# Wood for steam bending



## jonlan (Dec 21, 2015)

Hi Folks. Recently my local Rockler store had their steam bending chamber kit on sale and it occurred to me that building the kids a toboggan for Christmas might be a fun project. So I went ahead and bought it - built a box big enough to hold 6 foot long pieces of lumber out of pine, put in some dowels to keep them elevated and started reading about steam bending. Most of the articles I found encouraged you to pre-soak the wood before steaming it. Most toboggans I found were made out of Ash but I had a hard time finding any. Then I found one or two that were built out of maple (which I enjoy working with and is easy to come by here) so I tried that. I bought some pre-dimensioned 1×4s, cut them in half, and then split them each down the middle to make my slats. They came in at about 1.75×3/8 inch each. So then I filled a large garbage can full of water and let them soak for 3 days.

After that, I fired up the steam chamber, put the boards in, waited for it to get to 200 degrees, and then let the board sit in there for about 25 minutes at over 200. As expected, the boards came out hot and I attempted to bend them around the form I built. Out of 10 boards, 3 of them snapped. I was a little disappointed but had read that this can happen and assumed that was OK for my first attempt.

Long story short - the forms I built werent great and the maple boards turned out, but not awesome. So I decided to do some more research and try again. I came across Lee Valleys steam bending guide and was surprised to learn that they thought Oak was easier to bend than maple. So I went out, bought some red oak, and tried again. Same process, but this time I built a much better form.

I steamed them this morning, same amount of time I did the maple, and this time out of 16 boards, 8 of them broke.

So now Im wondering what Im doing wrong. I know that most places recommend you dont buy kiln dried lumber - but I Im pretty sure all of the lumber I bought was. Not sure where to source lumber that isnt and I was hopeful that the pre-soak would help on that end. The boards that broke seemed brittle to me and failed almost the instant I tried to bend them. So perhaps I just picked some bad boards. I went through the entire pile at the store and looked for the ones with the straightest grain.

Is this a common issue when steam bending? My form for the toboggan has just the front curve and is over a foot in diameter so it's not a crazy curve.


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## jacww (Aug 23, 2015)

jonlan,

I just did a bit of Google searching and stumbled upon this PDF of a pamphlet on steam bending wood produced by the US Dept. of Agriculture in 1957. I looked through the first few pages and it looks like it may help answer your questions….at least from a theoretical perspective.

https://www.fpl.fs.fed.us/documnts/usda/ah125.pdf

I too am looking at doing some steam bending at some point. This is being added to my list of resources.

I hope this helps.

TonyC


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## jacksdvds (Jun 13, 2015)

Many, many years ago, 1950, in my wood shop classes, some of my friends built toboggans from oak and I don't recall their having as much difficulty as you are experiencing. As you bend each slat are you clamping them to the form every several inches? It helps to bend slowly and let the wood fibers stretch. Make sure of grain orientation straight as possible with the bend. 




 a you tube link that might help


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## jonlan (Dec 21, 2015)

Thanks for the comments. I've been doing some googling too and have come across two other possible items that may help me.

1 - Many folks use a bending strap. I'll have to look into making one of these
2 - Folks who are working with kiln dried wood seem to be pre-soaking for 7 days, and in many cases including Downey fabric softener in the water!

Maybe I'll give both of those options a try and see how I do


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## JAAune (Jan 22, 2012)

Easiest thing to do is to start searching for local sawmills and get yourself some air-dried wood. The difference is night and day. Also, do get that bending strap whether you buy it or make one. Use tempered steel strapping if you can find it. Mild steel can stretch if the stress is too high.

If you can access it, this Michael Fortune article will help a lot.

Steam Bending

Here's some of the work I did using his techniques. Every piece of curved solid wood in that was steam-bent.


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## DrDirt (Feb 26, 2008)

jajunes pic has your answer…. the bending strap is key.

Wood is very compressible, but not very stretchy.
You need to bend such that you are "compressing the inside of the curve" … instead of tryint to stretch the outside curve

http://www.leevalley.com/en/wood/page.aspx?p=42173&cat=1,45866


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## runswithscissors (Nov 8, 2012)

DrDirt has it right about how the wood fibers move. Stretching the wood fibers equals breakage. The bending strap is to help force the bend into the fibers inside the bend. You often can see after you're done how the fibers have sort of folded and crumpled in on themselves.

Second, I think 25 minutes is too short a time. The wood has to be hot all the way through. Thinner wood, of course, heats through more quickly, but also cools off faster. As soon as it's cool, forget bending. You'll have to reheat. Soaking the wood may help the heat to penetrate deeply into the wood, but moisture itself has little to do with the bending. I regularly bend wood (oak, mostly) without any moisture at all, using a heat gun or other source of heat.

Also, I think white oak will bend much more readily than red (not sure about this; oak experts can weigh in). However, ash is quite a good bending wood, as is black locust. Also yellow cedar, but probably too soft for your project.

The shelf bracket was just a prototype. Total time involved in bending was less than 10 minutes. Didn't use a form, just freehanded with one end clamped in the vise, other end with a C clamp (clamping the bending strap and serving as a handle) The bent wood is white oak, about 5/16" thick. The strapping steel used for sling loads of lumber makes an excellent bending strap.

JAAune: that is beautiful work you have done, sir. I'm impressed.


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## psoper (Dec 11, 2018)

That is beautiful work JAAune.
My experience has taught me that straight grain, air dried (best about 15%) and a compression strap takes a lot of the frustration out of steam-bending. Also best to prep an extra piece because sometimes it just does not work

Here are some photos of a toboggan I made for my granddaughters


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## jonlan (Dec 21, 2015)

Gorgeous pictures and work by all of you! I've settled on trying the steam bending strap - but after a couple of runs to my local home improvement stores, I can't find a strap that's thick enough for the length of board Im attempting to bend. Im looking for straps in plumbing that are typically used for hanging pipe.

Do most folks just buy the one sold by Veritas? (http://www.leevalley.com/us/HARDWARE/page.aspx?p=42173&cat=1,45866)

Or have folks had luck making their own? I'd prefer to try and make my own first to see if it helps before I invest in a tool.


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## psoper (Dec 11, 2018)

HVAC hanging strap works well It is about 1 1/2 wide and much stronger than plumbing strap It comes in 100 foot rolls. I cut it about a foot long and then add wood or metal stop blocks


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## jonlan (Dec 21, 2015)

So Im sort of struggling to find a detailed process for bending with the straps. The example I have found are mostly for hot pipe steam bending. I'll keep googling, but can someone explain the basics to me? I assume its more than just holding the strap on the board while bending it.


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## runswithscissors (Nov 8, 2012)

Yes, both ends have to be held. I hold one end in my bench vise, the other with a C clamp. Needs to be clamped pretty tightly as a lot of force is imparted as you bend the wood. Bending quickly seems to work well with steam, but with dry heat bending, I do it gradually, increasing the pressure as I feel the wood yield to the heat. I usually over bend, as there will be a little spring-back. If you bend too far, you will need to reheat to reverse some of the bend.

You can see how he has clamped the strap in post #4. Practice on scrap wood before you commit your good stuff to the steam box (or however you want to do it).

If you want to try the hot pipe method, I'd suggest a hot stove pipe rather than water pipe, because you are going for a large radius bend. By the way, wear leather gloves.


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## AlaskaGuy (Jan 29, 2012)

There's also a whole bunch of YouTube video on making toboggan that cover the bending process. Some are better that others.


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## bold1 (May 5, 2013)

I have never steam bent any wood myself. But my father was involved in supplying wood for submarine keels during WW2. He told me they used Slippery Elm and placed the pieces into steam chambers where they could raise the pressure to force the steam into the wood before bending. I remember him saying they wanted the center of the piece to get to 160 degrees Fahrenheit or higher to change the polymer in the wood into a plastic state before they started to bend it so that the finished keel still had strength. I would say without knowing your core temp it would just be trail and error.


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## runswithscissors (Nov 8, 2012)

I suspect the real reason for raising the pressure was to raise the temperature. Billy Atkin (old time naval architect) said one time that steaming green white oak actually had the side effect of seasoning the wood. Except for surface moisture, the wood was no longer "green."


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## bold1 (May 5, 2013)

I don't know about that. I do know they still pressure treat lumber to force the chemicals throughout the wood.


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## runswithscissors (Nov 8, 2012)

True about pressure treated wood. They also puncture the wood with many little holes to let the chemicals penetrate.


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## jdh122 (Sep 8, 2010)

The USDA handbook suggests that there is no advantage to adding pressure: https://www.fpl.fs.fed.us/documnts/usda/ah125.pdf
That said, I know that quite a few people do use pressure (Engels Coachshop on YT, for example, who steambend very thick ash regularly).


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## pontic (Sep 25, 2016)

Type of wood can also help.I find that Ash bends the best for me; and yes air dried bents better.


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## steve104c (Jan 4, 2015)

Only steam the amount of you can bend right out of the steamer. You only have a few seconds to bend the steamed wood. The rules is to steam 20 minutes for every 1" of thickness. Take out the pieces one at a time and bend that piece before taking out the next piece. Steam bending is a little tricky. Also have steamer and your jig close to each other. The wood will cool faster than think. Always use heavy gloves even if you use tongs to remove wood from steamer. Skin will burn at. 130 -145 degrees and the steam will be 212 degrees. Have fun but be careful.


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