CNC 3018 PCB drill bit break

Good day everyone,

I ask for help with my CNC 3018 PCB board milling.

I’m new to CNC 3018 as beginner. I tried mill for PCB to made own Diy Z probe from YouTube,

YouTube link:
DIY Z Probe For CNC Machine - YouTube but PCB End Mill break

I downloaded Z probe from this link, I opened fusion 360 and save as NC file for UGS.

I successfully tested to mill on wood with V cutting bit, the I started mill with PCB mill bit size is 0.8mm, but it don’t cut the PCB board deeper. I tried to made deeper and it is worse to cut and PCB ugly look.

Check image below