Bending wood forms

[Ashwini Kaul]

Where do I learn about bending wood without steam or vaccumm?

I am interested in some projects... that require bending and while I know the concept - rip thin strips, glue up and set with clamps over a predefined form... some more instruction would be valuable.

Thanks!

[G Douglas Fowler]

I would suggest Lon Schleining's Wood Bending Mnade SImple published by The Tunton Press. The book comes with a companion DVD.

[Matt Day]

You could also scour the internet and find some good stuff, search for bent lamination. There's some great information on SMC about how thin you should go for the radius you're going for, etc. I did a bit of it a while ago and had fun and got great results, and the best way to learn is to practice after you've done some research. Good luck!

[Todd Burch]

There's really not much to it. Do an experiment! Risk free!

Make a form, cut your stock, figure out how you will clamp it while the glue sets, determine the order of operations for gluing it together, and dive in.

Last forming I did was to make a round hoop to use while emptying out my dust collector bins. I clamp the bags into the hoop and set the hoop on saw horses. I used SketchUp to determine the lengths of the 6 pieces I needed that were each 1/8" thick and 3/4" wide, that resulted in an (approx) 3/4" x 3/4" solid pine hoop. For the form, I simply cut a circle out of a piece of 3/4" ply. I cut each piece 3/8" longer than SketchUp said for the circumference of the circles, and tapered each end 3/8" down to nothing. I laid the longest piece in the waxed form first, and used spring clamps to hold it in position while I applied glue to the next piece. No springback considerations for a closed form. Leave it in the model for a couple days if an open form, to allow the glue to really set well.

When my house was being built, the stairmakers, when making the curved hand rail for the curved staircase, simply nailed blocking on the treads to use as the form.

[Mike Henderson]

I agree with Todd - it's not very difficult. One hint - when you make a form, make it convex rather than concave. The reason is that if you make it concave you'll have trouble getting all your clamps on - they'll interfere with each other because they'll all aim at the same point.

Mike

[Rick Lizek]

Use a band clamp for simple curves instead of regular clamps... faster and works much better overall. The MLCS Merle clamp is ideal.

[Joe Cowan]

I just finished a "Maloof" style rocker and did laminations on both the spindles and the rockers. I drew the line of the arc and cut it out of 8/4 poplar and used both sides, with the top side being a cawl. One thing I forgot to consider is the difference in arc as you go away from the bottom. The top cawl did not fit snugly in all spots, but it did the job. On my next one, I will use the bottom form and use multiple clamps to form the strips tight against the bottom form.

[Larry Edgerton]

What questions do you have specifically? I have done quite a bit of curved arcitectural millwork and I may be able to help you.

Mike makes a good point, but for a different reason. Even on larger laminations you want to do the inside [convex]form because on an outside [concave]form the stress in the wood is fighting you as you try to clamp. Use the wood to your advantage whenever possible.

Start your clamping in the middle.

Your laminations will want to slip by each other at the edge even if cut from the same board in a flitch, so have a plan and do a dry clamp to see problems.

Have a clamping plan. You have to be fast. If it is painted/outside I use resorcinal glue, and if it is inside or clearcoated I usually use West System. I do not like titebond for bent laminations because it creeps over time and the wood will forever be under stress. Any quality glue that does not creep will be fine. If you do not have a plan you can get half way through and the glue sets and you are done. I usually do large parts like facias and stair parts so that is a little more important for me, but small laminations need speed too.

After your form is built test your desired strip size on the form. If it will not easily conform, a stack of them will be much worse, thin them out.

If a part is being designed to fit a specific radius, design in some springback into your form. This is the part that is not scientific. Wood species and strip thickness have to be balanced to the radius that you are trying to achieve. In some cases the radius may just be too tight for the species that you want to use to be practical as some woods do not bend well at all. Again, a sample test may be in order. If I am doing a species that I have not bent before I still will do a test piece.

Remember that if you are decreasing the radius to compensate for springback that you need to keep your form long enough. Say you are doing a half circle at a 3' radius, but you decide to use a 2'9" radius to compensate for springback. So now when you make your form you need to add .78 feet beyond the half circle to make up for the loss in circumference, plus adding for the tails you will cut off.

I always add about 6" to the length give or take of both the form and the strips depending on the radius and the depth of the strips. Even when clamped to a form the ends come out a hair different radius so I make the piece long and cut these off.

Make provisions so your piece is not glued to your form when cured!

Don't be tempted to take it out of the clamps too soon. Double the glue manufacturers specs. I prefer epoxy, but a lot of people don't like it because they feel it is hard to deal with. To each his own.

At times if I have a face I do not want glue on because of stain, I will prefinish the face of the outside piece. The edges will have to be machined anyway so no worries there.

If you set up a support in the right position that will support the edge you can run the laminated edge throught the jointer. It can be run edgewise through a planer as well, but it will have a tendency to want to roll so you need something to hold it vertical. I have a roller setup that bolts to my infeed, but befor that I used waxed blocks of wood clamped to the table.

Gotta get to work, ice is melting finally......

Larry