Here is a very simple but highly useful accessory I made from a 13x13x40 mm block and a broken end mill.
There was some vibration due to the unbalanced rotating mass, something that I fix later adding a simple counterweight. And of course I took advantage of a not-perfectly trammed head to get a nice finish (about 15um less in the middle, not bad).
Finally a picture showing how useful is the side plate.
In the last working round I just note some upset behavior related to, I guess, thermal expansion. The DOC can increase, easily, 0.02mm after a couple of millimiters of feed. You can learn to deal with this, but now I think that a bigger mass cutting bit it’s a better idea (of course this doesn’t matter if you use coolant). Anyway, no matter what flycutter you use, I think a double finishing pass it’s always a good idea (0.03 and then 0.02 mm for example).