<p>I realised the simplest fix for this shortly after posting the question. In either your slicer or your printer controller (I use octoprint, so I added this there) add to the starting G-code something to lift the head so that it is above the point it is scraping across.</p>

<p>For example, change your starting G-code from something like:</p>

<pre><code>G28 ;Home all axis
G29 ;probe bed
</code></pre>

<p>To</p>

<pre><code>G91 ;Set to relative positioning
G0 Z10 ;move head up by 10mm

G28 ;Home all axis
G29 ;probe bed
</code></pre>

<p>(obviously remove G29 if you do not have a probe)</p>

<p>10mm should be more than enough to lift by unless you have something seriously wrong, but you can adjust the figure as needed.</p>

CC BY-SA 3.0
2016-10-18T07:50:18.823Z
2016-10-18T07:50:18.823Z
James T
<p>Marlin has a <code>Z_RAISE_BETWEEN_PROBINGS</code> setting that allows you to, well, raise the Z-axis before it moves to the next probe point. Increasing this value may solve the issue.</p>

<p>Auto leveling only compensates for skew of the bed, but it doesn't compensate for a non-planar bed. If your bed is bowed (apparently you're not using glass yet, so I assume you have a plain PCB which is quite susceptible to this) and due to this is higher in some spots than others, then the auto leveling may cause the hotend to scrape the high spots of the bed.</p>

CC BY-SA 3.0
2016-10-18T07:44:14.383Z
It seems its unclear what i was getting at. It levels fine, but the centre of the bed is lower than the left side, so when moving left to home the X when Z=0 (in the centre) it scrapes the bed. Z_RAISE_BETWEEN_PROBINGS doesnt apply when its homing X/Y. Also, no PCB bed, its an aluminium plate.
James T
CC BY-SA 3.0
2016-10-18T15:55:04.667Z
Yeah, if your bed isn't planar, you're kind of screwed :-( . Best to replace/upgrade to something better.
Carl Witthoft
CC BY-SA 3.0
2016-10-19T07:10:04.103Z
It is planar, its just angled such that the left side is higher than the right side, but only so slightly as it makes a difference @Z=~0mm
James T
CC BY-SA 3.0
2016-10-18T07:04:35.777Z
2016-10-18T07:04:35.777Z
Tom van der Zanden
<p>You can always add to the starting code as told in an answer above. Also for the scrapping, you might want to set Z_HOMING_HEIGHT to prevent further damage to the hotend. If the Z axis is below the homing height, on homing x or y will first cause z axis to travel to the homing height and then proceed with homing of x or y axis.</p>

CC BY-SA 3.0
2017-02-14T16:38:15.643Z
This sounds like exactly the answer you are looking for?
Mtl Dev
CC BY-SA 3.0
2016-12-09T14:12:55.747Z
2016-12-09T14:12:55.747Z
Himanshu
<p>Sounds like you need a different sensor? You have a lot of issues from the sounds of it. Also no code so cannot comment on your settings.</p>

<p>If it always scrapes the bed (sorry but its really unclear what is going on) then lower your sensor a bit.. Best I can give you with the provided info.</p>

CC BY-SA 3.0
2016-10-18T07:43:59.890Z
It seems its unclear what i was getting at. It levels fine, but the centre of the bed is lower than the left side, so when moving left to home the X when Z=0 (in the centre) it scrapes the bed.
James T
CC BY-SA 3.0
2016-10-18T19:45:13.790Z
Oh, so it sounds like you need a flatter bed. That said I would just tell simplify3d to raise the first layer height. That also said lowering your hotend calibration sensor by 0.05mm (or more) will have the same effect.
MakerModder
CC BY-SA 3.0
2016-10-19T07:09:14.657Z
Its not that the bed isn't flat... its just angled such that the left side is higher than the right side, but only so slightly as it makes a difference Z =~0mm
James T
CC BY-SA 3.0
2017-02-14T16:40:26.817Z
So your bed is flat, but not level.  Can you not level the bed with the adjustment screws?
Mtl Dev
CC BY-SA 3.0
2017-02-14T16:43:08.037Z
@JamesTrotter that is the definition of not a flat bed. We are not talking about warped beds. we know it's physically flat, but it is not relatively flat.
MakerModder
CC BY-SA 3.0
2017-02-15T20:05:25.283Z
@StarWind isnt the point of auto leveling to account for a bed not "relatively flat"?
James T
CC BY-SA 3.0
2017-02-15T21:53:27.020Z
@JamesTrotter Auto leveling is not part of the question. That said follow ups to my reply should be done in a chat. On my printers auto leveling is an assistance program that tells me hey, Right side is too low! Fix it! I think you are thinking the "leveler" screws the Y axis.. That would not work.. If you lowered one end of the Y axis by moving only one Z motor you would get binding and a very bad night. Also there would be no way to fix the X axis.
MakerModder
CC BY-SA 3.0
2017-02-16T08:31:08.653Z
@StarWind What? Auto-leveling is mentioned at the end of the question, and i don't get what you mean by "tells me hey, Right side is too low! Fix it! ", because it certainly does not do that. It adjusts the print head at all times along the Z axis so that it is always a constant distance from the bed, isn't that the _point_ of it? It doesn't "screw the Y axis?", i don't even understand what you are attempting to convey with that statement.
James T
CC BY-SA 3.0
2016-10-17T17:50:58.057Z
2016-10-17T17:50:58.057Z
MakerModder
<p>You need an offset to protect your XY movements for Z=0 even if the plate is planar or angled; for example my sensor is made for 10mm height from plate but measures 4mm due the plate is aluminum. The nozzle needs to be at least 1mm or 2mm below the sensor level. If I adjust the nozzle at 4mm or more this will be scratch the plate if any level variation on bed exist.</p>

<p>So I set an offset and Z safe movement on Auto homming, adding 3 or 4mm. When I press AutoHome the nozzle rise up to the safety level even if the nozzle is touching the bed.</p>

<p>You don´t need the Z=0 to start printing, when you Use the code G29 the printer will check the predefined test points to get the right Z=0 according the angled plate; if your plate is warped you will need a lot of test points but is much better to change it.</p>

CC BY-SA 3.0
2016-10-19T07:50:52.027Z
2016-10-19T07:50:52.027Z
Fernando Baltazar
<p>If the hot-end is at ~0 on the Z axis and I go to level it, as it approaches X = 0 it begins scraping along the bed, then when moving back to probe the center of the bed (after homing X to 0) it will scrape the bed again.</p>

<p>I want to add a glass plate but am worried this aggressive homing will smash the glass. How can I fix it? The printer auto-levels and runs Marlin.</p>

<marlin>
When leveling hotend always slams into bed?
James T
# When leveling hotend always slams into bed?

(Asked by: username_0 on 2016-10-17)

If the hot-end is at ~0 on the Z axis and I go to level it, as it approaches X = 0 it begins scraping along the bed, then when moving back to probe the center of the bed (after homing X to 0) it will scrape the bed again.

I want to add a glass plate but am worried this aggressive homing will smash the glass. How can I fix it? The printer auto-levels and runs Marlin.

**Tags:** marlin


---

## 5 answers

### Answer by username_0 on 2016-10-18. Score: 3 | Accepted answer

I realised the simplest fix for this shortly after posting the question. In either your slicer or your printer controller (I use octoprint, so I added this there) add to the starting G-code something to lift the head so that it is above the point it is scraping across.

For example, change your starting G-code from something like:

```
G28 ;Home all axis
G29 ;probe bed

```

To

```
G91 ;Set to relative positioning
G0 Z10 ;move head up by 10mm

G28 ;Home all axis
G29 ;probe bed

```

(obviously remove G29 if you do not have a probe)

10mm should be more than enough to lift by unless you have something seriously wrong, but you can adjust the figure as needed.


---

### Answer by username_1 on 2016-10-18. Score: 2

Marlin has a `Z_RAISE_BETWEEN_PROBINGS` setting that allows you to, well, raise the Z-axis before it moves to the next probe point. Increasing this value may solve the issue.

Auto leveling only compensates for skew of the bed, but it doesn't compensate for a non-planar bed. If your bed is bowed (apparently you're not using glass yet, so I assume you have a plain PCB which is quite susceptible to this) and due to this is higher in some spots than others, then the auto leveling may cause the hotend to scrape the high spots of the bed.

> **Comments:**
> **username_0**: It seems its unclear what i was getting at. It levels fine, but the centre of the bed is lower than the left side, so when moving left to home the X when Z=0 (in the centre) it scrapes the bed. Z_RAISE_BETWEEN_PROBINGS doesnt apply when its homing X/Y. Also, no PCB bed, its an aluminium plate.  
> **username_2**: Yeah, if your bed isn't planar, you're kind of screwed :-( . Best to replace/upgrade to something better.  
> **username_0**: It is planar, its just angled such that the left side is higher than the right side, but only so slightly as it makes a difference @Z=~0mm  

---

### Answer by username_3 on 2016-12-09. Score: 1

You can always add to the starting code as told in an answer above. Also for the scrapping, you might want to set Z\_HOMING\_HEIGHT to prevent further damage to the hotend. If the Z axis is below the homing height, on homing x or y will first cause z axis to travel to the homing height and then proceed with homing of x or y axis.

> **Comments:**
> **username_4**: This sounds like exactly the answer you are looking for?  

---

### Answer by username_5 on 2016-10-17. Score: 0

Sounds like you need a different sensor? You have a lot of issues from the sounds of it. Also no code so cannot comment on your settings.

If it always scrapes the bed (sorry but its really unclear what is going on) then lower your sensor a bit.. Best I can give you with the provided info.

> **Comments:**
> **username_0**: It seems its unclear what i was getting at. It levels fine, but the centre of the bed is lower than the left side, so when moving left to home the X when Z=0 (in the centre) it scrapes the bed.  
> **username_5**: Oh, so it sounds like you need a flatter bed. That said I would just tell simplify3d to raise the first layer height. That also said lowering your hotend calibration sensor by 0.05mm (or more) will have the same effect.  
> **username_0**: Its not that the bed isn't flat... its just angled such that the left side is higher than the right side, but only so slightly as it makes a difference Z =~0mm  
> **username_4**: So your bed is flat, but not level.  Can you not level the bed with the adjustment screws?  
> **username_5**: @JamesTrotter that is the definition of not a flat bed. We are not talking about warped beds. we know it's physically flat, but it is not relatively flat.  
> **username_0**: @StarWind isnt the point of auto leveling to account for a bed not "relatively flat"?  
> **username_5**: @JamesTrotter Auto leveling is not part of the question. That said follow ups to my reply should be done in a chat. On my printers auto leveling is an assistance program that tells me hey, Right side is too low! Fix it! I think you are thinking the "leveler" screws the Y axis.. That would not work.. If you lowered one end of the Y axis by moving only one Z motor you would get binding and a very bad night. Also there would be no way to fix the X axis.  
> **username_0**: @StarWind What? Auto-leveling is mentioned at the end of the question, and i don't get what you mean by "tells me hey, Right side is too low! Fix it! ", because it certainly does not do that. It adjusts the print head at all times along the Z axis so that it is always a constant distance from the bed, isn't that the _point_ of it? It doesn't "screw the Y axis?", i don't even understand what you are attempting to convey with that statement.  

---

### Answer by username_6 on 2016-10-19. Score: 0

You need an offset to protect your XY movements for Z=0 even if the plate is planar or angled; for example my sensor is made for 10mm height from plate but measures 4mm due the plate is aluminum. The nozzle needs to be at least 1mm or 2mm below the sensor level. If I adjust the nozzle at 4mm or more this will be scratch the plate if any level variation on bed exist.

So I set an offset and Z safe movement on Auto homming, adding 3 or 4mm. When I press AutoHome the nozzle rise up to the safety level even if the nozzle is touching the bed.

You don´t need the Z=0 to start printing, when you Use the code G29 the printer will check the predefined test points to get the right Z=0 according the angled plate; if your plate is warped you will need a lot of test points but is much better to change it.


---

