For flattening the tops of material a 16mm is probably as large as you want to go as it becomes less economic to pay more for larger cutters and just wear the end away. For side cutting then there is little to be gained in going up to a larger cutter as you won't gain rigidity considering the rest of the set up and the need to run the larger cutters slower will take the motor out of it's power band unless you go with solid carbide milling cutters.
Fly cutters will work but do need to be kept sharp they are also relatively slow to remove metal as you only get one cut per rev where you will get more with fluted cutters. They can also be a bit harsh on the drive train as unlike with a milling cutter you will get long periods of no tool engagement which can "knock" as the single cutter comes round each time. Something like these, the middle size 25mm head, swinging about 35-40mm dia would do
We have a few members here who use the two insert 25mm insert mill on their X2 size machines, if you do go down that route then I would suggest using the APKT inserts meant for non ferrous metal on all materials as they are sharper and put less strain on the machine. They won't cover quite such a large area as a flycutter but with twice a smany cutting edges and being able to run higher spindle speeds due to carbide will make quicker work of a job.
Both the flycutter and the insert cutter you would not want to take off more than 0.5mm per pass.
Remember that if the tram is out then the larger the diameter cutter the greater the chance of getting a concave surface so you really critical parts it can be better to make multiple passes with a sharp small 3 or 4 flute cutter of say 6mm dia
Edited By JasonB on 11/09/2023 07:04:36