By "better" I mean "more precise"...
With respect to a RepRap P3Steel or Wilson II, I am getting some 330 mm T8 leadscrews for the Z-axis movement.
There seems to be a choice between a lead of 1, 2 or 8 mm - the pitch is 1 mm in the first case and 2 mm in the last two cases1. However, there is precious little information about the advantages and disadvantages of each lead size in RepRapWiki - Threaded Rod - Leadscrew.
It seems to me that using a leadscrew with a 1 or 2 mm lead could result in a more precise Z-axis movement, as one rotation of the stepper results in a smaller increment in height. Therefore the layer thicknesses could be smaller.
However, is the minimum layer thickness not, also, dictated by the thickness of the filament, horizontal speed of the print head, nozzle size, etc.? Thus, at some point there would be no need for a super fine vertical resolution from the leadscrew, as it may be constrained by other limiting factors.
Of course, conversely, the use of a 2 mm lead would mean that the stepper would need to "work" four times as hard, than when using 8 mm, in order to raise the print head the same distance, as well as making the movement, during a "home", take four times as long (or, if you will, four times slower). In the case of a 1 mm lead that would become eight times...
Is it worth getting a leadscrew with a 2 mm lead, or is 8 mm sufficient?
By extension, would a 1 mm lead be even better, or just overkill?
- Pitch is the distance between the adjacent threads;
- Lead is the distance that a nut will turn with one rotation, and;
- Start is how many starting (or thread entry) points at either end.
So, for a leadscrew, with a pitch of 2 mm, if there is only one start to the screw then the lead is the same as the pitch. However, if there are four starts to the screw, then the lead will be 8 mm. If there are two starts to the screw, then the lead will be 4 mm. And so on.
For more information, see Wikipedia - Lead, pitch and starts.
Based on what I've learned over 8 months of printing:
What matters the most is getting a very accurate zero relative to the bed surface. An offset of 30 or 40 microns can strongly affect first-layer adhesion. Now, unless you put in some of the advanced auto-levelling sensors, the repeatability of the Z-axis limit switch may outweigh the precision of the lead screw itself. But if you've got a good limit sensor, then the more precision in the lead screw, the better you can set (and repeat) the position of the first layer.
I don't see a significant difference in strain on the drive motors if they have to run longer per mm of z-drive - just make sure the lead screws are clean :-)