Forming Curves In A Vacuum Press

I consider the vacuum press to be one of the biggest innovations in woodworking since the plunge router. It is a vast improvement over the veneer press which involves numerous clamps that have to be individually screwed into place. In addition to handling flat work, it is also an excellent tool for curved work. I used my vacuum press to form the curved lid for this chest. Whenever I make a project that involves some type of bentwood lamination, I usually like to make the curved components first, just in case there is any spring back. To begin, sketch a full scale side view of the top’s edge onto some ½ inch MDF (medium density fiberboard). I used a large compass to generate a curve that I liked. I decided to make the lid 5/8’s of an inch thick so I adjusted the compass and drew a second curve to represent the inside of the lid. Once I had this information, I built a form. Using a trammel arm made of ¾ inch plywood with my plunge router mounted to it, I cut the arc of the first rib. I also allowed enough room to attach some plywood skins to the top of the form. I used the first rib as a template to batch cut the rest of the ribs using a flush trim bit at the router table.

The vacuum press can generate over 1500 pounds of atmospheric pressure per square foot, so the forms you use need to be quite strong otherwise they will implode. I glued my ½ MDF ribs onto a base of ½ inch MDF spacing them approximately every 3 inches. After gluing and nailing on the sides, I let it dry. I then applied glue to several sheets of 1/8 inch bending ply and to the ribs and slid the assembly into the vacuum press. The vacuum press evenly distributes the pressure and when the glue dried I had a form with a uniform curve.

Now I could use the form to glue up the core of the lid. I used four sheets of 1/8 inch bending plywood coated with slow setting urea resin glue. Using multiple thin plys as opposed to a couple of thick ones helps to reduce springback. Next I banded the edges with pieces of figured maple that I resawed from the plank that I cut the 1/16 inch thick veneer from. After trimming the banding flush with the core, I could now put it back in the press to veneer the inside and outside of the lid.