First Attempt at steam bending - Advice?

[alex grams]

So I am working on some chairs from walnut and have their crest rail and back rails which need to be bent. I made a good steam box (inside dimensions 6x6x30) and a pressure cooker on a deep fry stand which I can vent the steam to the box. The box steamed great and was at 210+ for over an hour. I made two forms which to bend the two test pieces on, one being a male and one being a female (to see which worked better).

When i let the two pieces (4.5"x.75"x18") steam for an hour at 210+ I then took each out and tried to place it in the forms and clamp them down.

Observations:
- The box certainly gets hot...
- Dang it takes a lot of force to bend wood, or did I just not steam it long enough? With bessey parallel clamps I could barely get enough force to bend the two ends down over the male (convex) form, and could not fully bottom out the piece on the female (concave) form.

I hope I am describing this clearly enough. The male form takes two clamps to bend the ends down around the form, whereas the female form takes a single in the middle to pull the middle down and the form holds the two ends of the piece to shape.

Am i missing something on the bending? Did I not steam long enough? Should I expect this much resistance? It was pretty straight grained walnut, air dried (I have a hard time finding very green walnut). I figured I could use this as the curves are pretty minimal, about 1.5" deflection over an 18" board, a very gentle curve, much less than what I have seen achieved with steam bending. The wood went from the steam box to the form and clamped in under 1-2 minutes, so not a lot of time lost there.

I can post pics of the setup if that will help.

Other thoughts are I need to steam pieces at least 50% longer on each end than the final piece, that way I have leverage on the bending. So if I want a 17" long rail, I need to have a 17" center with 9" on each side for a total of 35"?

Thanks in advance, I could use some guidance here!

[Prashun Patel]

I'm researching this myself. Am interested in your set up. Can you post some pix?

From what I've read so far, the rule of thumb is 1hr per inch of thickness - which you seem to have done.

Can it be that yr walnut was too dry? I've read that you can soak the piece for a couple days prior to bending to make it 'greener'. I'm going to bet that you probably just need to steam it for a *little* longer; I have read that it's possible, though, to oversteam. So the key is testing.

Last, perhaps you could experiment with some other woods; all the examples I've seen seem to be done with oak. That might tell you if the difficulty is a function of wood species...?

[Dale Coons]

An inch per hour is the rule of thumb. I've done some steam bending for bows--you need to be quick about getting it in the form. It only takes a minute or so for the wood to start stiffening up, and the shorter the piece the more difficult it is to bend. 18 inches is pretty short--you probably need more time in the box. If you've got a tight radius (more than a couple of inches) you might have better luck with a longer piece of wood from which you cut what you need after it's bent. Inside the box, the wood should not be sitting on the bottom, but raised so that it can be surrounded by steam (and not be sitting in condensation). Your box should have a small hole on the bottom for condensation to exit (at the far end). You should be putting enough steam into the box so that some comes out the far end--that ensures the box is actually full of steam.

Good Luck!

[alex grams]

I had looked at the reviews on which species bend well, oak being the most favorable. Walnut seems to be an acceptable species, I just need to find straight grained pieces. Cherry is very common, but i hear most of the exotics/tropical species do not bend well. I have also read on oversteaming, but maybe another 15-20 minutes will help.

I will try and post pictures this evening, though I did not take any during the process I can still show the setup.

Thankfully the back rails are going to be 3/8, so hopefully much easier to steam and bend.

I am making a test chair from poplar for all of the joints and construction before I start on the final set of 4 chairs, but with steam bending the back board I wasn't sure how well poplar would mimic the bending characteristics of walnut, so I decided to use walnut for those test pieces to get a better understanding of how I can expect walnut to behave on the final chairs and refine my forms for its specific behavior.

[alex grams]

Dale, the box is 6x6x30 inside dimensions, with 3/4" x 1/4" cross rails for layering boards on, with 1.5" between each layer, so plenty of room for steam to move around. I incline the box by a few inches on the front/door side with the steam coming in from the opposite side through the bottom. I have three vent holes at the front/door side, one being 1/8" for a meat thermometer, and two being about 3/16" for steam venting. During the steaming process steam was very visibly coming out of the vent holes.

I may lengthen the box so I can bend a longer piece which I could them cut two chair backs from a single bend, that would require about a 50" piece, but would give me a lot more leverage in bending.

Another problem I have is I have to take steps in clamping as my clamps only have about 2" of travel, so they bottom out before the wood is fully bent, so I need to have a second clamp to start when the first bottoms out. This isn't a major issue, but costs time and is cumbersome.

[Mike OMelia]

Wow! That is some thick stuff to bend. Why not do it in laminations? If one wants a 1" bent beam and does it with 1/4" laminations, the resultant stresses in the final piece will be less. I bend stuff for guitar bodies. If 0.1" stuff must be heated to bend. It seems to me that building with laminations will also produce a more stable piece. No?

Mike

[alex grams]

Mike, not sure if you read what I wrote properly, I am only bending some 3/8" and some 3/4" pieces, not that terribly thick for bending from everything I have read.

But if bending doesnt work by itself, I may steam some 1/4" pieces to get the curve and glue 3 of them together for the back rail.

[Philip Duffy]

rived wood -- green - -- bends pretty uniformly. Very dry wood that is milled is far more difficult.
Speed of movement to the form, and proper wedging to the form is essential. Each form needs pegs placed so that you can drop the hot piece onto the form, anchor it and then force the wood to comply to the form- -- and do it decisively and quickly -- with a helper if possible. You have good equipment and good ideas so just keep cool and do it! Phil

[alex grams]

Philip,
Other woods aren't really an option as the project (Chairs + Table) are all walnut, so i need to find a way to make walnut suit the project, either with steam of laminate bending.

[Lee Schierer]

Moisture to the interior of the wood is needed for the wood to get more flexible. I would recommend soaking the pieces in water for several days before trying to bend them so the water penetrates into the interior of the wood. Then when the get heated up the water is already there and just needs to be converted to steam.

I found that when I did steam bending:

I had less than a minute to work before the wood would stiffen up.

Kiln dried wood doesn't like to be steam bent.

Make sure your forms are over bending what you want for curves as there will be spring back.

[alex grams]

As requested, some pictures of my setup. I can hold ~210 degrees on the opposite end of the box, so temperature/steaming seems to work great.

I tried a 3/8" piece for the back vertical stiles, and it bent MUCH more easily. It is still in the form, so I am interested to see how they behave when I take them out. The 3/8 behaved MUCH better than the 3/4, even though I gave the 3/4 close to an hour to steam. I somehow still expect a lot of springback on the 3/4 even after 24 hours dry time in the clamp. Though tomorrow will tell.

[James Baker SD]

I see that you have to clamp your pieces to both ends of your bending forms. Maybe you can modify the forms to have a "lip" that catches the work piece at one end (snug fit) so you can save the time of one pair of clamps. In your picture #3, if you had a lip trapping the work piece on one end, I would think clamps on the other end would be enough (that is don't waste time on that middle set of clamps, at least not initially).

I've also seen big complex legs clamped to the bending forms using U-bolts, metal bars with holes for the U-bolts and nuts tightened down with an air wrench. Very fast in applying the pressure.

I would also agree that air dried wood needs a pre-soaking in water before going to the steamer to get it a little closer to "green" Never tried kiln dried wood, but hear it is not a good choice.

For tough jobs a helper is wonderful.

James

[Beau Schless]

I'm building a toboggan and wonder if I could ask the forum to do a simple review of my intentions and answer a couple of questions if it's not too much trouble, please?

Wood:

My toboggan will be 14" wide and at least 6' long x 5/16" thick. I failed finding ash locally (which I wanted). But I did find a local mill that is selling me newly milled (green) white oak. I have ordered 5 ea 3/4" x 2" x 10' pieces from the sawmill. The mill is going to cut them 1" and run them through a planer both sides, so the outsides will be ready for use and 3/4" finished planed (they can't mill smaller than 1"). I plan on ripping each 3/4" wide piece into 2 ea 5/16" pieces (5/16" + 5/16" + 1/8" kerf = 12/16. or 3/4"). That will give me 10 pieces of 5/16" x 2" x 10' in total, more than I need (since I'm worried about breaking one or two when I steam them). I don't have a planer, but I can cut pretty straight and can sand out any kerf marks.

Steamer:

I plan on building a steam box out of 2" silver faced foam rigid insulation, taped together with insulation tape. I need to get the wood pliant for at least 3', so I plan on making the box around 6" x 5" x 4 feet long with the wood sticking out one end. Thermometer from my gas grill stuck through the insulation for control. On the end where the wood sticks out I'll cut a "bung" piece with slats to support the boards (and let the pieces project). I figure the steam will escape from there anyway, but I'll probably put a steam escape hole in the box anyway. It will have slight tilt and a drain on the "slat" end to catch condensation. I'll put dowels in the box to support the boards, and build a bung/stopper at the "steam" end. I intend to use a tea kettle and electric hot plate to heat the water. The tea kettle will have a 3/4" water pipe going into the steam box. I could use my kitchen stove, but will have to expect complaints from the wife, so would appreciate your opinion on the hot plate concept. I did use it to steam ribs (5/16" x 5/16" x 8' ) for a boat I built, but not sure I can get enough steam up for this bigger steam box.

Mold

I plan on having a 12" diameter on the toboggan's bend. I found a 12" sonotube (that they use for deck posts) for $7.00 that I can cut off around 16" to give me a 12" x 16" cylinder . It is cardboard and I am worried about it collapsing when I bend oak around it. I can fill with concrete (if you think it is warranted...and your opinion would be most appreciated). My intention is to insert 1" x 2" boards every three or 4 inches around the inside of the sonotube and drill holes for bolts to project out of the sonotube before filling it with concrete. The bolts will hold down cross members to clamp the wood in place with while it dries.

I'm still at the design stage for this (but the wood will be here at week's end). Any suggestions would be most appreciated (including alternatives to the sonotube if you have a suggestion for a "ready made" mold!...I considered a 5 gallon bucket, but it slopes).

Many thanks in advance. Any suggestions would be most appreciated!

Beau Schless

[ray hampton]

Beau, I will recommend a dual burner heating plate with two tea pots so that you can keep the steam going, when one pot are half full or half empty, fill it up then wait for steam before filling the other pot

[Jacob Reverb]

Steam the wood longer than you think you need to ... and get it bent and held in place faster than you think you need to.

[Tim Janssen]

I made a Seth Rolland hall table for one of my girls and her husband. I used cherrie. Don't know if it was air dried or kiln dried but I suspect it was air dried. I made a simple box out of 1-1/2 thick foam, held together with long deckscrews. I rented a wallpaper steamer from Home Depot and steamed the table top for 2 hours, then ran downstairs to my basement shop and "unfurled" it on my bench. Worked great. I suspect you have to steam it a lot longer then 1 hour.