Face Milling: 45 or 90 Degree Face Mill? - CNCCookbook: Be ...
At one time, octagonal face mills were at war with the 45 degree face mills for supremacy. The octagonal inserts have more edges, so you can rotate the insert if one gets chipped. But, tooling costs are usually only about 3 percent of the manufacturing cost, so the greater efficiency of the 45's eventually won out.