# 3DTouch: G-code to temporarily change probe points and Z home?

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:

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.

• 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 Mar 26 at 5:59
• 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 and raise the Z height after your G28 command. – 0scar Mar 26 at 11:09
• I can't join the files, I am going to edit the first post and add an example image of what I mean. – edea Mar 26 at 11:28
• 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 Mar 26 at 13:09