Bending wood by the process of lamination is not an exact science and takes practice. How wood bends is dependent on many variables, such as what species of wood is involved, the moisture content of the wood, the thickness, width and quantity of your laminants, what kind of glue is to be used, and how acute of a radius is to be bent. Unfortunately, these variables do not lend themselves to proven charts or tables that would make the process a bit more predictable. We have found that the bending of wood by laminating is an art that is picked up by experience and usually even when all the factors are taken into consideration, unless the finish product is to be mechanically held in place, the resulting product will more than likely have some spring back (change of radius). We always take some springback into our calculations and make adjustments for it.
Once a radius is determined (and in our case usually we need to layout for a stair pitch or angle as well) we draw the arc on a plywood laminating deck (see our pictures ‘Stair and Handrail Fabrication’). We use metal stantions or wooden 2×6’s as a laminating frame. If we are bending for a staircase we will build what we call a drum that is basically a curved wall. Once the wood to be used is resawn and sanded to its final dimention, glue is applied, the bundle is wrapped in several places with plastic wrap to keep the laminants in place for easy handling and with clamps spread out ready to work with (make sure to double the amount of clamps that you think that you need), we set the laminants in place, force the wood into position with muscle power (helps to have several extra hands) and start clamping either from one end or from the middle out both directions towards the ends. We will leave our laminant dry for as long as we can afford. The final radius is very dependant on how long the glue has to set up and again, what kind of glue has been used (most glue that we employ will have a extended cure rate where flexibility decreases with time). When the clamps are released and the laminant is taken off of the drum, the top and bottom edges are scraped of excess glue and the are trued and sanded. Simple as that!