Kerf Bending

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QUESTION: How are kerfs used for bending wood?

Steam Bending Plywood

QUESTION: If kerf bending is so easy, why would anyone steam bend thick strips or laminate thin strips?

Of all the ways to bend wood into a gentle curve, I think kerf bending is the easiest. It doesn't use special equipment as steam bending does, or a lot of forms and clamps as with bent laminations. It's just a matter of cutting a series of grooves (kerfs) to relieve the back of the curve. -This technique has been used in general construction to bend plywood around cabinets or solid wood around arched windows. But it can also be used in furniture. The Curved Front Table apron (page 18) and the top of the Tambour Clock (page 6) are a couple of examples.

QUESTION: How are kerfs used for bending wood?

A kerf is just a slot. When you cut kerfs for bending, you don't cut all the way through the wood —just part of the way. If you make a series of these deep kerfs side-by-side the wood becomes flexible, and can be bent in a curve, see photo.

What you're doing is relieving one face of the workpiece so you can bend it. The distance between the kerfs, their depth, and the wood you choose will determine the flexibility of the stock and the radius of the bend.

QUESTION: Do the kerfs ha ve to he consistently sjxiced, and if so, won't that take sortie kind of special jig for m y saw?

One of the nice things about kerf bending is that the spacing between the kerfs doesn't have to be exact. The piece will still bend. But if you want the curve to be as uniform as possible, you should use some form of in dexing. This can be as simple as a pencil line or just a brad or nail driven into an auxiliary fence (see page 15 for more on this).

QUESTION: After cutting all those keifs, I'm only left with a thin piece of wood. Wouldn t it be easier to just use a piece of veneer and bend it?

Though veneer will bend easily, it won't be as strong as kerf-bent wood. This is because the thin "web" that remains after the kerfs are cut is supported by the "ribs" left between the kerfs, see Fig. 1.

Veneer, on the other hand, could easily buckle and break if it's not supported. (Veneer can be wrapped around a solid piece that's cut to a curve, or even a piece that's been kerf-bent, see page 9.)

A piece of unsupported veneer is also likely to warp (usually cup) with changes in humidity. But on a kerf-bent piece, the ribs support the thinner wood and prevent warping, see Fig. 2. Note: A kerfed piece can be fragile until it's glued in place. Don't give in to the temptation to see how far it will bend. (I've done that and broken more than one kerfed piece.)

QUESTION: If kerf bending is so easy, why would anyone steam bend thick strips or laminate thin strips?

The main reason is appearance. If you kerf bend, the kerfs that are cut in the edge and back of the wood are visible.

Kerf-bent pieces also require a support piece. This piece adds to the strength of the bent piece and is usually a part of the project It may even hide the kerfs. On the Tambour Clock, for example, the front and back of the clock support the curved top and also hide the kerfs.

QUESTION: But what if the workpiece I'm kerf bending isn't attached, to any type of support? Is there any way I can strengthen the kerfed piece?

One way to strengthen the kerfed piece, is to simply apply glue inside the kerfs while bending the piece to shape. I use hot-melt glue to do this.

There's another method that both strengthens and hides the kerfs. With the piece held in its curved position, glue a slightly oversize thin veneer or plastic laminate to the kerfed side, see Fig. 3. Then when the glue dries, trim the laminate flush with the edges of the workpiece.

Kerf Bending

RIBS STRENGTHEN WORKPIECE AND PREVENT WARP

SUPPORT BLOCK

Warp Steam Bend Plywood Spoon Shape

SUPPORT BLOCK

RIBS STRENGTHEN WORKPIECE AND PREVENT WARP

GLUE VENEER OR LAMINATE TO KERFED SIDE

Warp Steam Bend Plywood Spoon Shape

LAMINATE STRENGTHENS PIECE AND HIDES KERFS

GLUE VENEER OR LAMINATE TO KERFED SIDE

LAMINATE STRENGTHENS PIECE AND HIDES KERFS

Kerf Bending

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