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producing steam for bending wood

2rwSC5WL7a's picture

Greetings fellow woodworkers

I am working on a set of chairs in the Arts and Crafts style and I have to bend the back rest rails. I am using kiln-dried quartersawn white oak. My first problem is one of supply - I can't find a unit to produce steam. The old kettles we used to make coffee with are no longer in production and the new ones shut off as soon as they hit 212 degrees. I have an old wallpaper steamer but its corroded inside. I would welcome any suggestions for a homemade rig.

Zav in Montreal

3fingerjack's picture

Steam Generator (post #154201, reply #1 of 12)

Hi Zav,

Quite a while ago I built some reclining Morris chairs out of quartersawn white oak using the steam bending technique. To generate the steam I used a propane burner, a gasoline can and a radiator hose. The burner is the type used with a big pot for heating water to cook crab or heating oil to fry a turkey. Make sure you use it outdoors. The gasoline can was purchased new and has never had any gasoline in it, only water. The radiator hose attaches to the spout of the gasoline can with hose clamps and extends into the steam chamber that holds the wood you want to bend. I think i used some kind of plumbing connector to make an airtight seal into the steam chamber.

Fill the gas can half way with water, place it on the burner and extend the hose into the steam chamber. Fire up the burner, place your wood in the chamber and wait for the steam. I think I let the steam saturate the wood for 15 or 20 minutes and then moved the wood to the bending form. You have to work very fast at this point, measured in seconds not minutes, so you don't lose the flexibility of the steamed wood. I used Bessy clamps and had trouble getting enough clamping pressure to close the form tight. If I was going to do it again, I'd use pipe clamps because they deliver more clamping pressure.

And don't forget that there will be spring-back in the piece of wood when you unclamp the form, so the radius of the form should be a little smaller than the radius desired on your finished piece.

Good luck with your project.

"There are some ideas so wrong that only a very intelligent person could believe in them." George Orwell

Scooter1's picture

I used a steam cleaner, an (post #154201, reply #2 of 12)

I used a steam cleaner, an electrical steam generator for cleaning curtains, engines etc.  It is safer than a propane unit and comes with pvc hoses to which I fitted a connector into a shop built steam box. 

Regards, Scooter "I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
joinerswork's picture

Zav, You'll have better (post #154201, reply #3 of 12)

Zav,

You'll have better luck bending if you can get green or at least air dried wood, rather than kiln dried stock.

 

Ray

Lataxe's picture

Bending slats (post #154201, reply #4 of 12)

Ray,

It's certainly true that the bending (and shaping beforehand) of green wood slats is a straightforward process.  I never have attempted the shaping and steam bending of kiln-dried wood but even air-dried stuff at around 15% is significantly more resistant to successful shaping and bending than the damper stuff.  It requires more effort to slice/shape the wood and also to tighten the clamps of the former on the result;  and it is also more prone to developing a crack, expecially if the timber is that way inclined (as is oak, for example).

My green woodworking friends also insist that kiln-dried wood (as low as 8%) can never be successfully bent, although I have never met one who actually tried it.  :-)  There is a green woodworking lore to the effect that, even if rehumidified, kiln-dried wood has suffered an enbrittlement that cannot be reversed.  Perhaps a wood technologist could comment on this allegation?

****

Just as important is the consideration of the grain within the wood - how it runs in the slat prepared for bending.  If sawn wood is being used (and that's the likely kind if its kiln-dried stuff from a timber merchant) the grain may run-out of the pieces used - i.e. not run parallel with the slat, meaning that the grain is not continuous from one end to the other.  If the grain runs out part way along a slat, the chance of the slat breaking rather than bending will be hugely increased.

The traditional method for making ladderback chairs prefers green wood for a number of reasons.  One of the most important reasons is that the greenwood can be easily riven along the grain so need not be sawn (which cannot always follow the grain).  When riven with a froe and carefully shaped with a drawknife then spokeshave, the slats may be made so that there is continuous grain from one end to the other.  When steam-bent, the slat is unlikely to break; when in use within the chair the slat will bend and flex to a remarkable degree as it is sat agin.

I like to make my ladderback slats very thin - slightly thicker than 1/4" at their thickest section - as they will then easily bend in the chair, forming themselves to each and every sitter; but with no chance of breaking because that continuous grain vastly increases their resilience.  I doubt if a 1/4" thick slat with grain running out along its length would last very long, when subject to child-wriggle or large-lady attack.

Lataxe (Cumbrian for "froe" and a bit of a cleaver hisself).

joinerswork's picture

Lataxe, old bodger, All you (post #154201, reply #5 of 12)

Lataxe, old bodger,

All you have said is just so.

I'll add from my side of the pond, that it is thought by some that it is of benefit to bend facegrain stuff, rather than rift or edgegrain.  That is to say, the growth rings ought to be oriented parallel to the bend  when possible, the idea being that the growth rings be able to "slide" past one another as the bending is being done.

The thinking I have heard on why kilndried stuff is poor for bending is that the "bound water" in the cell's walls is all gone, making the wood fibers more brittle even after steaming.  And, as you say, kd stuff is all sawn, with attendant runout of grain.

However, every rule has its exception, and so it is possible to steam bend even an "impossible to bend" wood like mahogany, even when it is kilndried, as the link below will I hope attest:

http://www.davidraypine.com/portfolio.php?spgmGal=Tables&spgmPic=9&spgmFilters=#pic

Of course one must be prepared for a certain % of failure, when attempting the impossible!

Ray

DanCC's picture

Bending oak... another story. (post #154201, reply #6 of 12)

I a,m postiing a link to a thread on another board taht deals with this subject.  Lataxe will be excused from being able to id the ship for which the oak is being shaped.  While not exactly on point, it is one of the most interesting essays in this area I have seen, even if most of us have not had to bend boards of anywhere near this size.

 

http://www.sawmillcreek.org/showthread.php?t=68664

DanC

SgianDubh's picture

"There is a green woodworking (post #154201, reply #9 of 12)

"There is a green woodworking lore to the effect that, even if rehumidified, kiln-dried wood has suffered an enbrittlement that cannot be reversed."

It's not really a lore Lataxe. There is significant truth in it due to a form of hysteresis. In this case it's because wood, once dried to, say, 7%MC (the norrm in North america) and therefore stiffened and hardened, never reverts to exactly its original suppleness. Wetting dry wood will make it supple again, but not as bendy as if it had never been dried in the first place.

Ray makes another useful observation, ie, it's generally best to bend wood with the growth rings following the bend, and even better if the pith side is towards the bend's centre. However, there are many examples of wood that has been compound bent, ie the piece is bent in more than one direction, as seen below in these ercol chair backs. There are more images of steam bending on anindustrial scale at the link below. Slainte.

http://www.richardjonesfurniture.com/Articles/gathering-09/gathering-09.html

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PurdueDan's picture

my steam setup (post #154201, reply #7 of 12)

I have attached a you tube video I made showing my set up.  I have bent over a hundred parts and most were extreme bends.   All my wood was air dried.  White oak bends the easiest by far. 

 

http://www.youtube.com/watch?v=JRZJ_ViEaBU

DonStephan's picture

Thanks. (post #154201, reply #8 of 12)

Thanks for going to the trouble to make and post the video.  I've thought a turkey frier would be the direction to go if I wanted to try making chairs, and your video was very helpful.  The 55 gallon drum is clever, not only to combat wind but also to provide a shield of sorts against the hot pot and burner.

jrockwoo's picture

Wallpaper remover steamer works great (post #154201, reply #10 of 12)

I bought a portable wall paper remover steam unit at a box store for about $40. Cut the hose and used some clamps and fittings to attach it to my box. Fill w/ water and plug into the wall. Very safe and can be used indoors.

KeithNewton's picture

Fish or turkey fryer is good. (post #154201, reply #11 of 12)

http://www.leevalley.com/en/wood/page.as...

   This site is so screwed up. After typing a page of advice, I went to get a link, only to return to a blank page. Now I remember why I don't show my face here much anymore. 

Here is a link to a free booklet that you must read before steam bending.  

 

Jigs-n-fixtures's picture

Steam Source (post #154201, reply #12 of 12)

I used a pressure cooker on a hot plate. 

Take of the jiggle weight fitting, install a 1/2-inch bulkhead fitting in it's place, and hook up the hose there.