Peripheral Milling

For peripheral milling, the axis of the tool is parallel to the surface being machined, and the operation is performed by cutting edges on the outside periphery of the cutter. There are different types of peripheral milling.

Slab Milling Slotting Side Milling Straddle Milling
The basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides. Also called slot milling, in which the width of the cutter is less than the workpiece width, creating a slot in the work—when the cutter is very thin, this operation can be used to mill narrow slots or cut a workpiece in two, called saw milling. The cutter machines the side of the workpiece. Similar to side milling, only cutting takes place on both sides of the work.

In peripheral milling, the rotation direction of the cutter distinguishes two forms of milling: up milling and down milling. In up milling, also called conventional milling, the direction of motion of the cutter teeth is opposite the feed direction when the teeth cut into the work. It is milling "against the feed." In down milling, also called climb milling, the direction of cutter motion is the same as the feed direction when the teeth cut the work. It is milling "with the feed."

The relative geometries of these two forms of milling result in differences in their cutting actions. For up milling, the chip formed by each cutter tooth starts out very thin and increases in thickness during the sweep of the cutter. In down milling, each chip starts out thick and reduces in thickness throughout the cut. The length of a chip in down milling is less than in up milling. This means that the cutter is engaged in the work for less time per volume of material cut, and this tends to increase tool life in down milling.

The cutting force direction is tangential to the periphery of the cutter for the teeth that are engaged in the work. In up milling, this has a tendency to lift the workpart as the cutter teeth exit the material. In down milling, this cutter force direction is downward, tending to hold the work against the milling machine table.