Indexable Milling Cutters & Milling Cutting Tools

Indexable Milling Cutters are specialised machining tools used in milling operations, which have been designed to efficiently cut, shape, or remove material from a workpiece... Read more below.

Indexable Milling Cutters Explored

So you are considering Indexable Milling Cutters and have heard that they are very efficient cutting tools that are used in machining operations to get you good results, but you are not sure if they are right for you?

Well, in this guide to Indexable Milling tools, we will answer every question you may have about them to help you make a more informed buying decision as to which one you need for your application use.

For example, we will discover how these milling tools are equipped with replaceable cutting inserts - typically made from carbide - which are then mounted onto the cutter body and why this is important for you.

Alongside this, we will discover what types of applications they are suitable for, what tasks they can easily handle - such as high feed face mills or milling, slotting, and contouring - and how easily they can do this.

So let us help you understand more about these types of cutting tools regardless if you are getting into indexable milling tools for the first time or just looking for the right spare part for a replacement. If you are still not sure, our friendly customer service team is on hand to help you as well.

What are Indexable Milling Cutters?

Definition: Indexable Milling Cutters are specialised machining tools used in milling operations, which have been designed to efficiently cut, shape, or remove material from a workpiece.

They do so as they feature replaceable cutting inserts, which can be made of materials like carbide, ceramic, or diamond, which are then clamped into the cutter body.

Unlike solid cutting tools, these inserts can be indexed (rotated or flipped) to expose a fresh cutting edge when needed and reduce your downtime and cost at the same time.

They are also available in various designs (e.g., face milling cutters, indexable end milling cutters, High Feed End Mills, and chamfer cutters), making these milling cutters available to be used for tasks such as contouring, slot milling, T-Slot Cutters, and profiling in industries like automotive, aerospace, and manufacturing, to name just three.

How Do Indexable Milling Cutters Work?

The key feature that makes indexable milling cutters cost-effective is the use of interchangeable inserts, which are made from hard materials like carbide or ceramic.

These inserts are then securely mounted into the cutter body and are designed to be easily replaced when worn or damaged.

As a result, this mechanism then gives you continuous operation without requiring you or your machinists to make frequent tool changes.

Key Components of Indexable Milling Cutters

Indexable Milling Cutters are made up of several areas; for instance, here you have:

Cutter Body

The cutter body then serves as the backbone of an indexable milling cutter.

This is typically made from high-strength steel to withstand the stresses of the machining processes. The cutter bodies are then designed to hold multiple inserts securely.

Types of Replaceable Inserts

There are multiple types of replaceable inserts available depending on your application's various shapes, sizes and grades.

For instance, here you have:

Carbide Inserts

Carbide inserts are then known for their hardness and heat resistance, making them suitable for high-speed operations as a result of this.

Ceramic Inserts

Ceramic inserts are then ideal for machining more hard and abrasive materials.

Cermet Inserts

Cermet inserts then give you a good balance between toughness and wear resistance.

Polycrystalline Diamond (PCD) Inserts

Polycrystalline Diamond (PCD) Inserts are then used to cut non-ferrous and abrasive materials like aluminium and composites.

Types of Indexable Milling Cutters Available

Indexable Milling Cutters also come in various types, allowing you to choose the right one for your application.

For instance, common types here consist of:

Face Milling

These indexable milling cutters are commonly used for face milling large, flat surfaces for high material removal rates.

Slot Milling

Slot milling indexable cutters are then ideal for creating precision slots and grooves in metal and non-metal materials.

Contour Milling

Contour milling indexable cutters are then used for complex contouring and 3D profiling - especially in aerospace and mould-making industries, to name two.

Shoulder Milling

Shoulder milling indexable cutters are then perfect for producing precise 90-degree shoulders or vertical walls in your workpieces.

Pocket Milling

Pocket milling indexable cutters can then efficiently remove materials from recessed areas or pockets in parts.

High-Feed Milling

High-feed milling cutters support high metal removable rates during the machining process, which ultimately leads to increased productivity.

Chamfering

Chamfering milling cutters are then ideal for adding chamfers or bevels to workpieces for finishing or assembly purposes.

Profile Milling

Profile Milling cutters handle intricate profiling tasks on components, such as moulds and dies, for instance.

Why Are Indexable Milling Cutters Good To Use?

Indexable Milling Cutters are advantageous to use for a number of reasons, such as for example:

Cost-Effectiveness

The replaceable insert mechanism is designed to significantly reduce your machining costs, as you only need to replace the worn inserts rather than the entire tool.

High-Feed Machining

Indexable milling cutters are designed for high-feed operations, enabling faster production rates and improved productivity.

Improved Tool Lifespan

Carbide inserts can be further advanced by adding coatings, this in turn extends the tool life more than uncoated inserts.

Various Designs

With various inserts and cutter designs available, these tools can also handle a wide range of machining tasks - as you can see above, from roughing to finishing.

Understanding Indexable Milling Cutter Insert Styles

The names of insert styles for indexable milling cutters also typically follow a naming convention set by manufacturers or industry standards (e.g., ISO or ANSI) and can look like AOMT, or APKT Inserts names.

As a result, you can tell by their name what the geometry, size, and application of the insert will be.

For instance, here you have:

Basic Structure of Insert Names

Letter 1 (Describes The Inserts Shape)

These indicate the insert's shape, such as square, triangular, round, etc.

Below we have listed the ISO code for inserts:

A: Parallelogram
C: Rhombic (80°)
D: Rhombic (55°)
H: Hexagon
L: Rectangular
O: Octagonal
R: Round
S: Square
T: Triangular
V: Rhombic 35°
TW: Trigon 80°

Letter 2 (Relief Angle)

This letter refers to the clearance (relief) angle on the insert.

N: 0° (Negative)
A: 3° (Positive)
C: 7° (Positive)
P: 11° (Positive)
D: 15° (Positive)
E: 20° (Positive)
F: 25° (Positive)
G: 30° (Positive)

Letter 3 (Tolerance)

This letter is referencing the tolerance class of the insert, most common ones being M,G and E, other letters include A,C,F,H,J,K,M and U

M: Pressed insert
G: Ground tolerance
E: High precision tolerance

Letter 4 (clamping and chip breakers)

This is denoting the way the insert is clamped into the cutter body and the chip breaker.

N: No clamping hole - no chip breaker (single sided)

R: No clamping hole - chip breaker on one face (single sided)

A: Cylindrical clamping hole - no chip breaker (double sided)

M: Cylindrical clamping hole - chip breaker on one face (single sided)

G: Cylindrical clamping hole - chip breaker on both faces (double sided)

W: Screw hole – chip breaker on one face (single sided)

T: Screw hole – chip breaker on one face (single sided)

U: Screw hole – chip breaker on both faces (double sided)

Numbers

You then have dimensions or application-specific codes, such as:

Size

Indicates the cutting edge length, thickness and corner radius in mm. Refer to ISO charts for exact sizes.

Application Codes

These denote specific insert series for a variety of features (e.g., APKT, RDMT).

Manufacturer-Specific Codes

Each manufacturer then may introduce its own naming styles (known as captive pockets) beyond the ISO standard, this is denoted by the letter X in the code. For instance:

APKT

A specific parallelogram-shaped insert with a positive rake and chip breaker geometry.

ADMT

Positive-rake inserts with specific chip-forming capabilities.

SNHX

A square-shaped insert with specific relief and tolerance.

ODMT

An octagon (8-sided) shape with a 15° positive rake angle with a general tolerance class on a single-sided insert and a cylindrical clamping hole.

TPGN

A triangular shape with an 11° positive rake angle, this insert would be manufactured to a ground tolerance on a single-sided insert with no chip breaker or clamping hole.

RDGT

A round-shaped insert with a 15° positive rake angle, this insert would be manufactured to a ground tolerance on a single-sided insert with a centre screw hole.

Application by Materials

Also linked in the ISO system, we can identify the material we are trying to machine by a letter and colour.

For example here some examples are:

P - Blue

Inserts optimised for steel.

M - Yellow

Inserts optimised for stainless steel.

K - Red

Inserts optimised for cast iron.

N - Green

Inserts optimised for aluminium or non-ferrous materials.

S - Orange

Inserts optimised for super alloys/heat resistant materials.

H - Grey

Inserts optimised for hardened steel.

GD or LD

Chipbreaker types for general or light-duty machining.

Examples Of Style Types

To give you some examples, here you have:

APKT 1604

This stands for the fact that it will give you a Parallelogram-shaped insert with a positive rake, medium tolerance, and dimensions (16 mm length, 4 mm thickness).

RDGT 12

This would then be a round insert designed for heavy-duty roughing or facing with a 12 mm diameter.

SEHT-T

Here, you are looking at a square insert with high-precision tolerance and a specific chip breaker or geometry.

SDMT 12

This would then be a square insert with clearance angles and medium tolerance, sized 12 mm.

SNHX-T

Here, you would then have a square insert with a specific chip-former and high rake geometry designed for efficient milling.

Why is the Maximum RPM of the Cutter Important?

The maximum RPM ratings will be etched on the indexable cutter body, this is to ensure you get the best possible cutting speeds.

The inserts you choose, the material you are cutting, the machine you are using, depth and width of cut and how rigid the overall set up of the component will ultimately determine the correct cutting data (speeds and feeds) - This in turn will improve your material removal rates and give you cleaner cuts as a result.

Consequently, this then allows you to choose the right cutter for various applications, from high-feed machining to precision finishing - reducing your cycle times - all while maintaining your accuracy and improved tool life.

Why is the Nominal Size Important to Know?

The nominal size here then gives you a standardised reference point for making sure that you have the correct compatibility with the machine tool holders and inserts.

For instance, accurate sizing here will give you correct engagement and stability during your machining operations - helping you to prevent misalignment from occurring while also improving your overall efficiency and precision of the milling process as you do so.

Why is the Radius Important to Get Right?

A precise corner radius on your inserts and cutters will improve your surface finish, reduce any stress concentrations that may build up, and improve the strength of the cutting edge as well.

It is also especially beneficial in reducing chipping during your machining, helping you get a longer tool life and better performance in challenging applications as a result.

Through Tool Coolant

Through tool coolant is a perfect way to distribute the coolant right to the cutting edge of the carbide inserts, helping to keep the carbide and also the workpiece cool as it machines. You will require a machine that is capable of delivering the coolant through the spindle for this feature to be used.

Why is the Body Diameter Important to Understand?

The body diameter then determines the cutter’s rigidity and machining capability.

For instance, a larger diameter will give you more stability while reducing your deflection rates during heavy cuts - while smaller diameters will improve your accessibility in tighter spaces, giving you more use across various applications as a result of this.

Why is the Minimum Bore Diameter Important?

The minimum bore diameter then ensures that the milling cutter can fit into narrow or confined spaces correctly.

This then gives you very high-efficiency machining of smaller or intricate features - improving their use cases and ensuring that you have a higher level of precision even in tight and complex workpieces as a result.

Why is the Cutting Diameter Important?

The cutting diameter will then define the maximum width of the material to be removed per pass.

For instance, larger diameters can improve your productivity for broader surfaces, while smaller diameters allow for more detailed work on intricate features.

Why is the Indexable Cutter Grade Important?

The grade of the insert material used then impacts your wear resistance, toughness, and heat tolerance.

For instance, higher grades here will give you a longer tool life, better performance under high-stress conditions, and the ability to machine a variety of materials easily as well.

Why is the Length Important?

The length then affects your reach and stability.

For instance, longer tools will give you access to deeper features, while shorter tools minimise your deflection and improve your rigidity during heavy machining - giving you more consistent and accurate results here.

Why is the Spigot Diameter Important to Know?

The connection between the spigot diameter of the cutter body and the spindle tool ensures a good strong secure connection. This reduces vibrations during machining, ultimately producing a cleaner surface finish and less wear on the inserts so prolongs tool life.

Why is the Number of Flutes Important?

The number of flutes that are on the cutter body will affect the amount of material removal and surface finish that can then occur.

For instance, more flutes will allow for finer finishes at faster cutting feeds, while fewer flutes allows for a larger chip evacuation space - making them ideal for roughing operations on softer materials.

Why is the Weight Important?

The weight of the milling cutter will then impact your machine tool's balance and stability.

For instance, lightweight tools reduce spindle strain and allow for faster machining speeds, while heavier tools improve your vibration dampening for high-load applications for example.

Why is the Maximum Cut Diameter Important?

The maximum cut diameter will then determine the tool's ability to remove material across wider surfaces.

A larger diameter, for example, will give you high productivity in your machining operations - particularly for roughing and finishing large workpieces, we should note here.

Why is the Torque (Nm) Important to Get Right?

A high torque rating on the machine will allow the milling cutter to handle tough materials and heavy cuts without the possibility of stalling.

Why is the Shank Length & Shank Diameter Important?

The shank length of the bit will then influence your tool's reach and stability.

For example, a longer shank will give you access to deeper features, while shorter shanks improve your rigidity and reduce vibrations - ensuring that you get precise and stable machining as an end result.

Why is the Diameter Important?

The diameter of the milling cutter will impact its cutting capacity and stability.

For instance, here, larger diameters will give you faster material removal, while smaller diameters, on the other hand, will give you more precision for that intricate work you need to carry out, as well as access to confined areas.

Why is the Diameter Range Important?

A wide diameter range then allows you more flexibility in machining different-sized features.

Why is the Height of the Bit Important?

The height of this cutting tool will then change its compatibility with your workpieces and any fixtures you are using as well.

For instance, the correct height will give you a tool that can access specific areas while maintaining the rigidity and stability necessary for you to complete accurate machining as you do so.

Why is the Form Important to Get Right?

The form of the milling cutter, such as round, square, or even more specialised shapes, will then control its overall application.

For instance, here, more specific forms will optimise the cutter for various tasks - such as roughing, finishing, or specialised profiles for example.<

Why is the Cutting Angle Important?

The cutting angle of the bit you choose will then directly impact your chip formation, heat generation, and surface finish.

Here, optimised angles for your application use will drastically improve your cutting efficiency, reduce your tool wear, and give you better material removal, all while maintaining your tool life as it does so as well.

Why is the Number of Teeth of this Bit Important?

More cutting teeth will help you to improve your surface finish and cutting efficiency, while fewer teeth will allow for deeper cuts and better chip evacuation.

As a result, it is important to get this balance right, as it is ideal when it comes to roughing and finishing operations.

Why is the Flute Length Important?

These are important as longer flutes allow you to get greater chip evacuation and improved performance in your deep cuts. Shorter flutes will give you more stability during high-speed operations and give you a good balance between the best precision and productivity here.

How to Understand The ISO Numbers on Indexable Milling Cutters?

ISO (International Organisation for Standardisation) numbers on your indexable milling cutters will help you quickly identify the cutter type, its geometry, and its compatibility.

This is because these numbers follow a standardised coding system that represents important details about the insert or cutter.

For example, these tend to be based around:

Typical Format

An ISO code for an indexable insert might look something like RCKT 12 04 M0-PM, with each section representing a specific attribute, such as:

Shape (1st Letter)

Example: R

Describes the general shape of the insert:

R = Round
T = Triangle
S = Square
C = Rhombic with 80° included angle
D = Rhombic with 55° included angle
V = Rhombic with 35° included angle

Relief Angle (2nd Letter)

Example: C

Indicates the angle of the insert’s clearance (how much it tilts away from the cutting edge):

A = 3°
B = 5°
C = 7°
P = 11°
N = 0° (flat, no clearance angle)

Tolerance Class (3rd Letter)

Example: K

Refers to the dimensional tolerance of the insert:

K = General tolerance
M = Medium precision
G = High precision

Insert Size (First Two Numbers)

Example: 12

Indicates the size of the insert, typically in millimetres or inches (diagonal length or largest dimension).

Thickness (Next Two Numbers)

Example: 04

Specifies the thickness of the insert, usually in millimetres.

Cutting Edge Configuration (4th Letter)

Example: M

Describes the cutting-edge type or geometry:

M = Medium edge prep
E = Sharp edge
T = Heavy edge prep

Special Features (Optional)

Example: 0-PM

Can represent various features, like chip breaker design, grade, or coating:

PM = Grade suited for finishing or medium cutting
MM = Universal chip breaker

Summary of RCKT 12 04 M0-PM

R = Round insert

C = 7° relief angle

K = General tolerance

12 = 12mm size

04 = 4mm thickness

M0 = Medium cutting edge with no additional features

PM = Chip breaker for finishing or medium cutting

Why is the Maximum Bore Depth Important?

The maximum bore depth of cut then indicates the tool’s ability to machine deeper holes or pockets.

This capability, for example, really is key for machining larger or more complex workpieces with precision, we should note here.

Why is the Shank Type Important?

The shank type of these indexable milling cutters is important as it gives you compatibility with your tool holders, providing you with a lot of stability and secure mounting as a result.

Here, you also have options like cylindrical, tapered, or Weldon shanks, which can cater to different machine requirements and improve your performance as a result.

For example, here, you can tend to get the following types:

Cyl/Weldon
Cylindrical
Cylindrical Densimet
R8
Seco/Weldon
Stepped Cylindrical
Threaded
Weldon
Straight Shank
Weldon Flat

Why is the Type of Mounting Important to Get Right?

The type of mounting here defines how the tool is secured in the machine.

For instance, proper mounting will reduce your vibrations, give you more stability, and improve your overall cutting precision during operations, for example.

So Are Indexable Milling Cutters Right For You?

As you can see, indexable milling cutters really can be indispensable bits for your milling machines, especially in modern machining which can require consistent High Feed Milling Cutters to function as expected when you need them.

This is because they give you a lot of cost-efficiency and use cases and are very high-performance cutting bits.

Consequently, we now hope that by understanding their components and applications, you can maximise your productivity and achieve the results you are after by getting the right bit for your use cases.

Contact Customer Support

If you are still not sure about which is the correct indexable milling cutter for you, or you need help, then for further information please contact our team, and we will be happy to help you understand which ones are perfect for you and your team. We can also help you with a number of other drill bits from Jobber Length Drills, Taper Shank Drills to the Right Twist drill set as well, or even cutter drill bits with a straight flute design to ones with a varying number of flutes and lots more - our team is here to help you.

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