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
Nice. I built a similar 12’ top bar with 12 guage strut but it wanted to twist (standing next to left side motor, looking toward the right side motor, the strut twisted clockwise) under stress. Ironically, I added a 2x4 along the top and that took away the twisting. One thing that is unfortunate about mine is that I was not able to install a top bar support close to the end of the left side due to a window where I needed to mount it on the wall of my garage. With your left most support ~1’ away from the end of the strut, its probably fine.
Thanks, I am pretty happy so far with the frame at 10’ as flex is concerned. Here is a better picture of the top bar supports, showing the top beam support sandwiched between two 1/4" steel brackets.
When I extend it to 12’ I would add extra supports for sure. But the truth I’m in no hurry to do that, since most of my jobs now, cut inside a 4’ x 6’ envelope, and I am I just slide the sheet into the sweet spot when I need to work on the end of the 4x8.