Process Glossary — Start Here
Milling is a machining process where a rotating, multi-tooth cutter removes material from a workpiece that's held stationary or fed into the cut. It's the mirror image of turning: in milling the tool spins and the part sits still (or feeds slowly); in turning, it's the other way around. This page covers the two calls that trip machinists up most — peripheral vs. face milling, and up-milling vs. down-milling — then points to the depth pages for feeds, speeds, and depth of cut.
A milling cutter — an end mill, face mill, or shell mill — is loaded into a rotating spindle and driven against a workpiece that's clamped to a table. Because the cutter carries multiple teeth, each one only engages the material for a fraction of every revolution, so the cut is interrupted rather than continuous. That's one of the biggest practical differences from turning, where a single edge stays engaged in a continuous cut on a rotating part. Milling machines come in vertical and horizontal configurations — vertical mills point the spindle straight down at the table, horizontal mills point it sideways — but the underlying cutting mechanics are the same either way.
There are two fundamentally different ways a milling cutter removes material. In peripheral (slab) milling, the cutter's axis runs parallel to the surface being cut, and material comes off the teeth around the tool's outside diameter — an end mill machining the wall of a pocket is a good example. In face milling, the cutter's axis is perpendicular to the surface, and cutting happens mainly with the teeth on the flat end of the tool as it skims across the top of the part — a face mill flattening a plate is the classic case. Most real cuts blend both actions at once (an end mill milling a pocket floor is face milling on the bottom and peripheral milling on the walls), but knowing which mechanism is doing the work in a given pass explains a lot about tool choice and finish.
Within peripheral milling, a second choice matters just as much: which direction the workpiece feeds relative to cutter rotation. In up milling (conventional milling), the feed opposes the cutter's rotation at the point of contact — the tooth enters with a chip thickness near zero and the chip grows thicker as the tooth sweeps through, exiting at maximum thickness. In down milling (climb milling), the feed direction matches the cutter's rotation at contact — the chip starts at its thickest right at entry and thins to nothing as the tooth exits. Climb milling is generally preferred wherever the machine, fixturing, and workpiece rigidity allow it: cutting forces pull the workpiece into the cutter instead of lifting it, and the edge isn't rubbing on a work-hardened surface before it bites, which usually means better finish and longer tool life. The catch is backlash — on older machines with loose table screws, climb milling's forces can drag the table forward and cause chatter or a dig-in, which is exactly why conventional milling is still the safer default on well-worn equipment.
This page is the starting point. For the numbers that actually set up a milling job — how fast the cutter spins, how fast the table feeds, and how much material comes off per pass — see the pages linked below.