<p>Your leadscrew probably is a 2&nbsp;mm pitch, <strong>4-start</strong> leadscrew. This means that there are actually 4 separate grooves on the leadscrew, each with a pitch of 8&nbsp;mm. Confusingly, this makes the total pitch 2&nbsp;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&nbsp;mm. Thus, in the Prusa calculator, you should enter a pitch of 8&nbsp;mm/revolution. Since you entered a pitch of 2&nbsp;mm, you ended up with a figure that is 4 times too large.</p>

<p>The reason leadscrews are made like this is that if you just had a single groove with an 8&nbsp;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.</p>

<hr>

<p>For the relative advantages and disadvantages of the various <em>leads</em> (8/4/2&nbsp;mm), as opposed to <em>pitches</em>, see also <a href="https://3dprinting.stackexchange.com/questions/4031/would-using-a-leadscrew-with-1-or-2-mm-lead-en-lieu-of-8-mm-result-in-a-better/">Would using a leadscrew with 1 or 2 mm lead, en lieu of 8 mm, result in a better printer?</a></p>

CC BY-SA 3.0
2017-06-17T20:53:02.427Z
Thank you for the hint, [here](https://www.amazon.com/gp/product/B014YJW5SW/) is a what I have bought, I will study your answer shortly.
morevitamins
CC BY-SA 3.0
2017-06-17T20:57:28.110Z
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!
morevitamins
CC BY-SA 3.0
2017-06-17T20:47:12.143Z
2017-06-19T07:43:58.487Z
2017-06-19T07:43:58.487Z
Tom van der Zanden
<p>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.</p>

<p>For Z axis, I have leadscrew with 8mm diameter and 2mm pitch.</p>

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

<p>I don't understand what I'm missing here. I have used <a href="http://www.prusaprinters.org/calculator/" rel="nofollow noreferrer">this</a> calculator to find <code>1600</code>.</p>

<p>Where I'm wrong on the math then?</p>

<prusa-i3><marlin><z-axis>
Why do I have to lower my Z axis steps per mm?
morevitamins
# Why do I have to lower my Z axis steps per mm?

(Asked by: username_0 on 2017-06-17)

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](http://www.prusaprinters.org/calculator/) calculator to find `1600`.

Where I'm wrong on the math then?

**Tags:** prusa-i3, marlin, z-axis


---

## 1 answers

### Answer by username_1 on 2017-06-17. Score: 3 | Accepted answer

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.

---

For the relative advantages and disadvantages of the various *leads* (8/4/2 mm), as opposed to *pitches*, see also [Would using a leadscrew with 1 or 2 mm lead, en lieu of 8 mm, result in a better printer?](https://3dprinting.stackexchange.com/questions/4031/would-using-a-leadscrew-with-1-or-2-mm-lead-en-lieu-of-8-mm-result-in-a-better/)

> **Comments:**
> **username_0**: Thank you for the hint, [here](https://www.amazon.com/gp/product/B014YJW5SW/) is a what I have bought, I will study your answer shortly.  
> **username_0**: 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!  

---

