<p>To allow negative axis values, usually, the way is to use <code>G1 S1</code> to <a href="https://reprap.org/forum/read.php?267,329935,330264" rel="nofollow noreferrer">disable boundary</a> checks and <code>G1 S0</code> to enable them.</p>

<p>Another way is to force homing Z, which means moving till an endstop triggers and then moving back up the specified motion via <code>G28 Z</code></p>

<p>Another alternative would be to send <code>G92 Z50</code> to set the Z-hight to 50, then <code>G1 Z-50 F200</code> to move that much down, rinse and repeat.</p>

CC BY-SA 4.0
2018-12-07T00:38:57.520Z
2018-12-07T00:50:25.910Z
2018-12-07T00:50:25.910Z
Trish
<p>My Prusa i3 MK3 forgot his home position and it now assumes that the Z 0.0 position is right at the top of the printer. I've <a href="https://shop.prusa3d.com/forum/assembly-and-first-prints-troubleshooting-f62/lowering-z-axis-if-head-is-at-the-top--t25773.html" rel="nofollow noreferrer">asked about this in the Prusa forum before</a> and at that time, I accidentally found a solution using Pronterface.</p>

<p>So I am now in the same situation again. The printer head is at the very top. It assumes that this is Z 0.0, so I can't move it down.</p>

<p>Calibrating Z does not help. It will always display</p>

<blockquote>
  <p>Some problem encounteres, Z-leveling enforced ...</p>
</blockquote>

<p>and some time later, it calibrates Z again, resulting in the same problem and so on (endless loop).</p>

<p>The Pronterface trick (pressing the home button) does not work any more. However, Pronterface seems to accept raw G-Code.</p>

<p><strong>Which G-Code command would I need to send to the printer to let the head move down?</strong> That would need to be a command that just rotates the stepper motor and does not consider the Z-axis value, so that the head effectively moves to negative Z values.</p>

<p>I have also tried:</p>

<ul>
<li>moving the head down manually while the printer was turned off. I'd like to avoid that. It just doesn't feel right. However, it worked after the third attempt and I was able to do a XYZ calibration. However, during bed leveling, it failed and went into the "some problem encountered" state again.</li>
</ul>

<prusa-i3><calibration>
Moving the Z-axis stepper motors below Z 0.0
Thomas Weller
# Moving the Z-axis stepper motors below Z 0.0

(Asked by: username_0 on 2018-12-06)

My Prusa i3 MK3 forgot his home position and it now assumes that the Z 0.0 position is right at the top of the printer. I've [asked about this in the Prusa forum before](https://shop.prusa3d.com/forum/assembly-and-first-prints-troubleshooting-f62/lowering-z-axis-if-head-is-at-the-top--t25773.html) and at that time, I accidentally found a solution using Pronterface.

So I am now in the same situation again. The printer head is at the very top. It assumes that this is Z 0.0, so I can't move it down.

Calibrating Z does not help. It will always display

> Some problem encounteres, Z-leveling enforced ...

and some time later, it calibrates Z again, resulting in the same problem and so on (endless loop).

The Pronterface trick (pressing the home button) does not work any more. However, Pronterface seems to accept raw G-Code.

**Which G-Code command would I need to send to the printer to let the head move down?** That would need to be a command that just rotates the stepper motor and does not consider the Z-axis value, so that the head effectively moves to negative Z values.

I have also tried:

* moving the head down manually while the printer was turned off. I'd like to avoid that. It just doesn't feel right. However, it worked after the third attempt and I was able to do a XYZ calibration. However, during bed leveling, it failed and went into the "some problem encountered" state again.

**Tags:** prusa-i3, calibration

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## 1 answers

### Answer by username_1 on 2018-12-07. Score: 1

To allow negative axis values, usually, the way is to use `G1 S1` to [disable boundary](https://reprap.org/forum/read.php?267,329935,330264) checks and `G1 S0` to enable them.

Another way is to force homing Z, which means moving till an endstop triggers and then moving back up the specified motion via `G28 Z`

Another alternative would be to send `G92 Z50` to set the Z-hight to 50, then `G1 Z-50 F200` to move that much down, rinse and repeat.


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