Boyan is right

2 rails each side are nonsense. The result will be huge loads to the rail bearings due to thermal distortions, nonparallel cuts etc. General problems with gantry types is non-optimised stiffens. Torsional displacement of the gantry beam define the stiffens of whole system.
Everything is assembled from standard profiles. I-s are known, do the simple test and apply load of 100N at the end of the cutter.
Don't be surprised.

regards