Continuing the discussion from Advanced Frame Design:
I finally got around to re-building a new frame after my top beam started splitting under one of the motors last year. I fastened two ledger boards (12 ft 2x4") into the studs of my garage wall and used a cheap laser level to keep everything straight.
For the top beam I used a 10 ft piece of superstrut and attached the motor brackets with fender washers and 1/4" bolts and cone-nuts. to attach the top beam to the frame I used 6 inch corner braces
attached with 1/4 in - 2 in timber screws.
I also ended up with a top feed chain configuration and used a cloths line pulley to help align the chain feed into the sprocket,
I went with a 10 ft top beam for now, but can easily wing on extra pieces of superstrut on both ends and additional frame supports to go to 12 ft if needed.
So, far it seems reasonably well calibrated and I was able to knock off a quick job using Inkscape and F-Engrave!