Author Topic: steam bending  (Read 4034 times)

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Offline meanewood

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steam bending
« on: December 24, 2013, 03:21:04 am »
I need some advise on bending an Elm stave sideways in order to bring the centerline to midpoint at the handle!
I intend to steam bend it and need to bring it about 2 inches back.
My main uncertainty is, after steaming it, do I bring to center only when clamping it to a board or do I need to go further and it would then settle back?
I've not done this before but my instincts tell me to take it 2 inches past center and it should move back to the required line?

Offline WillS

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Re: steam bending
« Reply #1 on: December 24, 2013, 04:00:37 am »
Generally speaking you would bring it beyond the required line, to factor in some "spring back" but the amount depends on the wood and the length of heating time.

Bending a bow sideways is a nightmare, it's nothing like as easy as bending reflex/deflex/tips etc but with patience and a solid setup it's workable.  Check out Del's blog, he has some excellent steam setups that work in situ so you don't have to dance around holding a hot lump of wood to get it from steam to clamps and have it cool down too much.  With steam the key is speed - you have literally seconds before it cools down too much to work with. 

One thing I've found works well is to steam, then clamp, then hit the hot area with a heat gun for a bit to blast some extra heat onto it.  Minimises the risk of losing too much heat and the wood cracking under the clamp pressure. 

Make certain you need to do all this though, as a bow that wobbles in and out of center is fine, it's only if the tips and dead center don't line up together that you have to move the bow with heat.

Offline Del the cat

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    • Derek Hutchison Native Wood Self Bows
Re: steam bending
« Reply #2 on: December 24, 2013, 09:52:49 am »
There's a lot of wood in a warbow, so it will need a lot of time under the heat.
I'd suggest giving a lot of though as to where you try and get the movement.... spread over a whole limb? Just at the centre? Just at the tips?
I don't think there is ever only one correct answer.
I think for sideways bends the key is patience... allow plenty of time* for the heat to get in there. Get it clamped ASAP or ideally in situ while it's still being steamed.
YES! Allow for some spring back... don't worry if you allow too much and go to far.
If you bend it too far, give it a gentle warming and it will start to relax back (suitable jigging to stop it going all the way back) (other folk dances are also available ;) )
Del
* Think of a number and double it!
Health warning, these posts may contain traces of nut.

Offline toomanyknots

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Re: steam bending
« Reply #3 on: December 24, 2013, 10:19:02 am »
The only thing I will add, is that if you don't get it absolutely perfect with steaming, you can always manipulate the way it twists (if it does) by messing with the cross section / removing material from the stronger side of the bow that is twisting. I have had a couple bows that twisted pretty bad that I fixed by doing this, I just got a hang of doing this and I think it is a valuable trick for a bowyer to have. If there is a big amount of twist, then the bow might end up having almost a right angled triangle cross section though in the end, haha.
"The way of heaven is like the bending of a bow-
 the upper part is pressed down,
 the lower part is raised up,
 the part that has too much is reduced,
 the part that has too little is increased."

- Tao Te Ching, 77, A new translation by Victor H. Mair

Offline Yeomanbowman

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Re: steam bending
« Reply #4 on: December 31, 2013, 07:24:10 am »
Elm springs back a fair amount so I'd go for the amount to correct the stave + 30 to 50% extra.  However, dry heat will make it stay put pretty much as is.

Offline occupant

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Re: steam bending
« Reply #5 on: January 02, 2014, 10:14:38 am »
I've tried steaming and not had much luck, any bend put in would come out shortly. I have had very good results with dry heat, it will darken the wood though.

Offline meanewood

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Re: steam bending
« Reply #6 on: January 03, 2014, 12:45:34 am »
Thanks guys
I'll try heat bending then.

Offline bubby

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Re: steam bending
« Reply #7 on: January 06, 2014, 04:36:01 pm »
I use a electric floor heater, i'll put the stave in the vice with the heat at the belly, with the direction to bend facing down, after it has warmed up I hang a bucket on it with some rock in it measure the distance from the ground before you add the bucket, then you can adjust the weight in the bucket till it goes past where you want and keep an eye on it if it goes past where you want turn off the heat and leave it alone till it cools, just put enough weight in the bucket so that it starts to bend
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