<p>Wouldn't it be better to mount lead screws with the motor on top and the bottom end unconstrained? Compared to the conventional way (motor on the bottom) the lead screw would be under constant tension rather than compression and any misalignment would always be &quot;pulled straight&quot; and in this way minimize z-wobble.</p>
<p>Here is a image for clarification:</p>
<p><a href="https://i.stack.imgur.com/7hSCU.png" rel="nofollow noreferrer" title="Illustration of wobble in both top and bottom mounted stepper motors with lead screws"><img src="https://i.stack.imgur.com/7hSCU.png" alt="Illustration of wobble in both top and bottom mounted stepper motors with lead screws" title="Illustration of wobble in both top and bottom mounted stepper motors with lead screws" /></a></p>
<p>With the motor on top the load of the bed will help to move the lead screw in line with the mount. In the opposite case the load tends to further increase any misalignment.</p>

The motor is mounted in a fixed position no matter if it's on top or bottom.
You can imagine the lead screw as a rod hanging down and supporting the bed in the Z direction only, because all of the XY rigidity comes from the Liner rails the bed is attached to it works just as well if the stiff rod is under compression instead of hanging from the rod.
Any forces that might "pull it straight" are the same forces that can cause Z wobble so you would not want to even try to use the misalignment to straighten a bent lead screw.
The only thing this that really changes with this orientation is if the lead screw is under tension or compression. Even a relatively thin lead screw can easy counter the forces of gravity and the forces is the same in both directions. Its easy and cheap to make a smooth rod or rail straight but not so easy to make a threaded one straight.