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Forum topic by Jeff Waggoner posted 12-13-2012 08:47 PM 1856 views 0 times favorited 23 replies Add to Favorites Watch
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Jeff Waggoner

87 posts in 1348 days


12-13-2012 08:47 PM

Topic tags/keywords: jig walnut shaping

I was trying to steam bend for the first time. I am using ½” air-dried walnut 5” wide. I left it in the steam box for about 45 minutes from the time it reached 212 degrees. I was bending around a form but no backer strap. I am thinking that a backer strap would help the delamination on the outside but I don’t know why the inside is all crinkled up. It seems like a compression strap would just make that worse. Is it possible that this is just a bad piece of wood?

If I can get this to work I am going to resaw it and do a bent lamination.

-- Jeff Waggoner, http://www.planeoldwood.com https://www.facebook.com/pages/Plane-Old-Wood/170375656316338


23 replies so far

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Loren

7571 posts in 2306 days


#1 posted 12-13-2012 08:51 PM

What you are doing won’t work.

...maybe if you had riven wood you could do that kind of a bend.

You need to really set up right to make that work. You
need a compression strap on the outside to start. No
way can it work without one except with green wood.

Are you trying to make a little piano?

-- http://lawoodworking.com

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DS

2131 posts in 1078 days


#2 posted 12-13-2012 08:52 PM

For the wood and thickness you want to bend, the radius is too extreme.

If I remember the numbers, more or less, you can get about 12% compression and only 4% expansion before seeing tearing and checking like you show in your pic. (This varies some depending on wood species and method of drying used)

The metal strap is usually affixed to the outside of the bend at the board ends to minimized expansion during bending, since expansion is less tolerated than compression.

If you use two, (or more), thinner strips to laminate this along the bend, you will likely have better success.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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Jeff Waggoner

87 posts in 1348 days


#3 posted 12-13-2012 08:54 PM

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StumpyNubs

6194 posts in 1458 days


#4 posted 12-13-2012 08:57 PM

Go with the bent lamination. You can bend anything if you cut it into this strips!

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com

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Jeff Waggoner

87 posts in 1348 days


#5 posted 12-13-2012 09:00 PM

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Mark Smith

497 posts in 698 days


#6 posted 12-13-2012 09:02 PM

Yes, what the others said. I’ve never tried bending wood, but I’ve read a lot about it and watched a lot of videos and I’ve never seen anybody try and bend that thick of a board around that tight of a curve. I’m actually surprised you got what you did get. I did watch a video where they bent plywood, but they cut slots (kerfs I think they’re called) onto the inside of the wood. I would think you may be able to do the same with solid wood, but that would only be if you couldn’t see the wood on the inside of the curve because it would have cuts in it.

-- Mark Smith, Tracy, CA., http://www.markscustomwoodcrafts.com

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Jeff Waggoner

87 posts in 1348 days


#7 posted 12-13-2012 09:08 PM

At Fine woodworking live Michael Fortune passed around a 4×4 about 18” long that he bent to 90 degrees. I am clearly no Michael Fortune!

-- Jeff Waggoner, http://www.planeoldwood.com https://www.facebook.com/pages/Plane-Old-Wood/170375656316338

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Viktor

447 posts in 2077 days


#8 posted 12-13-2012 09:33 PM

I’m pretty sure a board half as thick as your will steam bend just fine. Make two and glue them together. You could probably bend them simultaneously. Simple glue lamination will require pretty thin layers (<1/8”?) for this kind of radius. Considering the number of layers and their area I think this route could be even more challenging.

That form looks great!

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Jeff Waggoner

87 posts in 1348 days


#9 posted 12-13-2012 09:46 PM

One more question. After steaming the board to bend it, how long does it need to dry be for I can glue it?

-- Jeff Waggoner, http://www.planeoldwood.com https://www.facebook.com/pages/Plane-Old-Wood/170375656316338

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DS

2131 posts in 1078 days


#10 posted 12-13-2012 09:49 PM

1/10” plys are fairly common for laminated bending. I think I can buy them at my local hardwood supplier.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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zwwizard

189 posts in 2367 days


#11 posted 12-13-2012 10:03 PM

With Walnut, I would go with 1/8” thick lamination’s, leave it on the form for at least 48 hours. After taking off the form check to see how much moister is still in the wood. If still damp put the strips back on the form loosely until dry. When gluing up, put it back in the form for at least 24 hours. Its not a job that you can hurry.
There is a good book on the market;
Woodworkers Guide To Bending Wood
by Jonathan Benson

-- Richard http://www.PictureTrail.com/gallery/view?username=thewizz

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bondogaposis

2529 posts in 1009 days


#12 posted 12-13-2012 10:04 PM

1/2” thick is way too much for the radius you have there. I would go w/ 1/8” for something like that. You have to experiment a bit and to see how various woods performs. You already know that 1/2” is too thick. Try 1/8” and if that works may you could get by w/ 3/16” or 1/4”. From the form in your picture it looks like a double bend, you’re going to have to go thin to get that.

-- Bondo Gaposis

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Gshepherd

1472 posts in 859 days


#13 posted 12-13-2012 10:07 PM

How about soaking it a bit before you steam it. 45 minutes with 1/2 lumber. Looks more like your bending hot wood and instead of the fibers compressing they were cracking. I know you gotta move fairly quick. A outside form would be very helpfull as well. I use 1/16 thick steel with wax paper between the wood and strap.

Really try the soaking for about 45min to 1 hour before you steam it.

-- What we do in life will Echo through Eternity........

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Loren

7571 posts in 2306 days


#14 posted 12-13-2012 10:51 PM

If you want to use your existing form (I can tell it
took some effort to make it), resaw 4 strips 1/8”
thick, then bend them two of them to nest together
on a hot pipe, using a water spritzer. You may be
able to not pre-bend the other two layers once
the shape is fixed by laminating the first two.

Hot pipe pre-bending minimizes spring back
and will get you closer to the exact shape you
are looking for.

...otherwise the form has to be made to overbend
in order to compensate for spring back. Even
then, you might see failure or some of the dry
laminates at the edges (grain runout), unless
you pre-bend to some extent.

-- http://lawoodworking.com

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runswithscissors

957 posts in 683 days


#15 posted 12-13-2012 11:07 PM

Crinkling or crumpling of the wood on the inside of the curve is normal, and unavoidable when using a bending strap. Lace your fingers together at the tips, then slide them toward each other. That’s how the bend takes place, except that it’s usually only visible on close inspection. It’s just more extreme in your case. Also, Walnut is not the easiest wood to bend with heat—falls about midway between oak (very easy) and fir or luan (practically impossible). You can try soaking, but in my experience it contributes little. The steam is merely a way to get the heat into the wood. I have successfully bent white oak that had been drying in a loft for over 50 years, using only heat and no moisture of any kind (including steam). But that is an extreme bend you are trying there, and I agree with the guys who advise laminating. It’s messy but reliable. One way to avoid inevitable spring back with lamination is to pre bend with heat, let cool, then laminate. Also, the thinner the plies the less the spring back.
Another point: looking at your double curve (S curve), I would approach it by bending the principal curve first, letting it cool, then moving on to the secondary curve. Then laminate. Also, if you need to modify a bend slightly, there’s no need to steam it again. Just use a heat gun. Let the wood get plenty hot, then bend away. Be careful not to scorch the wood.
Another good book is “Wood Bending,” by Lon Schleining. He is very thorough and knowledgeable, and covers all methods (except dry heat, where I part company with him to some extent).

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