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Junkyard Dog
06-25-2018, 05:22 PM
This may sound silly, but I have a goodly number of 4x4x16 foot timbers that are pretty warped and twisted. I was thinking about building a steam box, or trying the plastic tube method to steam them one at a time and bend/twist them back into something resembling a straight board.

Building a box and plumbing it is no problem, nor is having a work station to clamp the pieces to while they are cooling. The issue is generating the steam. I have an old crock pot that is willing to donate its life to the cause. I guess my question is whether it's capable of making enough steam to do the trick.

Nutty idea right?

Peerie Maa
06-25-2018, 05:32 PM
At 4" thick you are looking at generating steam for 4 hours a pop. Will it hold enough water, or can you rig a method for monitoring and refilling it?

With unpressurized steam at 212° Fahrenheit, steaming for one hour per inch of thickness (regardless of the width) will soften the bond enough for bending. Substantial oversteaming may cause the wood to wrinkle on the concave face as the bend progresses. 2. Only air-dried wood of an appropriate species should be used.

Kiln-dried wood must not be used; the lignin in the wood has been permanently set during the hot, dry kilning process. No amount of steaming or soaking will weaken the lignin bond sufficiently for successful bending. The same applies to air-dried wood that has been allowed to dry and stabilize below 10% moisture content; the lignin will only partially plasticize with steam, not enough for successful bending of anything beyond a shallow curve.

https://www.leevalley.com/us/html/05F1501ie.pdf

Gib Etheridge
06-25-2018, 05:47 PM
Good luck. I would just take them to the local band saw mill and have him square them up.

Anyway, this makes a lot of steam for a long time. It's our salmon canning pressure cooker, directions on top.

18419

Pitsligo
06-25-2018, 06:06 PM
Does a crock pot put out enough heat to really generate a good volume of steam? I simply don't know.

For whatever it's worth, to "power" my steambox I used a 5-gal paint can, with lid, and a short section of radiator hose to get the steam to the box, heated atop a propane "shrimp boiler" burner. Pretty simple, fairly cheap, and I didn't need to requisition any of the kitchen appliances.

Alex

Greg Nolan
06-25-2018, 10:41 PM
The polyethylene tube method of steaming requires a lot of steady steam. A crock pot would not likely develop anywhere enough steam, and adding water (certainly necessary for a four-hour run) would interrupt the flow of steam a number of times. The poly tube method requires a good flow of steam because the tube offers no insulation to keep the steam from cooling; a traditional wooden box (or non-traditional box made of foam insulation) needs much less steam because the box, once heated up, holds the steam.

If you use the poly tube method, you have to make sure that the steam surrounds the wood -- easy enough with thin strips such as the gunwale being steamed in the picture below, but perhaps not so easy with a 4 x 4 -- the poly tube will want to sit tight to much of the surface of such a timber unless you take steps to insure a flow of steam around all surfaces of the wood.

My equipment sounds similar to Alex's above -- I use a propane turkey-fryer propane burner rated, as I recall, at 50,000 btu's to boil water in a 5 gallon old fuel can. I don't have to run the burner full blast once the water is boiling, but I do have to keep a good boil going, not just a simmer, to get enough steam. And if I have to add water, I can turn it up high till the water is boiling again.

18441

Junkyard Dog
06-27-2018, 10:10 AM
Thanks. I really like the pressure cooker idea. As for resawing, I need the boards to remain 4x4s, otherwise I'd cut them up and plane them down myself.

Junkyard Dog
06-27-2018, 10:12 AM
And, I do have access to a large propane bottle and a crawfish fryer. I really just need a lid for a pot.

Paul Schweiss
06-27-2018, 07:43 PM
My old steam is was a large commercial kettle, to which I installed a hot water tank style element that was made for boiling, like crab or lobster. It happened to run off 3 phase power because it was available. I made a plywood lid that had 2 holes for 2” hose that led up to the steam box. Additionally there was a drain hose from the box to return cooled water to the kettle. Last, there was a small hole for a dipstick so I could make sure the water stayed above the heating element.
The steambox was plywood, about 16” x 16” x about 12 feet.
No problem keeping box hot after everything had warmed up, next time I think I will add a second tank that will let water in to the boiler via a toilet bowl float so I would not have to be so paranoid about frying the heater element.
Use a crab cooker, a wood fire, my pot was just a heavy aluminum restaurant unit (hint on shopping direction), steaming is great fun, and if you have a crew you should steam everything, even if it does not require it...cuz the crew will automatically work faster with hot wood in their hands.

navydog
06-27-2018, 08:44 PM
I think you will be frustrated after wasting your time and money.

Paul Schweiss
06-27-2018, 08:57 PM
Well I think Navydog is saying that with all of the wettest, hottest, most abundant steam in the world, the real question here is how to judge how much twist to put in your jig to try to straighten the warped wood timber, so that when the wood has cooled and the clamps removed it will gain some semblance of ‘straight’, oh and also not warp again.

goodbasil
06-27-2018, 09:58 PM
here's a good one.
Try to find the magazine.
https://www.popularwoodworking.com/aug15/steam-powered

Gib Etheridge
06-28-2018, 12:19 AM
Well I think Navydog is saying that with all of the wettest, hottest, most abundant steam in the world, the real question here is how to judge how much twist to put in your jig to try to straighten the warped wood timber, so that when the wood has cooled and the clamps removed it will gain some semblance of ‘straight’, oh and also not warp again.

And I think he's right. Also, if the wood is inclined to warp and twist it will still be so inclined.

oldcodger
06-28-2018, 02:54 AM
In my limited experience it depends on the species of timber. Douglas Fir lost 50% of its bend after removing the clamps, Western Red Cedar about 15%.

Oldad
06-28-2018, 08:09 AM
Sorry, but I think you will be disappointed.

Dave Hadfield
06-28-2018, 09:58 AM
Skip it. It's a make-work project.

But steaming requires live-steam, not whisps. You want a jet of the stuff.

Pittsjock
06-28-2018, 12:53 PM
I make Windsor chairs so the sizes are materially different. I use a big box wall paper steamer (and a sealed 8" x 8" x 8' plywood box) and it works great - less than $75. All you need to do is cut of the special end on the steamer - the plastic steam tubing on mine slides nicely over some scrap copper tubing that I inserted into a hole in the side of the box. I think it would work fine for larger timbers - all a question of "cook time".

FWIW - 1 inch square white oak can be bent into about an 18 inch circle after 45 mins to 1 hour in the steam box. 3/8 inch can be bent to a 90 degree turn with care.

Patrick

David G
06-28-2018, 01:08 PM
Well I think Navydog is saying that with all of the wettest, hottest, most abundant steam in the world, the real question here is how to judge how much twist to put in your jig to try to straighten the warped wood timber, so that when the wood has cooled and the clamps removed it will gain some semblance of ‘straight’, oh and also not warp again.Precisely. I've done a bit of steam bending... and I'd have zero confidence in getting those sticks perfect. But I bet you could improve them. Seems like a lot of work for an undefined bit of potential improvement.

Junkyard Dog
06-28-2018, 02:45 PM
I think you will be frustrated after wasting your time and money.

I think you are right, but I've want to build a steam rig for some now, and it's not too much effort really. It would be a shame to throw away all those boards, so I don't mind giving it an admittedly very long shot.

It'll be a couple of weeks before I can get to it, but I'll post results after the experiment