Disc milling at a high depth

Hello everyone, I need to make a kind of throat at a very high depth with a mazak integrex e-670h using a hsk100 anti-vibration attachment 350 long from the big kaiser, 2 extensions of 100 and an anti-vibration extension of 180 big kaiser in diameter 63, I mount a hss disc cutter with a chipbreaker profile with a diameter of 100 thickness 6, a total exit of 800, the throat is 30 thick 15 deep in a hole with a diameter of 180 material 20mncr5 (iron), I have problems with bending of the 'tool that makes the cutter last a short time, I would like to know if anyone has ever done something like this and has something to advise me, I tried to look at the angle heads to totally change the method but there are none with such a leak, I hope to having explained myself and not having left anything out. hello and good luck.