<p>I am using a BLTouch clone (3DTouch), and with <code>G28</code> and <code>G29</code> in Simplify3D it auto-detects Z home right in the center of the bed and afterward it measures 9 grid points. For most of my printings, this is great, except for a special one.</p>
<p>This special one consists of one first print with a thin drawing and a second print on top of that drawing (obviously with the gap matching the drawing).
<code>G28</code> and <code>G29</code> are not an issue for the drawing print, but for the second print where the nozzle must not touch the center (since it would ruin the drawing and would measure a wrong Z home and a wrong Z probe point there).</p>
<p>So is there a G-code that indicates the printer to select Z home on a different position (determined by X and Y coordinates, outside the drawing) and to eliminate the central point of the grid (leaving the remaining 8 points)?</p>
<p>Obviously, I can't change the firmware every time that I print that special figure, so it must be through a script.</p>
<p>EDIT:</p>
<p>This is an example of the print, the very first layer:</p>
<p><a href="https://i.sstatic.net/ik3hl.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ik3hl.png" alt="enter image description here" /></a></p>
<p>Print 1: 0,4 mm layer of blue</p>
<p>Print 2: 0,4 mm layer of green</p>
<p>Print 3: Much thicker and bigger print of white filament that prints around the previous prints during the first 2 layers and start covering all by the third layer.</p>
<p>Imagine a box cover with a drawing on top. The first layers of each print must be as smooth and nice as possible as is it the visible one. I was doing this manually before installing the BLTouch with very good results, the drawing gets embedded in the final printing.</p>

CC BY-SA 4.0
2021-03-26T05:59:55.727Z
You're printing the same thing right in top of a previous print? Are you changing filament or something? Why not just have it print extra layers during the same print?
Rykara
CC BY-SA 4.0
2021-03-26T11:09:14.030Z
As there is already a layer laid out on the build plate you should not use `G29` to scan the plate again. As said in a previous comment, can't you join the 2 files? Alternatively, don't use `G29`, instead [load a saved mesh](/q/15952) and raise the Z height after your `G28` command.
0scar
CC BY-SA 4.0
2021-03-26T11:28:49.033Z
I can't join the files, I am going to edit the first post and add an example image of what I mean.
edea
CC BY-SA 4.0
2021-03-26T13:09:58.553Z
I could indeed load a saved mesh, that would solve the second time that the nozzle goes to the middle before printing.
Now I would just need to know how to tell the BLTouch to measure Z home in the coordinates I want.
edea
<g-code><bltouch>
3DTouch: G-code to temporarily change probe points and Z home?
edea
# 3DTouch: G-code to temporarily change probe points and Z home?

(Asked by: username_0 on 2021-03-25)

I am using a BLTouch clone (3DTouch), and with `G28` and `G29` in Simplify3D it auto-detects Z home right in the center of the bed and afterward it measures 9 grid points. For most of my printings, this is great, except for a special one.

This special one consists of one first print with a thin drawing and a second print on top of that drawing (obviously with the gap matching the drawing).
`G28` and `G29` are not an issue for the drawing print, but for the second print where the nozzle must not touch the center (since it would ruin the drawing and would measure a wrong Z home and a wrong Z probe point there).

So is there a G-code that indicates the printer to select Z home on a different position (determined by X and Y coordinates, outside the drawing) and to eliminate the central point of the grid (leaving the remaining 8 points)?

Obviously, I can't change the firmware every time that I print that special figure, so it must be through a script.

EDIT:

This is an example of the print, the very first layer:

[![enter image description here](https://i.sstatic.net/ik3hl.png)](https://i.sstatic.net/ik3hl.png)

Print 1: 0,4 mm layer of blue

Print 2: 0,4 mm layer of green

Print 3: Much thicker and bigger print of white filament that prints around the previous prints during the first 2 layers and start covering all by the third layer.

Imagine a box cover with a drawing on top. The first layers of each print must be as smooth and nice as possible as is it the visible one. I was doing this manually before installing the BLTouch with very good results, the drawing gets embedded in the final printing.

**Tags:** g-code, bltouch
> **Comments:**
> **username_1**: You're printing the same thing right in top of a previous print? Are you changing filament or something? Why not just have it print extra layers during the same print?  
> **username_2**: As there is already a layer laid out on the build plate you should not use `G29` to scan the plate again. As said in a previous comment, can't you join the 2 files? Alternatively, don't use `G29`, instead [load a saved mesh](/q/15952) and raise the Z height after your `G28` command.  
> **username_0**: I can't join the files, I am going to edit the first post and add an example image of what I mean.  
> **username_0**: I could indeed load a saved mesh, that would solve the second time that the nozzle goes to the middle before printing. Now I would just need to know how to tell the BLTouch to measure Z home in the coordinates I want.  

---

## 0 answers

