My last blunder I can recall was similar, was a threading tool that held the triangle shaped insert on edge. TNMA I recall? Well anyway threading up to a shoulder, cutting a 1"-8 thread, yes there was a thread relief, but running at 160 RPM, didn't give you much time to disengage the half nuts and wam! Pushed the work piece up into the chuck and side swiped the tool and pretty much wiped the insert off and destroyed the tool holder. Had to buy another one at about $100 a pop! This happen on a 16" Axelson with a CA size tool post and over 7-1/2 HP doing the damage!