Beautiful Flycutting

[tonyfoale]

If the mill head is not trammed accurately you will get a hollow surface.
For a given degree of misalignment you will get a flatter surface by making multiple passes with a smaller cutter. Lots of small scallops in place of one large scallop. Of course that takes longer.
It depends if you want flat or pretty.
Best to tram the mill accurately, 0.5 deg is a huge error if you want accurate milling (105 thou per foot). Even a tenth of that 0.05 deg is 10.5 thou per foot.

To put an example to those numbers, if your tool cutting diameter is 6" then if you make a 6" wide cut the centre will be 52 thou low for 0.5 deg error or 5.2 thou for a 0.05 deg error. If you make multiple passes with a 0.5" cutter with no overlap (which is the worst case because you would normally use overlap) then the flatness errors would be 4.4 thou and 0.44 thou respectively.

If you do not get the finish that you want with a well aligned head then you need to look at tool shape.