Processes / Step 7 of 11

Wood Bending: How Curved Parts Are Made and What to Specify

Solid wood is softened with steam and bent over a form, or thin veneers are glued up in a curved mold. The method sets the look, the strength and how well the curve holds its shape.

Send an RFQ What to specify

Wood bendingStep 7

Decides: Which bending method fits the part, the tightest radius you can order and how close each part stays to the drawing.
Goes wrong as: Cracked outer faces, wrinkled inner faces, curves that spring open and glue lines that let go.
Used for: Furniture components

Curved chair backs, bentwood rockers, arm rests, round table aprons and molded plywood seats all start as straight wood. There are three common ways to make the curve: steam bending solid wood, bent lamination of thin veneers in a mold and kerf bending, where saw cuts on the back let a board flex. Each one looks different, costs different amounts in tooling and fails in different ways.

Steam bending keeps the look of one solid piece with grain that follows the curve. Wood that has been steamed until it is soft can be squeezed a long way along the grain but stretched only a little, so the bender clamps a steel strap on the outside of the bend to push the stretch into compression. The part then dries on a form until the new shape sets. Bent lamination glues several thin layers together in a curved mold. The glue lines hold the shape, so the curve repeats closely from part to part and the radius can be tighter. Kerf bending is mainly used for hidden parts and curved panels that are covered later.

For a buyer the important choice is made before the quote: which method, which species and what tolerance on the curve. A drawing that only shows the final radius leaves the factory to guess. A good RFQ names the method, gives the radius with a tolerance and asks for a test bend in the actual species before tooling is paid for.

Wood bending: a bentwood chair with a curved back and woven seat

Where it sits in the chain

Not every product goes through every step. A pallet skips finishing, a turned leg skips veneering.

Methods and machines

What a factory may run for wood bending, and where each method fits. Ask which one your parts will go through.

Method	What it does	Fits
Steam bending, solid wood	Straight-grained stock is steamed at about 100 °C until it softens, bent around a form with a steel strap and end stops on the outside face, then held on the form or a fixture while it dries and sets.	Bentwood chair backs and legs, rocker runners, arm rests and parts where the grain must flow around the curve.
Bent lamination in a cold or heated mold	Thin veneers or strips are coated with glue, stacked and pressed between a male and female mold, or in a vacuum bag, until the glue cures. The glue lines lock the curve.	Chair shells, seat and back panels, curved frame members and repeat parts that must match closely.
Bent lamination in a radio frequency press	The same stack is pressed in a mold while radio frequency energy heats the glue lines, so the glue cures in minutes rather than hours.	High volume molded plywood seats, backs and shells.
Kerf bending	A series of saw cuts across the back of a board or panel leaves a thin face that can flex around a curve. The kerfs are then filled, glued or covered.	Curved aprons, cabinet ends and radius panels where the back face is hidden.
Coopering and stack lamination	The curve is built from short straight pieces glued edge to edge or stacked, then shaped by machining. No bending takes place.	Thick or very tight curves that no species can be bent to. Also short runs where a bending form is not worth the cost.

What you specify

These points decide whether two factories quote the same thing. Put them in the RFQ or the purchase order.

MethodName it: steam bent solid, bent laminated or kerf bent. If the look matters, say whether visible glue lines on the edge are acceptable.
Radius and toleranceGive the inside radius, the developed length and a tolerance on the curve, checked against a template or gauge. Tight curves on thick stock may need lamination instead.
Species and grainState the species and ask for straight grain with no knots, cross grain or short grain in the bend zone. Grain run-out is the most common reason a steam-bent part breaks.
Moisture contentSteam bending works best on stock that has not been dried all the way down, so ask how the factory brings the finished part to your target moisture after the bend sets.
Laminate buildFor laminated parts, state the number and thickness of plies and the face veneer species and grade. Name the glue type, including its water resistance and formaldehyde status.
Tooling and test bendsAsk who owns the forms and molds, what they cost and how many test bends will be made in your species before production starts.

Typical values

Published and common industry figures. They vary by species, product and factory, so treat them as a starting point and confirm on the quote.

Item	Typical value	Note
Moisture of stock for steam bending	About 12 to 20 percent	Air dried stock bends more reliably than stock kiln dried to furniture moisture. Typical, varies by species.
Steaming time	About 1 hour per 25 mm of thickness	Common rule of thumb at about 100 °C. Typical, confirmed by test bends.
Compression vs stretch of steamed wood	Compresses about 25 to 30 percent, stretches about 1 to 2 percent	Along the grain, for species that bend well. This is why a strap is used on the outside. Typical.
Veneer thickness for bent lamination	About 1 to 3 mm per ply	Thinner plies allow tighter radii and less springback. Typical.
Setting time on the form	Often one to several days	Until the part has dried enough to hold its shape. Depends on section and drying room. Typical.
Glue cure in a radio frequency press	Minutes	Compared with hours for a cold press with the same mold. Typical.

Defects and how to prevent them

What goes wrong at this step, why it happens and what to ask before production so it does not reach your warehouse.

Defect	Usual cause	What to ask or check
Tension failure on the outside face	The outside stretched more than wood allows, usually because the strap was loose, the end stops slipped or the grain ran out of the face.	Ask to see the strap and end stops, and specify straight grain in the bend zone.
Compression wrinkles on the inside face	The inside was squeezed too far, often from a radius that is too tight for the thickness or wood that was not steamed long enough.	Ask for test bends at your radius and thickness, and for the minimum radius the factory runs in your species.
Springback and shape drift	The part was released before it set, or moisture changed after release. Laminated parts spring back less than steam-bent parts.	Agree a template check after drying and again before finishing, with a stated tolerance.
Glue line failure in laminated parts	Too little glue, too short a cure, wrong glue for the moisture of the veneers or dirty plies.	Ask for a glue type with a stated water resistance and a break test on sample parts.
Checks and splits after drying	Bent parts dried too fast on the form, or end grain was not sealed.	Ask how parts are dried after bending and for moisture readings before machining.
Visible kerfs or ripples	Kerfs too deep or too widely spaced, so the face flattens between cuts or the pattern shows through the finish.	Approve a finished sample of a kerf-bent panel under side light.

Questions to ask the factory

Ask on a video call with the line running. Keep the answers in writing.

Which bending method do you use for this part, and why that method rather than the others?
What is the tightest radius you bend in this species and thickness without breakage?
What percentage of steam-bent blanks do you usually lose, and is that priced into the quote?
How long do bent parts stay on the forms, and how do you dry them to the target moisture after that?
For laminated parts, which glue do you use, how many plies and how do you check the glue line?
Who pays for and owns the forms and molds, and can you send test bends before tooling is approved?

How to write it in the RFQ

Example lines you can adapt.

Chair back rail, steam bent solid ash, inside radius per drawing plus or minus 2 mm checked on template, straight grain with no knots in the bend zone.
Seat shell, bent laminated, 7 plies, beech face and back veneer, glue with stated water resistance, test bends and mold cost quoted separately.

Send your RFQ and we match it with up to 3 factories that run this step for your product.

Materials and wood bending

How common species and panels behave at this step.

White oakOne of the best species for steam bending. Thick stock needs long steaming and careful drying on the form to avoid checks.
AshBends well and holds its shape. Common for chair backs and bentwood parts. Needs straight grain without run-out.
BeechThe classic bentwood species. Bends to tight radii when steamed and is widely sliced and peeled into veneer for laminated shells.
Yellow birchBends well and is peeled into veneer for molded plywood seats and backs.
Hard mapleBends moderately when steamed. Mostly used as thin plies in laminated parts where stiffness and a pale face matter.

Questions buyers ask about wood bending

Deeper guides on this step:

Steam Bent Wood or Laminated Bending: Which Method Fits Your Part
White Oak vs Ash: Which Species Suits Your Furniture Components

Background reading: Steam bending (Wikipedia)

Which is stronger, steam bent or laminated wood?

Both can be strong. A well bent solid part has grain that follows the curve. A laminated part spreads defects across many plies and holds its shape more closely. For tight curves and repeat accuracy, lamination usually wins. For the look of one solid piece, steam bending does.

Can any wood be steam bent?

No. Ring-porous hardwoods such as white oak and ash and diffuse-porous beech bend well. Most softwoods and plantation species such as teak bend poorly. Straight grain matters as much as species.

Why does a bent part open up after it leaves the form?

This is springback. Wood tries to return to its old shape until it has dried and set. Factories overbend slightly and keep parts on forms or fixtures until they hold the curve, then check them against a template.

Do I pay for the bending forms?

Usually yes for custom shapes. Steam bending forms are fairly simple. Molds for laminated shells cost more, especially for radio frequency presses. Ask for tooling cost on its own line and who owns the tooling.

Have a drawing ready?

Send it with species, finish and quantity. We match you with up to 3 wood manufacturers and reply within 24 business hours.

Get matched with a wood manufacturer