Many machines have two Y-Axis motors. If something goes wrong and you hear the grinding noises, the Y-Axis carriage will not be square with the X-Axis carriage. To fix the problem, you have to move the Y-Axis carriage to the back of the machine and square the Y-Axis carriage. This assumes that you don't have limit switches at the back of the machine. Is it possible to put timing belt and pulleys on the Y-Axis motors?