Peripheral milling is a milling process in which the cutting edges on the circumference of the cutter remove material. The cutter axis runs parallel to the machined surface.
Peripheral milling produces side walls, shoulders, slots and contours with high dimensional accuracy. At Vulcanus in Werl, Germany, it has been part of daily production for decades.
This guide explains how peripheral milling works, which cutters to use and how to set reliable cutting data.
Key Takeaways
- Axis orientation decides: In peripheral milling the cutter’s circumference cuts. In face milling the end face of the tool does the work.
- Clear classification: DIN 8589-3 groups milling by the active cutting edge and, separately, by the surface produced.
- Changing chip thickness: The chip is comma-shaped. On CNC machines, climb milling is usually the better choice.
- Watch chip thinning: At small radial engagement the chip becomes thinner. The feed per tooth must then increase.
- Rigidity before speed: Tool overhang, runout and workholding affect wall accuracy more than aggressive cutting data.
- Modern strategies: Large axial and small radial engagement make peripheral milling highly productive, even for roughing.
What is Peripheral Milling?
Peripheral milling, also called slab milling when producing flat surfaces, removes material with the cutting edges on the cutter’s outer circumference. The tool’s axis of rotation runs parallel to the machined surface. The end face of the cutter does not take part in the cut.
The process is one of the fundamental types of milling operations in machining. Typical results are side faces, shoulders, keyways, T-slots and contours. CNC shops mostly use end mills, while horizontal machines also run cylindrical cutters on an arbor.
Classic peripheral milling achieves a lower metal removal rate than face milling. Modern carbide end mills and dynamic toolpaths have changed that significantly.
How the Chip Forms in Peripheral Milling
Each cutting edge engages the material for only part of every revolution. During that time the chip thickness changes constantly between zero and a maximum. This creates the typical comma-shaped chip.
Two engagement values describe the cut:
- Axial depth of cut (ap): how far the cutter engages along its axis.
- Radial depth of cut (ae): how far the cutter steps into the workpiece across its axis.
In peripheral milling, ap is often large and ae comparatively small. This combination shapes cutting forces, heat generation and the right feed per tooth.
Classification to DIN 8589-3: Peripheral, Face and Face-and-Peripheral Milling
Peripheral milling and plain milling are often treated as opposites. Technically, that is misleading. The German standard DIN 8589-3 classifies milling by two separate criteria.
- By the surface produced: plain, circular, helical, hobbing, profile and form milling.
- By the active cutting edge: peripheral milling, face milling and face-and-peripheral milling.
Both criteria combine. The result is the terminology buyers and engineers search for:
| Process | Active cutting edges | Surface produced | Typical tool |
|---|---|---|---|
| Peripheral plain milling (slab milling) | Circumference | Flat surface parallel to the cutter axis | Cylindrical cutter, end mill |
| Face plain milling | End face | Flat surface perpendicular to the cutter axis | Face mill, cutter head |
| Face-and-peripheral milling | Circumference and end face | Two surfaces at an angle, e.g. a shoulder | Shell end mill, square shoulder mill |
| Peripheral profile milling | Profiled circumference | Profiled surface | Form cutter, side and face cutter |
We cover peripheral plain milling with cylindrical cutters in detail in our guide to plain milling. For very large flat surfaces, face plain milling is usually more economical.
Peripheral Milling vs. Face Milling: The Key Differences
Quick Comparison
| Feature | Peripheral milling | Face milling |
|---|---|---|
| Cutter axis to surface | parallel | perpendicular |
| Teeth in the cut | few, changing | many, even |
| Chip thickness | varies strongly (comma chip) | nearly constant |
| Surface | slight feed waviness, excellent side walls | high flatness on large areas |
| Metal removal rate | classically lower, high with HPC strategies | high on large surfaces |
| Typical applications | shoulders, slots, contours, side walls | top faces, mounting faces, pre-machining |
| Force direction | mainly radial | mainly axial |
Why Choose Peripheral Milling Operation
- Offers exceptional precision, essential for tasks like machining T-slots, keyways, gear teeth, and contour profiles.
- Produces excellent surface finishes, thanks to the controlled, sideways engagement of cutter teeth.
- Favoured in precision engineering, especially when working with fine tolerances or detailed parts.
Why Face Milling Still Has Its Place
- Excels in high material removal rates, particularly for broad, flat surfaces.
- Efficient for initial stock removal or roughing operations.
- Often less demanding on tool alignment, space-saving when the focus is volume rather than fine detail.
Climb and Conventional Milling in Peripheral Milling
In peripheral milling, the direction of rotation determines how chip thickness develops. In climb milling the chip starts thick and ends thin. In conventional milling it is the other way round.
| Criterion | Climb milling | Conventional milling |
|---|---|---|
| Chip thickness | thick to thin | thin to thick |
| Rubbing at entry | low | high, edge slides before cutting |
| Tool life | usually longer | shorter due to friction and heat |
| Surface | usually better | risk of work hardening |
| Machine requirement | backlash-free feed drive | tolerates backlash |
Modern CNC machines have backlash-free ball screws. Climb milling is the standard there. Conventional milling still makes sense on machines with backlash, hard casting skins or mill scale.
We explain the full decision in our guide to climb milling vs conventional milling.
Advantages & Disadvantages of Peripheral Milling
Advantages
- Exceptional Precision
By engaging only the outer edges of the cutter, peripheral milling delivers highly accurate, narrow cuts. It’s ideal for detailed work such as T-slots, keyways, and contoured profiles.
- Superb Surface Finish
Radial engagement and controlled tool paths often result in smoother, cleaner surfaces compared to more aggressive milling methods.
- Versatile Across Materials
With the right cutter and machine setup, you can efficiently mill steel, aluminium, stainless steel, and specialised alloys, maximising adaptability across projects.
- Minimised Surface Defects
Precise engagement reduces cutting shocks and mitigates risks like gouges or burn marks, especially important for high-tolerance components.
Disadvantages
- Lower Material Removal Rate
Peripheral milling tends to be slower than methods like face milling. For large stock removal, it’s less efficient.
- High Setup Sensitivity
Accurate cutter alignment and robust fixturing are essential. Any misalignment can cause chatter, increased tool wear, and poor results.
- Coolant Dependence
To maintain a stable cutting environment and extend tool life, applying appropriate coolant is often necessary, adding complexity to the setup.
- Tool Wear Risk
Extended machining without coolant or when milling abrasive materials may increase wear or risk of edge breakage, especially with HSS cutters.
Peripheral Milling Tools & Equipment
Cutter Types and Their Uses
| Cutter type | Active edges | Typical use |
|---|---|---|
| Cylindrical (slab) cutter (DIN 884) | circumference only | peripheral plain milling on horizontal machines |
| Shell end mill (DIN 1880) | circumference and end face | shoulders, steps, flat faces |
| Side and face cutter (DIN 885) | circumference and sides | slots, grooves, gang milling |
| End mill, HSS (DIN 844) or solid carbide (DIN 6527) | circumference, often end face too | contours, pockets, side walls |
| Roughing end mill with chip breakers | circumference | high removal rates, short chips |
| Square shoulder mill with indexable inserts | circumference and end face | 90-degree shoulders, larger diameters |
| Form and profile cutters | profiled circumference | radii, chamfers, special profiles |
A common mistake is confusing the cylindrical cutter with the shell end mill. The cylindrical cutter cuts only on its circumference. The shell end mill also has face teeth, so it produces shoulders in one operation.
Cutters with a helix angle enter the material gradually. This reduces force peaks and improves the finish. You will find more CNC machining tools in our dedicated guide.
Cutting Materials, Coatings and Tool Types
- HSS and HSS-E: tough and affordable. Good for one-offs, mild steel and soft materials.
- Solid carbide: high cutting speeds and dimensional stability. The standard in CNC production.
- Indexable inserts: economical for large diameters and high removal rates.
- Coatings: TiAlN or AlTiN for steel and stainless steel, DLC or polished uncoated edges for aluminium.
German tool standards also define tool types by workpiece material. Type N suits normal steels. Type H suits hard, short-chipping materials, and type W suits soft, long-chipping materials such as aluminium.
Machine, Tool Holding and Workholding
Horizontal machines offer high rigidity for cylindrical and side and face cutters on an arbor. Vertical machines are more flexible for end mills and contours. Read more in our comparison of vertical vs horizontal milling and our overview of the milling machine.
Tool holding is especially important in peripheral milling. Shrink-fit or hydraulic chucks hold the cutter rigidly and with minimal runout. Even a few hundredths of a millimetre of runout errors in CNC machining load individual edges unevenly.
The workpiece must be held securely across the feed direction. Radial cutting forces try to push it sideways. Well-designed jigs and fixtures prevent distortion and vibration.
Machining Parameters for Peripheral Milling
The Key Formulas
| Value | Formula | Unit |
|---|---|---|
| Spindle speed n | n = (vc × 1000) / (π × D) | rpm |
| Feed rate vf | vf = fz × z × n | mm/min |
| Metal removal rate Q | Q = (ap × ae × vf) / 1000 | cm³/min |
Here vc is the cutting speed, D the cutter diameter, fz the feed per tooth and z the number of teeth. Our guide to cutting speed shows how to calculate it correctly.
Starting Values for Coated Solid Carbide End Mills
| Material | Cutting speed vc | Feed per tooth fz at D = 10 to 16 mm |
|---|---|---|
| Mild steel, e.g. S235 | 150 to 250 m/min | 0.05 to 0.10 mm |
| Alloy steel, e.g. 42CrMo4 (AISI 4140) | 100 to 180 m/min | 0.04 to 0.08 mm |
| Stainless steel, e.g. 1.4301 (304) | 80 to 140 m/min | 0.03 to 0.07 mm |
| Grey cast iron, e.g. EN-GJL-250 | 120 to 200 m/min | 0.05 to 0.10 mm |
| Wrought aluminium alloy | 300 to 1000 m/min | 0.05 to 0.15 mm |
| Titanium alloy, e.g. Ti6Al4V | 40 to 80 m/min | 0.03 to 0.06 mm |
These are starting values for stable conditions. The tool manufacturer’s data always takes priority. For material-specific advice, see our guides to machining stainless steel and machining tool steel.
Chip Thinning at Small Radial Engagement
When radial engagement is less than half the cutter diameter, the chip becomes thinner than the feed per tooth. The edge then rubs more than it cuts. This costs tool life and generates heat.
Calculate the maximum chip thickness as follows: hex = fz × 2 × √(ae/D × (1 − ae/D)). For a target chip thickness of 0.06 mm and D = 16 mm, the required feed per tooth is:
| ae as % of D | ae at D = 16 mm | Factor | Required fz for hex = 0.06 mm |
|---|---|---|---|
| 5 % | 0.8 mm | 0.44 | 0.14 mm |
| 10 % | 1.6 mm | 0.60 | 0.10 mm |
| 20 % | 3.2 mm | 0.80 | 0.075 mm |
| 30 % | 4.8 mm | 0.92 | 0.065 mm |
| 50 % | 8.0 mm | 1.00 | 0.06 mm |
Worked Example from the Shop Floor
A solid carbide end mill with D = 16 mm and four flutes machines a wall in mild steel. The chosen values are vc = 150 m/min, ap = 24 mm and ae = 1.6 mm.
- Spindle speed: n = (150 × 1000) / (π × 16) ≈ 2,980 rpm.
- Without correction: fz = 0.06 mm gives vf ≈ 720 mm/min and Q ≈ 27 cm³/min.
- With chip thinning applied: fz = 0.10 mm gives vf ≈ 1,190 mm/min and Q ≈ 46 cm³/min.
The chip thickness stays within a safe range in both cases. The corrected feed, however, delivers around 65 percent more metal removal. At the same time, the edge cuts more cleanly and wears more slowly.
Milling Strategies: Roughing and Finishing with Peripheral Milling
Roughing with Large Axial Engagement
Dynamic or trochoidal milling uses almost the full flute length. Radial engagement stays small, often 5 to 15 percent of the diameter. This spreads heat and wear evenly along the edge.
The CAM software keeps the engagement angle constant. This keeps forces stable, even in corners. Read more about goals and parameters in our guides to CNC roughing and high speed cutting.
Finishing Side Walls
For finishing, leave an even stock allowance, typically 0.1 to 0.5 mm. The right machining allowance depends on the material and the previous operation. Even stock ensures even tool deflection.
- Short overhang: Every millimetre less noticeably increases cutter rigidity.
- Use climb milling: It delivers the better wall finish on CNC machines.
- Run a spring pass: A second pass without new stepover compensates for deflection.
- Choose more flutes: Finishing cutters with five to seven flutes run more smoothly.
Our guide to surface roughness explains which Ra and Rz values are realistic.
Common Peripheral Milling Problems and Their Solutions
| Problem | Common cause | Solution |
|---|---|---|
| Chatter marks | long overhang, unstable workholding | shorten the tool, adjust spindle speed, use variable-pitch cutters |
| Tapered or out-of-square walls | tool deflection | reduce stock, run a spring pass, choose a stiffer cutter |
| Built-up edge | cutting speed too low, sticky material | increase vc, use a sharp polished edge, improve coolant |
| Burrs on edges | dull edge, conventional milling at exit | use climb milling, change the tool, plan a deburring pass |
| Chipped edges | thick chip at entry, chip recutting | arc into the cut, clear chips with air blast or coolant |
| Short tool life | rubbing from a chip that is too thin | compensate for chip thinning, increase fz |
Many of these causes apply to milling in general. Our guide to common milling errors goes deeper. For specific measures against vibration, read how to avoid vibrations during milling.
Cooling also has a strong effect on tool life and finish. Which coolant lubricants are suitable depends on the material.
Applications: Where Peripheral Milling Is Used
Peripheral milling is used in almost every machining operation. Typical part features include:
- Slots and grooves: keyways, T-slots and dovetail guides. Learn more in our guide to slot milling.
- Shoulders and steps: mounting faces for bearings, flanges and guide rails.
- External contours: plates, levers and housings with a 2D outline.
- Profiles: radii, chamfers and special shapes. Here peripheral milling merges into form milling.
Key industries include mechanical engineering, special machine building, conveyor technology, vehicle manufacturing, and energy and plant engineering.
Peripheral Milling at Vulcanus: Precision from Werl
Vulcanus-Stahl & Maschinenbau has been manufacturing in Werl, North Rhine-Westphalia, since 1984. Our production is ISO 9001 certified. Peripheral milling is a core part of our CNC milling services.
We machine one-offs, small batches and heavy components. If you need a large part machining service, you benefit from rigid machines and experienced machinists. Through CNC contract manufacturing, we also handle turning, welding, sawing and assembly from a single source.
Every part goes through documented quality control for CNC machining. This gives you accuracy that matches your drawing. That is what precision manufacturing means to us.
Conclusion: Using Peripheral Milling the Right Way
Peripheral milling is the process of choice for walls, shoulders, slots and contours. For large flat surfaces, face milling is usually more economical. Combining both processes often gives the best result.
The keys are a rigid tool, climb milling on CNC machines and a corrected feed per tooth at small radial engagement. With these basics, tool life, surface finish and removal rate all improve together.
Looking for a partner for precision milled parts? Contact us and send us your drawing for a quote.
FAQs About Peripheral Milling
1. What is the difference between peripheral milling and face milling?
In peripheral milling, the edges on the circumference cut and the cutter axis is parallel to the surface. In face milling, the end face cuts and the axis is perpendicular to the surface. Face milling is better suited to large flat surfaces.
2. Is slab milling the same as peripheral milling?
Slab milling is peripheral milling used to produce a flat surface. It is classically done with a cylindrical cutter on a horizontal milling machine. DIN 8589-3 calls it peripheral plain milling.
3. What is face-and-peripheral milling?
Here the cutter works with both its circumference and its end face. This produces two surfaces at an angle in one pass, such as a shoulder. Shell end mills and square shoulder mills are the typical tools.
4. Should I use climb or conventional milling for peripheral milling?
On modern CNC machines, climb milling is usually the better choice. It extends tool life and improves the finish. Conventional milling helps on machines with feed backlash or on hard casting skins.
5. What machining parameters apply to peripheral milling?
The key parameters are cutting speed, feed per tooth, and axial and radial depth of cut. For carbide cutters in mild steel, vc is often 150 to 250 m/min. At small radial engagement, increase the feed per tooth to offset chip thinning.
6. How can I improve tool life and surface finish in peripheral milling?
Clamp the cutter short and with minimal runout. Use climb milling and compensate for chip thinning. Apply suitable cooling and run a spring pass when finishing.