Windsor Chair Resources

Windsor chairmaking tips-tools


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 Bending Basics

REPLY: The general opinion for hundreds of years among chairmakers and boatbuilders is that red oak is the one of the best if not he best steambending wood out there. There is actually physical reasons for that and ironically it's partly because of the one of the other properties mentioned, the smaller pores. Not only are they smaller in white oak, but there is also cellular structures internally that block these pores. This slows down steam traveling through the wood. Red oak has larger pores and nothing to block them off allowing the steam to quickly and readily move through the wood. You can take a 12" long piece of red oak put one end in a glass of water and blow in the other end and see bubbles in the glass. The other side of the coin is these open pores also allow rot spores easy and quick access so red oak isn't as desirable in situations where the wood gets damp, like boat bilges etc. JT  12/15/02

REPLY:  JT's point about the steam flowing into the red oak through the large pores may be correct. However, it is my understanding that what causes the wood to bend is heat. We use steam only because it is an efficient way to conduct heat. Wood also conducts heat, so there is no reason to think you have to transfer the heat in and through the stick of wood to be bent. That's as far as chair work goes. I don't know about boat building. Maybe in large boat building the plank is so big you actually need to flow steam into it to get the inside hot enough, and maybe that's why boatbuilders use red oak and not white oak. BG 12/16/02

REPLY: I disagree with Bg. In Understanding Wood. By R. Bruce Hoadley He states: "Steaming the wood increases the compressibility to as much as 30 % . Also, steam @ 212 f warms the wood and whatever moisture is already in the fibers: the moisture in the steam supplements the inital moisture content of the wood.

It's definitely possible to bend with dry heat, you're going to have more success with bending if it's with a little steam. RH 12/16/02

REPLY:  BG, I don't agree with you, if it's only heat that helps wood to bend, why steamboxes? Why not hot boxes or ovens? Try to put a spindle in your oven and see if it bends easier after 30 minutes. If you'll think about it all the woods suggested as suited for steaming are ring porous woods, oak, hickory and ash. I don't think that's a coincidence. I believe it's because the steam can travel through the wood easier. I agree steam or water is the medium for heat transfer, but there isn't another way I know of to do it without drying the wood out. I don't really know of any difference between bending wood for boats or chairs same woods and for small crage similar sizes. I'm sure good white oak is better than poor red oak. You use what you can find and what you are familier with. The bottom line should be if you are having problems bending one species, switching isn't likely to help. JT 12/16/02

REPLY:  I respect RH and JT's opinion, but I'll have to stand by the fact that it's really heat, not steam inside the wood, which makes the wood plyable and bendable. This is based on my experience with numerous red and white oak logs. The worst white oak bent better than the best red, especially on tight bends. Also, you will find that if you steam a stick too long the steam heat will actually dry out the stick. I have also heard that other cultures do in fact bend wood with fire heat, not steam. BG 12/17/02

REPLY: In addition to making Windsors, I also make oval shaker boxes. The wood I use to bend the tight radius of box is quarter sawn cherry. The method used for bending is submersion in 180 + degree water for at least 20 minutes. I've never had a failure. The cherry is cut to less than an eighth of an inch in thickness and it comes out of the water like plastic. I think the key to bending with dry heat, like around a hot pipe, such as guitar and violin makers use, is good moisture content in the wood.  BG2 12/17/02

REPLY: Found a few items of interest on the steaming front. "Heating the wet wood turns the water to steam which dissolves some of the bonds between fibers allowing them to realign, reforming the bonds when they cool. So, steam bending is the process of weakening, stretching and reforming wood fibers to the desired shape." "There are three basic ways of softening the wood fibers. The first is to heat moisture already in the wood. This means using already moist, green wood, or soaking dry wood to replace the necessary moisture, then using a fire, or other heat source to turn the water to steams. The second method is to create steam first, and then force the steam into the wood. The final method is to use boiling water to penetrate the wood fibers." From an article by Norm Kidder

And this from a Steam bending FAQ by Gregg Germain on the WCHA website:  "What you are doing when you are steaming wood for bending, is softening the hemicelluloses. The celluloses are polymers that behave the same as thermoplastic resins. [My thanks to John McKenzie for the last two sentences].

And you need BOTH heat and steam for this. I realize that some people in Asia "fire" bend their wood but invariably, that wood is quite wet - typically quite green. The Norse boatbuilders used to get their planks out for shipbuilding and sink them into a salt water bog to keep them limber until the time came to use them." As far as whether you can bend wood with just heat, it doesn't sound like you can unless it's very wet wood to start with and probably only then it's thin, once the moisture is gone you're out of luck unless you replace it. JT 12/19/02

QUESTION: I keep reading that the wood should only be steamed from anywheres of 20 minutes to 45 minutes. At what point do you start the timer once the wood is placed inside the steam box? Any advice would be greatly appreciated. RQ 12/19/02

REPLY: Start timing from when the steam starts pouring out of the vent holes. My reason for saying this is that when I first attempted steam bending, I had an insufficient heat source, and the steam never get to the point where it was jetting out of the vents. Steam would waft leisurely out of the holes. Parts exposed to this 45 minutes to an hour would break. So I think that the requirement for steaming is for *saturated* steam, and anything you get before you get to the point that steam appears to be forced out of the holes doesn't count for much. GB12/19/02

QUESTION: Should the steam box be already good and hot before placing the wood inside and letting them steam for the recommended time of 30 to 45 minutes or should I place the wood inside and start the time as soon as I see steam pouring from the vent holes letting me know it's good and hot inside? Any help would be appreciated. RQ 12/19/02

REPLY: My steambox is completely warmed up and steam pouring out before I put wood in and start the timer. JT 12/19/02

REPLY:I also put the wood in after the steam box has a good head of steam. It would be hard to determine just when the steaming effect would start to take place if you put it in at the beginning. BG2 12/19/02

Bending Jig Tip:

To find the nicest curve, roundness and "elbow bend" angle, I have found an easy solution that works for me:

Go to the local hardware store and buy a 5' length of copper tubing and keep bending and shaping it until it is "just right" for you and the chair you want to build. This gives you freedom to adjust and a good form to stand back and make sure it works for the chair you're building. Good Luck. DO 2/9/01

Drying after Bending

QUESTION:  I was wondering about steam bending and how long most of the builders like to let the pieces dry and reach equilibrium? In my case, I steam a bunch of parts at the same time to save on energy to run the cooker. My limit is always forms. After a day or two in the form, I have to tie the bends up(compress) to keep them from relaxing. Having done at least 100 bends I have tracked some pieces to see how much they enlarge if left untied even after drying for months. I'm not concerned about a comb piece flattening out as much as I don't like the outward pressure of the arm piece on a sack-b style chair. The armpost tenon is so close to the edge of the seat with end grain holding it. Like to hear other's thoughts on this "Achilles heel." D.O. 1/2/03

REPLY:  At the Windsor Institute classes they tie the ends tight and take them off the mold as soon as they cool (maybe five minutes). They then keep them in the furnace room for a couple days. In that amount of time the string goes from being tight to being lax (negative spring back). I don't get these results when I air dry the same parts, but there isn't very much spring back when I untie them. Certainly there is not enough spring back to be concerned about splitting at the arm stub joints. If that were the case, I might make more effort towards heating the parts during drying or making the bending form's radius a bit tighter. GB 1/2/03


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