Taking bow out of a piece of beech

[Why Not Indeed]

I have a piece of beech 2000mm*250mm. Pretty sure it was the window board in the kitchen when the house was built in the '60s.
I would like to use it as a shelf but it's got a fairly serious bow on it - clamp down one end, the other sticks up about 40mm.
I have tried screwing some twin-slot rails to it, this gets the bow down to a mere 15mm but then the whole thing weighs about 10kg.
Are there any tricks to taking the bow out? It's not a simple curve, it's more pronounced at one end.

 

[big-all]

is this a wall mounted shelve ??
and are you planning on intermediate mid to front off shelve support??
always plan bow up so load is your friend

 

[Odds]

Steam it.

 

[Why Not Indeed]

is this a wall mounted shelve ??
and are you planning on intermediate mid to front off shelve support??
always plan bow up so load is your friend

It's going above a door, so brackets at one end and in the middle, and then the other end is butted against a wall, so sitting on a batten fixed in to the wall.
The rebate is on the bow side, so makes sense to go bow side up anyway.

 

[Why Not Indeed]

Steam it.

How?
Steam iron?
I was wondering if misting it with water, letting it soak in then drying it with a hot air gun would count as "steaming".

 

[Odds]

 

[big-all]

i would wet it and overspring it the other way about half the amount
as in assuming the high point is around 20mm flip it and place a bit off timber between 8 to 12mm under the high spot and clamp the ends to the bench
having said that as its old wood you may just be stuck with what you have
also deviations above a door are very unlikely to visually be a problem

 

[Scally-Ho]

If you don't want to build yourself a steaming tunnel, then use kettles of boiling water and then clamp both ends with something in the middle to oppose the bow. Nothing too pronounced, just enough to flex it against the bowed direction. I've bent boat soft chines by this method. and successful each time.

 

[foxhole]

Made a cherry wood window board , it was orinally twisted and warped. Laid on a tarpaulin in the garden with timber underneath around the edges to form shallow pond and flooded with water, left it two weeks ( topping up water to keep it soaking) removed at two weeks and was completely flat again , clamped some 2x4 diagonally to it and let it dry 4 days in sun .
Perfectly flat .