Hello,
I'd rough it out lengthwise, for the reason Ken mentions; then finish it across the chord, because that's the way the air will go
Ideally I'd use a final finishing pass at 45 to the chord. The effect of these three passes will make it much easier for you to finish manually to the exact profile of the airfoil. (where unintended "bumps" or "ridges" are NOT a good thing!)
Ballendo
P.S. Use as large a radius ballcutter as you can for the finish passes...