Steam bending question

[Byron Barker]

I recently got in a conversation regarding the effects of steam bending. I am under the impression the wood absorbs heat and moisture during the steaming process. The heat drives further into the wood than the moisture, but the moisture acts superficially to allow more flexibility. The combination of the two is what allows for a safer bend than dry heat or moisture saturation alone. Best results are when the wood is pre soaked to gain additional moisture that can be heated within the wood more deeply to allow for a greater bend. However, I’m being told steaming actually dries the wood due to the heat? This must mean the interior that is subjected to the heat and not moisture, correct? It seems like every time I steam bend, the wood is soft and soaking wet. It is hard to believe it is actually drying out unless to say it is drying on the interior sections. Am I missing something?

 

[T. Ben]

From what I’ve seen from one guy on youtube who builds old coaches and wagons,Engels coach works,steam with light pressure,2lbs,will reintroduce moisture into the wood.

 

[DLJeffs]

I don't know the answer to your question Byron but when we bend guitar sides, certainly pre-wetting the wood helps. We line the bender with sheets of butcher paper which we also wet down. After the sides are bent to shape, we put them into a guitar body mold so they don't straighten back out. I assume while they're in the mold the wood dries back to it's original dryness per centage (maybe less because of the heat cycle), since the sides are thin, it wouldn't take long. Plus, we soak the bent sides at around 275-300F for around 10-15 minutes before we shut the heat blanket off so maybe that helps drive off some of the moisture.

 

[2feathers Creative Making]

Steaming has been used in the kilning process in certain Scandinavian countries for some time now as I recall. The explanation I received was it helped release the moisture from the cells by cooking the wood and slightly changing it's structure. (Read, bursting some of the cell walls) but I haven't done an intense study on it. I do know it seems to speed drying a little and help it keep what shape it was dried with.

 

[DLJeffs]

I've seen videos of people bending guitar sides using nothing more than a 6" diameter pipe, with a fire burning below so the hot fumes flow up the pipe. Using gloves, the luthier folds and coaxes the wood around the hot pipe to shape it. I don't recall water being used at all - just the hot pipe.

 

[FLQuacker]

Good article here.

Mastering the moisture dynamics in wood | Woodworking Network

Learn how moisture impacts the qualities of the wood product.

www.woodworkingnetwork.com

Not specific to bending as a process, but is full of info on how moisture relates to the process and can effect it.

 

[Byron Barker]

I've seen videos of people bending guitar sides using nothing more than a 6" diameter pipe, with a fire burning below so the hot fumes flow up the pipe. Using gloves, the luthier folds and coaxes the wood around the hot pipe to shape it. I don't recall water being used at all - just the hot pipe.

In bow making we say to steam green wood and dry heat seasoned wood. It isn’t explained why, but almost everyone knows this. After researching it more, it seems like steaming aids in the drying of green wood by means of expanding cell walls and literally steaming out the water. However, it seems to me that once the wood is seasoned, this process reintroduces more moisture than is currently present in seasoned wood. It is then quickly expelled as the wood equalizes to ambient moisture. It is also interesting that steaming wood curves often fails to hold the curve if not clamped to a form till it redries whereas dry heat seems to change the cell walls and will hold the shape better without a need to clamp for excess time.

 

[phinds]

Steaming has been used in the kilning process in certain Scandinavian countries for some time now as I recall.

Steaming of European beech, in particular, is done to enrich the color. This is also often done with Swiss pearwood veneer.

European beech, unsteamed and steamed

 

[Mike1950]

Steam kilns in Pnw was predominant way to dry.

 

[Byron Barker]

Steam kilns in Pnw was predominant way to dry.

But, this process is for lowering the moisture content in green wood, correct? The question I’m trying to get at is if I have a piece of seasoned wood and I steam it in order to bend the wood, is the wood taking in moisture or is it expelling more moisture? I understand that after the process, either way it’ll return to ambient moisture, but this doesn’t indicate if it does so by reabsorbing expelled moisture or expelling absorbed moisture.

 

[2feathers Creative Making]

But, this process is for lowering the moisture content in green wood, correct? The question I’m trying to get at is if I have a piece of seasoned wood and I steam it in order to bend the wood, is the wood taking in moisture or is it expelling more moisture? I understand that after the process, either way it’ll return to ambient moisture, but this doesn’t indicate if it does so by reabsorbing expelled moisture or expelling absorbed moisture.

If you are steaming seasoned wood, it is absorbing moisture. The steaming is done to introduce heat . The moisture is simply a carrier for the heat.

 

[Mr. Peet]

Steaming of European beech, in particular, is done to enrich the color. This is also often done with Swiss pearwood veneer.

European beech, unsteamed and steamed
View attachment 243386
View attachment 243387

Steaming actually alters the wood structurally ever so slightly. But this altering results in more stable wood over the common spectrum of wood use. The color altering was a side effect that became a desired result and many soon wanted the steamed wood for color reasons and failed to realize the structure improvements. American black walnut is often steamed not for structure improvement, but monetary gain. Steaming the walnut actually chases the heartwood coloring into the sapwood, creating more dark wood that sells better for overall higher profit.

But, this process is for lowering the moisture content in green wood, correct? The question I’m trying to get at is if I have a piece of seasoned wood and I steam it in order to bend the wood, is the wood taking in moisture or is it expelling more moisture? I understand that after the process, either way it’ll return to ambient moisture, but this doesn’t indicate if it does so by reabsorbing expelled moisture or expelling absorbed moisture.

Frank kind of hit your question. Yes, steaming dry wood does put water back into wood. I think I had read a paper that claimed, woods that were previously steamed were more easy to steam bend. Steaming can remove sugars and starches, making the wood less reactive / more stable. One reason some give boiling baths to their fruitwoods...

Hope that helps some.

 

[Mike1950]

I am sure it adds moisture to the

But, this process is for lowering the moisture content in green wood, correct? The question I’m trying to get at is if I have a piece of seasoned wood and I steam it in order to bend the wood, is the wood taking in moisture or is it expelling more moisture? I understand that after the process, either way it’ll return to ambient moisture, but this doesn’t indicate if it does so by reabsorbing expelled moisture or expelling absorbed moisture.

wood but- if wood was Kiln dried the moisture at cell level will never be the same (my understanding Of KD) Most that successfully steam bend wood do it with green wood. Green wood is more malleable.

 

[Mike1950]

I am sure it adds moisture to the

But, this process is for lowering the moisture content in green wood, correct? The question I’m trying to get at is if I have a piece of seasoned wood and I steam it in order to bend the wood, is the wood taking in moisture or is it expelling more moisture? I understand that after the process, either way it’ll return to ambient moisture, but this doesn’t indicate if it does so by reabsorbing expelled moisture or expelling absorbed moisture.

wood but- if wood was Kiln dried the moisture at cell level will never be the same (my understanding Of KD) Most that successfully steam bend wood do it with green wood. Green wood is more malleable.

 

[Mike1950]

Steam kilns in Pnw was predominant way to dry.

The mill I worked at had Giant steam kilns- probably 50+ ft high. The steam was created by burning the bark and other waste. More than 100% of electricity to operate the mill was created by huge boiler. There was no waste hauled away and this was mid 70s. when they opened those giant kiln door when it was 5 degrees out it was like a bomb cloud and it created snow downwind. if the temps on pine were not controlled right the kiln turned pine into un usable pretzels.

 

[brown down]

From the bending I have done in the past the wood doesn’t absorb water. The purpose of using steam to bend it is only to drive the temperature higher than you would be able to any other way without cumbusting. Same reason some Burls and woods can be dried by boiling them.

 

[Byron Barker]

From the bending I have done in the past the wood doesn’t absorb water. The purpose of using steam to bend it is only to drive the temperature higher than you would be able to any other way without cumbusting. Same reason some Burls and woods can be dried by boiling them.

This is what I’m talking about; there seems to be a lot of conflicting information about what happens during steaming. I noticed this right away when I began researching articles online by wood workers. It seems like either the process is different, the experiences are different due to the kinds of wood being steamed or there is miscommunication about whether the wood is green or seasoned. Still not sure what to think about it!

 

[T. Ben]

 

[Mike1950]

This is what I’m talking about; there seems to be a lot of conflicting information about what happens during steaming. I noticed this right away when I began researching articles online by wood workers. It seems like either the process is different, the experiences are different due to the kinds of wood being steamed or there is miscommunication about whether the wood is green or seasoned. Still not sure what to think about it!

Use green wood. dry wood does not warp green does because it is still malleable. simple test- take green 1x4 8' long put 10 lbs in center after spanning 2 sawhorses. do same with dry. come back in a month. I promise when you take weight off, the difference will be obvious. when you are trying to do something with wood it does not want to do, you want everything you can get on your side.
Now if you have dry wood, bent laminations is the way to go.

 

[Mike Hill]

Don't know much about steam bending except observation. There is a drum making company here that is unusual in that their drum bodies are of solid, dry wood. They cut to shape and thickness and put a scarf joint on the ends. Then put into a steam box and then bend into a full circle - intense. Every once in a while one cracks. I'm there occassionally buying their scrap - already dry, resawn, milled and sanded thin and sometimes purdy figure. I used to try to get their cracked pieces and they seemed usable - particularly some birdseye maple they had. Lil Mikey thought simple process of soaking the board and putting a heavy weight on it to straighten it. Wrong bucko! I eventually put a couple of anvils on it and it did not straighten! Whatever details they do, they do it right! Anybody needing any slightly curved birdseye maple?