What CNC do you have?
What software are you used to run it?
I used to oversee a linuxCNC run CNC that occasionally would not run the home routine correctly and homing the Z axis was where it went the wrong way. Only in that case it started down trying to find a limit switch rather than up where it would have. What ended up being the problem was that the Z axis limit switch was frozen in the closed position and it should have been open until touched by the Z axis. Replacing that limit switch fixed it.
If your CNC has never yet homed the Z axis properly then a setup file might have an incorrect value in to for the Z home routine.
4D

 

It is CNCEST 6090 CNC router.
The software is MACH3

 

Welcome to the forum @bitterlesson

 

g'day @bitterlesson , welcome to the forum.

 

Since my soft max is zero on Z axis, this results in chattering

Does the homing work if you disable softlimits? I don't think the softlimits are causing your "chattering".

 

hi,Welcome aboard!

 

Hi 4D not sure of your machine or software but I am pretty sure your home position and soft limit position can not be t he same value. If possible give pic of your G code .