Posted on Jun 15, 2021
End mill bits are essential for the cutting performance of a milling machine. HSS, Solid Carbide, ball-nose, bull-nose, v-bits, center cutting, flutes…when it comes to choosing the right end mill bit, it can get overwhelming: this IMTS guide is a complete overview of types, applications and specifications.
End Mills are a type of milling cutter and are essential for the cutting performance of a milling machine, the most widely used machine tool in the manufacturing industry. According to a recent data report by 'Strategyr' the milling machine market is expected to even grow further in the coming years. And end milling is one of the most common procedures in industrial machining and applications. This process differs from other operations due to the cutting teeth on the sides and end of the mill, the main difference compared to other cutters like drill bits (see below).
However, when it comes to choosing the right end mill, it can get overwhelming: HSS, solid carbide, ball-nose, bull-nose, v-bits, center cutting, flutes…Do you know what exactly all these terms mean? This article will give you a complete overview of end mill types, applications and a guide on how to pick the right one for you.
People not familiar with cutting blades might be a bit confused about the difference between end mills and drill bits. It’s fairly simple: the main difference becomes clear when you take a closer look at the shape and geometry of the bits and its flutes.
A drill bit is designed to cut (drill) directly into the material and create holes in the axial direction only. End mills can cut laterally into the material and create slots or profiles. Some types even cut in all directions and are therefore more flexible allowing for profile, tracer or face milling, plunging, contouring, slotting, drilling, and reaming operations.
In the figure above you can see the most important specification features to clearly describe end mills. In addition, we can categorize by type (such as Ball Nose, Square, etc.), the number of flutes as well as material and/or coating.
A typical product description would therefore look something like this:
All features determine what kind of applications the end mill is suitable for in terms of speed, shape, finishing intricacy and overall performance. Therefore, it is very important for you to know the basics before choosing an end mill set for your job. Next up, we will tell you about the most important types.
Below we have compiled basic characteristics of the most common end mill types. This is not an exhaustive list. There are more specialized products for custom applications.
Ball Nose End mills have a rounded tip. They are mainly used for 3D milling of contoured surfaces, groove rounding, pocketing, shallow slotting and other contouring operations. Can be used as the final cutter for some ‘finishing touches’.
Square or flat end mills are the most commonly used type. They are very versatile all-rounders for all kinds of applications such as profiling, slotting, side and face milling and plunging. Flat End Mills deliver perfect 90 degree corner cuts on your workpiece. Depending on the workpiece, they can be suitable for both roughing and finishing applications.
If an end mill bit comes with one end much thinner than the other one then chances are that it is a fish tail or router end mill. This design can plunge directly into the material and produce a flat surface without breaking out thanks to the thin cutter shape. They are also suitable for creating pockets, routing and contouring.
Very similar to square end mills with the distinction that bull-nose end mills have rounded corners that help distribute the cutting force evenly. Excellent for flat-bottomed grooves with rounded inside corners. have slightly rounded corners that help distribute cutting forces evenly to prevent damage to the blade and extend its life. They can create flat-bottomed grooves with slightly rounded inside corners and therefore most commonly used for mold milling operations.
Roughing end mills, as the name suggests, quickly remove a lot of workpiece material especially during heavy cutting stages. They deliver a quick, rough finish at low vibration that will then be fine finished with a different cutter.
V-bits get their name from a v-shaped pass created by. small angles and tips. These specialized end mill cutters are used for engraving, narrow cuts, lines or even signs. Generally speaking there are two main types; 60 and 90 degree V-bits.
These center-cutting tools can be used for plunging, and are designed to machine angled slots. They are generally used in die-casts and molds.
If you want to learn more, this Youtuber has an excellent introduction to the basic end mill types :
High Speed Steel End Mills are less expensive than carbide mills. They are suitable for a wide range of materials including a lot of metals and of course weed. You also can expect to use them for a long time before re-sharpening as they have a good wear resistance. HSS are the go-to cutter for most standard operations. The overall tool life is shorter though and you get more restrictions in terms of speed and performance.
Here is what you get for paying for the more expensive solid carbide end mills: higher rigidity, great heat resistance and substantially faster cutting speeds compared to HSS. This not only boosts your productivity but also allows you to cut a wider range of (harder) materials. Carbide end mills are often used for finishing purposes.
There are a plethora of distributors and manufacturers offering their milling cutters online, such as Harvey, Niagara, Janpro, Avvupro, Guhring, Mcmaster-Carr, and others. But, no matter which brand/supplier you choose to buy your end mills from, the truth is that there is no one-fits-them-all solution
We recommend that you ask yourself a few important questions before making a decision:
and so on (see below).
Once you have answered these and other questions you will have a better understanding of what type of end mill is needed for your applications. So let us take a closer look at the most important aspects that you need to take into consideration.
First ask yourself what materials you will want to cut with your new end mills set. This will narrow down the number of ‘potential candidates’ significantly as certain types of end mills are specifically made for certain metals/materials. For non-ferrous materials such as aluminum you will need different tooling shapes, materials and dimensions than for steel for example.
Sure, technically you can try to cut any material with the same end mill, but the cutting performance and the finish quality on the workpiece will vary from excellent to inacceptable. Using the wrong milling cutter will also pretty quickly result in broken tools. We are sure that you would like to avoid that.
Flutes are the spiral-shaped cutting edges at one end of the cutter. End Mills can have only one or two but also up to 12 flutes, however two to four flutes are most common. Everything above five flutes indicates finisher end mills used for very fine finishes. If you want to cut deep in materials such as plastics or aluminum then you want fewer of these cutting teeth. For harder material you need stronger cutting tools with more flutes and smooth (yet not so deep) cuts.
The number of flutes also affects the feed rate of your milling machine, the surface finish on the workpiece and the ability of your cutter to clear chips. The higher the amount of flutes of your end mill, the higher feed rate you will need to use or decrease the rotational speed. So make sure to check the speed capabilities of your mill and your spindle as this will directly affect the type of end mill you can use.
Apart from the flutes there are a few more end mill dimensions and specs to keep an eye on: the cutter diameter, the cut depth and reach as well as the tool profile, that we already discussed in detail in 4. Types of End Mills .
The cutter diameter defines the width of the slot that you can create with your end mill. It also affects the amount of chip removal for side milling operations. So before buying and/or mounting a cutter for your cutting job, make sure to choose an appropriate cutter diameter end mill to get a finished part according to the specifications.
Cutting Depth and Reach
The longest contact length required determines the depth of cut needed for your end mill. Ideally you pick a length that is just long enough to prevent overhang and to ensure a rigid, precise cutting process. A simple trick is to multiply the cutter diameter by five. If that number is higher than the required cutting depth, you might consider a necked reach solution.
In Fig 2. we have seen the helix angle of end mills already. Your average and mill bit will probably have a helix angle of about 30 degrees. If you want to reduce the cutting forces to minimize heat generation and vibration you need to use cutters with a greater helix angle. These end mills will also provide a better surface finish. However, you will have to make some compromises in terms of the feed rate at which you can cut and the cutting depth as well.
Finally, consider the end mill tool profile. Square, corner radius, ball-end, bull-end etc. serve different applications. This is just a reminder, as we have discussed each type in detail above.
End mill cutters that can plunge vertically into the material (perform plunge cuts) are center cutting end mills. Some bits cannot do that, because they have no cutting edge in the middle. They can only perform downwards cutting operations at roughly 45 degrees. So far, so simple. So why do center cutting and non-center cutting designs exist?
We talked about the importance of flutes before. Most two- and three-flute end mills are center-cutting types. Four flutes are sometimes used for non-center cutters. As so often, one main difference is the price. Center-cutting types are more expensive and re-sharpening the cutter will cost you more as well. That’s the price you pay for more plunging flexibility.
Non-center cutting mills are re-sharpened easier and also clear chips better. We advise you to go with center-cutting end mills if you can afford it. But if you are hardly ever plunging with 100% burial you can just opt for non-center cutting - you just need a ramp entry into the bottom of your cut for pocketing operations. The difference really comes down to how you cut.
A non-center cutting design also has room for more flutes which on average might allow for a faster feed rate while maintaining the same chip load.
Whether or not you should go for coated end mills set or not depends, again, on the application. A coated milling cutter can significantly boost cutting performance. You can set up more aggressive machining parameters, for instance SFM (Surface Feet per Minute), as the surface hardness of the coated tool is much higher. Usually you will also get better chip removal and a longer tool life. The most common coatings are Titanium Nitride (TiN), Titanium Carbonitride (TiCN), and Aluminum Titanium Nitride (AlTiN).
End mills provide a wide range of options for your machining operations. We hope this article helps you understand the different types and their applications better. You can find suppliers in the IMTS supplier database. If you want to learn more about end mills in general, make sure to check out our other blog entries.
If you are interested in even more detailed manufacturing-related content make sure to check out the IMTS Industry Channel. In these factory tours, we introduce new products and trends while visiting manufacturers in their facilities!