Why not use unsupported rails?

[ecat]

Our bouncy friend is correct in saying that we should also consider the worst case examples for supported rail.

1) Supported rail rigidly supported at both ends but without any underlying box section.
2) The deflection of the underlying box section sans rail.

Why?

Well, 1) gives us some idea of the contribution of the basic rail support structure and 2) gives us some idea of the contribution made by the box section itself.


Edit:
I would love to see a similar analysis of profile rail. Just how significant is the support structure? 20mm plate, 40mm and 90mm section, aluminium and steel. After all, £600 worth of rail is meaningless if the £100 worth of extrusion allows deflection on a par with round rail.