When it comes to the gantry, the force applied is primarily to the tool at the end of the spindle doing the cutting, right? I can visualize the spinning tool creating quite a bit of rotational torque as it engages the material. This would be amplified if it's a "hard" material or has inconsistent density like knots in wood. Other than that though, are we trying to apply significant horizontal force as the tool is cutting? If I'm running a router by hand, I don't push the tool hard to its limits; if the tool is sharp it's not necessary.