Yes, you'd surely need a gearbox for a rack and pinion or timing belt type drive because of the mechanical disadvantage the motor would acquire by being used in this fashion. Instead of one turn of the motor causing a movement of .2", you'd get a movement of 2 or 3 inches (without a gearbox). Not good, IMO.
What do the commercially made units do to solve the screw whip problem?
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)