The MX 8X14 carriage has a M6 threaded hole in the front center of the carriage. To add a carriage lock simply cut a 1.5" or 38mm by 1/8" or 3mm thick steel plate and drill a hole in the center to clear a M6 bolt. Next take a 40mm M6 bolt and install a spring that just fits over the bolt. the last part is a M6 locknut.  The carriage lock is in the above pic.  To install simply install the M6 screw in the carriage at the above location and install the spring, plate, and lock nut on the underside in the respective order.  The height of the screw and/or locknut may need to be adjusted to clear the frame bridging under the ways.  Once installed simply turn the nut counter clockwise to lock the carriage and clockwise to free the carriage.  This is a very simple upgrade that makes a huge difference on facing operations.