I don't know why this happened. Was testing hole size in some 3/4" pdf that had a white laminate on it. it was a 1/4" downcut end mill at 1ips because I wanted the holes accurate. I cut the hole checked the size went back to aspire to change the tool path a bit to loosen the hole up when I see a glow coming from the hole as the machine was just starting the next test hole. I grabbed a bottle of water but turned off the dc but not the vac.I had to move the sheet to make sure it was out as it was still smoking. Now See why it had spread fast.
it was a 3/8" hole and I was using a inside profile cut a climb and a regular.