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Use a small belt sander with a 120-grit sanding belt and a very light touch. Clean up the outside edges of the assembled bed frame.Drill pilot holes, countersink those holes, and screw in your wood screws. You’re now going to screw all four corners. In each corner, draw an “X” – this will help you locate where to put the screws. Flip your frame pieces over and refit together.At this point you’re going to center the middle support rail and attach it to the head and foot rails with two screws on each end. With everything glued and screwed, do another test fit.Use a countersink drill bit on each drill hole so you can sink the screw flush to the bed frame surface.You do not need to screw the center support rail, though you can. You’re going to put five sets of two screws each down each rail. Only drill the pilot hole into the first layer of wood.In the middle of the rail, drill two pilot holes – one about 1 1/2″ from the outside edge and one about 3 1/2″ in from the outside edge and a few inches away to the left. Use squeeze or bar clamps to hold everything in place. After laying out the DIY platform bed frame components, start gluing the top layer pieces to their corresponding middle layer pieces below using wood glue.This creates a 1″ ledge on both sides of the center support rail. Place the center support pieces in place by centering the lower (5 ½”) piece in the frame parallel to the side rails and then centering the (3 ½”) upper middle support piece on top.
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Line up the outside edges so that they are flush. Lay out the frame pieces with the middle layer on the bottom and the top layer above it.It’s going to fit on top and in the center of your middle support rail as shown (but you won’t attach it now). For the support rail, use your miter saw to cut a 1” x 4” x 8′ board down to a 1″ x 3 1/2″ width x 79 ½” length.Cut the side rails of your platform bed. Use your miter saw to cut two pieces of 1” x 6” x 8′ boards to 79 1/2” lengths. Then use a table saw to rip both pieces to a 4 ¾” width.Then use a table saw to rip both pieces to a 4 ¾” width. Use your miter saw to cut two pieces of 1” x 6” x 8′ piece of wood to 85” lengths. You’ll start with the head and foot rails. Begin on the top layer of your king platform bed frame.Dimension of the board should be 1” x 5 ½” x 78”. Use a miter saw to cut the support piece from a 1″ x 6″ x 8′ for this middle layer of your frame to 74” length.
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The outer dimension should be approximately 85” wide by 89” long, and the inside dimension should be approximately 74” wide by 78” long.
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