BUILD THE SEAT FRAME.
One important difference between the seat frame and the back frame is the positioning of the CPVC tubing. On the seat frame, one tube is inserted into the sides slightly out of line at the front to make the chair more comfortable for your legs.
1. Cut the seat sides (E), seat front (F), seat stop (D) and seat support (1) to length. Use the same methods as with the back frame to draw the centering line for the plastic tubing on the seat sides. Drill the tube holes into each seat side. Start the holes 2" from the front end of the seat sides.
2. Position a single tube hole on the seat frame 7/8" below the top edge and 1" from the front end of each seat side. This front tube provides a gradual downward seat profile for increased leg comfort.
3. To eliminate the sharp edges on the seat assembly, round the seat sides, seat support edges and seat front edges with a sander or router. Cut 1"-radius roundovers on the top front corners of the seat sides.
4. Use a combination square to mark a line across the width of the inside of the seat sides, 3 1/2" from the back edges. This is where the back face of the seat stop is positioned. Test-fit the pieces to make sure their positions are correct. Lay out and mark the position of the seat stop and seat front on each seat side.
5. Drill pilot holes to fasten one of the seat sides to the seat stop and seat front, as you did with the back assembly. Counterbore the holes. Connect the parts with moisture-resistant glue and deck screws.