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If you are just starting to get familiar with CNC milling machines, choosing the right end mill may seem like a daunting task. There are many different types, shapes, and sizes, so it’s hard to determine which one is the best. In this article, we will explain to you the main types of CNC bits and explain what each of them is suitable for. So you will understand better and be able to choose the right tool from the very beginning.
Applications by material
End mills can be classified according to the type of material they are designed to process, such as wood, plywood, plastics, or soft metals. Many online shops have tools to help you find things more easily by sorting them into groups. But even after choosing the material category, you still need to think about additional characteristics:
• Chip direction (upcut, downcut, or compression)
• Number of flutes
• Cutting diameter and length
Let’s explore these parameters in more detail.
Chip direction: upcut, downcut, and compression
Upcut end mills
These are ideal when the material is securely fixed to the work surface. Upward chip removal helps to clean the cutting area, reducing the risk of material sticking to the tool and minimizing overheating.
Downcut end mills
Downcut bits, which are best suited for simultaneous processing of several thin sheets, move the material downward during cutting. This allows you to press and align the lower layers, increasing accuracy and saving time.
Compression end mills
Compression bits combine both ascending and descending grooves. This bi-directional cutting action minimizes surface cracking and is ideal for laminated materials. However, they must be used with high precision: the transition point between flute types must coincide with the middle of the workpiece, and the tool must do its job in one pass to achieve the best results.
Number of flutes
End mills can have from 1 to 9 flutes, each of which is designed to perform specific tasks. The most commonly used options include:
Single-flute end mills
With only one cutting edge, these tools provide excellent chip removal and minimize heat generation. They are suitable for processing plastics (such as acrylic, PVC, ABS), foam materials, wood-based panels, and even some metals.
2-flute end mills
They are commonly used for roughing and are especially popular for wood processing. They are also compatible with plastics, but when used on metals, they should be checked for coatings. For metalworking, it is recommended to use a cutting angle of 45-55° to reduce resistance and prevent overheating.
3-flute end mills
They are designed for high-speed processing in industrial environments, especially complex or layered materials and stainless steel. A larger number of flutes ensures faster material removal, provided the cutting depth is properly balanced.
Diameter and length
When choosing an end mill, consider two parameters:
- Cutting diameter: choose based on the expected load. The following formula is usually used: milling depth ÷ 3 = optimal milling diameter.
- Shank diameter: must match the diameter of the collet of your machine. If not, you will need a compatible collet or adapter.
The cutting length must exceed the milling depth by at least 2-5 mm. If in doubt, it is better to use a slightly longer milling cutter than one that is too short.
Tool geometry and form
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End mills also vary in shape, which directly affects the cutting pattern. There are four main geometric categories:
1. Standard end mills
- Can have square, rounded or angled tips
- Flutes can be spiral, straight or rough
2. Tapered ball end mills
- It is used for 3D contouring or finishing, often with flat or spherical tips
3. Edge profile cutters
- They include decorative shapes and V-shaped tips, often used for making detailed profiles and finishing edges
4. Engraving tools
- Designed for fine detailing and finishing passes
- Some of them have non-cutting tips (for example, hollow points) for engraving with a side entrance without drilling
Conclusion
Choosing the right end mill means choosing the best tool for the job. It depends on how you’re going to cut, what you’re cutting, the number of flutes, and its shape. Different bits are designed for different tasks. If you choose the wrong tool, it can damage the parts being processed, break the tool, or even damage the machine. But if you understand the basics, you can easily find the right tools. This helps to make cleaner cuts, extends tool life, and provides better results.
