I suspect for a nice finish on a spherical pocket in 3.5" diameter aluminum,
the 7x10 will not do what you want. I have found that the capabilities of
mills and lathes are better described by the weight of machine rather than
by the size numbers. Here is more info on the 7x10 and other machines
in the Noisy/Dirty shop:
http://static.skillhouse.org/shop
On the other hand, FL Tech Toybox is offering a limited number of joint
memberships for cheap, and they have a 12x36 or 12x40 that would
be perfectly suitable.
Brian