Build your Headboard and Foot Board units. You are going to be building a puzzle essentially, that will fit together and sit perfectly inside a sandwich of surrounding boards. Use glue to attach adjacent boards and sandwich with side trim to secure in place. The Panels should be centered perfectly on the side trim pieces (1×2’s shown in green and blue) leaving equal spacing on either side. Use 2” screws to fasten the side, top, and bottom trim to the panel boards. Use your 3″ Screws to fasten one set of panels (probably the bottom)to the Center Board (red) and glue the top section to it. Be sure the panel boards are centered on the Center Board as well. You want everything to be centered with equal spacing on front and back. Don’t worry about the pieces not being screwed together vertically, this design is not dependent upon it. Instead it will be the side attachments that matter.

Fasten the Surrounding Boards to the Panels you just created. Use 3” screws and glue to connect. Be sure the Surrounding Boards are centered with equal amounts of overhang on front and back of each unit. Everything should feel nice and sturdy with no wiggle wobble.

Fasten the Units to the Legs. You will fasten from the inside of the Surrounding Side Boards into the Legs on both the front and back of the unit and on either side. Use 3” screws and glue. The Units will sit flush with the top of the Legs. Once they are secured in place, you will fasten the Top Trim Board in place using 3 1/2” screws and glue. This should have an overhang of 2 1/2” on either side and will sit centered on the units, but flush with the width of the legs.

Since this is for a King Sized bed, you have a few options where it relates to the Frame. The first option is to simply attach your metal bed frame to the Head/Fottboards themselves and add a Side rail to disguise and beautify (This is recommended for a much faster build and will save you quite a bit of money as well since you likely already have a frame since they tend to come free with your bed sets). You can also create adequate support for your mattress if you don’t have a frame by building a frame constructed of 2×4 joists with dimensions 1” longer than the width of your exact mattress and fasten them to the Side Rails and then to the Legs on the Head/Footboards. This is the recommended frame construction for not using the metal frame with your bed set since the 2×4’s should provide adequate support for the heavy mattress. I don’t recommend using slats for a bed set this heavy..I just don’t see it being the best solution here. Use 3” screws to fasten the 2×4’s to the Rails and use glue. Fasten the first and last 2×4 so that it sits perpendicular to the rails at the very front/back edge so you can use those joists to fasten directly to the head and foot boards. You can also use your pocket hole system to fasten the rails to the legs. I show the rails sitting centered in the legs, however you will want to place the rails at a location on the legs that best fits your exact mattress width. Mattresses are somewhat standard in size, but when you are talking about exact measurements…they are all over the board. You should fall somewhere near 76×80, but you could waver by 1-2” in any direction and this would be problematic if you haven’t secured your rails and joists accordingly.