[ifixcnc]

Lucky the door was cloed.

[Dolphin USA]

Ouch - I'd say...

[keebler303]

Dang! Is that a 1" holder?

[Jashley73]

I've seen this twice already on the same machine, and a crash was not involved either time. Once, the insert didn't even break. Too much stick out + chatter + time = fatigue cracks, and eventually a breakage. Notice the grainy texture, then the smooth texture? Grainy = fatigued material.

[Geof]

It is a classical fatigue failure but you have it backwards. The grainy part is what was still holding it together until it finally fractured. The dull area is where the fatigue crack propagated across.