I am building a staircase in an timber-framed barn project and need to put a curve into the top portion of the stairs. Never having done any steam bending, I am trying to find as much info as possible before trying it myself. the FH articles and messages seem geared towards smaller pieces and/or hardwood…not what I am doing. I will be bending approx 2.5″ x12″ dry pine timbers along about 6 feet of their length. I would appreciate any feedback and/or pics of steamboxes if anyone is willing to share.
I should add that bending glu-lam option was ruled out in hopes of maintaining the authenticity of the timber-framing. Trying to keep it real…
Thanks!
Shawn
Edited 4/5/2008 9:26 pm ET by shawncal
Replies
build a steam chamber, something like a pipe w/ water over a fire or something like that, then make a templtate with plywood nd blocks of wood. steam the pine in the chamber, then lay it in the template and clamp untill dry.
There's enough youth in this world, how 'bout a fountain of SMART??!!
Well you have a couple of obstacles in your way.
First off the scale. Your going to need to be able to
produce a lot of steam. I'm assuming you mean that you are bending
six feet of a larger beam, if not (I.E. your only bending 6"x12"x6'
disregard).
Pine doesn't bend as readily as some hard woods, so it depends
on the radius your after.Also if you could use green lumber it
would help.
They say one hour per 1" of thickness so 2.5"=2.5hours.Make sure
you have enough steam to last.
It's going to spring back, so you'll have to overbend it.No
real way to say for sure how much, An experiment is in order.
The steam box needn't be any thing fancy. Just hold the wood and
steam in. A ply wood box (preferably sealed on the inside) is all you need.
Make sure the steam can exit the opposite end, and put a bucket under
it to catch the drips.
You may be better off laminating if you can. More predictable
P.S.
Your going to need a pile of clamps.
Pine doesn't bend well at all, and that is very thick for steam bending. Bear in mind that when you are steam bening, it is the HEAT that makes the wood plastic, the steam is just a way to deliver the heat and also hellps prevent the wood from drying out.
Can you kerf bend instead? There are a couple of kerf bending techniques that might work for you.Cabinetmaker/college woodworking instructor. Cape Breton, Nova Scotia.
Steam serves to soften the wood cells and is key to the process.
Heat alone does very little unless the wood is wet to begin with.One can also submerge wood in hot water, or for smaller pieces or laminate strips, wrap them in a towel and pour hot water over them.A solid resource for bending wood is to browse http://www.WoodenBoat.com and join their forum.Pine doesn't bend well, but it will bend some after steaming, as will most any wood. You can also back the piece being bent with a steel strap as you clamp it to the jig to reduce spitting if the radius is on the margin.
Don't use a pressure fitting. Drill a one inch
hole out the top opposite the steam source.
It has nothing to do with pressure and you want the steam to flow through the chamber.
Simple is better. Presoaking can help somewhat, but not much Rehearse your removing from the chamber plan.
Time is of the essence.
Have your form ready and close at hand.
Edited 4/5/2008 6:37 pm ET by Henley
I have only done a little steam bending,but have made a plywood box the appropriate size for whatever project is to be done. For the steam sorce I purchased a turkey frying kit for about $50, drilled a hole in the lid for a pipe to the steam box.
System worked great, that is untill I didn't pay enough attention to the water level and melted the aluminum pot.
I've bent 1 1/2" oak, but it took forever to steam and sprung back more than I expected.
Can't you glue-laminate it instead? If you match the grain carefully and use urea-formaldehyde glue the joints should be inconspicuous if not invisible, and you get much more control over the bending.
If you do go with a steambox, I've had good luck making a box out of plywood or osb and wrapping it with rigid foam. Set up a commercial-size wallpaper steamer or a turkey fryer to feed lots of steam into the box. If you build the box tight, leave a pressure release valve at the opposite end to the steamer. Drill a hole and just set a piece of wood over the hole.
Pine and softwoods in general don't steam bend well. That size timber will need a big steam chamber and a source that can deliver enough volume for quite a period of time. Think 20 minutes per inch thickness. Also, kiln dried wood can be bent but not as well as air dried material. For more info on steam bending check out Michael Fortune or Lon Schleining. Both have written volumes on the subject.
As of late i have been doing a lot of circular work, If i were you , i would scrap the idea of steam bending . Your looking at a lot of steam , and time. And get aquainted with laminations with a form . Your also need to get aquainted with resin glues( is it stain grade or paint grade something tells me this au naturale), springback formulas, and the ability to read grain. Leave your frustration and bring your patience. You are gong to need more than two set of hands,
Here comes Rez..........
That's fairly thick stuff to steam if you've never done it before, and pine is not that great to steam because of it's cell structure. Think more about laminating something like what you got there. If you don't have a good size ban saw, have a wood shop resaw your material into bendable pieces.
Either way you do it, you'll have to build a jig or a form to clamp the piece to.
Got clamps?
There was something on TOH, I think, where the shipbuilders in Mystic Port were refurbishing the old ships and they were steam bending some REALLY big pieces of wood. The last time I did this, it just so happened that Fine Woodworking had a great "how-to" article and I did it just like they described. It worked great. I think it was in 2000 or 2001, I'm not sure.
For oak, it was 1 hour of steam for each inch of wood. Then I had to have a form ready.
The same applied to the ship builders..only the forms were huge. Not sure how you would do it...but resawing and gluing might work, depending upon the distance needed for glue-up, if you don't have the space to steam.
"The nearest thing to eternal life we will ever see on this earth is a governmental program" -Ronald Reagan
When you say, "it worked great", were you talking about pine timbers? I am getting the impression that pine is going to be tough to work with, and not sure if I would be wasting my effort as a first-time DIYer.
I am trying to keep the visible woodwork in this project looking as authentic as possible- that's why I didn't want to go the glulam route in the first place. However, I do have a small bandsaw mill, so cutting the timbers into thinner strips and making bent glulams is possible. Just not sure how real it will look...
thanks
shawn
If you keep the laminations in order, use a urea formaldehyde glue (i.e unibond 800) and glue it up in a vacuum press you will have a tough time seeing the glue line. Your results will certainly be much more prdictable that way.
Vacuum press? Is this for strength, or appearance (or both?) This is the part I am concerned about. Not having a vacuum press, my plan was to just glue and clamp the laminations in the order they were cut. Is this going to yield good results?
I can't seem to find any info on home-made bent laminated beams, on FH or google. Anyone know where I can get an education.
thanks
shawn
If you have enough clamps to get even pressure then it shoud work fine. That's the beauty of a vacuum prees, even clampng pressure throughout the whole peice. It can be done with regular clamps though. I beeleive that is how Stan Foster does his circular stair skirtboards.
The more I think about the pine the more
worrisome it seams to me.
You need completely clear stock to bend effectively,
that could be hard to find in large pieces.
Also it being pine I'd venture to say it must be
Green or your in for trouble. Someone mentioned using a strap. It would have to be
pretty big, and you'd need extra hands but that would help
considerably.
It was probably not pine. They were using stock for ship building...And the steaming and bending was very cool. I thought someone in this forum would have seen it as well and could tell us more of the details."The nearest thing to eternal life we will ever see on this earth is a governmental program" -Ronald Reagan
I didn't see that article; but for traditional wooden-ship frames, the preferred material was oak.
* * *
Don't remember who posted this bit of misinformation, but it is the heat and not the water-vapour in the steam which makes bending possible. Steam is simply a convenient way to deliver the necessary heat to the wood fibres. It makes no difference if the wood is dry or wet; when it is heated to a sufficient temperature, it will bend to the limit of its species. You can put the wood directly into or over a fire and heat it up that way, if you don't mind shaving off the charred surface wood later on.
The heat softens up the natural resins which hold the wood fibres together, enabling them to slide longitudinally against each other. The cellulose fibres have a natural elasticity, too, which is what makes it possible to bend a piece of cool wood to a certain extent, but to bend it further than that without pulling the fibres apart (in tension), you have to soften the 'glue' which holds each one to the fibre next to it.
The steel band is clamped to the outside of the curve, to prevent surface fibres from stretching too far and fracturing. Use of such a compression band can decrease the minimum bending radius by a very substantial amount over non-banded bending. (It is not needed if the curve required will be a gentle one with a large radius.)
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Hey Dinosaur,
I'm not taking part in your disagreement with whoever about
steam vs. heat.
Just wanted to reiterate that Green wood is much better
for bending. I just thought that would be important for
the original poster.
Also I have found soaking the wood prior to steaming
seams to help the process. Maybe it just speeds it up,
I don't know.
Water is an efficient conductor of heat--I bet that has something to do with it.
reiterate that Green wood is much betterfor bending. I just thought that would be important forthe original poster.Also I have found soaking the wood prior to steamingseams to help the process.
Green wood has a high cellular water content; seasoned wood that is soaked in a water bath doesn't...unless you soak it for approximately as long as it took to season the cellular water out of it in the first place. And probably not even then: Once the cells in wood fibres lose their water content, the cell walls dry out and break down.
But as Mike mentioned, water is a good conductor of heat, so any water contained in the wood would help speed getting the heat into the mass of the timber.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
So you could consider lignin a thermoplastic glue?
So you could consider lignin a thermoplastic glue?
LOL. Yup, the first all-natural, 100% bio-degradable thermoplastic glue.
Mother Nature's original Engineered Wood Product....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
That's exactly what I said, and then someone posted that it was water not heat that did it....I've been out of town, and haven't been back to reply to it.
There is a new European techinque for bending wood that involves heating it in a box (certain amount of mositure has to be present certainly to avoid damaging the wood), then compressing the wood along it's length....8-10%, something like that . When the wood is hot, the cells become plastic, and will basically slide past each other....the bends that are possible are extraordinary, about the same as you can get with ammonia. That technique doesn't really apply here....the equipment that i have seen in use is pretty expensive, but I did skim an article on the internet where someone was doing it in a small shop.
Anyway, I agree heat is the most important thing, and steam has traditionally been a good way to deliver the heat and retain some moisture.
Cabinetmaker/college woodworking instructor. Cape Breton, Nova Scotia.
I found some info.
"Wood Bender's Handbook"
by Zachary Taylor
- Wood that has been dried, by whatever means, to less then 10-percent moisture content will be difficult to bend successfully because the lignin is permanently set and cannot be plasticized completely by a steaming treatment.
Radius achievable with selected wood, assuming it is 1 inch thick, heated by steam, and bent with a supporting strap.
Wood species Min. radius in inches
Ash, American 4.5
Ash, European 2.5
Beech 2.0
Cherry, European 2.0
Chestnut, Sweet 3.0
Douglas Fir 15.0
Ebony 10.0
Elm 1.5
Greenheart 18.0
Hemlock 18.0
Hickory 2.0
Hornbeam 4.0
Larch 12.0
Lime 14.0
Mahogany, African 36.0
Mahogany, American 12.0
Oak, American White 1.0
Oak, European 2.0
Olive 12.0
Pine 36.0
Plane (European)
Sycamore (American) 2.0
Spruce 36.0
Teak 18.0
Walnut, European 1.0
Western Red Cedar 35.0
Yew 8.5
Dry bending-
Assuming that the workpiece is being worked at normal room temperature with moderate moisture content, say about 12 percent, the following information is worth noting. An equation supplied by the Forest Products Research Laboratory is a usefull guide of a wooden member. This is the equation: T X R= 0.02. T is the thickness of the workpiece, R is the radius of the intended curvature.
Simpler alternative: Multiply thickness by 50 to get radius.
Hope this is helpfull.
Chuck
Edited 4/11/2008 6:40 pm ET by Henley
From my experience in traditional wooden shipbuilding here are a couple possibly useful additions.
The descriptions of the simple plywood steam box are right on. Renting a big steam cleaner is a good heat source. Hour/inch.
With 3" white oak ship planks in moderate temps we plan for about 3-5 minutes of working time to get the bend in. Whoever said lots of clamps was also right on. Do a dry run or two to get efficient with your movements. Speed is key.
Good luck-post pics when you are done...
I built this a couple of years ago.
for the oven I used a peice of 12 inch HVAC return duct connected to a turkey fryer by a length of radiator hose. I'll never forget the looks on the hardware store employees faces when I told them what I was trying to find parts and fittings for.
The 2x12's cooked for about 2 hours, then you get maybe a couple of minutes to do your bending, so work fast. The spring back is something your just going to have to learn with a little trial and error. On my steps here, all the bent pieces are connected to something solid behind them for long term stability. The top cap of the handrail is two 2x12's laminated together with pl, and then pattern cut with a jig saw for the curve.
I was there for another project this past week, the whole thing looks good as new.
Edited 4/15/2008 12:11 am ET by drbgwood
trying again with pics