Deflection in precision rod rails

[irving2008]

I want to build table 1.2x0.8 meter.I will use supported 16mm rails on 1.2m long side.On 0.8 what have to use to have no deflection - supported rails 16mm or 20mm unsupported.

Depends on the load - two 20mm unsupported rails will each deflect 0.5mm approx under a 10kg load. Supported rails are better (they do deflect but its tiny compared to unsupported)