The fly mill is just one example of a milling cutter. As with drill bits, these are rotary tools used on CNC machining centers, live-tool lathes, and yes, manual milling machines. But where a drill bit's cutting edges are positioned at the very end of the tool, limiting it to axial material removal (i.e., holemaking), a milling tool also boasts cutting edges along its periphery, allowing it to remove material radially, from side to side. A huge variety of such tools exists:

For more information, please visit Guangzhou Ruiyi Technology Co., Ltd..

• The fly mill just discussed is a type of face mill, used to produce flat surfaces on metal and plastic workpieces. They are rarely found on CNC machining centers.
• Slotting mills and slitting cutters are just as their name describes, able to cut slots and narrow slits respectively in the tops and sides of parts.
• Dovetail tools are a special type of milling cutter that machines the angled grooves needed to join many machinery components.
• Similarly, gear cutters (also known as hobs) are used to cut gear forms, splines, and sprockets. For the most part, they require dedicated machinery.

Each of these is an application-specific cutter, limited to relatively small amounts of material removal and the creation of distinct part features. In a moment, we'll talk about the more general-purpose tools—the end mills, shell mills, and other workhorses of the machining industry. For now, though, it’s important to recognize that all milling tools (with one or two exceptions) are just as described previously—multi-toothed rotary cutters that utilize a shearing action to remove material along the periphery of the tool and, in some instances, can act like a drill as well.

In the world of industrial milling, two broad classes of cutting tools exist. These are solid milling cutters and indexable milling cutters. As the name implies, the first of these is made from a solid piece of cutting tool material—usually tungsten carbide, although high-speed steel (HSS) and cobalt milling cutters are also available for hobbyists and low-volume or light-duty machining operations.

Due to its material cost, solid carbide tools are generally smaller than an inch or so in diameter. Above this size, almost all milling cutters use indexable carbide inserts attached to a steel cutter body via small screws or clamps. They provide an effective yet affordable solution for the vast majority of all machining operations, although solid carbide tools are still used for small part features and for finishing work.

Straddling the fence between these two are so-called modular end mills, which employ a solid carbide head that threads onto a steel body. As with modular carbide drills, these cutting tools provide the performance and accuracy of solid carbide but at a far lower cost. And because a worn head can be swapped out in a few seconds, modular tooling also increases productivity.

One of the most commonly used of all milling cutters is the end mill. Solid carbide, indexable, and modular versions are available, as are ones with square, ball, and radiused cutting ends. They are used to machine slots and shoulders, mill pockets, and cut the inner and outer perimeters of various part features. As suggested earlier, some end mills have center-cutting capabilities, allowing them to plunge like a drill or ramp into a workpiece surface.

Shell mills or shoulder mills can be thought of as an end mill's larger, heftier cousin. They cannot plunge or ramp, but they can remove large amounts of material quickly. Due to their large size, most are indexable, often filled with dozens of carbide inserts. So are face mills, modern, multi-fluted versions of the venerable fly mill that opened this article, used to true up horizontal surfaces and make them both smooth and flat. And copy mills are similar in shape and function to ball-nosed end mills. These are a favorite of moldmaking shops, which use them to rough out large cavities before finishing with a solid carbide or modular end mill.

There's some overlap between all of these. For example, it's no problem using an end mill to machine the top surface of a small metal workpiece, but the wider and longer that surface becomes, the more reason there is to use a face mill. And some face mills can be used to cut square shoulders like a shoulder mill would, provided that shoulder is fairly shallow in depth. As stated previously, there’s a huge variety of milling cutters out there. The trick is knowing which one to use and how to apply it.

That's where Kennametal comes in. Granted, they're not the only cutting tool supplier out there, but they are one of the oldest, filled with experienced applications and support people. The tooling manufacturer also carries an extensive lineup of most every cutting tool mentioned here (sorry, no fly mills).

Its Duo-Lock series of modular end mills, for example, provides a best of both worlds solution to anyone needing solid carbide performance at an indexable price range. There are also high-feed “Beyond” style milling tools, the Mill 4 and KSSM series of shoulder mills, Fix-Perfect face mills, and much more. Most are available in material-specific or general-purpose carbide grades, and all are available either online or in-person through an authorized distributor. Long story short, Kennametal has milling cutters covered.

Shoulder milling

Shoulder milling operations include:

• Shoulder/face milling
• Edging peripheral milling
• Shoulder milling of thin deflecting walls

Shoulder/face milling

What is successful shoulder/face milling?

Shoulder milling generates two faces simultaneously, which requires peripheral milling in combination with face milling. For a finishing operation, achieving a true, ninety-degree shoulder is one of the most important requirements. Other applications like roughing operations can be made with close to 90-degree solutions with high chip removal ratios. Shoulder milling can be performed by traditional square shoulder cutters, and also by using end milling cutters, long edge cutters, and side and face milling cutters. Due to these numerous options, it is essential to consider the operational requirements carefully in order to make an optimal choice.

Choice of tools

Shoulder milling cutters

Shoulder face mills of conventional designs are often capable of milling “true”, 90-degree shallow shoulders. Many shoulder face mills are universal cutters and can be used advantageously for making holes, ramping, or full slots on components. They offer a good alternative to face milling cutters when milling axially deflecting surfaces or for milling close to vertical faces.

End milling cutters

The indexable insert and solid carbide end mills offer good solutions for shoulders requiring accessibility or where quality surface is the top priority. Repeatability between passes and true 90 degrees are the key features of these tools.

Long edge milling cutters

Long edge cutters are generally used for milling deeper shoulders and contouring wide components in one shot. Even using in conjunction with high-power machines will permit removing high chip volumes in roughing operations that can be finished using the same long edge cutter or solid carbide tools.

How to apply

Milling of shallow shoulders

This frequently used operation is generally performed by shoulder face mills and end mills. A shallow cut allows for a larger radial cut. Often these cutters can replace face mills, particularly when the axial pressure on the component is a limitation, and when there is a demand for accessibility close to vertical faces or fixture sections. Oversized shoulder cutter options provide for optimal accessibility when milling shallow shoulders located deep.

Milling of deep shoulders

Use repeated passes with shoulder face mills and end mills. To minimize surface errors, such as scallops and transition-edges between the passes, a high precision cutter that is able to produce true 90º shoulders is an absolute requirement. If shoulder depth is smaller than 75% of the cutting edge length, the quality of the vertical surface does not normally require extra finishing.

Use a single pass with a long edge milling cutter

A long edge cutter is a good solution for deeper, larger, and usually heavier shoulder milling applications. They have a high metal removal capacity and are generally used for rough milling as the resulting surface texture is characterized by side milling at high feed rates.

These cutters make demands on:

• Stability
• Spindle condition
• Chip evacuation
• Tool holding
• Power

Radial forces are considerable, making this a tough side milling application.

Shorter long edge cutters are suitable for:

• Radially large but shallow shoulders.
• Full slotting at a depth equal to the diameter, which can make up for machine limitations

Longer versions are intended for:

• Milling of shoulders with moderate radial depth.
• Edging in powerful, stable machines

Are you looking for tool recommendations?

Find our cutting tools here chevron_right

Need advice?

Ask us a question chevron_right

Want to learn more about the basics of metal cutting?

Are you interested in learning more about Square Shoulder Milling Cutter? Contact us today to secure an expert consultation!

Register for our free e-learning chevron_right

Milling of shoulders located deep

Oversized shoulder cutter options provide for optimal accessibility in milling shallow shoulders located deep. For those shoulders that are located at even larger depths, up to 3xDc, use extensions with the Coromant Capto® coupling. For longer assemblies, damper adaptors are the solution. Long edge cutters are also available in oversized versions to be used for deeper shoulders located deep. However, the radial depths of cut are more limited.

Application checklist and hints

Generally speaking, these tips and hints are valid for all shoulder milling applications.

• Down-milling is always the first choice and is especially important for shoulder milling due to the 90° entering angle
• Machining should be performed in a manner that directs the cutting forces towards the support points of the fixture insofar as this is possible. Up-milling can, therefore, be a favorable alternative in some cases
• Selection of cutter pitch is dependent on the stability of the entire system, including the machine tool, workpiece and its clamping, as well as the workpiece material
• In ISO 40 machines and smaller, coarse-pitch cutters are recommended due to limited stability
• Coarse-pitch cutters are also recommended for machining components mounted high up on a cube fixture
• The positioning of the cutter on the workpiece is extremely important and should receive extra attention
• When DC/ae >10, the feed, fz, should be adjusted in accordance with the hex value to achieve a good result and avoid edge breakdown
• If the shoulder depth is smaller than 75% of the cutting edge length, the quality of the vertical surface does not normally require extra finishing
• Choose a tougher carbide insert grade than for face milling
• If long edge cutters are used, the conditions are demanding, therefore, an even tougher grade may be required
• The deeper the cut, the more important it is to choose a lower cutting speed in order to avoid vibrations
• When vibrations occur, decrease vc and increase fz, check against the recommended hex value!
• Ensure that enough machine power is available for the chosen cutting data

Tool holding

• Pay special attention to power requirements when taking large cuts, particularly with long edge cutters
• Tool mounting has the greatest influence on the milling result for cutters smaller than 50 mm
• The larger the cutting depth, the more important the size and stability of the coupling become, since the radial forces are considerable when using shoulder face mills, particularly long edge milling cutters
• Coromant Capto® couplings provide optimum stability and the smallest deflection for all types of cutters – particularly important with long or extended tooling

Rolling into cut

• Smooth entrances into the cut are essential for avoiding vibrations and extending tool life, particularly when milling shoulders
• Program the cutter to roll into the cut; always generate a chip thickness on exit that is zero: together this will ensure both higher feed and longer tool life
• This method is most suitable for applications in which you are milling around external corners, as it avoids sharp changes in the cut
• Keep the cutter engaged in a continuous cut

Milling of shoulders using side and face milling cutters

Side and face milling cutters are also used for milling shoulders, particularly if the configuration is narrow yet radially wide. These cutters are often the only possible solution for back-facing of hidden shoulders and faces.

Edging peripheral milling

What is successful edging peripheral milling?

Machining an edge is really a side milling operation applied in contouring tool passes. Side milling and edging are options of peripheral milling.

Choice of tools

• Thin edges are generally produced by end milling cutters, while deeper or thicker edges are generated by end mills using repeated “shoulder milling” passes, or by long edge cutters in a single pass
• Shoulders with depths of twice the diameter are effectively machined using long edge milling cutters or solid carbide cutters. For such deep shoulders or thick component edges, a radial depth of cut of 0.5 times the diameter is recommended
• Side and face milling cutters can also be used for edging or peripheral milling
• A large helix ensures a sufficient number of teeth in cut and a smooth cutting action for edging at small radial cutting depths
• A close pitch or extra close pitch type of cutter is especially suitable for edging. This is also true when milling thinner edges or shallow ledge type shoulders using 90º end mills

How to apply

Surface texture – radially generated

When there is no run-out in the cutter, the height of the cusp, h,
will be equally high and can be calculated using the formula:
Profile depth / cusp height

When there is a run-out in the cutter, the feed per tooth, fz,
and consequently the height of the cusp, h, will vary depending on the TIR.

fzfz run-out

As mentioned, surface texture and climbing tendencies may limit the feed rate, especially when the radial depth of cut is small.

When using the side of an end mill to mill a profile, a series of ‘cusps’ are generated. The height of the cusp, - h, is determined by:

• Cutter diameter, DC
• Feed per tooth, fz
• Tool indicator reading of the run-out, TIR

Indexable insert cutters will always have a higher TIR than solid carbide cutters. Also, the larger the cutter diameter, the greater the number of teeth, which increases the distance between the high and low spots of the cusp.

For best surface finish:

• Use a solid carbide cutter
• Use a high precision power chuck with Coromant Capto® coupling
• Use the shortest possible overhang

Feed recommendation (disregard hex):

• Indexable insert cutters, start value fz = 0.15 mm/tooth
• Solid carbide cutters, start value fz = 0.10 mm/tooth

Note: The worst surface quality is achieved if only one cutting edge generates the surface, due to bad run-out of the cutter.

Application checklist and hints

• A critical factor in peripheral milling is achieving a suitable feed per tooth, fz
• The feed value, fz, has to compensate for the cutter engagement, which influences the chip thickness
• Feed per tooth, fz, should be multiplied by the modification factor. This will give a higher feed rate with a smaller arc of engagement, and at the same time ensure that the chip thickness is large enough. However, the modification factor may not always be fully applicable: surface texture and climbing tendencies may limit the feed rate

Are you looking for tool recommendations?

Find our cutting tools here chevron_right

Need advice?

Ask us a question chevron_right

Want to learn more about the basics of metal cutting?

Register for our free e-learning chevron_right

Related information

Face Milling Guide

Explore tips on selecting tools and optimizing face milling operations for best results. chevron_right

Profile Milling

Learn about the various stages, tools, and techniques involved in profile milling operations. chevron_right

Milling Overview

Learn the critical factors for successful milling and different milling operations. chevron_right

Groove Milling

Overview of tools and methods for different groove or slot milling operations. chevron_right

For more Carbide Cutting Toolsinformation, please contact us. We will provide professional answers.