Help bending bubinga - a newbie to wood bending

[Adam Dickson]

Hey there fellow wood-o-holics. This is my first post. While I have been woodworking forever, I am a total neophyte when it comes to bending wood. I am beginning a project where I need to bend bubinga at a radius of about 3 inches. I am making a shape that is essentially a arc segment - about 120 degrees of arc (think rainbow). The arc will be about 1.25" thick and 2" wide. I have built my MDF form, which is essentially a triangular shape with the top rounded off with the radius I need for the ID of the arc.

I am planning on doing bent lamination using my vacuum press to 'clamp' the shape while the glue dries. However, the radius is quite small for such a stiff wood, and if I cut the strips sufficiently thin so they will not break when I bend them, there will be many, many strips and I will waste a lot of wood in cutting them. A strip thickness of about 0.1" seems reasonable, but that is still much too stiff to bend on my form.

For those of you with such experience, should I try to steam-bend the strips first, then use the vacuum press to make the final shape? Is there a way I can do this all in one step instead of two (steam bend, then cold form)? In order to steam the parts I would need to build a simple steamer first. Another option is heat-forming (like for the side of a guitar), but I do not have the specialized heating blanket, and I am disinclined to spend the $100+ for a one right now.

I have tried cold forming with pine for my prototype, but I couldn't keep the strips from cracking. Anyone have any advice?

[Jim Neeley]

Adam,

I haven't tried this with bubinga but you should be able to cut kerfs in the back side nearly through the wood, letting only a thin portion of the wood bend as the rest will just close the kerfs. I've seen people do that for other bending. You'd really end up with a series of short, straight segments so you'd have to play with it to see how it'd work.

[Chris Fournier]

I don't think that your plan will be successful as described. I would experiment with 0.625" thick laminations and make a two part mechanical press - you can use clamps of course. If you need 120 degrees of an arc them laminate 180 degrees and you can trim back to the required 120 degrees, this will give your a nice "fair" piece with no nasty kicks etc.

I have done a fair bit of this type of work and a vacuum press hasn't really got the stuffing to bend your lamination - the membrane is the weak link.

[Brian Tymchak]

I have no experience with bending wood. However, I remember a New Yankee Workshop program where the wood (can't remember what species) was soaked in a water bath for a while and then clamped in place. I believe he was trimming out a small circular table with 1/8" trim. The glue was a polyurethane that cures with moisture (Gorilla maybe?) I don't have any idea how well this would work with KD Bubinga. Might be worth a try before investing in a steam box.

[Richard Coers]

Have you glued bubinga before? I would suspect you will have more trouble keeping the laminations stuck together than the actual bending process. Lots of natural oils in that wood, make for trouble. I have no personal experience, just what I have read. I was going to guess the bending would be tough, but some Google work shows that it steam bends nicely for chair parts, but your radius may even make that difficult. You sure picked a challenge for your first bending project!

[Jamie Buxton]

First steambending your laminates, then cold-laminating, does help some. You get to use laminates that are somewhat thicker than if you do only cold-bending.

I'd cold-laminate the piece in stages. If you press all the laminates in one shot, your press has to apply enough force to bend them all. And these laminates around that tight a bend will take a lot of force. If you glue up just half the laminates, your press has to supply just half that force.

Me, I'd probably not make that part with bending. As you're realizing, bending to that tight a radius is quite challenging. Instead, I'd bandsaw the whole piece out of one big hunk of bubinga. Or I'd make a blank that's several pieces of bubinga. Each piece would be a straight segment covering perhaps 60 degrees of the bend. Then I'd use the bandsaw to cut the actual curve on that blank. You can also use smaller angles for the segment -- make each segment cover just 30 degrees of arc, or even less.

[Joe Hillmann]

On way to prevent splitting when steam bending is to use a leather belt on the back of the piece you are bending. When you clamp the piece of wood to your form clamp the end of the belt as well and when you go to bend it do most of the bending by pulling on the belt. Using this method have wrapped spirals around 2 inch pipe with wood that would crack when wrapped around a 12 inch diameter form without the belt.

Using a belt may also help prevent cracking if you try cold bending it too.

Also if you go with steam bending it is best to use wood that is as fresh as possible (hasn't fully dried) if you are using wood that is fully dried then you want to use air dried rather than kiln dried, and if you have to use kiln dried I would suggest soaking the wood for hours or days beforehand to help make it pliable.

I have never worked with bubinga but these are all tricks I use when bending local woods.

[Bill Wyko]

I happen to have done a lot of Bubinga bent lamination. Use plastic resin glue, it dries hard and has no rebound. I'll try to dig up pics of the big curved humidor I built with Bubinga.

[Chris Padilla]

A 3" radius is VERY tight to bend wood. Why do you need to bend wood at all? Get stock large enough and simply cut out the arc.

[johnny means]

Back when wooden edges in kitchens where in vogue, I had to make 3" bent laminations on a fairly regular basis. My advice is to ditch the vacuum press and get yourself some cheap ratchet straps. Pile on about two or three straps and you'll plenty of nice even pressure.

[johnny means]

A 3" radius is VERY tight to bend wood. Why do you need to bend wood at all? Get stock large enough and simply cut out the arc.

I'm sure the idea is to avoid endgrain and crossgrain.

[Chris Padilla]

I'm sure the idea is to avoid endgrain and crossgrain.

That is reasonable...make it up with segments of wood and then trim it with a router.

[Adam Dickson]

Thanks to all who offered their advice! Very helpful indeed to be able to pull from such a vast wealth of experience. As johnny means suggested, my motivation for bending is to avoid endgrain and crossgrain. Also, I am going to laminate 3 contrasting layers into the arc (perhaps maple or some other light colored wood), and I would like that contrasting piece to follow the contour of the arc. This piece is sort of a memorial piece I am making for display at my wedding to commemorate my father who passed away back in 2000. The contrasting strips are to represent his three children. My other motivation for bending this piece is also to learn how to bend wood. :-) Noting like jumping into the deep end of the pool!

The strap or leather belt idea sounds promising. I will likely try all these suggestions and see what I am successful with.