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.

Is the deflection what is ruining the tool or is it chatter that is making the tool wear out. The obvious answer for chatter is to slow down the RPM. Could you make a one piece extended holder just small enough to access the feature instead of stacking extensions?

First of all, thanks for your interest, by eliminating the anti-vibration extensions I would have to make a handcrafted support that would probably solve the bending problem for me but the vibrations would give big problems

Maybe make it so it uses 1 anti-vibration extension. If it is only a few parts slowing down the RPM and the feed rate to maintain the proper chip load is probably your best bet.

Now I am trying to use a cutter with 3mm thick carbide inserts with a very good cutting edge and it seems to work very well I just have to improve the durability of the insert