The upholstered chair cushions for the dining chairs use a 3/4” Birch plywood insert as a platform. I cut the plywood using a circular saw and table saw. I then pattern route the chair insert and add round overs to prevent upholstery fabric from ripping and to help shape the upholstery foam.
Corner blocks on chairs serve two purposes. The corner blocks offer rigidity to the chair rails and prevent the rails from racking. They also provide a platform for the a seat insert to sit on. Since I’m using an upholstered plywood seat insert, I decided to place the top of my corner blocks 3/4” below the top surface of the chair rails.