Steam-Bending Base Moulding

Is it practical to bend base moulding around a curved island? February 15, 2009

I've just completed construction of a curved island back which consists of a 36" radius quarter circle with a 2' straight section on each end of the radius - a fairly large curve. I bent the rails using 3, 1/4" thick pieces of solid maple in a bent lamination to make 3/4" thick parts. Now I need to bend a piece of base moulding to go around the base of the curve. I want to use 4 1/4" x 5/8" moulding which is already profiled on the shaper. Is it possible to steam bend this piece without the use of metal straps and elaborate setups? How much over-bend?

Forum Responses
(Furniture Making Forum)
From contributor M:
I've never tried steam bending maple. Perhaps, if the piece is stained, you could substitute beech. It steam bends well. Why not laminate on the same forms as the rails, then profile on the shaper with a bearing instead of a fence?

From contributor J:
What's so elaborate about metal straps? This is cheap and easy, and likely to be worthwhile with a wood that doesn't bend particularly well. Lee Valley's excellent steam bending booklet notes that maple can be difficult.

For a one-off, improvised situation like this, I don't know that there's a meaningful formula for springback/overbend. I suspect you'll just have to guess, and have a spare blank available in case you need to try again.

Since you have a curve with straight sections on both ends, you'll have to compensate for the (guessed at) springback by making the form's radius smaller and having the two straight sections at some acute angle. You'll need to coordinate the decreased radius with the angle between the straightaways on the form, so that you end up with the right length of curve between the straightaways. If the 36" radius is at the inside of the curve then you need 56 1/2" of curved molding between the straightaways. For example, you could use a radius of 32.4" on the form, with the straightaways 80 degrees apart.

From contributor C:

Steam bending works best with air dried woods that are still a little green (15% to 25%MC). Below that MC and it will probably split. Strapping shaped molding will be hard because you need to keep the steel strap against the wood, or it has another chance to split. And shaped molding is probably kiln dried, so not a good candidate for bending.

Fine Woodworking Magazine did an article recently on laminating moldings where the author took 2 pieces of shaped molding and sawed them both up into 1/8" slices with a 1/8" kerf, except he offset it 1/8" so that the kerf of one board lined up with the sawn portion of the other plank. Sort them, bend them and glue them up. It looked like it could work really well.