The milling surface generation can be axial, radial or sculptured, which depends on which kind of tool you are using and what process we are following.
Axially generated surface
The surface finish generated will replicate the shape of the bottom of the insert. An insert with corner radius (RE) will generate cusps. The size of the cusps depends on radius and feed.
Inserts with a parallel land (BS) are capable of making a flat surface. Depending on the axial tolerance and run-out of the cutter, the insert with the lowest position will create the milling surface finish.
Corner radius (RE)
Parallel land (BS)
To generate the best milling surface finish, it is important to ensure that the feed per revolution (fn = fz x zn) is less than 80% of BS.
As the cutter diameter increases (and for extra-close pitch cutters), the number of teeth as well as feed per revolution increases, requiring a larger BS. As soon as the feed per revolution exceeds the width of this land, the axial run-out of the cutter will affect the surface finish.
For best milling surface finish, use:
- Wiper inserts or milling inserts with BS at least 25% larger than fn
- Cermet inserts for a mirror finish
- Cutting fluid to avoid smearing
A wiper, or long parallel land, allows for finishing in larger diameters. The wiper is placed below the standard inserts, ensuring that this is the insert generating the surface. Max fn should not exceed 80% of BS.
Round inserts, or inserts with a large corner radius, are extremely productive, but they will not generate a high-quality surface. The larger the cutter diameter, the worse the surface finish.
Radially generated surface
When using an end mill, a shoulder mill or a side and face mill cutter, a radial surface is generated. For a radially generated surface, it is the side of the tool that generates the profile.
Each tooth produces a cusp (h). The width of the cusp is equal to feed per tooth, fz, and the depth of the cusp is determined by the relationship between the cutter diameter and fz. The theoretical size of the cusp generated is minimal.
Sculptured surface generation
When using a ball nose end mill, a sculptured surface is generated.