Thats a possible reason there, thanks. It also could be a bit of crap under the tool maybe - this was a tiny tool with a 0.2mm tip so not a lot of contact area.

It would mean carnage if it happened on the Bridgeport though, I am not using probing on the main spindle as have now sorted out fixed-height tooling etc, but when i have the engraving spindle fitted i will need to use it then as the spindle only has Er20 collet.