My concern is mainly that the movement on the designated X axis may not be accurate.It is analogous to a wide drawer and they are prone to jamming or going out of square quite easily because the short runners aren't long enough to provide directional stability and I suspect that the same situation will pertain here.I strongly suspect that a moving table on the Y axis only will be better for stability and a Z axis with bracing,that traverses the gantry would be better.I would probably go for some external diagonal bracing on the X axis too.What family of steppers are under consideration?