Determine bench width using the headboard posts as the guide. Measure the headboard from the inside of one post to the inside of the other post. Transfer this post-to-post dimension and cut a 2” x 4” to this width using the miter saw.
Using a table saw, set the rip guide to rip the 2” x 4” exactly in half. These two pieces of 2” x 2” create the front and back of the bench seat perimeter band. Rip another short length of 2” x 4” exactly in half (about 12” - 14” in length). These two pieces will be cut to the exact length to create the two side bench seat perimeter bands.
Carefully measure the exact width of the remaining true-cut 2” x 4” (it should be very close to 4”). Double this dimension (approximately 8”), then cut the two 2” x 2” pieces to this measurement. Lay out all four pieces onto a level workbench. These four pieces will frame the bench seat perimeter band. Clamp the perimeter band together to form a rectangular frame for the seat.
Now prepare all four perimeter band pieces to be screwed together using a pocket hole jig. Note: Pre-drill the holes on the bottom sides of the bench seat so as not to be seen from the top.
With the side perimeter band holes drilled, lay out the pieces and clamp them in place. Screw the pieces together to make the perimeter band.
Measure the inside width dimension of the seat. Cut two lengths of true-cut 2” x 4” to this dimension and insert them into the frame to dry-fit the bench seat. Clamp the inside bench pieces together. The bench should fit snugly with the seams and joints “tight.” Notice any gaps once the seat is clamped together? If so, minor trim cuts may be made to tighten up the gaps and joints.
Once the seat is confirmed to be “tight,” prepare to screw the seat pieces into the perimeter band by removing the clamps and the two 2” x 4” seat pieces. Place the seat wood into the jig and pre-drill 6 to 8 pilot holes in each piece to secure it to the perimeter band. Remember to set up the pocket hole jig and wood to pre-drill the pilot holes on the underneath side of the seat.
Lay out the perimeter band and seat pieces onto the level workbench and clamp the seat pieces to the perimeter band again. Screw the seat pieces and perimeter band together. The bench seat is now ready to attach to the headboard.