### Why do I have to lower my Z axis steps per mm?

• First, X and Y axis works perfectly, I measured well. I have plugged all jumpers, and use a very standard ramps 1.4 setup with standard Nema 17 200rev 1.8 motors and A4988 drivers.

For Z axis, I have leadscrew with 8mm diameter and 2mm pitch.

I calculated it should be `1600` steps per mm.
Problem is when I call `G1 Z5` it goes to 2 cm. So I lowered my setting to `400` steps per mm and problem solved.

I don't understand what I'm missing here. I have used this calculator to find `1600`.

Where I'm wrong on the math then?

• Your leadscrew probably is a 2 mm pitch, 4-start leadscrew. This means that there are actually 4 separate grooves on the leadscrew, each with a pitch of 8 mm. Confusingly, this makes the total pitch 2 mm, since the distance from one groove to the next is 8mm divided by 4 grooves. However, one revolution of the leadscrew will still move the nut by 8 mm. Thus, in the Prusa calculator, you should enter a pitch of 8 mm/revolution. Since you entered a pitch of 2 mm, you ended up with a figure that is 4 times too large.

The reason leadscrews are made like this is that if you just had a single groove with an 8 mm pitch, the nut would need to be made very long to enable it to make contact with a sufficiently long portion of thread. By increasing the number of grooves, you can get away with a shorter nut. With lower pitch (lead-)screws you don't need multiple starts, since the lower pitch means the same length of nut is in contact with more thread.

Thank you for the hint, here is a what I have bought, I will study your answer shortly.

You are just amazing! I feel real guilty just reading `2mm pitch` in the product description and verifying by looking at the lead teeth. Indeed, product title says 8mm `screw` pitch. TIL nut matters! Thank you!