Bending wood in steam

[Tom Dulaney]

The bog-'standard method of bending wood is to put itnin a steam environment for a few minutes, remove it, place it on a jig, and then bend.

But could you reduce the risk of a delamination by creating a jig that allowed you to bend the wood with steam or vapor actively hitting it?

Wood seems to cool down rapidly upon being removed from a steam container/submersion. Every little degree counts when you're doing an extreme bend, as in the Scythian bow tips. Even when you get it on to the jig quickly, delamination can happen.

Has anyone ever used such a device?

[JNystrom]

I've seen here some thick plastic/fibre bags that people have used. They have used them while bending too. I would be interested also about this. I've soaked the wood in water for days, then used a heatbox and veritas strap.

[bownarra]

Green wood of the correct species will bend into any shape you need. For sharp tips bends I prefer to use naturally bent pieces. Another way is to bend two thinner sections and then laminate.
I soak for a day or so (if green) then boil under water, 45mins per 1/2" thickness then straight onto the form. When I do this correctly there are no problems now but it took a lot of practise!

[DC]

 If you are properly set up with everything ready and nothing goes wrong normal steaming works almost as well as steaming in a plastic bag. The bag has the advantage of you being able to continue steaming after it's bent, I think that helps a bit. That said I find that the plastic bags are very slippery and can make clamping difficult.

[JNystrom]

bownarra: Problem with that is finding the green wood when you need it. For me it was much much easier to get a stockpile of fresh maple that i will be using for some time still to the future. In a perfect world, yes, use fresh wood and everything is easy.

[bownarra]

bownarra: Problem with that is finding the green wood when you need it. For me it was much much easier to get a stockpile of fresh maple that i will be using for some time still to the future. In a perfect world, yes, use fresh wood and everything is easy.

As I said OR use thin pieces laminated together OR use pregrown pieces.....
When making hornbows its a good idea to try and make everything 'perfect'. The house of cards starts getting unstable overwise.....

[gorazd]

 .... I did the turkish hornbow with laminated siyahs. Glued 4mm laths from black locust together
I prebend the laths with dry heat in form then glued them (in form )with hide glue.

bownarra: Problem with that is finding the green wood when you need it. For me it was much much easier to get a stockpile of fresh maple that i will be using for some time still to the future. In a perfect world, yes, use fresh wood and everything is easy.

As I said OR use thin pieces laminated together OR use pregrown pieces.....
When making hornbows its a good idea to try and make everything 'perfect'. The house of cards starts getting unstable overwise.....

[Tom Dulaney]

Of course, the typical steam bending method works most of the time (with some practice).
But what really happens to wood that has been bent to an extreme curvature? Even if it didn't crack or delaminate, I have to imagine that cellular damage is occurring.
Could a steamed bend mitigate some of it?

[bownarra]

Heat weakens wood (IMHO  ).
So you should use the minimum amount of heat necessary to do the bend.
Boiling under water is more effective than steam for heat transfer IMHO.

[JNystrom]

Heat weakens wood.
So you should use the minimum amount of heat necessary to do the bend.

Can you provide proof for this? At what amount are we speaking of? 20min, 40min, 60min?

I disagree that there is any harm done within 0-60minutes of heating wood (steaming, boiling). Many people state heat weakens wood, but they never provide scientific proof for it.

[High-Desert]

I’ve used the plastic tube method many times for doing extremely difficult small circle forms that can take awhile to form and clamp down and cool too fast with the normal method of steaming. I just used the vacuum packing bags that come in a giant long tube. I tape the end to my steam tube and close the end up a bit and you can put in in your form and take your time. I do prefer the regular steaming method for recurves and other mild bend as the plastic can be a pain, but it does buy you time.

[PatM]

The second BB described heating while already in the form.

 Wood bends by being compressed on the inside of the curve, not stretched on the outside.