Z probe position

[dvician 0]

Hello.  New to all this and I am getting the hang of it.  Did some multi color prints and all worked well.   That is, because each color was on top of the previous at 0,0.   Each print, the probe checks Z height at 0,0 and prints on top with the new color.

 

Now I have a design the next color layer has nothing at 0,0.  

 

I can make the file and put in a Z offset, but I am afraid when I load this file, the previous job will be on the plate, and the head will want to move to 0,0 to "G28 home all axis"

 

How can I tell it to probe in a different location?  I can have it probe elsewhere on the plate and use z offset in Cura.  Or, I can have it probe Z height at a location on the top of the previous print (about 21mm above the plate.

 

I cannot figure out how to do this, please help.

Thanks.

[Slashee_the_Cow 291]

How a printer responds to a G28 command is entirely up to its firmware... and its firmware usually wants to probe roughly the middle of the plate, depending on printer. You can change this command so that it only homes certain axes (in this case you'd want X and Y but not Z), it would just need a quick post-processing script (let me know if you need me to whip one up). Or you could remove the auto home entirely, but it's generally better to home as many axes as you can to help ensure accuracy.

Edited October 9, 2023 by Slashee_the_Cow

[dvician 0]

Thanks for the offer to help.

 

I have decided to try to insert a "filament change" post processing at the layer in question.   It is a big print so I actually have to wait until tomorrow for more material to print and it will be about 20 hours to get to the layer in question, so I have to start it at a time I will be there when it is ready.    

 

I'll let you know if it works the way I need.

 

Thanks again.

[gr5 2,179]

I strongly advise you don't wait 20 hours but instead do a test print that takes maybe 20 minutes.  You can print super fast as well because underextrusion doesn't matter much for test prints.

[gr5 2,179]

Is this a delta printer?  It sounds like (0,0) is in the center of the printer and that usually only happens on delta printers.

[Slashee_the_Cow 291]

12 minutes ago, gr5 said:

I strongly advise you don't wait 20 hours but instead do a test print that takes maybe 20 minutes.

3D printing rule #7: Always test in small scale first.

 

I can't remember all the rules, but off the top of my head, #3 is "don't lick the hot end".

[dvician 0]

good points all.  I will add a filament change step at like layer 10 instead of 280 and see how it actually works.

This is an Ender 3.   By 0,0 I just said that as it appears the Z probe goes to about center of the plate after it homes X and Y.   I had just learned how to split and set Z in 3D builder so I figured if I could get it to probe Z somewhere in the corner away from my build it would work perfect.

 

The downside to the filament change or another pause is that I have to be on the spot at that point in time, whereas with the split files, I can do the 2nd one anytime after the first one printed...just got to get the head out of the way to find z.

[Slashee_the_Cow 291]

7 hours ago, dvician said:

just got to get the head out of the way to find z.

Easiest method: open the bottom mesh in Cura, scale it so that it's the correct size, then look it the bottom left corner:

That tells you the bounding box of the entire model. So I know that to put another model on top I need to set its Z position to 20:

I've just greyed out the one below for the demo image, it should be deleted entirely so only the top model is in the Cura project. You might have to turn off Drop Down Model which will automatically make Cura move the model so that its bottom is touching the plate.

 

More complex method: You can look at the g-code file for the first part to work it out.

 

For every new layer there'll be a comment like this:

;LAYER:165

Just before each of those there be a section something like this:

;MESH:NONMESH
G0 F300 X110.376 Y101.184 Z20
G0 F12000 X110.376 Y100.849
G0 X100.993 Y100.915
G0 X100.919 Y119.033
G0 X101.05 Y118.951
;TIME_ELAPSED:4850.377663

One of the G0 commands (in this case the top one) contains a Z co-ordinate. Mine isn't exactly the hardest to figure out (I'm making a 2cm cube, so it's 20)

 

Slightly complex method: import the second model into Cura and set its Z to that top Z height.

 

Complex method: If you want to set the Z height of the extruder manually, you need to add the initial layer height of the next mesh to find your starting Z co-ordinate. I'm using .12mm layers but with an initial layer of 0.2mm (to help it adhere) so the starting Z height for the extruder if I printed the same model on top of itself would be (finishing z + initial layer height), or for me (20 + 0.2 = 20.2).

Edited October 9, 2023 by Slashee_the_Cow
added simple answer

[gr5 2,179]

The "drop" down model feature is not in the cura settings - it's under menu "Preferences" "configure cura" and it's one of the checkboxes.  Once you've done that you can click on the part, click on the move tool, and type in any value for the Z offset.

[Slashee_the_Cow 291]

3 hours ago, gr5 said:

The "drop" down model feature is not in the cura settings - it's under menu "Preferences" "configure cura" and it's one of the checkboxes.

That setting changes Cura's behaviour to automatically drop down models in new projects.

Dropping down (or disabling it) for individual objects is still done from the move panel on the sidebar.

[gr5 2,179]

Oh!!  I've never seen that before.  It works!