer alone.
Kerf bending is especially useful when the finished curve will be supported by other parts of a project.
Best Wood for Kerf Bending
Kerf bending works with a variety of materials, including plywood, hardwood, softwood, and hardboard.
However, not every material bends equally well.
The wood's grain structure and tendency to split can make a significant difference in the results.
Kerf Bending Plywood
Plywood is one of the easiest materials to use for kerf bending.
Its layered construction allows the thin remaining plies to flex more easily than a comparable thickness of solid wood.
Hardwood plywood generally works well, and Baltic birch plywood is an especially good option.
Because Baltic birch has multiple thin, consistent plies, it's well suited to the closely spaced cuts used in kerf bending.
However, plywood has one drawback: The remaining face veneer can crack when the board is bent too tightly.
This becomes more likely with long panels or closely spaced kerfs that allow the material to bend to a very small radius.
Careful cutting and bending help reduce the risk, but some cracking is possible.
Kerf Bending Solid Wood
Solid wood can also be kerf bent, and the remaining wood fibers can provide considerable strength.
Some species work better than others.
Good candidates include:
- Softwoods: Yew and cedar
- Hardwoods: Oak, walnut, and ash
Very hard woods, such as hickory, can be difficult to bend. Woods prone to splitting, such as pine, can also present problems.
Grain direction is particularly important when working with solid wood.
Always cut the kerfs perpendicular to the grain.
This leaves continuous wood fibers running through the thin webs, helping them resist breaking as the board bends.
Cutting the kerfs parallel to the grain increases the likelihood of splitting.
Kerf Bending Hardboard
Hardboard is another material worth considering.
Although it isn't commonly used as an exposed surface in fine furniture, it has an advantage for certain curved applications.
Hardboard can often be bent into both concave and convex shapes without cracking.
This makes it a useful option for projects that incorporate S-shaped curves.
How to Cut Kerfs for Bending Wood
The table saw is the easiest tool for making a series of evenly spaced kerfs.
A standard combination blade works well for plywood, while a crosscut blade is a good choice for solid hardwood.
The challenge isn't making the cuts themselves. It's keeping the spacing consistent from one kerf to the next.
A simple keyed auxiliary fence attached to your miter gauge makes the process repeatable.
Step 1: Make a Keyed Miter Gauge Fence
Start by attaching a long auxiliary fence to your table saw's miter gauge.
Make a cut through the auxiliary fence to establish the exact position of the blade.
Next, measure the desired distance between kerfs and mark the location for an indexing key.
The key fits into the previously cut kerf and positions the workpiece for the next cut.
For this jig, a simple #4 screw makes an effective indexing key.
Drive the screw into the auxiliary fence at the marked location, then cut off its head with a hacksaw.
The remaining screw shaft fits neatly into a standard 1⁄8"-wide saw kerf.
Unlike a finger-joint jig, this setup doesn't require extremely precise indexing. The individual kerfs will be hidden in the finished project, so the main goal is consistent spacing.
Step 2: Set the Kerf Depth
Before cutting, adjust the table saw blade so it stops short of cutting completely through the workpiece.
For solid wood, a good starting point is to leave approximately 1⁄8" of material intact.
This remaining web allows the board to flex while preserving continuous wood fibers.
For plywood, the ideal depth depends on the thickness of the individual plies.
Rather than relying strictly on the 1⁄8" rule, set the blade to cut partially through the second-to-last ply.
This leaves the outer ply intact and provides a flexible connection between the ribs.
Make test cuts in scrap material before cutting the actual project parts.
Step 3: Cut the First Kerf
With the blade height established, position the workpiece against the indexing key.
Hold the board securely against the miter gauge fence and make the first cut.
Use appropriate workholding and keep your hands clear of the blade.
Step 4: Index the Workpiece for Additional Cuts
After making the first kerf, reposition the workpiece so the indexing key fits into the slot you just cut.
Make another pass through the blade.
Repeat the process across the section of the board that needs to bend.
The indexing key automatically establishes the spacing for each cut.
Once the kerfs are complete, the board will be noticeably more flexible.
The next step is determining how tightly it can bend.
How to Determine Kerf Spacing for a Bend
The distance between kerfs has a major effect on the radius of the finished curve.
Closer kerfs allow a tighter bend, while wider spacing produces a more gradual curve.
However, spacing also affects the strength of the workpiece.
Adding more kerfs increases flexibility but reduces the amount of solid material connecting the ribs.
Using fewer kerfs leaves more material intact, but concentrates bending forces into fewer locations.
The goal is to find a balance between flexibility and strength.
Kerf Spacing and Bend Radius
For the kerfing setup described here, the following measurements provide useful starting points.
These measurements are starting points rather than universal rules. The actual bend depends on the blade's kerf width, material thickness, remaining web thickness, and wood species.
Always make a test piece before cutting the final workpiece.
Finding the Balance Between Strength and Flexibility
It's tempting to use the widest kerf spacing possible to preserve strength.
But widely spaced kerfs can make the workpiece difficult to bend because the bending force is concentrated in fewer locations.
This can increase the risk of splintering.
On the other hand, extremely close kerfs create a very flexible but fragile workpiece.
For many applications, 1⁄4" spacing is a practical lower limit.
If you need a curve tighter than approximately a 6" radius, another bending method may be more suitable.
How to Make a Smooth Kerf-Bent Curve
One drawback of kerf bending is that the finished surface may not form a perfectly smooth curve.
Instead, the surface consists of a series of slight flats, or facets, between the kerfs.
The wider the kerf spacing, the more noticeable these facets become.
Closer spacing produces smaller facets and a smoother appearance.
Sanding Solid Wood Curves
Solid wood generally provides more material for smoothing the curve.
A hardwood sanding block works well for gently blending the facets.
Use gradual strokes that follow the curve.
Be careful not to sand so deeply that you reach the kerfs beneath the surface.
Sanding Kerf-Bent Plywood
Plywood requires a lighter touch.
The outer face veneer is usually thin, and aggressive sanding can quickly expose the underlying plies.
With widely spaced kerfs, the facets may be too pronounced to remove without sanding through the veneer.
Narrower kerf spacing produces a smoother curve that requires less sanding.
Use a hardwood sanding block and work carefully.
Avoid power sanders for this operation. They can remove material too quickly, especially on plywood.
How to Strengthen Kerf-Bent Wood
Kerf bending makes wood flexible by removing much of its thickness.
That also means the finished piece needs additional support to maintain its shape and provide adequate strength.
Even solid wood with relatively wide kerf spacing is weakened by the cuts.
In most projects, the curved piece should be attached to another component that supports the ribs and holds the desired radius.
Use Structural Backers
One approach is to attach the kerf-bent panel to a larger assembly.
For example, a curved end table can use shaped plywood top and bottom panels to establish the radius.
The kerf-bent panel is glued along the edges of these parts.
Support blocks behind the curved panel provide additional rigidity.
By connecting the ribs to the surrounding structure, the assembly supports the curved shape.
Reinforce Curves with Laminate
Some projects don't have a surrounding structure that can support every rib.
In these cases, a flexible backer can provide additional stability.
Plastic laminate or paperback veneer can be attached to the back of the kerf-bent panel.
The backer connects the ribs and helps the workpiece retain its curved shape.
Use a suitable adhesive, such as epoxy or contact cement, and hold the assembly against a bending form until the adhesive has cured.
This approach is especially useful for curved cabinet panels that don't have continuous structural support along their edges.
Woodworking Projects That Use Kerf Bending
Kerf bending can be used in a wide range of projects.
Some common applications include:
- Arched cabinet and bookcase tops: Create curved sections that can be supported by the surrounding case.
- Curved furniture panels: Form rounded fronts or sides for tables and cabinets.
- Router table cabinets: Build curved panels reinforced with laminate or veneer.
- Decorative woodworking: Add curved details without laminating multiple thin strips.
- Small projects and lighting: Create unusual shapes that would be difficult to make from solid stock.
A good example is the Modern Desk Lamp from Woodsmith Issue 236.
The lamp uses kerf bending in an unconventional way, with cuts made in the top and bottom of the blanks to create the curved shape.
Kerf Bending vs. Steam Bending and Bent Lamination
Kerf bending isn't the only way to make curved wooden parts.
Each bending technique has advantages depending on the project.
Kerf Bending: Quick setup, uses common tools, works with plywood and solid wood, but can weaken the workpiece and often requires reinforcement. Steam Bending: Produces continuous solid-wood curves without saw kerfs, but requires steam equipment, suitable wood, and careful bending. Bent Lamination: Produces strong, stable curves with smooth surfaces, but requires thin strips, a bending form, and glue-up time.
Kerf bending is often the simplest choice when the curved piece will be supported by other project components.
For structural parts that need to remain strong without additional reinforcement, bent lamination or steam bending may be better options.
Kerf Bending Tips for Better Results
Before starting your next kerf-bending project, keep these points in mind:
- Choose the right material. Baltic birch plywood and straight-grained hardwoods are good starting points.
- Pay attention to grain direction. Cut kerfs perpendicular to the grain when bending solid wood.
- Set the correct blade depth. Leave approximately 1⁄8" of material in solid wood or an appropriate remaining ply thickness in plywood.
- Use a keyed fence. An indexing key makes it easy to cut evenly spaced kerfs.
- Test the spacing. Start with the approximate radius guidelines, then adjust for your material and blade.
- Avoid excessive sanding. Especially with plywood, it's easy to sand through the thin outer veneer.
- Plan for reinforcement. Use backers, structural supports, or laminate to strengthen the finished curve.
Create Curved Woodworking Projects with Kerf Bending
Kerf bending is one of the simplest ways to add curves to a woodworking project.
With a table saw, a basic indexing jig, and careful attention to kerf depth and spacing, you can turn a rigid board into a flexible panel that follows a curved form.
The technique works with plywood, solid wood, and other sheet materials, making it useful for everything from cabinet panels to decorative furniture details.
The key is understanding how the kerfs affect the wood's flexibility and strength.
Once you've mastered those details, kerf bending opens up a wide range of possibilities for incorporating curves into your woodworking projects.
Build a Curved End Table
Give your next woodworking project a graceful curve with this distinctive end table. Kerf-bent panels create the rounded front, while shaped plywood components and internal supports help hold everything in place. It's a practical way to put this bending technique to work.
EXPLORE THE CURVED END TABLE → Put Kerf Bending to Work in a Furniture Project
