Step 5: Install Center Support Beam
Installing the center support beam for the platform bed, begin by marking the very center of both sides (head/foot side) of this bed. Also mark for our 1/2" inch gap to find where the 2x4 support stud beam should go.
Then trace lines around where you want to install the 2x4 Stud support bracket and disassembly your platform bed so you can drill on screws better and hammer in some built in notch on the support bracket.
Do the same for the opposite side, then measure the length from that stud support bracket to the other support bracket on the other side and cut a 2x4 stud of that length. That measurement should be within an inch or two of the length of your mattress size.