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This video brought to my attention the 8 mm lead of the Ender 3's Z axis screw, which seems like an exceedingly bad choice from a standpoint of accuracy with respect to common grid alignments in the Z direction. In particular, with the stepper having 200 full steps per rotation, the 8 mm lead consumes all the powers of two out of 200, leaving 25 full steps per mm - and 25ths of a mm are not a typical unit that layer heights/feature heights are going to be in. It seems like a 5 mm lead would be ideal, giving you 40 steps per mm, evenly divisible by 3 powers of 2 and one power of 5, for exact tenths and exact eights.

Is there a motivation behind the choice of 8 mm lead? Is this common for other printers, and are there printers that use a 5 mm lead, or 5 mm replacements that work well?

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I've not seen trapezoid lead screws with 5 mm lead, you can get 5 mm lead ball screws though.

On one printer I use 4 mm lead screws to get native 0.02 mm resolution (so 5 full steps for 0.1 mm, 10 for 0.2 mm, etc.). I also geared down 8 mm lead screws with a 2:1 ratio (e.g. to use a single Z-stepper driving a belt that drives 2 lead screws), works fine.

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Well, you can use the screw with the size you can get easily, but sometimes can be messy at the time to mount to the printer, for example I'm using on two printers a standard thread 1/4 which measures 6.35 mm so is a little hard to coupling.

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However milling the thread this can be mounted correctly, but the screw is soft and can be bent or warped easily making your printer wobbly and and produces failed prints.

enter image description here

However I´m satisfied with the printing quality and I can set prints with 0.1 and can increase 0.05 by 0.05

Now I want to mount an screw of 10 mm to minimize wobbling generated by those warped (bow) that repeats variation on size (x,y) on every cycle or every revolution. The 10mm screw are completely straight. I don't think that the stepper motors can be compromised with an extra weight.

So, Z layers can be at 0.05 mm but it can be achieved 0.02 mm tested until now. But wider diameter can achieve smooth edges.

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    $\begingroup$ Please reread the question, it is not about diameter, it is about the lead (the advancing) of the nut. $\endgroup$ – 0scar Jun 20 '19 at 7:36
  • $\begingroup$ Yes, I know thats why I specified that z layers can be at 0.05mm but it can be achieved 0.02 tested until now. But wider diameter can achieve smooth edges. $\endgroup$ – Fernando Baltazar Jun 21 '19 at 16:17
  • $\begingroup$ @0scar Also refers to 5mm lead screw :) that size will wobble the printer and won't get well shaped borders, no matter if he worried about advancing z height. $\endgroup$ – Fernando Baltazar Jul 3 '19 at 5:37
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    $\begingroup$ True, such a small diameter screw (if that is what you mean) gets you into wobble issues pretty fast, that is just too thin to have rigidity. $\endgroup$ – 0scar Jul 3 '19 at 6:54

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