steam bending & laminating 1" thk Spruce~

[Cliff Rohrabacher]

I need to get a round geometry about 2" thick by about 60" diameter with an opening in the center about 45" diameter.

I have two (outdoor dining) tables I'm planning (they'll be coated in epox or catalyzing urethane so they'll be weather proof).

The tables will be based on rounds of glass plate (1/2"-thk-*-46"-dia). The table geometries are "U" shaped so they can be used as stand alone separates or brought together to make a larger dining platform.

The diameters 46" for the glass and the wood surround of 60" dia' have circumferences of 144.51" and 188.49" respectively

I'm using conventional shaker type tapered legs: 4 each table. They are about 4.375" at the top where they'll join the tables.

The round geometry is proving to be a bit of a baffler.
I'm working with 1"thick * 6"wide * 8'long, long spruce boards. I am thinking that the best way to get the round shape to surround the glass AND provide a place wide enough to mount the legs is to:
1.) Rip the spruce into strips about 2.5" wide.

2.) apply to the the ends of the ripped strips some kind of joint pre-cut joints such as long slow tapered scarf or finger joints ('cause no board will do the circumference alone). - OR - joint 'em with a finger cutter bit after they are bent up?

3.) build a steam box & steam the ripped strips and clamp 'em in a frame to set and dry (end result a 2.5" thick laminate of 1" strips).

4.) then glue (epox) the ripped & steam-bent pieces up .

5.) figure out & build a router bridge to flatten the 60" dia' round glue up (I'm thinking that it'd be better to move the work and leave the router stationary).

I am guessing that this is the time to build that big Torsion box I have planned., Because I'll need a flat table for both the circle bending frame as well as the router bridge.

I'm a little concerned about the ends of all those strips. They will be a long running spiral when assembled and the ends need to integrate nicely.

I'm wondering if I should not build the bending frame to make all the strips conform to a circle slightly smaller than my end result to compensate for spring-back.

I have never used a steam box. My prior bending was all thin work on musical instruments bending freehand over a hot pipe. This'll be very different.

Any steam benders out there with thick wood experience? Got any advice tips info on drying time before glue up etc?

Any one have any ideas about the end joints for the bent pieces? Maybe I should joint 'em on the router table with a finger jointing bit (I'd have to buy one) after they are all bent up~??


Any ideas about this at all I'd like to read 'em.

Gracias

[Jamie Buxton]

I wouldn't go to the work of steam-bending that spruce. Instead I'd leave it straight and flat, and laminate it into the 2" thickness you need. The individual pieces of wood would have their grain direction running roughly tangential to the circle, and I'd bricklay it so that the end-to-end joints in one layer are not at the end-to-end joints in the next layer.

[Jim DeLaney]

I've never tried to bend spruce, but since it is/was used a lot in boat building, I'll assume it's fairly bendable. Air dried, or (better yet) green wood will bend better than kiln dried stuff.

For a 1" thick piece, you'll likely need some physical help - either in the form of strapping to support the outer perimeter, or else use a series of blocks and wedges along your form to coax the wood into place. An extra pair of hands - or two - will be of great help, too.

You'll have to work quickly, and have your forms absolutely ready to go prior to taking the wood out of the steamer, because you'll have less than a minute to get the bending done before the wood cools enough to be non-bendable.

As for joining the pieces - you'll have to do that after the bending. I can't imagine a scarf joint of finger joint that will hold up to the heat and steam, and not come apart during the bending process.

Have you thought about making the 'wheel' by gluing up segments into an octagon, or even a hexidecagon, with overlapping or splined joints, then using a router circle jig, or a bandsaw, to cut the circles? It might be easier, and will probably warp less than a bent circle, so you won't have as much flattening to do.

Good Luck, and have fun. It sounds like an interesting project.

[Cliff Rohrabacher]

I wouldn't go to the work of steam-bending that spruce. Instead I'd leave it straight and flat, and laminate it into the thickness you need. The individual pieces of wood would have their grain direction running roughly tangential to the circle, and I'd bricklay it so that the end-to-end joints in one layer are not at the end-to-end joints in the next layer.

Are you thinking about lots of pieces about 39" long by 4" (or so) wide fastened with lots and lots of glue and clamps (or glue and screws)~??

[Cliff Rohrabacher]

I've never tried to bend spruce, but since it is/was used a lot in boat building, I'll assume it's fairly bendable. Air dried, or (better yet) green wood will bend better than kiln dried stuff.

Yah this was bought wet soaking wet. It's pretty dry now and I've been using it for outdoor furniture made some Adirondack chairs here http://www.sawmillcreek.org/showthre...15190#poststop

For a 1" thick piece, you'll likely need some physical help - either in the form of strapping to support the outer perimeter, or else use a series of blocks and wedges along your form to coax the wood into place.

Yah huh? I won't have help I was thinking of using leverage, force, and tapered entry points to the forms. I have never steamed wood so this is all new turf for me.
I have seen pics of steam boxes. I wonder if a covering of that foam insulation board on the outside ( or inside) would be a good idea. I can get a huge cheap pot
from WALL MART and plumb some pipe to it

You'll have to work quickly, and have your forms absolutely ready to go prior to taking the wood out of the steamer, because you'll have less than a minute to get the bending done before the wood cools enough to be non-bendable.

Less than a minute. EEEK. I'm wondering if a full inch won't be too thick for the 48" diameter. I just have no information.

As for joining the pieces - you'll have to do that after the bending. I can't imagine a scarf joint of finger joint that will hold up to the heat and steam, and not come apart during the bending process.

Yah I was thinking of a finger joint bit or a scarf cut. the finger joint can be applied after the bend and a scarf can be hand cut in situ as I am in the glue up process. Since this'll be heavily coated with epox or catalyizing urethane I may as well not sweat the little gaps cause they'll be fillable.

[quote]Have you thought about making the 'wheel' by gluing up segments into an octagon, or even a hexidecagon, with overlapping or splined joints, then using a router circle jig, or a bandsaw, to cut the circles? [quote]

Yes. Somehow the idea of steaming and bending and gluing up appeals to me and I'm sort of convinced that it'll be way stronger (I could be on a fantasy flight here tho).

It might be easier, and will probably warp less than a bent circle, so you won't have as much flattening to do.

Tell me why you think a bent up, laminated, epoxied, glue up will warp. I was of the impression (subjective of course) that it wouldn't bend much at all.

[Jamie Buxton]

Are you thinking about lots of pieces about 39" long by 4" (or so) wide fastened with lots and lots of glue and clamps (or glue and screws)~??

Here's a drawing. I've made the glue-up an octogon, but it could be something else. For clarity, I've drawn the top layer separated from the bottom layer, but in the real thing they'd be together. Notice that the end-to-end joints in the top layer do not fall on the end-to-end joints on the bottom layer.

You can barely see the grain direction, but it runs tangential to the circles.

I'd laminate this thing up, with both layers, and then cut the inner and outer circles with a router jig.

[Robert Miller]

Any steam benders out there with thick wood experience? Got any advice tips info on drying time before glue up etc?

Any one have any ideas about the end joints for the bent pieces? Maybe I should joint 'em on the router table with a finger jointing bit (I'd have to buy one) after they are all bent up~??


Any ideas about this at all I'd like to read 'em.

Gracias

.........

I can help you with you this. I've built several boats and steam bent many planks.
First the rule of thumb is one hour in the steam box for every inch of thickness.
You need to get the temp. in the box to 212degrees. This is my steam box.


It uses a new 5 gal gas tank as boiler and a propane burner with radiator hose. You need to be sure to have enough water so that you do not run out for a solid hour. I use a meat thermometer in a hole in the top for temp.
There are dowels running through the sides of the box that act as racks to circulate steam evenly.
UNDER NO CIRCUMSTANCES ALLOW ANY STEM PRESSURE IN THE BOX

If you are bending a sharp curve presoak the wood for a few days. Steaming acts by softening the wood cells. You must have moisture to give up in the box or the wood may crack.
Make a form to hold the shape and leave it in the form for 24 hours to dry.
Remember that you will get some spring back so allow a little more shape in the form to allow for it. After its dry , release from the form. If you are using lamination's glue and reset in the form.
Here's a few pics of my steam box in use.
Let me know if you have any other questions.



Here is my boat I'm building from scratch.Using the steam box.

[Cliff Rohrabacher]

First the rule of thumb is one hour in the steam box for every inch of thickness.
You need to get the temp. in the box to 212degrees.

I have been googling around and there seems some good info out there. The time & temp you have is clearly the norm. I think the Gas Can may be the best way to go - it's big and already plumbed

What are you using for a conduit to the box? Radiator hose? PVC steel a combination?

Did you insulate the box? I'm thinking of a foam insulation. Won't seal it but then I'm not building a pressure vessel. I'll likely just nail it together and let it leak. Foam insulation seems like a good idea.

Nice couple of steam boxes you have there. I especially like the nautical theme on the second one ;-)


I have read a fair bit about bending with Ammonia both hot and cold seems to be possible depending on how it's done. I've read that an overnight soak in water and ammonia will make the wood very rubbery. I absolutely have to try this~!!

I have found comments like this about ammonia:
"Using steam and ammonia water we've been able to tie wooden strips into knots." {found on the AeroDrome forum}

Bruce Hoadley mentions ammonia it in his book.

There is a really good article in bending here:
http://www.tai-workshop.com/english/tech-2(b)-e.html
where the author mentions ammonia.

Some people think it's necessary to have anhydrous ammonia but others report using water and ammonia and even steam from a mixture with good results.

Make a form to hold the shape and leave it in the form for 24 hours to dry.

Thanks. I might have tried to pull it as soon as it was cool to the touch. With lots of pieces this process may take a few days.

Nice looking boat BTW. Mahogany?

[Cliff Rohrabacher]

First the rule of thumb is one hour in the steam box for every inch of thickness.
You need to get the temp. in the box to 212degrees.

I have been googling around and there seems some good info out there. The time & temp you have is clearly the norm. I think the Gas Can may be the best way to go - it's big and already plumbed

What are you using for a conduit to the box? Radiator hose? PVC steel a combination?

Did you insulate the box? I'm thinking of a foam insulation. Won't seal it but then I'm not building a pressure vessel. I'll likely just nail it together and let it leak. Foam insulation seems like a good idea.

Nice couple of steam boxes you have there. I especially like the nautical theme on the second one ;-)


I have read a fair bit about bending with Ammonia both hot and cold seems to be possible depending on how it's done. I've read that an overnight soak in water and ammonia will make the wood very rubbery. I absolutely have to try this~!!

I have found comments like this about ammonia:
"Using steam and ammonia water we've been able to tie wooden strips into knots." {found on the AeroDrome forum}

Bruce Hoadley mentions ammonia it in his book.

There is a really good article in bending here:
http://www.tai-workshop.com/english/tech-2(b)-e.html
where the author mentions ammonia.

Some people think it's necessary to have anhydrous ammonia but others report using water and ammonia and even steam from a mixture with good results.

At this site:http://www.allbusiness.com/furniture.../644819-5.html
I found this comment:

Back in 1964, scientists at the New York State College of Forestry at Syracuse discovered that ammonia would soften the matrix bonds in wood, with both anhydrous ammonia and compressed gaseous ammonia used in varying degrees of success. The scientists found that ammonia breaks down the hydrogen
bonds within cell walls and within the lignin matrix. This allows molecular movement when subjected to tensile or compressive forces. Once the ammonia evaporates from the wood, new bonds are made creating a permanent set; in simple terms, this can be considered similar to the process of adding a permanent wave to hair.
The process is reversible by further ammonia treatment. Chemical set is not recoverable by treating with hot water or steam; unlike with steam and hot water bending treatments, no stresses or strains are bent into the wood. Thus, the new shape is like other kiln or air dried wood. It is ready to be machined, glued and finished.
Several experiments with ammonia have shown that wood, especially hardwoods, can be used to make numerous unique furniture designs. It has also been used to help disintegrate wood in the manufacture of hardwood panels and chipboards. The process may also clear the way for better utilization of raw materials and new, economical designs.
Experiments with Anhydrous Ammonia
Several experiments with anhydrous ammonia in pressurized vessels have been highly successful. Pressure vessels are used because the anhydrous ammonia vaporizes and dissipates at atmospheric pressures and temperatures above -28F.

Make a form to hold the shape and leave it in the form for 24 hours to dry.

Thanks. I might have tried to pull it as soon as it was cool to the touch. With lots of pieces this process may take a few days.

Nice looking boat BTW. Mahogany?

[Robert Miller]

Thanks, the boat is all Honduras mahogany.

The gas can is connected by a radiator hose. You can do this on a smaller scale by using a electric coffee/tea pot for a steam source.
You can make a good steam box with one sheet of foil covered insulation from the big box store. Score the sheet and bend it into a box and use duck tape to seal the corners. Just plug the ends with a scrap.
You can also use a piece of 6 inch pvc pipe.
ONCE AGAIN, NO PRESSURE!!!!!

My box is just plywood ,but i use it a lot.

[Cliff Rohrabacher]

My box is just plywood ,but i use it a lot.

And the adhesive doesn't come unglued from the heat and moisture~?? Oh my~!!

[Cliff Rohrabacher]

Here's a drawing. I've made the glue-up an octogon, but it could be something else.

Thanks Jamie. I may end up with a flat stock work up. I'm limited to a fixed board width of about 5" but that only means more pieces.

I haven't abandoned my idea of bending. In fact I'm rather enamored of the idea but the over all level of effort I'll have to invest may drive me in another direction.

[Jim DeLaney]

...Tell me why you think a bent up, laminated, epoxied, glue up will warp. I was of the impression (subjective of course) that it wouldn't bend much at all.

What I meant was that the original bent circle might well warp and require quite a bit of flattening before finishing. Once it's completely dried from the steaming, and is sealed and finished, it shouldn't warp much - just the usual movement from moisture variation, etc.