Cut six Legs and two Back Legs from a 1x8 board, as shown in the cutting diagram. Cut the angle, as shown, on the Legs (but not the Back Legs) using a jigsaw. Then sand the cut edges smooth. With your pocket-hole jig set up for 3/4" material, drill pocket holes on four of the Legs, making sure they mirror one another as shown.
Glue and clamp the Foot Rail to the two leg assemblies that have angled sides, and then secure the parts by driving four 1 1/4" flathead wood screws through the Foot Rail from inside, and into the leg assembly. Attach the other leg assemblies to the Head Rail in the same way.
Cut two Rail Cleats from a 2 x 2 board, as shown in the cutting diagram. Then Drill 10 evenly spaced pilot holes for #8 flathead screws that will be used to attach the Rail Cleats to the Side Rails.
Now you need to drill holes for the connector bolts that will be used to hold all of the leg/rail assemblies together. To do that, first clamp the head rail assembly and the foot rail assemblies to the side rail assemblies. Now lay out four holes, as shown. Then drill the holes all the way through each Leg and Rail using a 1/4" drill bit. The connector bolts will pass through these holes. Unclamp the assemblies. Next, you need to enlarge the holes in the Rails to 3/8" to accept the connector nuts that the connector screws thread into.
Cut three Headboard Supports from 1x6 boards, as shown in the cutting diagram. Then cut the angled shape in each one using a jigsaw. Sand the cut edges smooth. Next, drill pocket holes in the Headboard Supports where shown. Note that you’ll need to make two that are “mirror images.” That way, the pocket holes will be on the inside faces of the outer Headboard supports, and won’t show when everything is assembled.
Cut four Headboard Slats from 1x6 boards, as shown in the cutting diagram. Then cut one Headboard Top to length from a 1x3 board.
Now you can attach the Headboard Slats and the Headboard Top to the Headboard Supports. Start by attaching the lowest Headboard Slat using 1 1/4" coarse-thread pocket hole screws. Then attach the Headboard Top. Now add the uppermost Headboard Slat, making sure the edge is flush with the Headboard Top, as shown. Finally, add the two remaining Headboard Slats. Positioning them so there are equal gaps between all of the Slats.
Attach the Headboard assembly to the Headboard Cap where shown using 1 1/4" coarse-thread pocket hole screws. Cut two End Cleats to length from 2x2 boards, as shown in the cutting diagram. Then attach the End Cleats to the Head Rail and Foot Rail where shown using glue and three evenly-spaced 2" flat-head wood screws.
Cut one Center Support, two Center Post Sides, and two Center Post Ends from 1x6 boards, as shown in the cutting diagram.
With 16 connector nuts and bolts, attach the rail assemblies to the headboard and footboard assemblies. Set the Center Support assembly in place and screw the ends to the End Cleats using two 1 1/4" flat-head wood screws at each end. With that done, you can give the bed a final sanding, and paint or stain it to your tastes.
Cut eight Slats to length from 1 x 6 boards, as shown in the cutting diagram. For these, you can use lower-grade pine boards. Once you have the platform bed set up where you want it, lay the Slats on the Rail Cleats and Center Support, spacing them evenly. The Slats don’t have to be screwed in place. The weight of your mattress will hold them in position. Once you set your mattress in place, your bed is ready.