§1Many teeth, small bites
Where a lathe tool cuts continuously with one edge, a milling cutter cuts intermittently with many: each tooth enters, removes a small chip, and leaves, the next tooth following. The load is shared and the cut is interrupted.
This has two consequences that shape all of milling. Because several teeth share the work, a milling cutter removes metal quickly and can machine flats, slots, profiles and pockets that a lathe cannot. But because each tooth cuts only intermittently, it enters and leaves the work thousands of times a minute — an interrupted cut that hammers the edge and demands tougher tool geometry than continuous turning. The feed is therefore reckoned per tooth, not per revolution (§4), and the rotation sense relative to feed matters (§3). Milling is turning’s complement: less continuous, far more versatile.
Contents§2The main cutter types
Milling cutters divide by how the teeth are arranged relative to the spindle — on the periphery, on the end, or both — which decides what they can machine.
| Cutter | Teeth | Machines |
|---|---|---|
| Slab / plain | periphery only | wide flat surfaces (horizontal mill) |
| End mill | periphery + end | slots, pockets, profiles, shoulders |
| Face mill | face, insert-tipped | large flat faces, efficiently |
| Side-and-face | periphery + sides | slots and steps (horizontal) |
| Slitting saw | thin periphery | narrow slots, parting |
| Form cutter | profiled periphery | gears, radii, special shapes |
| The end mill is the general-purpose workhorse of the vertical mill, cutting on both its end and its sides so it can plunge, slot and profile. The face mill, carrying replaceable carbide inserts, is the efficient choice for surfacing large flats — the milling counterpart of the indexable turning insert. | ||
§3Conventional and climb milling
The single choice that most affects a milling cut is the direction the cutter rotates relative to the feed — conventional (up) or climb (down) milling. They behave oppositely (the hero).
In conventional (up) milling the teeth meet the work moving against the feed, so each chip starts at zero thickness and grows — the tooth rubs before it bites, which work-hardens the surface and wears the edge, but the cutting force lifts the work and the setup is tolerant of backlash in the table screw. In climb (down) milling the teeth move with the feed, so each chip starts thick and thins to nothing — the tooth bites cleanly at once, giving better finish and tool life and pressing the work down onto the table, but the force pulls the work in the feed direction, so any backlash in the table screw lets the cutter snatch the work forward, which can break the cutter or scrap the part. The rule: climb mill for finish and tool life on a rigid, backlash-free machine (most modern CNC); conventional mill on older machines with worn screws, or where the skin is hard or scaly.
Contents§4Speed and feed per tooth
Milling speeds and feeds start from the same cutting speed as turning, but the feed is built up from the bite of each individual tooth.
An 80 mm face mill with 8 teeth cutting steel at 120 m/min: spindle speed N = 1000 × 120/(π × 80) = 477 rev/min. At a feed per tooth of 0.1 mm, the table feed is v_f = 0.1 × 8 × 477 = 382 mm/min. Feed per tooth is the real cutting parameter — it is the chip each edge takes — so a cutter with more teeth is fed proportionally faster at the same chip load, which is exactly why face mills carry many inserts: more teeth, more feed, more metal removed for the same edge bite.
§5Material removal rate
The metal removed per minute is the cut’s cross-section swept at the table feed — width of cut times depth of cut times feed rate.
Continuing the face mill above (v_f = 382 mm/min) over a 50 mm width at 3 mm depth: MRR = 50 × 3 × 382 = 57 300 mm³/min = 57.3 cm³/min. That single figure sets both how fast the job is done and how much power the spindle must supply, since power rises with removal rate. As in turning, the three parameters — speed, feed and depth — are chosen together to remove metal as fast as the cutter life, the finish and the machine’s power and rigidity allow.
§6Choosing a cutter
Cutter choice follows the feature to be made and the material, then the balance between tooth count and chip room.
The feature leads: a flat face calls for a face mill, a pocket or slot for an end mill, a deep narrow slot for a slitting saw, a repeated profile for a form cutter. Then tooth count is traded against chip clearance — a coarse-tooth cutter with fewer, deeper flutes clears chips well and suits soft, gummy materials and heavy roughing, while a fine-tooth cutter gives more edges for finishing and hard materials but less room for chips. Material sets the cutter substance (high-speed steel for general work and tricky shapes, carbide inserts for speed and hard or abrasive work) exactly as the cutting-tools and carbide pages describe. Feature → cutter type → tooth count → material is the selection chain.
Contents§7Quick reference
The working core of the page on one card rack.
Nature
many teeth, interrupted cut
feed reckoned per tooth
Types
end mill (slot/pocket)
face mill (flats)
Direction
climb → finish, rigid machine
conventional → worn/old machine
Feed
v_f = f_z × z × N
Removal
MRR = a_e × a_p × v_f