Using more 1"x1" aluminum extrusion, I made a frame for the y and z motion of the gantry.  The y motion is similar to the x motion; a pair of linear rails with bearings will allow it to slide freely with the motion being controlled by the motor(s).  The z axis is using a lead screw to control the motion, with a linear rail to help guide everything.  For simplicity, I used a 3D printer bed for the main plate that mounts to the bearings for the y direction.  This frame will mount to the bearings on the x-axis linear rails and slide freely within the system.  The linear rails will need to be cut to length, but the hardened material will require me to find a different way to cut it aside from the band saw I've been using up to this point.