Z axis moves below set zero

[whensparksfly]

I have ajuster the motor tuning its not perfect but very close.now when I move the dro it's movement matchs the z axis.I load g code move the torch to the top of the materal zero all the axis press reg move up the z from the materal the run the g code .the torch will move down to materal then carry on down toward s the table then eventually will start to cut

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