There’s no sewing required for this seat cushion — it’s just a simple “wrap.” This upholstering isn’t hard to do, but it can be fussy getting it to look good. Practice with scrap materials before you do your final seat cushion.
Start by fitting the seat plywood in the chair opening and allowing space for the leather. The final fit should be just slightly loose. Check the fit by placing scraps of your leather in all the corners between the frame and plywood. Round the plywood corners to a 1/8" radius, and aggressively ease the top and bottom edges with coarse sandpaper. Drill 1"-diameter air relief holes in the plywood about 5" in from each corner.
Trace the seat plywood pattern to the seat foam and the leather. Cut the foam leaving an extra 1/2" all around, and cut the leather leaving about 3" extra all around. Adhere the foam to the seat plywood top with spray adhesive.
Set the plywood and foam on the leather and start “wrapping.” Set your stapler to light pressure so you can “baste” the staples, which means setting them shallow so they are easy to remove.Tack the front edge down in the middle. Pull the rear edge tight, and tack it down in the middle. Remove the front edge staples, pull the front edge tight, and tack it again in the middle. Now do the same with the sides. Increase the tension of the leather on all four sides until it looks good on top.
Set your stapler pressure for full depth. Pull the leather tight, and staple toward and into the corners. Pinch the leather in the corners, and use a knife or scissors to trim away the waste. Hammer the leather in the corners down to flatten it, and then add a few more staples.Trim away any excess leather from around the seat cushion.
Set the upholstered cushion in the chair. It should fit tight. If you find any odd bunching areas on the cushion edges, you can lightly hammer them down to flatten them out. Fasten the seat cushion to the chair, driving screws up through the corner blocks.