that's a cool idea , but with the bearing face at around 65 rc and if the shaft is hardened then the surfaces are slippery on each other, with the servo's moving the plate back and forth. as the plate gets heavier with your project then I think the bearing might slip on the shaft on the X and Y , it may not slip on rotation axis , with threads it can't do that with the take up nut on the acme thby brentallard - Mechanics