There are two categories of forms, or molds, that can be used to press wood into the desired shape and then hold it under pressure until the wood dries and, if necessary, the adhesive sets.
The first type is called a solid form, which is made of individual pieces of material stacked together and resembles a curved block of wood. They second type, called a ribbed form, consists of evenly spaced ribs. The form you choose depends on the size of the project you plan to make, the radius of the curve, and the equipment you have in the shop. There are several variations of each type of form. I will describe the uses for and the construction of each variation.
No matter what type of form you make, you will need some extra length and extra width, usually between ½” and 1″, on the form because the wood on the outside of the radius has to travel a slightly larger distance than the inside laminations do. With any type of form, make sure it is as smooth as possible and the pressure you apply is uniform.
Solid Forms
Solid forms are used for solid-wood laminations, steam bending, and some narrow panels. They can become too wide, heavy, and cumbersome for wider panel work. Solid forms can be made of plywood or MDF stacked to about ½” to 1″ over the desired width of the lamination. If you are using solid forms with steam bending, watch out for uneven areas, lumps, or voids on your forms, which can contribute to failure on the inside of a curve. Also, be certain the wood fibers are pressed down against the form to help keep the grain structure intact. If the fibers lose contact with the surface in any one area, they can blow out or fold there.
Ribbed Form
Ribbed forms are constructed of individual ribs spaced 2″ to 6″ apart. The spacing lightens up the forms and makes them ideal for making bent panels wider than the bent laminations. Ribbed forms can be made of one or two parts.
One-part ribbed forms can be used to form bent panel laminations inside a vacuum bag. This process is referred to as the inside technique. These forms can be used to bend panels in a variety of shapes and sizes. For more complicated curves, such as an S curve or the W and spiral curves, the form can be outside the vacuum bag. This is known as the outside technique.
Two-part ribbed forms are made with male and female sides. This type of form can be used in veneer press or clamped with thick cauls to distribute the pressure evenly when a vacuum press is not available.
Most two-part ribbed forms are made by attaching a series of evenly spaced ribs parallel to each other, and covering them with some type of blanket or pad to span the distance between the ribs and provide a smooth surface for the laminations to rest upon. The layers of wood to be laminated are placed in between the upper and lower halves of the form, and pressure is applied. When the adhesive between the layers sets, the panel is removed, and it maintains its shape.
