Shoulder milling

Shoulder milling operations include:

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• 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

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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):

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• 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

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The term “milling” refers to the manufacturing process of using a circular cutting tool on the ends and sides of a material blank to make a finished part. That’s obviously just a very general summation; there are actually around 30 different types of milling operations, 15 of which (the most commonly used ones) we’ll go over in this article. 

Common Milling Types

You’ll find that most milling types are self-explanatory with exactly what they do or how they work in their name, but here’s a little more info on each one.

1. Face Milling

Face milling is beloved in the manufacturing world because it can be used to make accurate and smooth surfaces, even on larger pieces. It can make pockets and steps in metal by flattening the material and smoothing out the top. A face mill has cutting edges on its face, which is the part that looks like a disk, and these cutters work by shaving off material from a workpiece horizontally until it reaches the depth required (this will be preset by you). This image explains how it works:

5. Shoulder Milling

Shoulder milling removes material from the side of a workpiece (the “shoulder” or “sidewall”) with different cutting tools, like end mills, to make flat, 90-degree angles, like steps.

6. Side Milling

A side milling cutter or end mill is used in side milling to shave thin layers of material from the side of a workpiece. This is the way to go for flat or contoured surfaces. Xometry’s very own Aaron (our marketing SVP) explains more about this milling process in the below video.

7. Profile Milling

If you have to make complex shapes and profiles on a surface, profile milling will be your best friend. It uses a tool with multiple cutting edges to make curves and angles and also has a ball tip that moves around, smoothing everything out. It sometimes (but not always) uses multiple axes to make the cuts. Getting an axis to cooperate in manual milling is, putting it mildly, impossible, so the process often is used with CNC (computer numerical control) machines. Profile milling is used to make dies, molds, and other parts with more detailed surfaces, like this:

8. Saw Milling

Saw milling works with a large, thin, and round cutting tool that has lots of teeth (like a circular saw blade). This fairly quick and easy process is also known as “slitting” because it makes thin slits in a material. The blade of the tool can cut straight down in a vertical line or move along the surface for different types of cuts. 

9. CAM Milling

CAM (computer-aided manufacturing) milling can make parts that most humans would find impossible to create by hand. It’s an automated process, with the cutting tool being controlled by a computer. Human effort is only needed to design the digital blueprint for the part with exact instructions on how to make it in the language that it can understand (don’t worry, there are tools for this) and then feeding it to the computer and switching it on.

10. Gear Milling

As you may have guessed, this milling method has been specifically designed to make gears and gear teeth (like the toothed wheels found in car engines or clocks). It’s done with gear hobbing cutters, or milling cutters, which remove material to make the gear teeth. For simple gears, manual machines are used, but for complex ones, manufacturers tend to go the CNC route.

11. Angle Milling

Angle milling makes beveled edges and angled features on parts. You can use specialized tools with this process, like tapered milling cutters that are cone-shaped or parallel-faced cutters that are flat but can be adjusted at a tilt to get the angle. To get the right tilt, you’d have to use a tilting arbor or four (or more) axis machine.

12. Form Milling

Form milling makes contoured and detailed shapes on a surface with either a specialized milling cutter in the exact shape or profile you want or generic cutting tools (the latter is a somewhat repetitive process, similar to profile milling). It’s used a lot in automotive, aerospace, and mold-making, and many times with a CNC machine.

13. Straddle Milling

Straddle milling involves mounting two milling cutters on an arbor and positioning them next to each other to create parallel slots, grooves, or surfaces on your chosen material. Because it has two cutting tools, it can essentially finish a piece in half the time. We see this process used often for keyway milling and machining flats on opposite sides of a shaft.

14. Plain Milling

It might not have a very interesting name, but plain milling is still a useful manufacturing method. It’s pretty basic, removing material from a surface using a flat, horizontal cutting tool, and it is used for making square or rectangular features. Here’s what that looks like:

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