Hi Tom,
For 6061 AL you can use the 1/8th (#102) or 1/16 (#112) square endmill.
Feeds and Speeds
1/8th in AL 6061
9200 RPM
.01" DOC
8 IPM Feed
1 IPM Plunge
Heres a project using the blue fixturing wax to hold aluminum, this product works really well: