[lammps-users] About constant velocity

Dear all,

I have done some large simulation of nanometric cutting with the aid of LAMMPS. There are four types atoms, and the cutiing tool is the type 4. The cutting tool is applied a constant velocity with the command “velocity set tool -2 0 0”.
However, I found that the tool put up in vertical direction while moving forward, you can see clearly in the attached snapshots.
But I did set the tool’s y-velocity as 0, how can it move up?
I am so puzzled, I hope you will give me some advice.

Best regards,