I needed some sort of support for the build plate on the Delta printer I am designing & came up with this idea. There are quite a few variables you can change, but most of the ones you really need to adjust to your design are nearest to the top of the program. I still have not decided on the size my Delta will be which is another reason I wanted to be able to easily change the sizes. I included STL files for 3 sizes. The 310mm OD & 220mm OD are probably the most common used. This design may change, since I am not sure whether the heat bed & glass will attach directly to this or whether I need to make another bracket for that. The large 406mm OD I had to make in six 60 degree wings to fit on my print bed. I might have been able to make it in three 120 degree wings if I made the center Internal diameter larger. You have a choice of 30, 60, 90, or 120 degree wings although 90 probably does not work well for a delta. Let me know if any of the variables do not work as expected. It is difficult to check every possibility.
I included openscad files for the wing & brackets. Make sure you make the bracket hole sizes & offsets the same on main file as well as the brackets you use. I used M3 bolts & 12mm long & locknuts will work in the current configuration. I only M3x14mm & M3x16mm, so they will work but the bolt will extend beyond the locknut. The default hole size is 3.5mm which works for M3 bolts on my machine. I originally used M4 bolts, but it did not seem like they were really needed. For the center supports, you can use either a circular or the smaller oval brackets. I would test print 1 or 2 wings with the brackets before printing all the parts. For your situation, the STL files I included may not work for you, but you can easily change them with the customizer or using openscad or your machine. I thought with the larger size I am starting with, the circular bracket would give better support. This Part will have some flex in it, but with a delta just about all the weight should only be at the 3 points along the outside of this build plate support. I think 120 degree wings are the ideal size to use. You might be able to make a square version with this, but you will probably have to adjust the code some.
One of the photos I show it connected at the top of my delta as it was easier to photograph. I am using 3/4" electrical conduit (EMT) for the horizontal supports in my design.
I printed my parts at 40% infill .2mm layer height. The customizer version (ParametricBuildPlateWings_rev22.scad) defaults to the settings I used for the 310mm OD & 300mm Hole Pattern. There are lots of possibilities, so play with the variables until you get to the design that works best for you.