I had bought a third rack frame some time ago when I ordered a DotCom Q117 S/H module for the Atomic Synthesis System. When that order arrived I had simply pulled the Q124 multiple out and put the Q117 in it's place. Two rack frames were full and I moved on.
After working a side job at the beginning of July it was time to add some new modules and bring that third rack frame in to play. It was at this point that the law of unintended consequences decided to visit the Command Center. Anywhere that I could mount the third frame, in the rack that housed the first two, was going to be too far for the power leads to reach. Mounting it in the rack next door would bring another set of problems with routing to and from the mixer.
Fortunately the back of the rack had threaded screw holes every few feet and one set happened to line up exactly with the best location for the power supply. I already had some very sturdy shelves that came with two of the rack units.
Once the shelf was mounted it only took a few minutes to rearrange the modules and hook them up to the power supply.