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End Mills: A beginner’s Guide

There are many factors that define the objects that can be created using a CNC mill, but the most important is the end mill. From a distance, they are drill bits, but you can also make horizontal cuts. Some end mills are recommended for plastics to avoid excess heating, while others help to prevent the wood from tearing out. With all the different specifications for end mills and the diverse models on the market, selecting the right one can be challenging. So, how do you pick the right model for your operations?

Keep reading to learn more about end bills and how to select the best options based on your projects. 

To Mill or To Drill? 

Before looking at the different types of end mills, it is important to start by understanding their difference with drill bits. Because any material, from metal to wood, can be cut using a CNC machine, why should you go for an end mill and not a drill bit?

Drill Bits 

  • Make round holes down into a workpiece using a rotating drill. 
  • Most drill bits use flutes that give them a sort of twisted appearance. 
  • Most high-speed steel and carbide drill bits are fluted. 

End Mills

  • End mills cut rotationally in a lateral or horizontal direction. 
  • Come in a wide variety of diameters, lengths, and flutes. 
  • End mills are used for profiling, reaming, counter-boring, and slotting.
  • End mills make it possible for precision parts to be cut on workpieces, such as plastics, circular boards, and jewelry designs.


Common End Mills on the Market: How Do You Pick the Best?

End mills fall into several categories, and it is important to factor in every fine detail because it will ultimately determine the bores and cuts you can make on a workpiece. Here are some of the most important ones: 

  • Straight vs. Tapered End Mills  

End mills can broadly be categorized into two, the straight and tapered models. The model you select depends on the targeted geometry of the finished part. When you use a tapered end mill, you get a larger cross-section area compared to straight end mill models. The tapered model is also the better option for angled walls. However, you should go for the straight end mills for vertical walls. 

  • Size  

Size is the most crucial factor that ultimately determines what you can do using an end mill. The large models are good for plunging but do not get a lot of details.  Note that with CNC milling, the end mill radius will form the radius of the internal corner. This implies one thing – you will rarely have a perfect square inside when using the large end mills. To get the dimensions and shape that you want, smaller end mills are used to clean the edges. Remember to be extra careful with small end mills because they can be fragile.

  • Fishtail End Mills

Fishtail end mills are used for cutting simple profiles in workpieces. For example, if you want to cut out letters on a piece of wood, the fishtail end mill will be the perfect pick. These end mills cut using the side, and they ramp down into the workpiece, as opposed to plunging. Note that, unlike the straight or tapered, or straight end mills, the fishtail models can create nice corners at the bottom of the insert part.

  • Base-Nose End Mills  

These end mills come with a dome-shaped tip. They are recommended for high-detail contours, such as mold or relief artwork. They also work well for die-making. Note that because of the round tip, you will need to make more passes to get the finished cuts. 

  • Coatings  

Another crucial consideration when selecting an end mill is the coating. Although end mills are made of different coatings, the commonest are the tungsten carbide and high-speed steel (HSS). HSS tools are considered stronger than carbide because the latter can shatter under intense pressure. Again, HSS is cheaper, but it comes with one challenge – it dulls faster compared to carbide. 

Picking the right end mill for your job is all about striking the perfect balance of the factors that come together to make the tool. Remember that the standard procedure in CNC milling is changing out the tools depending on the step of your operation. Therefore, the best practice is to have a range of end mills, engraving bits, and drill bits in your tool box.