Tom Beaumont

Product Training Manager

18 years engineering experience, specialising in 3 & 4 axis CNC milling, turning and horizontal boring.

Solid milling and indexable milling are two different approaches used in machining operations, specifically in milling processes. Each method has its advantages and most suited application, but the choice between them also depends on various factors such as the material being machined, the desired precision, the complexity of the workpiece, and cost considerations.

What is Solid Milling?

Solid Milling involves using a single-piece cutting tool made from solid material, typically high-speed steel (HSS) or carbide. The tool has cutting edges and these edges remove material as the tool rotates. Solid Milling Tools are available in various shapes and sizes, including end mills, slot drills, ball nose, rippers etc.

What are the Advantages of Solid Milling?

Rigidity: Solid milling tools are generally more rigid than indexable tools, which can lead to better surface finish and dimensional accuracy.

Precision: Solid milling tools are well-suited for applications that require high precision and tight tolerances.

Smaller Diameters: Solid milling tools are most suited to smaller diameters and are generally more cost effective up to Ø16mm.

Higher Cutting Depths: In smaller diameters the depth of cut is generally longer in solid milling, especially in ranges with extra-long length or long reach geometries.

Versatility: Solid milling tools feature a wider range of geometries than indexable such as corner radius, ball nose, rippers/roughers and more.

Suitable for lower powered machines: Some solid milling cutters which are at the lower end of the performance spectrum, such as HSS or Powder Metal, are suitable for lower powered or manual machines.

What are the Disadvantages of Solid Milling?

Increased cost in larger diameters: In larger diameters generally above Ø16mm, solid carbide tools can be more expensive with higher tool replacement costs.

More frequent tool changes: When the cutting edges wear out, the entire tool must be replaced or re-sharpened (resharpening reduces the diameter).

Brittle: Solid carbide milling tools can be brittle and susceptible to chipping or breakage, especially when machining harder materials or unstable conditions. This can lead to unexpected tool failures and potential damage to the workpiece.

What is Indexable Milling?

Indexable Milling involves milling bodies with replaceable carbide inserts. These inserts have multiple cutting edges and are mounted on the tool body. When the cutting edge becomes dull, chipped, or worn, the insert can be easily replaced (or rotated to another cutting edge), avoiding the need to re-sharpen the tool.

What are the Advantages of Indexable Milling?

Cost-effective in larger diameters: Milling bodies are made of a cheaper material, generally steel, whereas the inserts are carbide. This makes them more cost effective in larger diameters. Instead of replacing the entire tool, only the insert needs to be replaced when it becomes worn.

Larger diameter machining: Indexable milling bodies are available in larger diameters with some indexable face mills going over Ø315mm.

Time-saving: Replacing an insert is faster than re-sharpening a solid tool, leading to reduced downtime. Inserts also have several cutting edges which can be indexed round for even less tool changes.

Better for heavy machining: Indexable milling tools can endure increased load and disruption which makes them capable of heavier machining applications.

Insert grades: The replaceable carbide inserts are available in different grades to suit various materials, only the insert needs changing when you are cutting a different material, unlike solid milling tools that are limited to the materials they can machine, the whole tool needs changing if you are changing from one material to another e.g. machining aluminium one day then stainless steel the next.   

What are the Disadvantages of Indexable Milling?

Limited Rigidity: Indexable tools may have slightly less rigidity than solid tools, which can affect surface finish and accuracy in some cases.

Reduced Accuracy: Tolerance on milling holders are generally looser compared to solid carbide therefore can be a lower precision.

Application Limitations: While indexable tools can be versatile, some specialised, intricate or high-precision applications may require solid tools.

Not suitable for smaller sizes: Indexable tools generally only start from Ø10mm therefore are not suitable for machining smaller diameters.

Unsuitable for low power machines: Potentially low power machines may not have the capabilities to run larger indexable milling tools. Always check required cutting data before purchasing.

What are replaceable head milling tools and what are the benefits?

Replaceable head milling tools, also known as Modular Milling Tools or milling cutters with interchangeable heads, they consist of a separate tool body and replaceable cutting heads or inserts. These tools offer the advantages of both solid milling and indexable milling, combining the rigidity and precision of solid tools with the cost-effectiveness and convenience of indexable tools.

Replaceable head milling tools allow for the replacement of only the worn or damaged part (the cutting head/inserts), reducing tooling costs compared to entirely replacing the tool. Different cutting heads or inserts can also be used with the same tool body, allowing for versatility in machining different materials and applications, Modular Milling Heads are particular suited to long reach applications and the screwed adapters are available in different lengths.

Indexable Milling Materials / Grades compared to Solid Milling

In indexable milling, the inserts generally come in a variety of grades and chip breakers for different materials and applications. This increases their versatility because in some multi-material systems you can machine every material with the same holder, thus reducing overall tooling costs.

Whereas, in solid milling, particularly at the higher end of the spectrum, end mills tend to be more material specific. This increases their performance but at the expense of material versatility.

Indexable Milling Applications / Compared to Solid Milling

When dealing with heavier cutting operations with a higher required force, typically roughing or semi-roughing, an indexable tool is the recommended choice due to its substantial cutting force and power consumption.

However, if the operation involves delicate cuts and requires precise accuracy and surface finish, a solid tool may be necessary.

What Tool Holders are used for Indexable Milling?

Face Mill Arbors: Face mill holders are designed for holding face mills, which are large-diameter cutters used for facing and surface milling. They often have a flange that provides stability and supports the larger cutter.

End Mill Holders: End mill holders can also be used for indexable milling, particularly when using end mills style indexable tools. These holders offer good rigidity and accuracy for various milling operations.

Screwed Shank Modular Adapters: These are designed to clamp screw onto threaded shank milling heads and are usually used for long reach applications due to the extreme lengths of the adapters.

Hydraulic Chucks: Hydraulic tool holders use hydraulic pressure to provide a secure grip on the tool. They offer excellent rigidity, vibration damping and a tool run out of 3 microns, making them suitable for high-speed and precision milling applications when holding endmill type indexable milling bodies.

What Tool Holders are used for Solid Milling?

Some common types of Tool Holders used for solid milling can include:

ER Collet Chucks: Collet chucks are versatile and widely used for general solid milling applications. They provide good runout accuracy of 10 microns and are suitable for light to medium-duty milling operations. They are popular and come in various sizes to accommodate different tool diameters.

End Mill Holders: The most conventional method of clamping Weldon shank solid tools for general purpose milling. End mills holders, also known as side lock arbors are a popular tool holder found on the shopfloor.

Hydraulic Chucks: Hydraulic tool holders use hydraulic pressure to provide a secure grip on the tool. They offer excellent rigidity, vibration damping and a tool run out of 3 microns, making them suitable for high-speed and precision milling applications.

Shrink Fit Tool Holders: Shrink fit holders use heat-induced expansion and contraction to securely hold the tool. They provide high clamping forces and are often used in high-speed machining and long reach applications to minimise tool vibrations.

What Tool Holders should you use in Milling Applications?

The range of CNC tool holders available can make it a daunting task in selecting the right one for your milling operation. When selecting a tool holder for milling you need to be aware that they can all come with different run-outs, rigidity, gripping torque and balance. Higher performance holders will be more accurate at faster speeds which ultimately improve productivity, however the initial investment will be more.

Summary

In summary, solid milling is preferred for smaller diameters and when high precision and rigidity are essential, while indexable milling is more cost-effective and timesaving for larger diameter or heavier machining operations. The choice between solid and indexable milling can also depend on the specific machining requirements, material properties, and machine capabilities.

For expert advise on choosing the right solid or indexable tool for your application, please contact our technical team on 01924 869 615 or email sales@cutwel.net.

Comprehensive range of Indexable Milling tools for square shoulder, face high feed, copy and plunge milling.

From general purpose to material specific high performance milling cutters.

High performance solid carbide modular milling heads with screwed shank adapters.