my previous 3d printer that i had built used threaded rods for the linear motion along the z axis, while this seemed to work fine there was a particular point upto which we could get accurate. No matter what we did after that the z axis accuracy seemed to be at that particular state. The individual layers were still visible and our printer could be easily distinguishable from a professional printer. We worked hard and toiled day and night calibrating it but to no avail.
the problem was that we happened to be using threaded rods. Threaded rods were never meant to be used for linear motion, they have designed for exclusively for fastening objects together, hence their threads don't have a very good finish and have a lot of friction with the nut, they also have a very low efficiency in terms of transferring power. Hence you will need to get a powerful motor to carry a relatively smaller load.
Lead screws on the other hand were designed to transfer load along the linear direction, they are popularly seen on lathe machines. They have an efficiency varying from 30% to 90% and hence make it a better option over threaded rods, they are also better at handling tensile and compression loads, since they are made of a slightly different material.
Threaded are way cheaper than lead screws and very easily available in most hardware stores unlike lead screws, but lead screws though more expensive have better accuracy and precision. If you could afford it I would definitely recommend lead screws.
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