Bending Plywood Questions

[BillPappas]

I need some help. I am designing my home office furniture (desk) and want it to have some curves. So I am considering laminating together 5 pieces of 3/8 inch bending plywood to serve as the legs. The legs will be about 2 inches thick and almost as wide as the desk top so they will be fairly substantial in size. I have never used bending plywood before so I have a couple of questions I thought someone might be able to help me with. A crude drawing is attached...

1. What kind of a radius might I be able to achieve with 5 pieces of bending plywood.

2. Should I try and laminate them all at once in the vacuum bag or laminate 2 pieces, then the 3 and finally put the 2 lamminated pieces together?

3. How strong or maybe better said how much weight would the laminated leg support when the force is applied from top which is shown in the attached picture as "Force - High". The top of the desk would sit on the laminated legs so it will have some weight to it and then all the stuff that goes on the top of the desk like a monitor, keyboard, etc.



Any thoughts or ideas are appreciated.

Regards,

Bill

[Tarhead]

Good info and formula on kerf cutting here:
http://www.tai-workshop.com/english/tech-2(b)-e.html

[gordonmt]

I did some bending wood project in my past but I have never used plywood as the bending medium. I have always used solid wood and without a steamer rack or other more specific equipment, I needed to rip my peices down to about 1/8 inch or maybe a little wider.
I soaked the wood in water for several hours (overnight) then I clamped the wet pieces into the shape I wanted and let them dry. After drying, remove from the shape clamp and then glue together and put them back into the shape clamp.

The end product is extreamely strong and has virtually not spring back tendancy. Once shaped and glued, it's done.
Here is a picture of the result of bending wood.

[rbdoby]

Bill,

I haven't much experience bending wood and I haven't tried bending ply but here's my thoughts.

A 10" or 12" radius would be as tight as I would go with 3/8" bending ply. I you want a smaller radius you may have to use thinner bending ply.

I'm guessing that your legs will be about 24" wide. I would do the glue up in stages like you stated. 2, then 1, then 2. Takes longer but uses a lot less force bending 2 sheets of ply than 5.

Seeing that the finished leg will be 2" thick I wouldn't worry too much about the weight of the stuff that you will put on our desk. 250 lbs. at most? Wood will move with changes in humidity but it should be negligible.

Rick Doby

[Badabing]

Bill, can't help much with your questions but I thought I'd offer another idea: Why not use some hardwood to create a skeleton in the shape you want and then cover it with bending ply? Then you would get the curves you like without having to laminate anything and the hardwood skeleton would give you the strength needed.

		Just a thought.

BTW, Mark your plant stand and coat rack are awesome!

[gordonmt]

Thanks Joe, It was a fun project to do.

[BillPappas]

Originally Posted by Tarhead

Good info and formula on kerf cutting here:
http://www.tai-workshop.com/english/tech-2(b)-e.html

Great article - Thanks

As always some great advice from many of you for me to think about. Heating is out as the pieces are to big....I need to remember that heating can assist in the bending process. The one idea on building a frame has potential I was just concerned that it may not have the strength needed but I guess that can be resolved with thicker ribs and I could use plywood since it would give multi-directional stability and strength.

Gordon - nice plant stand and coat rack!

Regards,

Bill

[rhett]

A word of caution about 3/8 bending ply. The exterior surface is very rough and if you plan on veneering over it you will need to use a backed veneer or two pieces oriented perpendicular to one another, as the ridges will telegraph through the veneer. I like the interior rib idea, like a bent torsion box. You can then easily skin it with 1/8 MDF stapled to the form. This material is usually free at plywood supply houses as it is used for cover sheets on stacked goods. Bondo the staples and proceed with the veneer.

[dino drosas]

First; an answer to Mike's question. Bendable plywood has all of its plys oriented in the same direction so that it bends with very little effort, and has very little strength unless it is attached to a form or is glue laminated together. You should easily be able to achieve a 6" radius and by gluing 5 layers together, strength will be the very least of your worries. I would build a form the shape of the inside of the curve you want and then glue all 5 pieces at one time clamped to the form as in any glued lamination. Use an extra piece on the outside as a cawl to prevent any clamping indentations since the plywood is somewhat soft. Also, place clear wrap between the 5th and 6th piece so there is no chance that they get glued together. I would use plastic resin glue because of the length of its open time, its strength and the fact that it does not creep. Make your laminations oversized and trim to length and width after the come out of the form.

[BillPappas]

Thanks again for all the insight and good advice.

I went out and purchased one piece of the bending ply and it is amazing how flexible it is and how rough. I am at this point planning on building a form and using the vacuum bag to create the laminate leg. I may add a layer of 1/8 inch Luan to the outside to cope with some of the roughness of the plywood. Then do a double veneer for the final exposed layers. I a now attempting to draw the leg and turn it into a template to make the form.

Regards,

Bill