Quote Originally Posted by JAZZCNC View Post
Put the rails on the front plate and the bearings on the back plate. This way the rails help stiffen the front plate.
The carriages then go low on the backplate and it makes for a very stiff z axis with max support where it's needed.! close as possible to the cutting end.!
If the rails are contributing significantly to the stiffness of the material you are using for the Z-axis then that material should be made thicker/stronger. Still definitely put the rails on the front plate, but primarily for the second reason - the supporting carriages are closer to the bed.