Hey guys,
I have done some research on building a steam chamber for bending wood. I found alot of plans on the internet for PVC but when I went to buy the parts the guy in plumbing dept told me that PVC wouldn’t be the way to go that it couldnt support the extreme temperature. I know I could go with steel but man is that expensive. I really want to get a setup so if you guys have any suggestions or advice. Let me know. Thanks in advance.
P.s. I still never decided the best way to supply the steam. I heard just a whistling tea pot would work. ??????????
Aaron
Replies
I joined two 4 foot lengths of 8" galvy steel chimney pipe for the main chamber. One end is sealed with a tight fitting exterior plywood plug trimmed with weather strip. The other has a hinged door of exterior ply that jams shut with weather strip and a catch. Holes drilled every 12" along two sides of the pipe are fitted with hardwood dowels - this supports the stock inside the pipe. A "robust" electric kettle is fitted to the underside of the plugged end of the pipe. Condensed water drains via a weep hole near the door. Water is encouraged towards the weep hole by cradling the unit about 2 inches higher on the kettle/plug end.
The kettle cost $20. Everything else was free.
My concern with the PVC would not be heat and/or pressure. It's not a sealed unit - the condensed water must be allowed to drain and the hot water vapor simply follows it (and so, no pressure build). My concern would be the diameter of the PVC. Too small, that is.
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A good friend makes Windsor chairs. His steamer is a 12" x 12" x 8' box made from yellow pine and exterior plywood. One end is sealed. One end has a latched door. A rack of strapping and dowels support the stock inside the box. The steam feed is a 4 inch stove pipe fit to a clean paint can that sits atop a propane burner. It's very basic but has served him well for many years.
i have done a very little steam bending using two very different techniques
first was to bendsome maple rope molding(about 3/4 inch) to a 12 inch radius using a kettle on a hotplate coupled to setup in abs pipe, 1 1/2 dia in this case
the kettle was joined to an abs y fitting and the staight legs of the y had pipe fixed into them, the upper end was sealed and the lower end left open for drainage of condensate a kettle on a hotplate wont shut off at high temperature and also has a round spout that fits a standard sink tailpiece fitting ensuring a good seal
the second method was used to bend pieces of cedar for the rollsroyce model posted in the gallery today
i used a microwave oven with pan of water in the bottom to steam the pieces. even though the pieces didnt fit in the pan, it worked perfectly, 1/16 inch pieces took about 15 minutes on high and then bent to about 3 inch radius
One of the cleverest guys I know framed his boat as follows.
For steam source (he was bending big bits of wood) he used an old, wood-fired hot-water boiler.
The cool part was that he bought plastic bag stock from somewhere. Basically several hundred feet of tubular plastic, maybe for newspapers, I'm not certain. If the frame was 10' long, he'd cut 20' of bag stock, fold it back over itself to get a two-layer, ten-foot piece, which he'd slip over the oak.
He connected the hose to the bag (I forget what he used for hose), turn on the steam, and let it cook for the requisit time. Then, with the frame located correctly fore and aft, he used a come-along to gradually pull the frame down into position and the desired shape. No box, no rush to bend it before it stiffened up.
The man that's got this down is Brian Boggs. He's available on this forum.
If you're doing smallish pieces, 4" PVC (schedule 40) is perfectly acceptable; but you should rig some sort of support for the pipe, since the heat will cause it soften and sag.
Lee Valley sells a simple kettle that works fine, but it will take longer than a serious steam generating system (like a new gas can, heated with a hot plate, etc.).
http://www.leevalley.com/wood/page.aspx?c=2&p=42176&cat=1,45866
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"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
I appreciate the talk about "boxes' but my major concern is a source of air-dried wood. I have been unable to find a source for anything except kiln-dried in SE Michigan.Frosty
JFrostjr
Air dried wood? DIY!
Go to a sawmill buy wood and sticker it up.. You'll buy it so much cheaper than at the lumberyard you'll be amazed.. Rough rule of thumb one year per inch of thickness but buy yourself a moisture meter to keep yourself honest.. about $99.00 gets you a decent one.. You'll save more than that on your first purchase..
frosty,
For steaming, the greener the better. Many if not most windsor chairmakers bust their bent parts out of green logs, and bend as soon as possible. If using sawn lumber, you must select for straightest grain possible, and try to orient the growth rings parallel to the sharpest part of the bend, that is imagine the bark on the outside of the bend, not its face. The idea is that the "layers" of wood formed when the tree grew can slip past one another as their lignin softens from the heat of steaming.
I've bought wood at the sawmill and had very good luck with bending it. Ask for green, rather than airdried, lumber. In this case, at least ;-)) frenchy is right!
Ray
Thanks. I'll give that a try. My problem has been that most (all except one) of the sources of wood in this area, that I have been able to find, carry kiln dried. That appears to be the standard.I am fortunate that my primary source, Armstrong Lumber, on M-59 east of US 23, is top flight. They stock at least 30 species, in various thicknesses and lengths and are really nice people. I'll look futher for a mill that has just-cut material.Thanks, Frosty
Ray, I am not so sure that you should say the greener the better. There can't be any benefit to having a lot of free-water in the cell cavities. This would just keep the wood from reaching the desired temperature over a given time, and can cause some damage to the cell walls from the hydraulic pressure rupturing them as it escapes.I have steamed DRY lumber before, just for a test, and checked the MC right after getting it on the forms, and found it to have 18 - 20% MC. For this reason, having that as a starting point makes sense to me.
Keith,
I'm no authority on steam bending. Most of my "knowledge" has come from advice given me by a friend who builds windsor chairs. I'll defer to his experience as he's bent hundreds of bows, combs, and arms for his chairs. He prefers to bend dead green wood, doing all the bendings he can get from a log as soon as he busts it open, ending up with bendings for all his chairs for the next year after he's done steaming. I could give you a theory that the moisture in those cells is like putting sand inside a piece of copper tube before you bend it, preventing wall collapse/ kinking, but I'd just be blowing smoke, er, steam. Or maybe it's as you posit, maybe those ruptured walls are more flexible.
I've steam bent dry wood (even kiln-dried mahogany, which "can't" be bent) too, when I can't get green. The little bit of bending I've done ( slats and crests for a couple dozen chairs, the occasional windsor repair, several dozen set of snowshoes)has taught me to expect a much higher rate of bending failures if I start with dry wood, or sawn wood, no matter how long it is steamed.
Regards,
Ray
Ray, you're right. Sawn wood used in steam bending suffers from more failures than riven wood. Riven (aka cleaved) wood splits following the grain creating planks with continuous grain from end to end. Sawn wood cuts randomly across the grain leading to short grain which is more likely to lead to tension failure in particular on the outside of the bend.
Kiln dried wood is also not favoured for bending. It too can be bent but requires longer heating and failures are more likely, usually ascribed to its brittleness and kiln conditioned hardness. Kiln dried wood is also almost always sawn wood, so kiln dried and sawn is not an ideal combination.
Your friend is right to say that green wood bends easiest of all. Green wood is defined as being at Fibre Saturation Point (FSP) or above. 30% MC represents FSP for most wood species. Freshly felled trees typically are at 40%- 60% MC, but some can hold as much as 200% water. It depends largely on the species and the site the tree grew on, e.g., a willow alongside a stream or on swampy ground. Wood that has dried to below FSP and regained moisture is 'green' if it reaches FSP or above.
For the most part people that do a lot of steam bending settle on a preference for the wood MC being just below FSP-- about 20% to 25% MC-- typical air dried levels here in the UK.
The reason most commonly cited for this is that at FSP and below the cells are certain to be empty of water. The empty lumen give the cell walls a bit of wiggle room allowing them to distort with less likelihood for rupturing. The argument is that cells completely or partially filled with fluid tend to distort and also burst more often causing additional loss of strength over and above mere cell wall distortion.
How much additional strength loss is caused by the extra cell wall rupture through bursting I'm not sure. It may not be much, or it could be significant. Evidently your friend's practice of using freshly felled wood is not causing him problems in his Windsor chair making activities, so perhaps it's not significant. Slainte.
Richard Jones Furniture
Edited 4/22/2007 7:04 pm by SgianDubh
Thanks Richard,
Always good to hear from you.
Ray
I just used 3/4" exterior grade ply for mine. Works fine. Drill holes through the sides for dowels to support the pieces. PVC will work, since it's not under pressure. It'll just get a bit soft and bendy. You may have to insulate it, though.
Mike Hennessy
Pittsburgh, PA
Haven't tried it yet, but my plan for a box is to use 1" or 3/4" foil faced urethane foam insulation board, with the corners (mitered or not) held together with duct tape.
Waterproof, heat tolerant, ridgid, and insulated.
my set up is PVC with a camp stove and a tea kettle, works just fine for what i have done.
Aaron, that salesman has no understanding of what you are wanting to do, so don't let that stop you. There are plenty of people using PVC. It may get soft and sag, but you can make a wooden trough to support it along its length.
I wouldn't use any metal, because it is normally too good a conductor of heat,. and you should remember that the goal is to heat the WOOD. You should insulate your chamber, and drill a little hole through it to insert a food thermometer so you can see what the temperature is at any time.
I've had good luck bending 20' canoe gunnels in a couple of pieces of 4" ABS (black plastic) pipe coupled together. I used an old (antique) gas can filled with water on top of a camp stove with a short section of garden hose plumbed in. Very crude, but free.
Hope this helps,
Matt
Aaron,
I used a piece of gutter drain 4" X 6" X 8' plugged the ends, weep hole to drain and rented a wallpaper steamer and drilled a hole on the underside for the hose. Worked just fine.
ASK
Aaron,
I've used both a plywood built chamber and a PVC built one and both worked about the same. My source of steam was an old wallpaper steamer, it was safe and gave off more than enough steam.
I built my box two years ago from 5/8" exterior grade plywood. It measures 6" x 6" x 4' long. It has 1/4" dowels located 1" up from the bottom of the box. These are spaced 6" apart. My steam source is a 1 gallon galvanized steel utility can connected to a 1" I.D. radiator hose. This is then connected to the steam box via a 1" threaded pipe nipple that is screwed into the back panel of the box. For return drainage of condensate, locate the pipe nipple so that it's inside diameter lies just below the surface of the inside of the box. For a heat source, I use the auxiliary burner of my Weber grill and rest the box on top of the grill's lid. Works great every time. Only downside is that you must use it outside.
I was concerned with structural integrity of plywood, even CDX, so I made mine from 1x6 and 1x8, dowel racks, epoxied joints, screwed together. It lasted approximately two loadings before self destructing. The sides warped out, for the most part regardless of the grain orientation (flat sawn, HD just didn't have any good q/s #2 SPF). A small split in one bottom board ran the length and is now a 1/2" gaping split. I can't decide cover it with duct tape or to fill it with expanding foam. :-)
So what was your perceived problem with CDX? do you still think it is a bad idea?
Now you know why I built my second box from cdx. My first one was made from 1x6 ponderosa pine. It lasted only one "episode". While patiently waiting for my oak to become pliable, I heard an enormous bang. The entire bottom board had split from end to end. It was cool but it became kindling.
Our Venture Crew just finish 12 pairs of cross country skis bending 1" x 6 foot milled pieces of ash. This is the fourth in a series of projects that include a tobaggon, a dog sled, show shoes and now skis. The tobaggon, we boiled the wood ends and bend. The Dog sled had 1" runners with a 90 degree turn.For the last three, we build a simple box out of OSB. We lined the box with 1/2" foil covered foam board. We placed dowels across for separation and support. We made two entry holes in the bottom for 4" flex pipe from dryer/home heating Y and slipped it over a 5 gal galvanized gas can. The gas can fits perfecting into a turkey frying burner. It gets water up to the boil quick and can make lots of steam.Many times we would run 3-5 hours, adding more water, on a workday or campout making pieces. In the end, destroy it, since low investment. I would get a little ratty near the end, but would work just fine.
Here is a serious kettle, for that big job.Philip Marcou
That ought to set you up tp bend railroad ties!Frosty
Steam boxes made from ply with dowels for supporting stock work very well and last a long time, the best way to provide the steam is with a wall paper stripper, disconect the hose from the applicator and plug straight into the box. Works a treat!
Made this myself works GREAT!!
"The Ultimate Steam Box" by Mike Dunbar on page 68 of the Feb. 1995 #43 issue of American Woodworker. Dont tell FW
If Mike Dunbar builds it, it's worthwhile. My kinda guy.
PVC schedule 40 will be fine. I have steamed and bent alot of wood without any problems. I used 4 foot lengths of 6 inch schedule 40 joined in the middle and glued with regular pvc cement. Use a radiator hose from an auto supply store for the transition to the boiler. You can use an old style gas can which are still sold at farming supply stores for the boiler. Go to an discount store and buy a propane burner for camping or better one intended to boil corn or whole turkeys. Those bases have about the same dimension as the gas can base.
PVC works, but needs to be thoroughly supported, or it'll bend. My favorites are of marine plywood, and I've used galvanized duct. Since it's the heat that makes wood more pliable, any way you can heat it will do, and in a pinch I've used a hot iron. Chinese ship builders put framing timbers in the fire - literally. Lastly, the greener your material the easier it is to bend when heated, and the workpiece will actually be drier a few hours after you've steam bent it.
Gary W
gwwoodworking.com
Edited 4/20/2007 2:07 pm by GaryW
http://www.woodenboatvb.com/vbulletin/upload/Wooden Boat magazine and it's forum have a lot of info on steam bending.
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