The lock works like tightening two nuts against each other on a threaded shaft to reduce play in the threads. Backlash is the pause in travel when changing direction of rotation of any threaded crew. Because both sides of the thread don't rub on the nut at the same time (they would quickly wear out), one surface is pulling or pushing the nut when the screw is turned. When you stop and change directions, the screw turns a slight amount while the thread picks up the other side and begins to move the nut in the other direction. The looser the fit of the threads, the more "backlash" occurs. In essence, it is the amount you can turn the handwheel in the reverse direction before movement occurs on an axis. . An adjustment is provided on the X- and Y-axes to reduce the leadscrew backlash. Backlash is not a "fault" of a machine, it is simply a physical reality that must be taken into account when machining. You adjust to a known or acceptable amount using the locks and then remove it from the machining operation by always approaching your cut from the same direction with the backlash already eliminated before the cut begins.