Second CNC table build, here we go again....

[Robin Hewitt]

So what is the bending force on your gantry from accelerating the Z axis components?
Suppose that is 3kg of motor, slide, torch, screws and stuff. Wild over estimate.
We know that 1kg force will accelerate 1kg mass at 1G because that is what happens when you drop it.
So to accelerate 3Kg mass at 0.5G requires a force of 1.5kgf
Why do you need 30kg of gantry to withstand 1.5kg in X and Y?
Perhaps it is the 3kg in Z you are worrying about?
Perhaps you should take a few gantry length bars, support them at either end, put a weight in the middle and see how far they actually bend.
Maybe 30kg is not necessary after all?
Maybe 30kg is only there to accelerate the 27kg it contributes all by itself?