Reusable molds typically comprise melamine, which you can find at home improvement stores, in the aisle where you’ll find shelving. It is a particleboard with a plastic laminate. The material releases more easily than wood and also doesn’t have a wood grain texture to worry about. Melamine is also affordable and with this design can be reused.
I am using pre-cut shelves because there is edge-banding on all four sides. If you use long strips of melamine, the back edge is normally unfinished.
Next, I took the 8-inch-wide shelves and began by ripping them down into 4-inch pieces. Nothing that I am planning to cast in this mold will be thicker than that, and by splitting them I can get two planks out of each shelf.
I have a long strip of 1” x 1” pine. Leaving the guard on the band saw in the same position, I went ahead and cut a few pieces of that.
Next I ran a bead of wood glue on the edge of each melamine board and positioned the pine pieces on top. I used a brad nailed to tack the piece pieces in place as well.
While the pieces are drying, I cut a couple of pieces for different sizes of bottoms to the mold out of more of the melamine shelves. There’s nothing special about this, and this doesn’t need to be done ahead of time. I would advise cutting these pieces on a case by case basis specifically measured to fit the project you are working on. I’m cutting these as a demonstration.
Once the glue is dry and you have base pieces, you can put it together. I am using a pinwheel pattern, as shown, to clamp these in place using the measured base piece as my guide.
This mold can be used, and reused for a wide range of sizes, and also stores nice and flat once it is unclamped.