Build an outdoor loveseat for your yard

Give it a rest
While you're waiting for the glue to dry, create the backrest assembly using the third U-shaped frame you set aside earlier. The backrest and the back support are built as a separate component, then added to the bench. Use the curved template you made to trace the shape, then saw along the lines, trim the uprights to 16 1/2" long, and then sand the cut edges smooth as you did with the legs. Create a 3/8"-deep x 3"-long dado in both uprights to accept the backrest.

Rip the backrest piece to width, trim to length and round the corners to a 2" radius. Rout a 3/8" roundover profile on all sides and ends. Get ready for dowels by drilling three 1/4"-dia. dowel holes in each upright, 3/4" deep in a triangular pattern. These dowel joints will connect the backrest to the back support assembly. Use dowel centres to transfer the locations of these holes to the backrest. Drill the dowel holes in the back, glue and clamp up.

Frame it
Join the entire backrest frame to the seat assembly using 3/8"-dia. x 1 1/4" dowels. Centre the backrest frame onto the seat and make a couple of registration marks across the joint with a pencil so you can easily return the parts to the same spot. Drill pairs of dowel holes every eight inches along mating parts of the seat back; use dowel centres to align the holes. Dry-fit the joint, making adjustments if needed, then reassemble with glue.

Assemble the seat
Cut the six pieces of 2x4 lumber you'll need for the seat slats. Make them 52" long and 3 1/4" wide. Lay the slats on the seat frame, centred on the middle seat support with a 1/4" gap between each board. Use the inside edge of your handy leg template to draw an 8 1/2"-rad. curve on just the front two slats. Cut the curve and rout a 1/2" roundover profile on all the seat slats, including the ends. Go slow, taking light passes to avoid tearout on the end-grain. Rout a 3/4" roundover profile on the top of the front seat slat, then sand everything up to 150-grit.

Attach the seat slats to the seat frame using more dowels. Starting from the back, mark and dowel each seat slat. The four slats in the centre have a pair of dowels in each seat support located 3/4" in from each slat edge. The front and back slats have dowels located every eight inches along the edges. Use the same technique you employed earlier to drill aligned dowel holes. Drill, glue and clamp up slats until the seat is together.