Z axis not able to remain constant during lateral move

Hi all,

I am building my second mini kossel printer. The first one workes well and I able to print with it.

The second one is giving me a lot of hard time. The problem is that the Z axis will not remain constant while the printer moves on x and y axis.
I bring the printing head as close as possible to the plate using pronterface and then I start moving in 10 mm increments on the X and Y axis. While moving, the head will raise to about 1mm while moving to the back (+y) and will start touching the plate coming forward (-y). The same happens on the X axis. Negative x will make the head raise and positive x will make it start digging in the plate.

So far, I have tried with no results:
- make sure the plate is level
- make sure the endstops are at the same height on the towers
- make sure the belts are tight
- make sure the arms (the 6 arms from the moving cart to the extruder) are of the same size
- make sure the arms can move free
- make sure the towers are at the same distance from each other
- make sure the settings in Marlin for the diagonal_rod and the others are good

I do not understand what makes it different for this printer then the other one I've done. They are exactly the same.
Can you please advise?

Thank you!
Zoli

Have you checked the horizontal offset? That value will change the cupping or doming behavior.

Hi,
Thanks for the quick reply!

I am not sure if I got your answer right...
Are you talking about this line:
// Horizontal offset of the universal joints on the carriages.
#define DELTA_CARRIAGE_OFFSET 22.0 // mm

If yes, then the answer is yes, That is the correct value for my mini delta.

Thank you again,
Zoli

Start at 1905.1 in this document:

[docs.google.com]

Hi Nebbian,

Thank you for the link. I didn't know that such a detailed document exists.
I am currently at work but later this evening I will try that section.

I will post back my findings.

Regards,
Zoli