The plan for fixing the legs to the frame was to use long M8 bolts and threaded inserts. The idea is that the legs are removable. Simply because the finished desk size will will probably be too big to move through doorways into the studio.
Here is the detail for the way the front bolts and inserts will fit into the frame. (The rear ones are the same but with 75mm bolts instead of the 105mm ones required at the front.)
Here are the M8 bolts, washers and Type D threaded inserts (Type D are the kind you screw into an oversize hole with a hex driver, other types are driven in with a hammer, I believe):
Of course you can’t buy 105mm M8 bolts (well not in the hardware specialist I use!) and although you can get 75mm M8s, they were out of stock, so I ended up with 80mm long ones. So out came the vintage hacksaw again to get them to the right size. Handy hint. You should put a nut onto a bolt you are about to cut because taking the nut off afterwards clears the burr from the inside of the thread and it makes putting the nut on later much easier. Yes, I forgot for the photo!
So came the moment to clamp the legs to the frame and measure and drill the holes:
And bolt the components together:
And here is the desk so far, with the legs safely bolted on. I also dry fitted the framing for the 6U rack bays (which I totally forgot to photograph as I cut them):
Next up will be cutting and fixing the desktop sections.