Milling is versatile because one machine can perform many operations just by changing the cutter, the toolpath, and the setup. Underneath all of them are three fundamental contact modes: face milling (cutting with the end of the tool to make flat surfaces), peripheral milling (cutting with the side of the tool to size walls and profiles), and end milling (using both the end and the side, which is the most common and flexible). From these come slotting, pocketing, profiling, drilling, boring, and more. Understanding the operations, and the difference between climb and conventional milling, helps you design parts that machine cleanly and quote accurately.
This guide explains the operations and when each is used. For the machines that run them, see types of CNC machines and our CNC milling service; for axis counts, 3-axis vs 4-axis vs 5-axis.
The Three Fundamental Modes
Face milling uses the end face of the cutter to generate flat surfaces, typically to square up stock or establish a datum. Large multi-insert face mills remove material stably, and a light finishing pass produces a clean flat.
Peripheral (plain or slab) milling cuts with the cylindrical side of the tool, used to size outside profiles, shoulders, and vertical walls. Because cutting happens on the side, controlling tool deflection through rigid workholding and short tool reach is key to accuracy.
End milling uses both the periphery and the end of an end mill, making it the workhorse of CNC milling. A single end mill can side-mill, slot, face, pocket, profile, and contour, which is why most machined features are made this way.
Common Operations
• Slotting fully engages an end mill across its width to cut channels, keyways, and grooves. It is productive but heat-intensive, so chip evacuation and feed control matter.
• Pocketing clears internal cavities, usually with a helical or ramping entry followed by stepped passes to remove material efficiently.
• Profiling and contouring walk the tool around the part’s periphery to bring it to net shape, including complex curves and, with the right tooling, 3D surfaces.
• Drilling produces holes, often integrated into a milling program; some center-cutting end mills can plunge, though dedicated drills are better for deep or precise holes.
• Boring enlarges and finishes an existing hole to a precise diameter and finish that drilling alone cannot hold.
• Chamfering and shoulder milling prepare edges and create stepped features.
Specialized operations round out the set: slitting or saw milling for narrow, deep slots and parting; straddle milling with two cutters for square or hex features; form milling for contoured profiles; and 3D surfacing with ball-nose cutters for sculpted shapes.
Climb vs Conventional Milling
How the cutter engages the work matters. In conventional (up) milling, the tool rotates against the feed direction, so each tooth starts with a thin, rubbing cut that thickens to the exit. It tolerates backlash and less rigid setups, which is why it suits manual machines, but it generates more heat and tool wear. In climb (down) milling, the tool rotates with the feed direction, so the chip starts thick and thins out. On a rigid, backlash-free CNC machine, climb milling gives a better finish, lower tool wear, and is generally preferred. Harder materials especially benefit from climb milling.
| Conventional (up) | Climb (down) | |
| Feed vs rotation | Opposed | Same direction |
| Chip | Thin to thick | Thick to thin |
| Best for | Manual, less rigid, backlash | Rigid CNC, better finish |
| Tool wear | Higher | Lower |
How to Choose
Most parts use a sequence of operations: face mill to square the stock and set a datum, end mill to cut profiles and pockets, slot for keyways, then drill and bore holes to size. The operation follows the feature, and a good CAM program orders them to balance speed, finish, and tool life, typically roughing first and finishing thin walls last. On rigid CNC machines, default to climb milling for finish and tool life. The practical takeaway for designers: standard features like flats, pockets, slots, and holes machine cleanly, while very deep pockets, tiny internal radii, and thin walls drive up cost.
Have a part to mill? Request a quote and our team will plan the operations and flag anything that affects cost.
Frequently Asked Questions
What are the three basic types of milling?
Face milling (cutting flats with the tool’s end), peripheral or plain milling (cutting walls and profiles with the tool’s side), and end milling (using both, the most versatile). Operations like slotting, pocketing, and profiling build on these.
What is the difference between climb and conventional milling?
In conventional milling the tool rotates against the feed, with the chip going thin to thick; in climb milling it rotates with the feed, with the chip going thick to thin. Climb milling gives a better finish and less tool wear on rigid CNC machines, while conventional milling tolerates backlash on manual machines.
What is end milling used for?
End milling is the most versatile operation, using an end mill to side-mill, slot, face, pocket, profile, and contour. It produces most of the features found on typical machined parts, which is why it is so common.
What is the difference between drilling and boring?
Drilling creates a hole with a drill bit, while boring enlarges and finishes an existing hole to a precise diameter and surface finish. Boring is used when a hole must hit a tighter tolerance than drilling can hold.