Milling cutter tools are used to remove material from the surface of a workpiece, helping to shape metal or plastic into the desired form. These tools come in many designs and sizes, each suited for a specific task. In this guide, we will walk you through the different types of milling cutters, the materials they are made from, and practical advice on how to choose the right tool for your project.
What Is a Milling Cutter Tools?
Milling cutters are rotary tools attached to milling machines. These machines rotate the cutter at high speeds while feeding it into the workpiece to remove material. The goal is to shape the workpiece by cutting away unwanted areas, either on the surface or deeper into the material.
How Milling Cutters Work in Milling Machines
A milling cutter functions by rotating at high speed while cutting edges on its periphery and face engage the workpiece. Unlike a drill bit that cuts only in the axial direction, many milling cutters can remove material in multiple directions, thanks to their flutes—or helical grooves—that carry chips away from the cutting zone.
A typical milling setup holds the cutter in a spindle that can accept single-point or multi-tooth tools. The workpiece is moved in relation to the cutter along one or more axes—often X, Y, and Z—to perform operations such as slotting, facing, profile milling, and contouring. Modern computer numeric control (CNC) mills can synchronize these axes with precision, allowing complex three-dimensional shapes to be machined.
Types of Milling Cutter Tools
Manufacturers divide milling cutters into several categories based on their shape, orientation of cutting edges, and intended application. The six primary categories are:
- Face Mills
- Fly Cutters
- End Mills
- T-Slot Cutters
- Form Mills
- Slitting Saws
Each category contains specialized subtypes designed for specific tasks. The following sections describe these options in detail.
Face Mills
Face mills have multiple insert pockets around their outer diameter. Each insert has a cutting edge that engages the workpiece during a horizontal cut. Face milling produces flat, even surfaces across large areas. The inserts sit at the cutter’s periphery, allowing large-diameter tools to remove broad swaths of material in fewer passes. Operators often select face mills for primary surfacing and heavy stock removal.
Fly Cutters
Fly cutters consist of one or two single-point cutting tools mounted on a rotating arbor. They operate much like a lathe tool cutting across the workpiece surface. Fly cutters leave a characteristic scalloped finish that machinists can minimize by using small depth-of-cut values and higher spindle speeds. Fly cutters suit light face milling operations, especially in job shops where tool cost must remain low.
Subtypes include:
1. Rotary Carving Fly Cutters
A rotary carving fly cutter holds a small rotary tool head instead of a simple point. These cutters carve intricate patterns in wood or plastics. These cutters also engrave shallow designs on glass or soft materials.
2. Multi-Layer Rotary Fly Cutters
A multi-layer fly cutter holds several rotary tips on the same arm. These cutters cut multiple layers of thin material, such as fabric or composite sheets, in one pass. These cutters maintain the cutting profile without distortion.
3. Point Fly Cutters
A point fly cutter uses a single carbide or high-speed steel point. These tools cut with a tiny tip, delivering high finish quality and minimal chatter.
End Mills
An end mill has multiple cutting edges on its end and sides. These tools can cut axially (into the workpiece) and radially (along the side). These features make end mills more versatile than drill bits, which only cut axially.
There are various sub-types of end mills:
1. Flat (Square) End Mills
A flat end mill, also called a square end mill, features a straight cutting edge at 90 degrees to its sides. These tools perform slotting, profiling, and plunging operations. These tools produce crisp corners and flat bottoms in pockets.
2. Corner Rounding End Mills
A corner rounding end mill has a small radius on its tip. These cutters create slightly rounded edges on a part’s profile. These radiused edges help improve part strength and reduce stress risers.
3. Ball Nose End Mills
Ball nose end mills have a rounded tip. Machinists use them for 3D contour work and curved surfaces because the round bottom leaves a smooth finish. The ball shape distributes cutting forces evenly and reduces ridges on the workpiece.
4. Radius End Mills
A radius end mill has rounded corners along its edges. These tools reduce stress concentration on the cutter and the workpiece corners. These features help prevent chipping and improve tool life.
5. Corner Radius End Mills
A corner radius end mill, sometimes called a hog mill, features multiple serrated flutes and a pronounced radius. These tools remove large amounts of material in roughing operations. These cutters achieve high feedrates and leave a rough surface that most finishing tools will clean up.
6. Undercutting (Lollipop) End Mills
An undercutting end mill, also known as a lollipop cutter, has a spherical cutting portion offset from the tool’s centerline. These cutters dive into workpieces to machine undercuts and hidden features.
T-Slot Cutters
T-slot cutters, also known as Woodruff cutters, cut T-shaped grooves into workpieces. The angled teeth on the periphery create the slot’s bottom and vertical walls. Manufacturers commonly use these cutters to prepare fixture plates, machine tables, and structural supports that require secure bolt heads or sliding keys.
Form Mills
Form milling cutters carry unique profiles that match the desired contour on the workpiece. Machining helical gears, mold cavities, and detailed contours rely on form mills. Subtypes include:
1. Corner Rounding Form Mills
Corner radius cutters, also called radius cutters, cut rounded profiles and chamfers. Machinists use them for decorative edges and transition features.
2. Inserted-Tooth Form Mills
An inserted-tooth form mill uses replaceable carbide or steel inserts mounted on a steel body. These cutters offer easy maintenance and quick index-ability when a tooth wears out.
3. Convex Form Mills
A convex form mill features an outward-curving profile. These cutters produce inward grooves on the workpiece. These shapes appear in decorative moldings and mechanical cams.
Metal Slitting Saw Cutters
A slitting saw is a thin circular cutter that slices through material. These tools excel at cutting narrow slots and parting off sections of a workpiece. Variations include:
1. Cylindrical Milling Cutters
These are thick slitting saws with only peripheral teeth, designed for heavy-duty slotting and high material removal rates.
2. Plain Slitting Saws
A plain slitting saw has cutting teeth only on the outside edge. These saws run at high speeds to slice through non-ferrous metals and steels. These tools often have a concave relief on each side to avoid rubbing.
3. Side-Teeth Slitting Saws
A side-teeth slitting saw has cutting teeth on both its circumference and faces. These tools maintain slot width more accurately when cutting deep grooves.
4.Plain (Slab) Milling Cutters
Also known as slab cutters, these tools have helical or straight teeth on a large-diameter disc. Machinists use them for light milling of flat surfaces parallel to the spindle.
5. Concave (Radius) Slitting Saws
Concave slitting saws have a curved edge that produces a convex shape on the workpiece. These saws cut smooth semi-circular grooves.
If you’re unsure about which milling cutter to use for your next project, it’s always a good idea to consult with a machining expert. BOYI TECHNOLOGY has 20 years of experience in the processing field and specializes in providing CNC milling services. If your work continues, please contact us for professional insights and quotations for milling parts.
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How to Choose the Right Milling Cutter Tools
Selecting an optimal cutter involves balancing workpiece material, machine capacity, surface finish requirements, and economic factors.
Number of Teeth
More flutes increase material removal rate and surface finish but reduce chip clearance. Use fewer flutes (2–3) for aluminum to prevent chip packing, and more (4–6) for steel to improve feed rates. Higher helix angles provide smoother cutting action but reduce axial rigidity. Choose 30°–45° helix for general milling.
Tool Size and Diameter
Larger diameters remove more material per pass, but require more spindle power. For face milling, a cutter 1.5× the spindle diameter is often recommended. High L/D ratios increase tool deflection. Keep L/D ≤ 3:1 when possible.
Optimize Cutting Parameters
Refer to tooling suppliers’ data for initial starting points, then adjust based on tool wear and surface finish. Roughing passes can remove up to 50% of cutter diameter; finishing passes should not exceed 15%.
Tool Coating and Coolant Strategy
Flood coolant or high-pressure mist can help remove chips and reduce cutter temperature. However, some operations (e.g., finishing cast iron) benefit from dry cutting. Match coating to material. Diamond coatings excel on composites and aluminum; AlTiN handles high-temperature steels.
Account for Tool Holder and Runout
Excessive runout shortens cutter life and degrades finish. A machinist should use precision tool holders and inspect taper fit. For very small tools (under 5 mm), even slight runout can break the cutter.
What Materials Are Used to Make Milling Cutters?
The performance of a milling cutter depends not only on its shape but also on the material it is made from. Here are the most common materials used:
High-Speed Steel (HSS)
HSS is an improved version of carbon steel that includes elements like tungsten, chromium, and molybdenum. It is more wear-resistant and retains its hardness up to about 650°C. It’s widely used for general-purpose milling tools.
Carbon Tool Steel
Carbon tool steel contains 0.6–1.5% carbon and small amounts of silicon and manganese. These materials make cutters that are easy to sharpen and economical to produce. These cutters work well at speeds below 250 °C. These cutters suit low-speed machining of soft metals such as aluminum, brass, and magnesium. These cutters lose hardness rapidly above 250 °C, so they need coolant and frequent resharpening.
Stellite
Stellite is a cobalt-based alloy that remains stable at high temperatures. It is commonly used in high-volume applications such as engine component manufacturing. Stellite tools are tough and wear-resistant but are expensive and hard to machine.
Ceramic
Ceramic cutters use aluminum oxide or silicon nitride ceramics. These cutters resist heat and wear better than carbide or cermet. These cutters cut superalloys, hardened steels, and exotic materials at very high temperatures. These cutters remain sharp at 1000 °C but require rigid machines and stable setups to avoid chipping.
Cemented Carbide
Cemented carbide combines tungsten carbide particles with a cobalt binder. This material stays hard at temperatures up to around 1,000 °C. Machinists use carbide cutters for high-speed roughing and finishing on steel and stainless alloys. They often coat carbide tools with titanium nitride (TiN) or aluminum oxide (Al₂O₃) for extra wear resistance.
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Conclusion
Milling cutters come in many shapes, materials, and sizes. Each cutter type suits certain geometries and material conditions. Proper selection also depends on machine power, spindle speed, coolant usage, and precise tool holding. When in doubt, consulting tool manufacturers’ catalogs and testing small batches can help refine the best choice for a given milling application.
FAQ
Manufacturers typically use separate cutters for roughing and finishing. Roughing cutters have fewer, larger teeth to remove material quickly. Finishing cutters have more teeth and finer geometry to produce smoother surfaces.
Use the shortest possible tool, reduce L/D ratio, lower radial depth of cut, and ensure rigid tool holding. A cool running temperature and proper coating also reduce wear that leads to deflection.
Machinists mount end mills in the spindle or a tool holder. They program the machine to move the tool along X, Y, and Z axes to create slots, pockets, profiles, and contours.
Tool chatter happens when the cutter vibrates due to poor support, long overhang, excessive feed rate, or wrong speeds. To prevent chatter, shorten the cutter overhang, slow down feeds, increase spindle speed, or add damping by using a stiffer setup.
This article was written by engineers from the BOYI TECHNOLOGY team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, metal parts, and plastic parts manufacturing.
