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Milling Tools Guide for Beginners to Get Started

Milling Tools Guide for Beginners to Get Started

Milling Tools Guide for Beginners to Get Started

Getting the right tools is essential when you get into milling work.

Milling tools are cylindrical rotary cutting tools used on milling machines to perform various milling operations. Cutting edges in a milling tool are usually on the face or periphery of the tool. For machining, these tools are selected based on the work material and type of cut that needs to be made.

This article explains milling tools by discussing various aspects like tool types, materials, surface coatings, holders, etc., and how to select the right tool for your job.

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Milling Tools - An overview

In milling, a multi-edged rotating cutting tool removes material from the workpiece.

These tools are mounted on a milling tool holder connected to the machine's spindle.

Depending on the operation, milling tools having multiple cutters, varying lengths, specific coating, etc., are used for the job.

These tools are used in different types of machines ranging from manual to CNC milling machines.

Knowing different milling tools helps you choose the right tool for a job, as your choice can significantly affect the cut quality and job duration.

Types of Milling Tools

Milling machines use different tools to create various shapes and features.

Types of milling tools
Types of milling tools
Milling ToolPurpose
End MillFor profiling, slotting, pocketing, and boring operations
Face MillTo machine a smooth surface
Ball CutterTo machine spherical contours or curves
Fly CutterCheaper alternative to a face mill
Slab Milling ToolTo continuously remove a large amount of surface material
Side Milling CutterTo cut parallel vertical slots
Staggered Milling CutterTo cut parallel vertical slots with less chip interference
Concave & Convex CutterTo machine convex and concave surface contours
Woodruff Milling CutterTo cut keyways
Hobbing CutterTo cut teeth, splines, or sprocket gears
List of milling tools and their purpose

End Mill

Parts of an End Mill
Parts of an End Mill

End mills can cut materials axially and laterally as they have cutting teeth on the sides and end face.

They are usually flat at the bottom and have one or more flutes. They are made from HSS or cemented carbide and are commonly used in a vertical milling machine.

Face Mill

Face Milling
Face Milling

Face mills are similar to end mills but only have cutting edges at the sides. Multiple cutting teeth in the form of carbide inserts distribute the cutting load.

It is designed for facing operations and horizontal cuts up to a limited depth.

Ball Cutter

Ball cutter
Ball cutter

Ball cutters have hemispherical cutting ends and are used to machine spherical contours or curves at the workpiece edges. These tools are primarily used in machining centers.

Fly Cutter

Fly Cutters
Fly Cutters

Fly cutters make broad, shallow cuts on the workpiece. They generally have one or two cutters inserted in the cutting tool body and are used for face-milling operations.

Face mills perform a better job than fly cutters, but they tend to be more expensive.

Slab Milling Tool

Slab milling cutter
Slab milling cutter (Source: F&D Tool Company)

Slab mill tools have straight or spiral cutters at their periphery.

They are used on horizontal milling machines to remove large amounts of surface material to produce flat shapes.

Side Milling Cutter

Side milling cutter
Side milling cutter (Source: Toolmex)

The side milling cutter utilizes cutting teeth on the sides and the periphery. They are used for straddle milling operations and for cutting slots.

Staggered Milling Cutter

Staggered milling cutter
Staggered milling cutter (Source: Travers Tool)

Staggered mill cutters are similar to side mill cutters with teeth at the periphery and side.

The side teeth are arranged in a staggered manner which helps to prevent chip interference. It is suitable for milling slots having more depth than width.

Concave & Convex Milling Cutter

Concave and convex milling cutter
Concave and convex milling cutter

Concave and Convex milling cutters are formed cutters designed to mill convex and concave surface contours equal to a semicircle or less.

The required diameter of the circular form determines the cutter size.

Woodruff Milling Cutter

A woodruff milling cutter
A woodruff milling cutter (Source: MSC Industrial Supply)

Woodruff cutters have cutting teeth on the periphery of a disc connected to a straight shank.

They have concave sides that provide clearance. These cutters are used for cutting keyways in shafts. 

Hobbing Cutter

Hobbing Cutter
A hobbing cutter

A hobbing cutter has helical cutting teeth with grooves that aid in cutting and chip removal. They are used for cutting teeth in the workpiece.

Specially designed hobs are also available for cutting splines and sprocket gears.

Materials Used to Make Milling Tools

Milling tools are made of different materials, each offering specific advantages to the cutter, thereby helping in the machining process.

The primary considerations for selecting the tool material are workpiece material, production quantity, quality, and type of machining.

Following are some of the common cutter materials used in milling tools.

MaterialBenefits
Carbon Tool SteelMost affordable
Best at low-speed jobs
High-Speed SteelHard
Resistance towards wear
Maintains a sharp cutting edge longer
Cemented CarbideVery hard and ductile
High cutting speed
Good surface finish
CeramicHigh-speed finishing and roughing jobs
Extended tool life
Increased strength and toughness
Cubic Boron NitrideOffers better thermal and chemical stability
Diamond ToolExtremely high thermal conductivity and melting point
Wear resistant
Low friction
Different materials used to make milling tools and their benefits

Carbon Tool Steel

Some end mills made out of carbon tool steel
Some end mills made of carbon tool steel

Carbon tool steel is an alloy of iron and carbon, having other elements in trace amounts to improve its properties.

It is one of the cheapest materials for making cutting tools and is suited for low-speed jobs.

These alloys often contain different trace quantities of manganese, silicon, and copper. In some cases, chromium and vanadium are added to improve hardness and grain size.

Tools made from these materials resist abrasion and maintain a sharp cutting edge.

Carbon tool steel cutters are used to machine soft metals such as aluminum, copper, magnesium, etc.

They are limited to working at temperatures under 250℃. If the tool heats beyond this threshold, it'll lose its hardness, which impacts the milling job.

High-Speed Steel (HSS)

3 flute HSS endmill
3 flute HSS endmill

High-speed steel is a high-carbon steel alloy that combines steel with molybdenum or tungsten and small amounts of chromium and vanadium.

The alloying elements considerably improve their properties, increasing hardness, wear resistance, and efficiency at high operating temperatures.

Heat treatment of HSS is essential for enhancing its properties as heating changes the steel's internal structure, resulting in increased hardness.

It can retain the tool's hardness up to 650℃, but manufacturers recommend using a coolant for increased tool life.

HSS tools can maintain their sharp cutting edge even after a long job cycle. You can even re-sharpen them multiple times, providing a long tool life.

Several grades of HSS milling tools are available, each having varying properties.

Cemented Carbide

Some cemented carbide end mills
Some cemented carbide end mills

Cemented carbide has a high hardness and strength making it optimal for cutting tools.

It is made by mixing carbide particles with a binding material such as cobalt.

The metal binder provides ductility to the tool while carbide contributes to the hardness resulting in long-lasting resilient tools.

Carbide tools have a high cutting speed and can retain hardness at temperatures up to 1000°C.

Machining operations using these tools result in a better surface finish. It is used in high-volume machining and for cutting rigid materials such as stainless steel.

Due to high material cost, carbide tools are usually produced as inserts, while the shank is made of carbon tool steel to reduce tool cost.

This results in cost savings without compromising cutting performance.

Ceramic Tool

Ceramic Tool
Ceramic Tool (Source: MSC)

Ceramic tools usually are made of aluminum oxide or silicon nitride.

Tools made of aluminum oxide are used for high-speed finishing operations, while silicon nitride tools are used for rough machining jobs.

Many other additives are added to improve ceramic tools' strength and toughness, thereby increasing their tool life and productivity.

Ceramics tools provide excellent high-temperature performance by retaining their hardness and chemical inertness. They are also highly resistant to corrosion and wear.

They are remarkably faster than HSS and suitable for dry machining as coolant is not required. This is due to their lower friction coefficient at the cutting interface and low thermal conductivity.

Cubic Boron Nitride

Cubic boron nitride end mills
A cubic boron nitride end mill

Cubic boron nitride (CBN) is an inorganic compound of boron and nitrogen which exhibits varying properties in different forms.

The cubic crystalline form is similar to diamond and slightly softer but possesses better thermal and chemical stability.

It does not exist naturally but is produced in laboratories and widely used in abrasive components and cutting tools.

Tools made of boron nitride can be used for precision grinding and cutting hard materials due to their lower wear rates and ability to maintain tolerances.  

It stays thermally and chemically stable at temperatures up to 1300°C. It also forms a layer of boron oxide at the surface, which prevents further oxidation at high temperatures. 

CBN tools should use oil-based coolants as the oxide layer dissolves in water, increasing the wear rate.

Diamond Tool

Diamond milling cutter
Diamond milling cutter (Source: AGRINDTOOL)

Diamond is a hard material with extremely high thermal conductivity and melting point.

Its high strength, wear resistance, and low friction coefficient makes it suitable to use as an abrasive and in cutting tools.

The diamond grains are bonded at the cutting edge using sintered metal alloys, resin, ceramic, or other bonding materials.

Diamond-coated milling tools provide a good surface finish and result in a highly precise machining operation with close tolerances.

It is used to machine tough materials such as carbide alloys, ceramics, and non-ferrous metals such as copper and its alloys.

These tools are not suitable for use with steel as diamond does not remain chemically inert at high temperatures and may react with iron and other metals.

Tool Coating

DLC coated end mill
A Carbide End Mill with Diamond-like carbon (DLC) coating

Most cutting tools come with some form of coating to improve their surface properties like hardness, resistance towards wear, surface oxidation, fatigue, and thermal shock.

Improved performance and longer tool life are also achieved due to the surface coatings applied to the milling tools.

The thermal insulation effect of coatings improves hot hardness. Coatings also aid in lubrication by providing a smooth cutter surface that minimizes friction and improves chip removal.

MaterialBenefits
Titanium NitrideEconomical
Improves tool life
Resistance to wear and abrasion
Aluminum Titanium NitrideAllows for high-speed machining of hard metals
Resistance to thermal shock and oxidation
High hardness
Titanium Aluminum Nitride NanoSuperior tool life
Increased run time on ferrous metals
Hard and tough
Zirconium NitrideImproved lubricity (less friction between the tool and stock)
Hard and resistant to abrasion
Titanium DiborideHigh strength and hardness
Resistance to erosion
Good adhesion to the cutter
Best to work on aluminum and magnesium alloys
Diamond CoatingsTo work on non-ferrous materials like graphites, ceramics, composites, carbides, etc.
Different tool coating materials and their benefits

Coatings Suitable for Cutting Ferrous and Exotic Materials

The following coating materials provide good cutting performance to the tool when cutting ferrous and exotic materials like ceramics, hard plastic, etc.

Titanium Nitride

Titanium nitride is a general-purpose coating having a golden color and is one of the most common materials used to coat cutting tools.

It improves the tool's life, wear resistance, abrasion resistance, and cutting performance.

Aluminum Titanium Nitride

Aluminum titanium nitride is a composite coating. It is primarily employed on tools used for high-speed machining of hard metals in harsh conditions.

It provides high hardness along with resistance to thermal shock and oxidation. Adding aluminum also results in the retention of hot hardness.

The high hot hardness allows for dry operation with high feed rates and improved tool life.

Since the aluminum oxide layer is produced at high temperatures, it has reduced thermal conductivity.

Titanium Aluminum Nitride Nano

Titanium Aluminum Nitride Nano (TiAlN Nano) is a premium blue-colored coating that provides superior tool life and cycle times on ferrous metals than other coatings.

When titanium aluminum nitride is mixed with silicon, it produces a nanocomposite coating, further improving the tool's hardness and toughness.

TiAlN Nano coating is suitable for machining more rigid materials such as hardened steels, tool steels, etc. It is not recommended for machining aluminum.

Coatings Suitable for Non-Ferrous and Non-Metallic Materials

The following coatings are best for milling tools used to machine non-ferrous (aluminum, copper, titanium, etc.) and non-metallic materials.

Zirconium Nitride

Zirconium nitride coatings improve the tool's hardness, abrasion resistance, and lubricity.

The coating forms a hard ceramic layer on the tool's surface, about 2 - 5 microns thick.

It improves the cutting performance on non-ferrous materials and is widely used to coat cutters, bits, etc.

Suitable materials include non-ferrous alloys such as brass, copper, bronze, and aluminum. It improves tool life by up to 5 times over non-coated tools.

Titanium Diboride

Titanium diboride is a ceramic with high strength and hardness. It provides exceptional resistance to erosion during machining and has good adhesion to the substrate. 

The coating minimizes material build-up at the cutting edge resulting in increased tool life. It is recommended when working on aluminum and magnesium alloys.

Most other coatings react with aluminum during cutting, but titanium diboride has a low affinity towards aluminum.

Diamond Coatings

Diamond coatings come in various forms and structures. Due to its low operating temperature range, it is considerably higher in cost and suited for specialized applications with non-ferrous material.

It works on graphites, ceramics, composites, carbides, and other non-ferrous metals and alloys such as aluminum, copper, brass, etc.

Structure of a Standard Milling Tool Holder

The tool holder is the machine part that connects the tool to the milling machine.

It firmly holds the tool to effectively transfer the cutting force to the workpiece with utmost accuracy and accounts for runout and balance of the milling operation.

There are three major components on a tool holder:

Parts of a milling tool holder
Parts of a milling tool holder

Taper

Tapper is a cone-shaped part on the tool holder that is connected to the spindle.

The tool holder is selected based on the spindle design, as a machine only accept tool holder having a specific type of tapper.

Many tappers are available based on the mounting style, such as Morse taper, NMTB taper, etc.

Flange

A flange is a gripping component of the tool holder.

Robotic components on machining centers, like the automatic tool changer (ATC), use the flange to grab and move the tool from the spindle.

Collet Pocket

A collet is a segmented band or sleeve used to tighten a shaft. The collet is inserted in the pocket and tightened using various collet nuts.

Types of Milling Tool Holders

Tool HolderBenefits
Collet ChuckSupports tools of multiple sizes
Can be customized
Best for high-accuracy finishing operations
End Mill HolderCan hold large and heavy tools used in heavy machining jobs
Higher grip force than collet chucks
Hydraulic Tool HolderOffers a high degree of precision
Easy to work with
Ideal for tools like drills, reamers, end mills, etc.
Milling ChucksIts symmetrical design provides high accuracy and good balance.
Can hold many types of tools
Has minimal runout and axial movement
Shrink Fit HoldersUniformly grabs the tool shank because of the thermal effect
High gripping force
Only requires minimal accessories
Different tool holders used to hold milling tools

Collet Chuck

A collet chuck set
A collet chuck set

Collet chucks are versatile tool holders designed for using multiple types and sizes of cutting tools. It uses a slotted collar to hold them firmly. 

They are available in different sizes and types and can be custom-made for specific applications. These tool holders are preferred for high-accuracy finishing operations.

Single-angle and double-angle are the two types of collet chucks available.

ER collets are an example of a single-angle system having high concentricity and balance. They are suitable for drilling and light milling operations at high speeds. 

Double-angle collet systems are used where sufficient clearance is not available. It is a simple chuck design but lacks the concentricity and grip required for high-speed precision operations.

End Mill Holder

End-mill-holder
An end mill holder

End mill holders are used to hold milling tools for heavy machining operations. They have a higher grip force than collet chucks, and it rigidly holds the tool in place using set screws.

They are available in various lengths and have a tapered design with a small nose diameter resulting in improved rigidity and reduced vibrations.

Hydraulic Tool Holder

A hydraulic tool holder
A hydraulic tool holder (Source: Schunk)

Hydraulic tool holders are used for a process where a high degree of precision is required. Hydraulic fluid forces help center the tool with uniform pressure, resulting in concentric and rigid tool holding.

The tool is placed in the holder, and the screw is tightened, which causes the hydraulic pressure to rise. This pressure increase causes the sleeve to expand and hold the tool shank.

Hydraulic tool holders are very efficient as they allow for high removal rates and are ideal for tools requiring high accuracy, such as drills, reamers, end mills, etc.

Milling Chucks

A milling chuck set
A milling chuck set (Source: Glacern)

Milling chucks are rigid and accurate tool holders with a high gripping force. They have a symmetrical design which provides high accuracy and good balance.

They are designed for a specific tool size, and reducing collets are used for lower-diameter tools. They are highly versatile in terms of the types of tools they can use. 

It has a straight collet that provides uniform clamping force, increasing rigidity and having minimal runout and axial movement.

They also have a simple locking system that locks the tool in place with high force. These properties make it suitable for heavy milling applications at high speeds. 

Better tool-holding properties also contribute to longer tool life and better surface finish. These holders are preferred for large-diameter milling tools.

Shrink Fit Holders

A shrink fit holder
A shrink-fit holder

Shrink fit holders have an undersized hole for the tool. The hole's size is thermally expanded to fit the tool in place.

Once the holder cools down, it uniformly grabs the tool shank to provide an even clamping force on the tool. 

Uniform force distribution results in high concentricity, and material contraction provides high grip force. It has a considerably higher grip force than hydraulic holders with similar levels of runout. 

Induction heaters are used to heat the holder leading to reduced tool changing time.

The tool holder only requires minimal accessories, but you have to invest in the tool holder's heating and cooling equipment for efficient operation.

Hence it requires a high initial investment, but the benefits outweigh the cost as it can significantly improve production rate, tool life, and quality.

How to Select The Right Milling Tool for Your Job - Tool Selection Guide

Selecting the right tool can contribute a lot towards achieving the project goals.

There are a variety of factors and considerations which play a significant role in choosing the right tool.

A lot depends upon the material to be worked upon and the shape and form of the workpiece required.

To determine the right cutting tool, you must also consider the average cutting speed, direction (plunge or feed), and the required finish.

Investing in a more robust cutting tool contributes to the project's overall quality while preventing breakage and slippage during the process. Also, they minimize wear and result in accurate machining.

Milling tools with a higher chip clearance make rougher cuts, while tools with multiple flutes remove less material and are best at finishing operations.

For a balanced setup, use rough tools at the start to remove material and then run a final round using a finishing tool.

Note that setting the correct speed and feed rate depending on the material and cutter in hand is essential for accurate milling.

Generally, the feed rate (IPM) is determined by multiplying speed in RPM, chip load in inches per tooth (IPT), and the number of flutes.

IPM = RPM × IPT x No. of flutes

IPT, also known as chip load, is the measurement of the amount of material that a cutter removes per revolution of the cutting tool.

Selecting the right tool holder can positively influence the results of machining.

It should provide the necessary gripping force at the required speed apart from having an optimal runout and balance for the operation.

Milling tools can cost anywhere between $10 and $1,000, or even more if you are looking for some fancy options.

Generally, adjustable tools like a face mill with replaceable inserts cost more than tools having inserts welded into them.

Final Thoughts

Milling is a major cutting operation in various manufacturing processes.

The advancements in tool design, material, coatings, and machines have greatly improved cutting performance at a reduced cost.

Cutting tools having better operational capabilities are usually costlier, but they compensate for the cost through higher cutting speed, quality, accuracy, longer tool life, etc.

Investing in the right tool having higher quality and grade gives dividends in the long run by significantly improving the quality of the finished goods.

It is crucial to understand and have knowledge of new developments in tooling to perform an efficient and economical operation. 

Frequently Asked Questions

What are the types of milling machines?

There are mainly four types of milling machines - knee type, column type, fixed bed type, and planar. The knee and column-type machine move the workpieces in the vertical direction, and the saddle moves in the transverse direction. The fixed bed-type milling machine has a moving spindle that can move in one or all directions. Lastly, planar-type milling machines provide vertical movement to the tool, and the table moves to give feed.

How to select a cutting tool based on the milling machine?

The right cutting tool for a milling machine is decided based on the machine's power, rigidity, operational capabilities, tool holder, etc.

What are the limitations of a milling machine?

The limitations of a milling machine depend on its work area, the number of axes, tool clamping range, spindle speed, power of the motor, machine's overall construction, weight, etc. 

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Hey I'm John. I talk about CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com

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John

Hey I'm John. I talk about CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com

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