I had some friends over and we started work on designing the frame. I hate construction lumber and we decided to use as little as possible. I finally chose a lvl beam for the top to make sure the motors didn’t change while in operation and to be the primary strength of the frame. We thought we could use it and a sheet of MDF to fight the construction lumber and keep everything as true as possible.
We built a basic rectangle with vertical 2x4’s in the middle and edges of the mdf, and then two more 8" to the left and the right (the width of my wall) so that I can add supports for cuts all the way to edge in the future.
Then we measured the horizontal distance between the boards and made identical top and bottom cuts between boards to keep everything square. The horizontal boards were inserted between the vertical boards and bolted together with pocket screws. We weren’t worried about strength because that would be covered by the mdf and lvl wood.
We screwed the mdf to the boards in the center and sides, then cut two identical boards to match the distance we wanted between the top of the mdf and the bottom of the lvl. We placed the two boards on top of the mdf, lined up the lvl to the boards, and added a couple of long screws through the lvl and frame to keep it in place for the next step
I drilled 1/2" holes through the lvl and frame every 2’, or so. I glued metal inserts into the holes so that I could move the motors out and in based on the material thickness used without worrying about the bolts eating into the holes and taking the lvl out of square with the mdf. I bolted it all together with carriage bolts and wing nuts.
I started with the wingnuts facing out and realized that was a problem because the chains would probably get caught on the nuts. So I took them out one by one and reversed them.
I then bought some 1 1/4" dowels and a 1 1/4" hole drilling bit and drilled holes every 4" along the bottom of the mdf, making sure I lined the drill up exactly each time so that the material would be level with the mdf.
Now I can pound in dowels wherever I need to support material. I drove a couple in, added the foam backboard and some 3/4" plywood, then flush cut the dowel to the material