The seat had some springback, so I drafted the shape for the backsplat planning for more springback. I got less than I was anticipating but I think the shape that came out is still going to fall within an acceptable range for comfortable sitting.
Making the form took several hours. First I made a 1/4” template of the curve, shaping it carefully with rasps and using my critical eye. Then I used the template to make a 2-part template in 1/4” material – by cutting the shape carefully on the bandsaw the template parts fit very well together.
The curved plywood spines used in the laminating were ganged together and clamped, then I drilled and put screws through. I drew the shape using the templates on the top of the screwed together layers and band sawed the blanks out. Then I drilled and countersunk the 1/4” templates and attached the template one at a time to the blank. I cut out the templates on my overarm router but you could do it on a router table with a bearing-guided pattern bit just as well.
The 1/4” ply I used is just the birch veneer stuff left over from some cabinet backs. It bent beautifully in the forms. All the work of making the forms carefully paid off because the glue line on the backsplat is clean and tight all around.
I considered just making a 1-sided form and doing it in my vacuum bag, but I wasn’t confident the vacuum would pull the parts as tightly into the shape a 2-part form would. It was another excuse to use the book press too.