How to bend wood - Bending wood is not the daunting task that it appears to be at first glance. Depending on the degree of bend, and whether or not the bend is compound, there are a couple of methods for bending wood.
First, you need to have a form to bend your wood around and clamp to to hold the desired shape. Most bent wood will have a certain degree of “springback”, so you must build your form with an allowance for this. And, unfortunately, there is no established formula for determining the degree of springback that a given species of wood will produce. Springback is also influenced by the bending method used. That is to say that steamed wood will spring,(how to bend wood )
or “unbend” more than wood that is laminated and glued. Another variable is the type of glue used in laminating.
As a general rule, the tighter the bend, the more the wood will spring back, making the allowance a matter of trial and error at best.
As laminating thin strips is the easiest method, we’ll begin with that process. The finished thickness of the project will have a direct bearing on the size of the strips to be used, but generally, the heaviest strip to use is about ¼” thick. Tight bends may have to be done with 1/8″ strips or thinner, depending on the wood species. Sounds like a lot of experimenting, but I’m afraid that’s a necessary evil.
The form required for laminating can be as simple as a piece of pipe or as complex as a multi-station die. I like to keep things as simple as possible.
When laminating thin strips, you can minimize effort and spring back by soaking the strips before bending, and clamping them in the mold without gluing. Once they are dry, remove them from the mold, spread the glue and re-clamp them in the mold. Line the mold with waxed paper to prevent the lamination from sticking to the mold.
When I soak strips, I do so in an open container, and depending on the wood and the size of the strips, I soak them from 15 minutes to overnight. I also mix in a half cup of fabric softener per gallon of water. I find that it softens wood nearly as well as fabric.
If the project is small, and open time on the glue is not a factor, I’ll use poly-vinyl-acetate, or aliphatic resin glue. If I need more working time, I’ll use epoxy or resorcinol.
I stay away from the quick setting epoxies, however, because they rarely harden to the extent that the slow sets do. If you’re using light colored wood, resorcinol dries to a reddish color which might be objectionable on a finished project.
When bending thin woods such as guitar sides, the wood is commonly soaked as above, but it is bent over a hot bending jig, either electric, or heated with a propane torch. Brittle woods are supported on the outside of the bend with a thin stainless steel band to help prevent cracking.
Green woods can be bent much in the same way, or by heating the wood over hot coals or with a good heat gun.
For projects where lamination is objectionable, or when the wood is to be bent in compound curves, a steam box is the answer. One can be made fairly economically from PVC pipe, but it needs to be supported to keep the pipe from deforming.
The ends of the pipe need to be closed with a screw cap on at least one end, to allow access to the interior. Fit the other end of the pipe with a DWV reducing tee, and attach a radiator hose to the side outlet and to a new gas can large enough to hold sufficient water to last through the job. The water may be heated with a hot plate or a propane burner.
Drill through the pipe slightly below center in two or three locations and insert dowels for the wood to rest on. Steam must be allowed to circulate freely around the wood for even penetration. A hole about ½” in diameter should be drilled in the cap furthest from the steam
inlet to allow circulation. When you build the support frame for the steam box, pitch the box
toward the steam inlet to allow the condensation to return to the water supply.
Rule of thumb says that wood should be steamed fifteen minutes per inch of thickness, but here again, some experimenting will be necessary.
The wood needs to be placed into the form as quickly as possible, because as the wood cools, it is more difficult to bend. Make sure that your wood is at least two feet longer than the finished part, because it’s nearly impossible to bend a 3/4″ piece of wood that is less than a foot long, so that last foot will have to be cut
off after the wood is dry.
Clamp the wood in the form securely, and leave it there until it is completely cool. If you are working with multiple pieces, place them in the steam box a approximately the interval required to place the piece in the form and clamp it, and remove them from the box in the same order.
With a little practice and a little luck, it shouldn’t take long to become proficient in wood
bending. Good luck with your project.