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Expert Guide to CNC Milling

Nathan Smith

Technical Support

10 years engineering experience, specializing in CNC 3 & 4 axis milling, measurement and inspection.

When Considering CNC milling operations there are many facets to take into consideration.

 

Over time we have been asked all sorts of queries from customers who have varying levels of knowledge and experience. I have summarised below some of the most frequently asked questions that I am asked on a regular basis...

Introduction to CNC Milling

CNC (Computer Numerical Control) milling is a type of machining process that uses computerized controls and rotating cutting tools (milling cutters) to remove material from a workpiece to create a specific shape or design.

There are several types of CNC milling techniques and operations, including:

  • 3-axis milling: This is the most common type of CNC milling technique, where the cutting tool moves along three axes (x, y, and z) to remove material from the workpiece.

  • 4-axis milling: In this technique, the cutting tool can rotate around an additional axis (usually the A-axis) to perform operations like drilling and tapping at different angles.

  • 5-axis milling: This technique allows for even more flexibility, as the cutting tool can move along five axes (x, y, z, A, and B) to perform complex operations on the workpiece.

Common milling operations include:

Face Milling

End Milling

Square shoulder Milling

Profile Milling

T-slot Milling

Trochoidal Milling

Slotting

Dynamic Millng

Ramping

Circular interpolation

Plunge Milling

HPC Milling

High Speed Milling

Thread Milling

Groove Milling

Barrel Milling

What is CNC end milling?

End milling is a type of CNC milling operation that involves using a rotating cutting tool, called an end mill (or milling cutter), to remove material from the surface of a workpiece. The end mill is a cylindrical tool with cutting edges on both the end and the sides, allowing it to perform a variety of cutting operations, such as slotting, drilling, and profiling.  It usually has 4 or more teeth or flutes, although 2-3 flute milling cutters can be used for end milling.  End mills usually have a sharp 90-degree corner, although some have corner radii, ball noses or a chamfer edge preparation.

During the end milling operation, the cutting tool is positioned perpendicular to the surface of the workpiece and moves along the surface while rotating. The cutting edges of the tool remove material from the workpiece as it moves, creating a slot, hole, or other feature.

The end milling operation can be performed in a variety of directions, including parallel to the surface of the workpiece, perpendicular to the surface, or at an angle. The cutting speed, feed rate, and depth of cut can be adjusted to achieve the desired surface finish and dimensional accuracy.

What is CNC face milling?

Face milling is a type of CNC milling operation that involves cutting a flat surface on the top of a workpiece. The cutting tool used in face milling is typically a cylindrical tool with multiple cutting edges or teeth. The tool is positioned perpendicular to the surface of the workpiece and rotates while moving along the surface to remove material.

The face milling operation can be performed using a variety of tools, including end mills, fly cutters, or face mills. End mills are typically used for smaller workpieces and can remove material quickly, but they can produce a rougher surface finish. Fly cutters use a single point cutting tool to produce a smooth surface finish, but they require multiple passes to remove material. Face mills are most commonly used and are designed to remove material quickly and produce a smooth surface finish in a single pass.

During the face milling operation, the cutting tool removes material in a series of overlapping cuts, called passes. The depth of each pass is determined by the thickness of the material being removed and the size of the cutting tool. The cutting speed, feed rate, and depth of cut can be adjusted to achieve the desired surface finish and dimensional accuracy.

Face milling can be used to create flat surfaces, as well as angled or contoured surfaces, by tilting the workpiece or the cutting tool. This operation is commonly used in manufacturing industries to create precision parts for machinery, automotive, aerospace, and other applications.

 

What is square shoulder milling?

Square shoulder milling is a type of CNC milling operation that involves cutting a square shoulder on the edge of a workpiece. The operation is performed using an end mill, which has multiple cutting edges and a square end for cutting a flat surface.

During the square shoulder milling operation, the cutting tool is positioned perpendicular to the surface of the workpiece and moves along the edge while rotating. The cutting edges of the tool remove material from the workpiece, creating a square shoulder with a flat surface.

The cutting speed, feed rate, and depth of cut can be adjusted to achieve the desired surface finish and dimensional accuracy. The square shoulder milling operation can also be performed in multiple passes to achieve a deeper shoulder or to remove more material.

What is slot milling?

Slot milling is a type of CNC milling operation that involves cutting a slot, keyway or channel into a workpiece. The operation is performed using a cutting tool called a slot drill, which traditionally has 2 cutting edges (2 flutes), however with modern geometries 3-4 flute milling cutters are often used to slot.

During the slot milling operation, the cutting tool is positioned perpendicular to the surface of the workpiece and moves along the surface while rotating. The cutting edges of the tool remove material from the workpiece, creating a slot with a flat bottom and straight sides. Multiple passes can be used to create a deeper or wider slot if required.

What is t-slot milling?

T-slot milling is a type of CNC milling operation that involves cutting an inverted T-shaped groove into a workpiece. The T-shaped groove is commonly used to create a channel for holding and securing fixtures or work holding devices in place.

The T-slot milling operation is performed using a cutting tool called a T-slot cutter, which has multiple cutting edges and a T-shaped profile. The T-slot cutter is positioned perpendicular to the surface of the workpiece and moves along the surface while rotating. The cutting edges of the tool remove material from the workpiece, creating a T-shaped groove with a flat bottom and straight sides.

Prior to using a t-slot cutter, a slot drill must first be used to create a standard slot, the t-slot cutter is then used to create the horizontal profile of the “T”.

The cutting speed, feed rate, and depth of cut can be adjusted to achieve the desired surface finish and dimensional accuracy. The T-slot milling operation can also be performed in multiple passes to achieve a deeper T-slot or to remove more material.

What is CNC trochoidal milling?

Trochoidal milling is a type of CNC milling operation that involves using a cutting tool to create a series of overlapping circular cuts. The technique is named after the trochoidal path that the cutting tool follows as it moves through the material.

During the trochoidal milling operation, the cutting tool is positioned perpendicular to the surface of the workpiece and moves along a circular path while rotating. The cutting edges of the tool remove material from the workpiece as it moves, creating a series of overlapping circular cuts. The technique is designed to reduce the amount of tool wear and increase material removal rates.

Trochoidal milling is often used in high-speed machining applications to remove large amounts of material quickly and efficiently. The technique is especially effective when machining hard or difficult-to-machine materials, such as titanium and Inconel. It is particularly suitable for machining deep slots and can be a more effective machining method than using indexable milling tools.

The benefits of trochoidal milling include:

  • Improved tool life: Trochoidal milling involves using a circular cutting path, which spreads the cutting forces across multiple cutting edges of the tool. This reduces the amount of wear on any individual cutting edge and can significantly improve the life of the cutting tool.

  • Increased efficiency: Trochoidal milling can help increase material removal rates by using multiple cutting edges of the tool at once and minimizing the amount of tool engagement. This can help reduce machining time and improve overall efficiency.

  • Improved surface finish: The circular cutting path used in trochoidal milling can help produce a smoother surface finish than traditional milling techniques, particularly when machining harder materials.

  • Reduced vibration: Trochoidal milling can help reduce vibration and chatter during the cutting process, which can improve machining accuracy and reduce the risk of tool damage or breakage.

  • Versatility: Trochoidal milling can be used with a wide range of cutting tools and materials, making it a versatile technique for many CNC milling applications.

The cutting speed, feed rate, and depth of cut can be adjusted to achieve the desired surface finish and dimensional accuracy. The trochoidal milling operation can also be performed in multiple passes to achieve a deeper cut or to remove more material.

Overall, trochoidal milling is a specialized technique that can help improve machining efficiency and reduce tool wear in certain applications. However, it requires careful consideration of cutting parameters and tool selection to achieve optimal results.

 

What is circular interpolation milling?

Circular interpolation milling is a type of CNC milling operation that involves cutting circular arcs or circles using a cutting tool that moves along a circular path. This is achieved by programming the CNC machine to follow a circular tool path at a specific radius, which can be used to create complex geometries or shapes.

Circular interpolation milling can be used to create a wide range of features, including circular pockets, holes, grooves, and curves. The cutting tool can be angled to create tapered features or chamfers or programmed to follow a spiral path to create helical shapes.

What is dynamic milling?

Dynamic milling is a type of CNC milling operation that involves using advanced software algorithms to dynamically adjust the cutting parameters of the tool in real-time during the operation. This allows the cutting tool to maintain a consistent load and engage more of the cutting edges, leading to increased efficiency and reduced tool wear.

During the dynamic milling operation, the cutting tool is programmed to follow a specific toolpath while cutting the material. The software continuously monitors the cutting conditions and adjusts the cutting parameters, such as the spindle speed, feed rate, and depth of cut, to optimize the performance of the tool.

The benefits of dynamic milling include:

  • Increased efficiency: Dynamic milling can significantly increase material removal rates by maintaining a consistent load on the cutting tool and utilizing more of the cutting edges. This reduces the need for multiple passes and can help reduce cycle times.

  • Reduced tool wear: By maintaining a consistent load and engaging more of the cutting edges, dynamic milling can help reduce tool wear and extend the life of the cutting tool.

  • Improved surface finish: Dynamic milling can help achieve a smoother surface finish by reducing the amount of vibration and chatter during the cutting process.

  • Greater flexibility: Dynamic milling can be used with a wide range of materials and cutting tools, making it a versatile technique for many applications.

  • Overall, dynamic milling is a powerful technique that can help improve machining efficiency and reduce tool wear in many CNC milling applications. However, it requires specialized software and cutting tools, as well as careful consideration of cutting parameters, to achieve optimal results.

What is HPC milling?

HPC (High-Performance Cutting) milling is a type of CNC milling operation that involves using specialized cutting tools and techniques to remove material at high feed rates and with deep cuts (typically 1xD when slotting, or 1.5xD by 0.5xD when side cutting). The cutting tools used in HPC milling are typically designed with 4-5 cutting edges, variable or multiple helix design and a strong core which allows for increased material removal rates and improved efficiency.

The benefits of HPC milling include:

  • Increased material removal rates: HPC milling can remove material at significantly higher rates than traditional milling techniques. This can help reduce machining time and increase productivity.

  • Improved accuracy: The high speeds and feed rates used in HPC milling can help improve machining accuracy by reducing the effects of tool deflection and other cutting forces.

  • Reduced tool wear: HPC milling uses specialized cutting tools that are designed to withstand the high cutting forces and heat generated during the operation. This can help reduce tool wear and extend the life of the cutting tool.

  • Improved surface finish: HPC milling can produce a smoother surface finish than traditional milling techniques, particularly when machining harder materials.

  • Reduced energy consumption: HPC milling can be more energy-efficient than traditional milling techniques, as it can remove material at higher rates and with less energy input.

 

What is CNC barrel milling?

Barrel milling is a machining technique that involves using a special barrel or cone shaped cutting tool to remove material from a workpiece. The barrel-shaped tool is designed to produce a specific type of curved surface or contour, such as a curved slot or a rounded corner.

During barrel milling, the cutting tool is rotated while simultaneously being moved along the surface of the workpiece. The curvature of the tool allows it to remove material in a controlled manner, producing a smooth and even finish. The technique is particularly useful for creating complex shapes or contours that would be difficult to achieve with traditional milling methods.

Barrel milling is commonly used in the manufacturing of parts for the aerospace, automotive, and medical industries, among others and especially in 5 axis machining. The technique can be used on a range of materials, including metals, plastics, and composites. However, the effectiveness of the process can be influenced by various factors such as the tool geometry, cutting parameters, and the material being machined.

Overall, barrel milling is a versatile and efficient technique for producing complex shapes and contours, but it requires CADCAM software and expertise to perform correctly.

What is thread milling?

CNC thread milling is a type of CNC milling operation that involves cutting threads into a workpiece using a cutting tool that moves along a helical path. Unlike traditional thread cutting methods, such as tapping or die cutting, thread milling uses a single cutting tool to create the entire thread profile in one pass.

CNC thread milling can be performed using a variety of cutting tools, including solid carbide thread mills, indexable thread mills, and multi-tooth inserts. The choice of cutting tool will depend on the desired thread size, pitch, and depth, as well as the material being machined.

The benefits of CNC thread milling include the ability to create precise, repeatable threads with a high degree of accuracy and efficiency. It can be used to create both internal and external threads and can be performed on a wide range of materials, including steel, aluminium, brass, and plastics. Additionally, because the cutting tool is not subjected to the same level of stress as with traditional thread cutting methods, CNC thread milling can provide longer tool life and reduce the risk of tool breakage.

What is plunge milling?

Plunge milling is a type of CNC milling operation that involves plunging a cutting tool into a workpiece to create a slot, pocket, or other recessed feature. Unlike conventional milling, which moves the cutting tool along a path that follows the workpiece contour, plunge milling moves the cutting tool straight down into the workpiece, allowing for efficient removal of material from a specific location.

Plunge milling can be performed using a variety of cutting tools, including end mills, slotting cutters, and drills. The choice of cutting tool will depend on the desired feature size, shape, and depth, as well as the material being machined.

The benefits of plunge milling include the ability to quickly remove large volumes of material from a specific location, as well as the ability to create deep, narrow slots or pockets with a high degree of accuracy and efficiency. Additionally, because the cutting tool is only in contact with the workpiece for a short period of time, plunge milling can provide faster cutting speeds and reduce the risk of tool wear or breakage.

What types of milling cutters are there for CNC milling?

There are many different types of milling cutters available, each designed for a specific milling operation. Some of the most common types of milling cutters include:

  • End mills: These are the most common type of milling cutter and are used to remove material from the surface of a workpiece. They have cutting edges on the end and the sides of the tool.

  • Face mills: These cutters have a large diameter and are used to remove material from the surface of a workpiece in a broad, flat area. They have cutting edges on the face of the tool.

  • Ball end mills: These cutters have a rounded tip and are used to create curved surfaces or complex shapes. They have cutting edges on the ball-shaped tip.

  • Slot drills: These cutters are used to create slots in a workpiece. They have cutting edges on both the end and the sides of the tool.

  • T-slot cutters: These cutters are used to create T-shaped slots in a workpiece. They have a straight cutting edge and a T-shaped slot that guides the cutter.

  • Fly cutters: These cutters are used to create a flat surface on a workpiece. They have a single cutting edge and are rotated at high speeds to remove material.

  • Chamfer cutters: These cutters are used to create chamfered edges on a workpiece. They have cutting edges that form an angled bevel.

  • Thread mills: These cutters are used to create threads in a workpiece. They have a spiral cutting edge that follows a helical path.

  • Roughing end mills (rippers): These cutters are used to remove large amounts of material quickly from a workpiece. They have multiple cutting edges and are designed for high-speed milling operations.

  • Shell mills: These cutters are used to remove material from the surface of a workpiece in a circular path. They have cutting edges on the face of the tool and are designed for high-volume milling operations.

There are many other types of milling cutters available as well, each with its own unique design and application. The choice of milling cutter will depend on the specific milling operation being performed, as well as the material being machined and the desired finish.

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