Making the radius stick (sanding block)

I made a radius stick sanding block for the back.
Nothing special here draw the arc, spokeshave it and ensure squareness.
Finally glue some ply wood to join the 2 sticks to have enough area for sandpaper.

Spoke shave the radius stick (2 sticks)

Glue them together with 2 spacer block in between.

Apply glue to the plywood.

Clamping time

Can see the arch here.