2 inch ribs should be plenty thick for a final assembly. Your challenge is clearly keeping it flat during assembly. When the whole thing is assembled, the ribs really just force the top and bottom sheet to work against each other. Depending on loads applied, one sheet may be in tension. The ribs would transfer that force to the other sheet creating an offesting compression.
In aerospace applications, they will use composite materials sandwiched over a honeycomb core or foam core. The torsion box is the same principle. The taller the ribs, the stiffer the box. Still, a two inch rib evenly glued on edge to the top and bottom should be plenty stiff. Taller ribs may not deflect much duing assembly.
Consider the deflection you observed in the MDF rib before glue-up. Can you get that assembled box to flex like the individual member?
-Dax
In aerospace applications, they will use composite materials sandwiched over a honeycomb core or foam core. The torsion box is the same principle. The taller the ribs, the stiffer the box. Still, a two inch rib evenly glued on edge to the top and bottom should be plenty stiff. Taller ribs may not deflect much duing assembly.
Consider the deflection you observed in the MDF rib before glue-up. Can you get that assembled box to flex like the individual member?
-Dax
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