Thread: hmmmm, pallet timber WON"T steam bend?

Steam bending is normally used to form material around gentle curves. Your form looks to be fairly sharp at the bend point and I doubt that anything would bend around it happily, including 3mm laminations. Also you need a lot more clamp points set into the form. The normal approach is to drill a row of holes that can accept the fixed head of clamps around 120 to 150mm back from the face of the form, and separated by about 150mm. The work is then steamed, and quickly clamped at one end of the form, then fed around the form in the shoe, with clamps applied progressively as the timber contacts the form, then finally pulled up tight. By having a lot of clamp points drilled into the form, it is easy to set each clamp to pull at a tangent to the form at the point where the clamp is located, eliminating the tendency for the clamps to slide and loosen. In your first pic, the clamp nearest the camera would tend to slide along the back of the form as you tightened it, making for fairly ineffectual clamping.

Some pallet timber has also been heat treated, which might further interfere with the ability to bend it.

I think you've hit the nail on the head MS. I will give it one more go with the proper steel straps but it felt like the lignum had already been set by age or, more likely, kiln drying?

Thanks too Malb, the clamps you noted were only added as a last minute (desperate?) gesture when the polyester straps didn't pull it around the former as it normally does. Also, the "CRACK" when it broke was the sound of dry, brittle timber not timber that had been in the steam box for 3 hours!

fletty

The heat treatment is not like kiln drying...it takes it to a much higher temperature...200 degrees or so -

http://en.wikipedia.org/wiki/Thermally_modified_wood

A bit of searching before I built this box came up with info on bending timber. Best to worst was - green, air dried, kiln dried with heat treated just about a no no.
The mahogany veneer I uses was kiln dried, only 1/16" thick but still didn't want to go round the curves even after 2 hrs in the steam box.

Mark

It could also be that some timbers are not suitable for bending. Bootle's book lists good bending timbers in the description of properties. The difficulty with pallets is that almost any timber can be used so identification is a problem.

Regards
Paul

Originally Posted by Master Splinter

The heat treatment is not like kiln drying...it takes it to a much higher temperature...200 degrees or so -

http://en.wikipedia.org/wiki/Thermally_modified_wood

Thanks for that link MS, it explains a lot. I chose the pallet because it looked like it was made of some beautiful, dark hardwood BUT I now believe it is 'thermally treated' something-or-other and is now well beyond bendable!

Originally Posted by Old-Biker-UK

A bit of searching before I built this box came up with info on bending timber. Best to worst was - green, air dried, kiln dried with heat treated just about a no no.
The mahogany veneer I uses was kiln dried, only 1/16" thick but still didn't want to go round the curves even after 2 hrs in the steam box.

Mark

Mark,
I LOVE that box, or is it a chest? It looks like a shaker box with punk and attitude! I did a lot of research on timber bendability in the thread below .....
https://www.woodworkforums.com/showth...t=fletty+chair
...but I hadn't come across the effect of thermal treatment before. Normally I can steam bend green timber easily with just the polyester strap clamp but yesterday's encounter with thermally treated timber (and medieval police ) has confirmed your comment about a bendability no-no. It didn't even make a decent crossbow ... strong enough but too brittle!

Originally Posted by Bushmiller

It could also be that some timbers are not suitable for bending. Bootle's book lists good bending timbers in the description of properties. The difficulty with pallets is that almost any timber can be used so identification is a problem.

Regards
Paul

Hi Paul,
In the chair thread above, I even found that timber from different parts of the same tree bent differently? I had, on one hand, a book extolling the bendability of Australian red cedar and, on the other hand, a bin full of snapped Australian red cedar chair slats!
Rather than waste another 4 hours like yesterday (2 hours to get the boiler up to temp and 2 hours of steaming), I think I'll finally get a moisture meter and put some science rather than hope into it?

PS, congratulations on the article, you look EVEN younger!

fletty

I bet you didn't soak it ........and I don't mean pouring Red into you, try give back some moisture before steaming

Crossbow looks good little ruff but it'll impove

Green timber makes the best ballistae arms anyway.

..alright, alright ...it WAS me that gave the cops your address!

fletty

Ray - my mahogany strips had a week in a rain barrel before steaming but still didn't want to bend.
I've found a nice piece of fresh cut ash for the next try.

BTW a crossbow is on my to-do list, but with a steel bow. I could forge the ends but would need to find a blacksmith willing & able to temper it for me!
Either that or I could shape one out of an old leaf spring with my trusty angle grinder trying not to lose either the steel or my temper in the process....

Mark

Water in wood is in two places:
a) "free water" in the empty volumes of the wood fiber cells
b) "bound water" which is a part of the structural matrix of cellulose, lignins and pectic substances on the wood cells walls.

"air-dried" under cover to a constant weight, the residual water (MC approx 12 - 14%) is the bound water. The principle of a steam box is to use hot water vapor as the energy
transfer to get the bound water (and free water, if present) to heat up. This in turn heats the pectic substances which are not fiberous. Instead, they behave like waxes and plastics which soften with heat. NOW, you do the bend.

I can think of several reasons why your steam-bending effort was so disappointing:
1. Some of the air dried MC was cooked out in a kiln ( rare to suppose it can be replaced.)
2. Whatever species the pallet wood was, the hardwood fiber was of such a short length that the bends passed the bursting strength.
You can't compare what you did to the ease with which conifer wood can be bent >90 degrees. Great fiber length.
Plus, when you look at the magnificent bent-wood boxes of the Haida people, the actual bent wood layer in the corner is about 3mm thick.
3. Despite the dimensions, the wood was not hot/wet steamed for long enough.
4. The wood was not face-sawn to ease the bend. Radially cut or quarter-sawn woods, even conifers, are wicked to try to bend.
Pallet woods are cut, even here, to maximize the yield from the saw log. Certainly not with any artistry in mind!

I'm not the sort of person that gives up and so my bending rig is getting more and more 'complex' ...Heath Robinson has nothing on me?

image.jpg

I fired up up the boiler this morning and went for a run (city to surf is in 8 weeks ), roughly cut a piece of hairy oak that I know has only been air dried and put it in the yum cha steamer after it got up to temperature.....
"you haven't forgotten that we are going out today?"
"no, of course not but I have forgotten the details ......."
"oh yes, that's right, of course I'll be ready in an hour............"
shave...
shower.....
dressed....
steam bend......
out......
and, when I got home.....

image.jpg

OK, the obvious issues are that this isn't a random piece of pallet timber AND it is supposed to be a 'U' not a 'J' but it IS progress!

fletty

I like the new toy Fletty can we have more info please? That digital gauge thingy looks like some smick trammel.