Which end mill to level my acrylic bed?

[HankMcSpank]

Old thread I know, but I've just got my fly cutter!

(I went for the one blackburn_mark suggested .... http://www.ebay.co.uk/itm/Fly-Cutter...item3f0cb22c9d )

I now need some guidance ....

So the thing is the fly cutter has an 8mm shank, but my modest spindle (200W) only goes up to 6mm collet size. So I used my mini lathe to turn the shaft down, but while doing so the lathe control board blows, to get the remaining 0.5mm off the shank, would you believe I attached a benchtop test psu directly to the lathe's dc motor (needs must!)) ...the PSU only goes up to 60V (vs 180V the motor expects) so the motor turned slower than normal but I got there in the end.

So I slaps the the fly cutter in my CNC spindle & turn it on ...."woah there fella!" ..... Vibration City, Arizona!! (btw: this particular tool scares the life out of me -a sharp bit of metal hurtling around that I can't even see..... god forbid if that cutting tool ever flies out of its holder).

So I backs the revs right off (fortunately my spindle speed goes down to about 800rpm) & sets the thing off cutting. I've got my CNC aluminium bed topped with 5mm acrylic. Sure enough it's well out of true...the right side of the bed is higher than the left & the front of the bed is lower than the rear! (that'll be why I'm getting such crap result wrt pcb milling)

ok, to my question, the fly cutter is only cutting on one side of it travel as the blade spins around from about 1 o' clock to 5 'o' clock (in other words looking at the spindle from the front, the actual fly cutter is only cutting the surface on the right hand side) ....presumably this means my Z axis is not bang perpendicular (the cutting radius is about 48mm) ....is such an assumption correct or could it be something else causing this (fly cutter shaft, spindle shaft etc). Does it even matter - wrt fly cutters - if the cutter doesn't cut equally around it's full travel? Yeah, I know to you guys it'll be obvious...it's only when I hit issues like this - no matter what I mighnt sometimes con myself - that I realise what a totally un-engineering mind I really have.