Steaming and bending wood: Grab a crying chair

I've designed and built some custom canoes. Thus far I've been successful on the steaming. I'm teaming up with a partner to design a very fancy voyageur canoe with some unique angles. He always told me "You'll need a crying chair for a project like this. Despite what you do, some pieces just don't bend to expectations."

Well, luckily I didn't need a crying chair for my last project. However, before I tackle this one I would like to know the following:

Q: Is there a good book or technical resource that lists the various woods that can be used for steaming/bending, including required temps, pressures and recommended material thicknesses?

I would rather refer to a good technical resource than attempt to bend something that just won't bend!!! ...and end up in the crying chair :-o)

Cheers - Joseph

 

"Wood - A Manual for its Use As A Shipbuilding Material" specifically Volume IV.

 

You'll also find guitar makers and luthiers who bend thin but quite wide strips using a bending iron - usually electric element heated. If you are doing strip lamination in thin sections it might help, even if partly to prebend.

I'm always a bit wary of using steam if you want to glue later with epoxy which hates moisture. OK if you can let it thoroughly dry. So a 'dry' bending method may be preferred.

 

Bending wood is an art, not so much as the actual act of bending it, but selecting the right species and how it's cut.

The classic mistakes are picking a species that doesn't like to bend, such as mahogany. Some species just are brittle or other wise not as well suited to bending. Another common issue is grain run out, so that during the bend the piece breaks or partly tears out along an edge. Next up is the cut. If you are attempting bend slash cut lumber, you better back it up with something (plywood, metal strips, etc.) or the flat grain will literally explode on the outside of the curve.

Lastly, expect some breakage, it's the nature of the beast, so get over it. I made a huge mahogany double door several years ago, with a curved top jam (of course). I had about 50% breakage in my attempts to get the jam stock to conform to the jig. This is normal, especially for mahogany. 25% breakage for the novice bender, using commonly bent species shouldn't be considered unreasonable.

 

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

 

Excellent tips and resources all! PAR, I have not tried steaming & bending mohogany. Must definitely wear the patience hat for that.

I must say Western Red Cedar, Ash, Walnut were wonderful to work with. Cypress was a pain to cut (fibers a lot like fiberglass!), but with patience and a fine kerf blade you can tame it.

Thanks again! Some good reading ahead

 

Maybe this will help. The "hot pipe" method works very well in certain cases.

http://www.finewoodworking.com/how-to/bending-wood/118053.aspx?channel=3

There are also chemicals that can be used to facilitate bending, anhydrous ammonia for one.

 

I have bent wood on dozens of kayaks, canoes and dingys. I have found that to steam bend wood in a typical wood steamer only works if you cut green logs from the proper species, carefully plan your cuts so you you end up with straight grain, defect free, "bending" wood, and than use it green. Also each piece will have slightly different moisture content, and different densities, you can not use the published tables sucesfully for time in to bend properly. You have to go by feel, break enough and you start to feel the peices that have been "cooked" enough to bend without breakage. One expert told it to me like this: it is like cooking spagetti, too long and it turns to mush (the grain buckles on the compression side), and not enough it is too stiff and it splits on the outside. You pull it out, set it in your jig, and carefully push on it so you can just feel the grain giving way. Stop before you split and put it back in the steamer if necessary.

When I did this with the low grade salvaged wood I found I would split up to half of my ribs, most could not be salvaged. If you stop early you can usually shave off the spilt with a really sharp knife and than cook it some more and than sucessfully bend it.

All of that is WAY too much work, not just in preparing the wood, but also you have to make twice as much rib stock as you need. I almost gave up on steam bending, but kept experimenting with different approaches, and I found it!

I have found another method that results in NO or only one rib in a whole boat splitting. This method works for old dry wood, for wood with defects, run out and knots, the method is not "cook" time sensitive, does not require special equipment, and results in all most all of the ribs successfully bending without damage.

find or make a very large pan and bring the water in it up to a near boil (where the bottom is all covered in bubbles) and put the ends of the rib stock into to soak. min of about 30 min, for up to several hours, it is not time sensitive, and all but the most severe defects in the wood can be ignored. Take each peice out and put it in your bending jig (I use a metal strap backing made from plumbers metal tape with foam backed tape on it), and push on it as far as it will go, and than put it back in the water and take the next peice, repeat. I work my way through the stack, switching the ends in the water (unless you have a really big tray of water you can keep hot). When I finally fit them to the frame I dip both ends into the heated water and than push it into place on the frame and clamp it there. Than go to the next one. If it will not bend far enough I but it back in the hot water and go to the next one, and come back to it later. by the time I have the whole hull full of ribs, the first ones are fully cooled and mostly dry. letting it dry overnight is usually all it needs to take adheasive or even finish the next day.

I have found that white oak, and Alaskan yellow cedar are the very best to work with for bending. but I have seen more skilled builders even steam bend western red cedar and doug fir this way (which are not considered good woods to steam bend). I find slaved old lumber, remill them on my table saw tilting the blade to match the grain angle so I get strips with the grain flat in the piece (on the small boats I build I only need ribs 0.2 to 0.25" thick and about .75 to 1" wide).

Personally I think doing anything other than boiling the wood is a waste of time, too much work and too much breakage. not so with boiling it, it puts all the moisture it needs into it, and it provides a very uniform heat to the wood. Alaska yellow cedar is the best to steam bend by boiling, but more costly. White oak (often I have salvaged from old shipping crates or floor boards, very low grade wood), also works well, is common and inexpensive.

Other wood and other methods may work too, but that is what I have found to be the best for my low quality salvaged wood and low skill (and low patience) building method.

Good luck.

 

In my very limited experience (4 gunwales) I used the usual wallpaper stripper with plastic drain pipe as the steam box.

I wish I had known about this method at the time.
https://www.youtube.com/watch?v=--iPQIwSEJM

 

Petros, I have never tried to steam white oak, and I'm glad to hear it's possible. I used it for the seat frames in the last voyageur I designed & built (see attached pic). This is a racing boat for a 14 man crew. The boat weighs about 275lbs. It glides very nice, slices through waves and leaves a lot of competitors in the rear view mirror. Very easy to steer too. I put my young 14-year-old son in the aft steering seat with a large 60" steering oar. He steered our race team around with no issues and held a fine course.

The next boat will be a classic voyageur with more fancy curves (curved bow tips, larger, slanted gunwales and perhaps some other special touches. I'll be designing it from scratch.

 

I'll definitely have to try the method in that video on the gunwales. Great channel too!

 

Heat is what does the trick, assuming you have sufficient moisture content. The white oaks bend very well (one of the best). I often soak a piece before bending for a few days, completely submerging it in water. Then a heat gun is used, as it's "talked" or convinced to to jig. You do have to be careful and not scorch the wood.

 

A heat gun for "talking" to the wood. It will either comply or make good fire wood!

 

The heat raises the temperature of the water in the cellular structure, within the piece. This makes the walls of each cell compliant, when asked to bend.

 

Bear in mind, that if you are putting epoxy and glass on the boat, you can use that to help bend timbers.

As a test, get a thin strip of some wood, and cut two test lengths.

On one piece, epoxy some 6 oz tape to one side - this will be the outside of the bend.

Then, set up the two pieces so you can apply weights. You will find that the one with the light glass on the outside edge will bend like a fishing rod without breaking.

eg

http://greencanoe.weebly.com/more-inside-stories.html