Z axis set position

Hey guys. So I am using RAMPS 1.4 and Marlin firmware on a cnc machine that I am using to cut foam. I am using a metal plate that that I have connected to the ground of my z-min endstop that completes a circuit when it touches my end mill bit which is connected to the signal by an alligator clamp. The plate is set on top of the material I am milling so the zero should be at the top of the material. The clamp is removed after homing. I want to know if there is any way to subtract the thickness of the metal plate in the firmware from what the new zero is determined to be. I might be going about this all wrong. I don't know. Any suggestions would be awesome.

Thanks.

You can reset the home position with G92, see here: [reprap.org]

Say your metal plate is 1mm thick and your tooltip is currently resting right on it. You can account for the thickness with the following command:

G92 Z1

This is telling Marlin that the Z-height you are currently at is 1mm above 0.

Thanks sirphillip. This is want I needed. But will I be able to do this after homing?