You may need to over bend your parts to account for this.
Bent lamination designers.
So your best bet with heavilyt curved parts is to either steam bed the material to shape or do a bent lamination.
When you unclamp your dried part it is going to spring back a little bit from the stresses in the bent wood.
Bent plywood bent laminated birch solid birch moma in 1940 charles eames and eero saarinen up and comers who would become 20th century design luminaries entered the museum of modern art s organic design in home furnishings competition.
Creating the 3d model of your mold.
To design the curvature of my bent lamination i opened up fusion 360.
Alvar aalto paimio chair 1931 32.
I used fusion 360 free to hobbyists.
There is no formula.
The concept is actually pretty simple.
A few thick laminations will tend to spring more than many thin pieces.
Since bent lamination is used only for narrow parts such as drawer fronts table legs and aprons and chair parts the form can be fairly narrow.
I wanted to use the shape of my skateboard in the mold so i uploaded a svg i designed in illustrator into fusion and extruded the skateboard shape 5 inches.
Mdf is the material of choice for making forms because its edges can easily be shaped into smooth curves with a bandsaw and files or spokeshaves.
A note on form design here.
After using an oscillating sander to clean up the inner curves and a disc sander to clean the outer curves trace your shape to another mdf board using your sanded shape and then rough cut the same shape only this time leave at least 1 16 of an inch between your cut and your pencil line.