I'm a bit confused by this issue, but here it is:
When I test each stepper motor, they all behave correctly.
For example 'stepper_buzz stepper=stepper_z' moves front left corner (up first and then down) 10 times as expected.
I get the exact same behavior for _z1, _z2, _z3. All move (up first and then down) 10 times.
When I try to home the z axis 'g28 z' The two front motors (z, z3) move up and (z1,z2) move down for about 2 seconds. This binds the gantry and makes a horrible grinding noise.
It will then stop and wait a few seconds then all motors will turn the same direction and the gantry will go down and hit the endstop. The gantry is not level at all, front is higher up and back is closer to the build plate.
Any suggestions?