On Jun 26, 10:40 am, Todd wrote:
On Jun 25, 10:03 am, wrote:

On Jun 25, 10:36 am, Todd wrote:

A piece of 1" red oak can be bent to radius of 1" if supported by a
metal strap and 11.5" unsupported according to "wood Bending Handbook"
published by Woodcraft Supply.

I think you meant that one inch oak can be bent to a radius of one
foot! I am sure most caught that though.

Nope, the book says 1" or 25 millimeters. Unsupported it's 11.5
inches. (My experience is that a radius of 1 foot is achievable with
out the metal strap support.) I'll grant you that it seems impossible
and I'm looking for another source in my office but I can't put my
hands on it just now. I know that Thonet did some very impressive
bending in the chairs he made. The book states that these are the
results of tests done on air-dried steamed material 1 inch (25.4 mm)
thick. Part of the "support" they refer to is that the work piece is
attached to a metal strap on the outer surface that is clamped to the
work piece by applying clamping pressure on the ends of the pieces,
i.e. the clamp faces are pressing on the end grain face of each end,
this is critical for this kind of bending. It is not just having a
"backing" strap. Clamping pressure must be applied to the end grain
faces as the piece is bent.

Sounds like some pretty serious control of several aspects of the
process would be necessary. Don't think I could get better than one
foot radius with much consistancy on 1 inch thick oak with the setup I
have.

snip---

Sounds like some pretty serious control of several aspects of the
process would be necessary. Don't think I could get better than one
foot radius with much consistancy on 1 inch thick oak with the setup I
have.


I can imagine a 12" Radius or possibly bending to a 24" dia.

Based on my test...I can not imagine a 1" radius though I read the
same in my research. Anyone have hands on?

thanks
marshall

wrote:
On Jun 25, 10:36 am, Todd wrote:
A piece of 1" red oak can be bent to radius of 1" if supported by a
metal strap and 11.5" unsupported according to "wood Bending Handbook"
published by Woodcraft Supply.

I think you meant that one inch oak can be bent to a radius of one
foot! I am sure most caught that though.

No the original post is correct.

That sounds about right to me as long
as the strap is fixed at both ends so that the neutral axis is pushed
to the outer radius. Also, remember that it is primarily the heat that
plasticizes wood and that you do not gain any additional softening by
heating the wood beyond the boiling point of water.

Exactly, if you heat it to much it either crushes, or tears. Like I
said, a general rule is 15 min/quarter inch of thickness.

Nope. If you get it too WET, it will crush and/or tear. If you heat it
too much, it drives off the moisture in the wood and it becomes brittle.
The typical failure mode it a sharp break.

Luthiers use dry
heat as did barrel makers. I have never had very good results from
simply getting the work piece wet, it must get hot.

The whole point of using steam is that it heats the wood quickly and
evenly to a consistent temperature, the boiling point of water
(100C/212F). The moisture helps to carry and transfer heat more
efficiently than dry air does.

If you need to do further testing for your application before building
a steam box you can try boiling the piece of wood or wrapping the
section that you need to bend in rags and pour lots and lots of
boiling water over the rags.

A note. Once wood has been steamed once, the cells will not soften
again with heat.

Not exactly. As long as it has been steamed, it can be re-steamed. If
you heat it any higher, such as is done during kiln drying, it alters
the lignin in the wood and make bending it more difficult. However, I've
seen good bending results with kiln-dried oak that was subsequently
steamed, but you can't achieve as small a bend radius with it.

Also, when you remove the part from the steam, you
have literally seconds, maybe 7-10 to get the part bent or it will
cool and lose it's ability to bend, it will most likely crack.

This is a common myth that is pure bunk. It takes ~1 hour to heat 1"
thick wood sufficiently in a steam box, so there's no way that it can
cool enough in a few seconds to make any difference in how it bends. In
fact, one of the biggest causes for failures/breakage during steam
bending is rushing it. It takes a little time for the fibers in the wood
to slip and the thicker the wood, the more time it takes. Bending
should be done smoothly, deliberately and as quickly as the wood will
allow, but you have a LOT more than a few seconds to bend it.

On Jun 28, 10:27 am, Brian Nystrom wrote:
wrote:
On Jun 25, 10:36 am, Todd wrote:
A piece of 1" red oak can be bent to radius of 1" if supported by a
metal strap and 11.5" unsupported according to "wood Bending Handbook"
published by Woodcraft Supply.

I think you meant that one inch oak can be bent to a radius of one
foot! I am sure most caught that though.

No the original post is correct.

That sounds about right to me as long
as the strap is fixed at both ends so that the neutral axis is pushed
to the outer radius. Also, remember that it is primarily the heat that
plasticizes wood and that you do not gain any additional softening by
heating the wood beyond the boiling point of water.

Exactly, if you heat it to much it either crushes, or tears. Like I
said, a general rule is 15 min/quarter inch of thickness.

Nope. If you get it too WET, it will crush and/or tear. If you heat it
too much, it drives off the moisture in the wood and it becomes brittle.
The typical failure mode it a sharp break.

Luthiers use dry
heat as did barrel makers. I have never had very good results from
simply getting the work piece wet, it must get hot.

The whole point of using steam is that it heats the wood quickly and
evenly to a consistent temperature, the boiling point of water
(100C/212F). The moisture helps to carry and transfer heat more
efficiently than dry air does.

If you need to do further testing for your application before building
a steam box you can try boiling the piece of wood or wrapping the
section that you need to bend in rags and pour lots and lots of
boiling water over the rags.

A note. Once wood has been steamed once, the cells will not soften
again with heat.

Not exactly. As long as it has been steamed, it can be re-steamed. If
you heat it any higher, such as is done during kiln drying, it alters
the lignin in the wood and make bending it more difficult. However, I've
seen good bending results with kiln-dried oak that was subsequently
steamed, but you can't achieve as small a bend radius with it.

Also, when you remove the part from the steam, you
have literally seconds, maybe 7-10 to get the part bent or it will
cool and lose it's ability to bend, it will most likely crack.

This is a common myth that is pure bunk. It takes ~1 hour to heat 1"
thick wood sufficiently in a steam box, so there's no way that it can
cool enough in a few seconds to make any difference in how it bends. In
fact, one of the biggest causes for failures/breakage during steam
bending is rushing it. It takes a little time for the fibers in the wood
to slip and the thicker the wood, the more time it takes. Bending
should be done smoothly, deliberately and as quickly as the wood will
allow, but you have a LOT more than a few seconds to bend it.

Now I will disagree with you. I have several steam boxes and have
steamed a lot of oak and other lumber... But I will let the OP make
the call. Nice to see you again Brian.

On Sun, 24 Jun 2007 02:19:52 GMT, Brian Nystrom
wrote:

wrote:
....
A good alternative steam source is a Wagner Wallpaper Steamer. They're
~$50 and produce enough steam to run a decent sized box, at least big
enough for the stock the poster is asking about.


Talking of alternatives - nobody mentioned the cold water method in
tihs incarnation of the wood bending thread - which is reputed to turn
planks to spaghetti:
add ammonia - soak overnight.

Disclaimers:
1) not tried it.
2) may take some of the beef out of the wood.

Brian Whatcott Altus OK

Brian Whatcott wrote:

On Sun, 24 Jun 2007 02:19:52 GMT, Brian Nystrom
wrote:


wrote:

...

A good alternative steam source is a Wagner Wallpaper Steamer. They're
~$50 and produce enough steam to run a decent sized box, at least big
enough for the stock the poster is asking about.



Talking of alternatives - nobody mentioned the cold water method in
tihs incarnation of the wood bending thread - which is reputed to turn
planks to spaghetti:
add ammonia - soak overnight.

Disclaimers:
1) not tried it.
2) may take some of the beef out of the wood.

Brian Whatcott Altus OK

They do not recover full strength after ammonia...

cavelamb himself wrote:
Brian Whatcott wrote:

On Sun, 24 Jun 2007 02:19:52 GMT, Brian Nystrom
wrote:


wrote:

...

A good alternative steam source is a Wagner Wallpaper Steamer.
They're ~$50 and produce enough steam to run a decent sized box, at
least big enough for the stock the poster is asking about.



Talking of alternatives - nobody mentioned the cold water method in
tihs incarnation of the wood bending thread - which is reputed to turn
planks to spaghetti:
add ammonia - soak overnight.

Disclaimers:
1) not tried it.
2) may take some of the beef out of the wood.

Brian Whatcott Altus OK

They do not recover full strength after ammonia...

And it's noxious to work with. No thanks.