Large commercial shops prepare curved marquetry panels by building up veneer lamination with the use of heated hydraulic or pneumatic presses to maintain the curvature as the glue cures. The small shop, unequipped with large machinery, may be hard-pressed for ways to create curved furniture panels. This problem presents an even greater challenge to the marquetarian desiring to overlay such work. I found that the use of specially built cauls and the standard homemade veneer press will produce satisfactory results.
I will illustrate this method with the example of a mahogany church tabernacle measuring 18″ x 18″ x 21-3/4″. Each of the three stationary sides and the door panel have a shallow bell curve with a 1″ deflection from level and measure approximately 13″ square. Quartered panels with the same curvature deflection as the sides form the roof of the tabernacle. All remaining structures are made from solid mahogany.
I built two identical curved cauls, or sets of forms, for the purpose of building curved panels with the intent of overlaying marquetry. Each set consisted of concave and convex halves cut to the exact curvature (though larger in dimensions) of the final panel. One caul was reinforced for use in the veneer press, while the other was built to cradle the marquetry facing during construction and prior to overlaying.
I constructed the marquetry design in its 1/28″ veneer thickness on the convex half of the non-reinforced caul to avoid the undue strain on joinery which would occur if attempt were made to glue a flat marquetry face onto a curved surface. Marquetry built on a curve naturally has more dimension to each piece around the curve than the same design created on a flat surface. When lifted, it shows a built-in curve and if laid on a flat surface, would disintegrate. Therefore, it should remain in the caul, trapped between upper and lower halves. You may work on the underside of the marquetry, if necessary, by simply assembling the two halves, sandwiching the marquetry, and inverting the whole caul. Removing the convex half reveals the underside of the marquetry which is continually supported by the concave half. When not working on the marquetry itself, assemble the three part sandwich to stabilize the veneer against humidity changes.
Making The Cauls
I started work on the cauls by making a cut-out card template of the curves to be used. Note that the radius of curvature of the concave caul is greater, by the thickness of the finished panel, than that used for the convex caul. These curves then became the standard for both sets of cauls. I nailed four pieces of 1″ x 4″ x 15″ pine together in a stack of each caul and then transferred the curves to the top piece, centered in both directions. Additionally, I marked five symmetrical, widespread positions on the face board and drilled through the stack with a 5/8″ spade bit. These holes will eventually hold dowels which define the length of the caul. I then cut the stack on the line of the curves with a bandsaw yielding two halves.
After removing the nails and inserting dowels in the holes, I spaced the caul parts equally along the length of the dowels and secured them with finishing nails. The cauls now assumed their final dimensions. I attached heavy non-corrugated cardboard over the open lattice cauls with small nails or staples. To further strengthen the surface, I glued two or three layers of white oak veneer with the grain running from top to bottom on the cauls. (You could also use thin, flexible plywood, which would be easier to assemble and stronger as long as you could get as much curvature as needed; I used the cardboard-veneer layers because the materials were readily available and because I could achieve the exact curve I wanted.)
Each half caul also received two cross supports on its outer side. The caul set to be used in the veneer press received three support pieces on each side of the half caul to assure even pressure on the final panel.
Please continue reading in part #2 of this article.