I forgot to send the spindle to X0 A0 after probing for a bit change and started the G-code job. The first bit motion was to plunge to the cut depth and because of my mistake it was still over the chuck. Thus it broke the bit and marked the chuck… I added the following lines to the program start:
G20G91 Z2.00
M3 S24000
G4 P10
For me this raises the spindle two inches then starts the spindle at 24000 rpms and pauses for 10 seconds for the spindle to come up to speed.
I added M5 to the program stop
This way if I forget to go to X0 A0 the bit will be high enough to clear the chuck when I tell g-sender to start the G-code running.