It's fairly new TTS tooling, but the end mill was pretty old. It does have a chipped tooth now, I assumed it happened when it started cutting too deep, but perhaps it did so another time and I didn't notice, thus causing vibration and the pulling out? I had done several cuts before and with a new end mill, several cuts after and no problem.

While I am on the subject, I am cutting out a rectangular piece of 1/4 plate that's 5x7", taking two cuts of .13. Would you just take one cut of .26, or would you use a bigger endmill with multiple/single cuts.

When I was doing stuff like this on my Bridgeport I would cut up to 1 1/2 times the cutter deep in one pass.