Hot water bath for bending wood

[cynff]

I would like to bend a long (about 3m) piece of wood to make a frame drum (see my original post). I have some kiln dried Ash wood planks for this purpose. I have seen on the video that Ray Mears did of Pinock Smith's birch bark canoe building, that it is possible to bend wood with a large pan of water heated over a fire. The wood is placed vertically in the hot water and a ladle is used to pour the hot water over the wood. I think Pinock was using green wood. Does anyone know if this method would work with kiln dried wood?

I have heard of placing the whole piece of wood in a hot bath, and steam using steam. However, for the size of wood that I have I'm thinking try the simplest approach first.

 

[nigelp]

Could you use a length of waste water pipe partially, or fully blocked at one end with a rag. Then pour boiling water down the tube to soak, or bath the wood?

 

[Broch]

I use down-piping, with a restricted but not sealed end, and feed it with teh steam from a paint stripper steamer.

 

[cynff]

I use down-piping, with a restricted but not sealed end, and feed it with teh steam from a paint stripper steamer.

That's a great idea thanks. could you clarify what you mean by a 'restricted but not sealed end' please.

Do you mean the pipe that is connected to gutters to drain rain water, or household waste water pipe?

 

[cynff]

Could you use a length of waste water pipe partially, or fully blocked at one end with a rag. Then pour boiling water down the tube to soak, or bath the wood?

i don't know how I would keep the water hot with a plastic waste water pipe.

 

[Broch]

That's a great idea thanks. could you clarify what you mean by a 'restricted but not sealed end' please.

Do you mean the pipe that is connected to gutters to drain rain water, or household waste water pipe?

Drain pipe - or whatever plastic pipe will accommodate the size lath you're steaming. You can buy it in 2.4m and 3.6m lengths from builders merchants.

You don't want an open end that lets the steam out too quickly but at the same time you want the steam to flow through the pipe (I actually run it laying on the floor). I made a nozzle from a plastic bottle for the inlet and similar for the outlet - so reduce the wide pipe diameter down to a couple of cms.

 

[Toddy]

I have to ask....why 3m ? because that's a heck of a circle size.

I watched folks make bodhrans and the wood they bent was less than a metre and a half in length....and that was cut down in the scarf to make the rims. Even plied up why do the full length at 3Metres ?

 

[HillBill]

Thats not quite how steam bending works. You first need a form (in this case a 3m circumference circle) made of a suitable material. Then you need to steam the whole thing you want to bend (soaking in hot water is not steaming). This takes several hours. Then you need to form the steamed wood around your form. Clamp in place bit by bit, whilst still steaming it, and leave until dry. Perhaps several weeks. depending on various factors. For a single item... not economically viable, but if just for a hobby or you REALLY want to do it... crack on. Starting with a kiln dried plank is problematic, due to grain orientation and dryness. You're not gonna get a plank that follows the grain for 3 metres. You need a good young tree/sapling, split and form while green, following the grain.. (similar to making a bow)... Its not a hard thing to do, if you know how to do it. If you dont... best of luck.

 

[Broch]

That's a 1m diameter bodhran - huge! 45cm would be a sensible size so less than 1.5m length.

 

[Dave Budd]

As said above, hot water is not steaming and won't work as well. You need the whole plank to be of a uniform moisture level for it to bend uniformly. The amount of time that the wood needs to be in steam depends on species, starting RH and most of all thickness of board: the steam has to penetrate the wood fully.

Kiln dried planks of ash will bend ok, but with the caveat that wherever the grain has been truncated it can split out. That said, if you bend the wood with the end of the truncation on the inside of the bend and the board is a bit thicker than necessary, then you'll often be fine. Most people that use ash boards are going to have to use sawn not riven wood and I know a number of folks that make the central rings inside yurts in exactly this way (from sawn ash boards). I'm assuming that the 3m is wrong, unless it is a yurt ring sized drum?

I've used drain pipe as a steaming tube, but it didn't work twice on account of the pipe softening below 100C. I ended up with a droopy pipe hanging over my bit of wood! Soil pipe is a bit better as it's thicker. Double walled soil pipe (the sort with a corrugated outer layer) best and what I use (wrapping lagging around it helps to insulate, but not necessary really. Basket makers often use heavy duty plastic sheets to steam willow in, so you could try that if no pipe is available. https://www.musgrovewillows.co.uk/w...zNjk4ODIkbzEkZzEkdDE3NjczNjk5MDMkajM5JGwwJGgw Even a long plastic bag (like Musgrove's sell for soaking willow in) would work and I've seen ship builders steaming planks using this method.

I use my kelly kettle as a steamer, but most people use a wallpaper stripper.

How long to steam, how far you can bend, how fast you can bend, how long you've got until it stiffens, how long to leave clamped, etc are all down to experimentation though

 

[cynff]

As said above, hot water is not steaming and won't work as well. You need the whole plank to be of a uniform moisture level for it to bend uniformly. The amount of time that the wood needs to be in steam depends on species, starting RH and most of all thickness of board: the steam has to penetrate the wood fully.

Kiln dried planks of ash will bend ok, but with the caveat that wherever the grain has been truncated it can split out. That said, if you bend the wood with the end of the truncation on the inside of the bend and the board is a bit thicker than necessary, then you'll often be fine. Most people that use ash boards are going to have to use sawn not riven wood and I know a number of folks that make the central rings inside yurts in exactly this way (from sawn ash boards). I'm assuming that the 3m is wrong, unless it is a yurt ring sized drum?

I've used drain pipe as a steaming tube, but it didn't work twice on account of the pipe softening below 100C. I ended up with a droopy pipe hanging over my bit of wood! Soil pipe is a bit better as it's thicker. Double walled soil pipe (the sort with a corrugated outer layer) best and what I use (wrapping lagging around it helps to insulate, but not necessary really. Basket makers often use heavy duty plastic sheets to steam willow in, so you could try that if no pipe is available. https://www.musgrovewillows.co.uk/w...zNjk4ODIkbzEkZzEkdDE3NjczNjk5MDMkajM5JGwwJGgw Even a long plastic bag (like Musgrove's sell for soaking willow in) would work and I've seen ship builders steaming planks using this method.

I use my kelly kettle as a steamer, but most people use a wallpaper stripper.

How long to steam, how far you can bend, how fast you can bend, how long you've got until it stiffens, how long to leave clamped, etc are all down to experimentation though

Thanks @Dave Budd for the detailed reply.

I have a couple of questions:
What does "starting RH" mean?

When you say "wherever the grain has been truncated", do you mean where the board has been cut across the grain?

 

[cynff]

That's a 1m diameter bodhran - huge! 45cm would be a sensible size so less than 1.5m length.

Ah yes, there is quite a lot of overlap to join the two ends of tge frame together. That figure was a bit of a guess. it's a project I keep coming back to every few weeks.

 

[HillBill]

Thanks @Dave Budd for the detailed reply.

I have a couple of questions:
What does "starting RH" mean?

When you say "wherever the grain has been truncated", do you mean where the board has been cut across the grain?

I read it as Relative Humidity. (moisture content both in, and around the wood) Could be wrong though.

And yes, where the grain has been 'Cut through'

 

[HillBill]

Ah yes, there is quite a lot of overlap to join the two ends of tge frame together. That figure was a bit of a guess. it's a project I keep coming back to every few weeks.

a 3m straight piece will give 0.955m of diameter...(end to end) How big (diameter) of a drum are you intending to make?

 

[Dave Budd]

Yes, RH is shorthand for relative humidity, moisture content, or the amount of water in the material. Moisture meters used to check how wet a piece of timber is measure the % not a quantity of water, so the humidity is therefore relative to the outside

Also, yes truncated means cut through.

 

[Falstaff]

Kiln dried is a rather general description that can cover a wide range of moisture content- I've seen it at zero -( unbeliveable, didn't think that was possible), and now wood-stove fuel is sold at 20% and called kiln dried. Construction CSL specifies and is sold as being somwhere in the region of 8% (I've forgotton the figure).
I've seen low content "kiln dried" wood left somewhere damp /outside and it's % go up beyond 20%.
Question for maybe Mr Budd - if the OP soaks his store "kiln dried" in say, a water-filled drain pipe, for long enough to refill the wood's internal capilliaries, might that make it easier for him to then steam and bend?

Flexible stainless steel chimney liner is not expensive for a 3-4m length and can take the heat, and has a natural ability to bend - if laid flat then the desired bend can be slowly obtained by either a "bow-string cord" (Not easy, high safety risk issue) or better by pegging it out on the ground and moving the pegs in as it bends.
It can be wrapped in insulation if need be, or possibly laid in a long fire, moving the coals as it bends, as for making a large carriage wheel hoop (see, Victorian Farm tv series for live example of that.)

 

[demographic]

Last place I saw steam bending used metal duct pipes with plywood end caps and a wallpaper stripper to provide the stea..
That was to bend the gunwhales for boats.
They steamed it and got a shift on to bend it round a form in one go before the lignin hardened up.

 

[demographic]

Some bumf from Lee Valley tools about some of the techniques.
Clicky here.

 

[Dave Budd]

If I remember rightly, kiln drying effects how the cells absorb moisture as well as the initial drying. So kiln dried wood will rehydrate to any moisture levels, but I think it's more easily dried out again than air dried wood that has rehydrated to the same level. 'Kiln dried' is taking the moisture content extremely low before it then settles at whatever it needs to be for the job (firewood, construction, pre-treatment for other treatments, etc). I forget the actual temperature required, but it is hotter than I thought and certainly hotter than air drying temperature!

The idea of soaking it before steaming would certainly speed up the steaming process, but I don't know whether it would be by a lot given the planks are going to be quite thin (unless the drum is made from 50mm thick timber!).

I don't think bending the wood inside a flexible steamer would work. The wood wants to dry out in the bent shape and I suspect the steamer would keep it damp for too long.

Anything is worth experimenting with though . Don't just read, get some wood and try some things