I had a look at the vertical milling attachment to my Emco Compact 5 (and also for 8).
Clamping of the quill is exactly the same as described in this topic. In the manual for the Emco C5 it is explicitly said to use bolt nr 3 for clamping. The bolt nr 3 (equivalent to bolt 84 in this topic) is M6 and also through the casting with a nut in a hex hole at the other end.
And I have to admit: for my column it is also (very) difficult to clamp the quill with an allen key! Actually, I never used it. Instead until now I used the fine feed to set the quill at the required height. And as far as I experienced it stays at that height during milling.
But I learned something: clamping of the quill of my Emco Compact 5 needs also improvement!
Regards,
Jouke