Unlike drill bits that only move in the axial direction, end mills are designed to produce lateral cuts as well, making them versatile. The different types of end mills can be used to create slots, plunge, drill, trace, and ream in all directions. When selecting end mill types for your CNC application, at least three factors will influence your decision: the desired shape, workpiece material, and surface finish. However, there are more variables in play.

Below, we detail the different types of end mills and what to consider when choosing which type is best for your machining requirements.

How to Choose an End Mill

Here is the basic geometry of an end mill and the names of its different sections that we are going to use more often in this discussion:

Often, you’ll be asked to choose end mills based on their type, number of flutes, and coating. These options play an important role in the success of machining operations.

Understand the Different End Mill Types and Their Applications

Types	Identification	Applications
Square end mills	Also known as flat end mills; have sharp edges at corners and generate a 90° angle to produce a flat-bottomed groove	A versatile tool for general milling applications, including profiling, slotting, side and face milling, and plunging
Weldon end mills	Come with a flat section on the shank to avoid slippage during machining operation	For easy pull out during machining hard metals, like titanium
Ball end mills	Produce radius equal to half of the tool diameter	Multi-dimensional contours in molds or dies
Radius end mills	Also known as bullnose end mills; have a square nose with slightly rounded corners for even distribution of cutting forces	For cutting a specified radius, such as in mold milling operations
Finisher end mills	One square end coupled with high flute counts for creating a smooth surface finish	Side milling operations where both high chip removal and smooth finishing are required
Drill end mills	A 60- or 90-degree point on the end of the tool with two or four cutting edges	Spotting, drilling, milling, and countersinking
Roughing end mills	Numerous teeth in the flutes to remove large surface area at once	To remove large areas of material in one pass at the sacrifice of surface finish
Rounding end mills	A 90° profile coupled with rounded corners to remove sharp edges without breakage	For rounding off sharp external edges of a workpiece
Undercutting end mills	A ball end mill with curvy edges over a long shank, appearing as a lollipop	To create undercuts during multi-axis machining applications

Measure the Stickout

The term “stickout” represents the overall length of an end mill. A particular type of end mill can be available in different lengths. The depth of cut required determines the ideal stickout. A stickout that’s too short may lead to the collision of the spindle mandrel with the workpiece during operation, while more stickout may cause the shank to move in the opposite direction of cutting force, leading to cutting tool deflection. Ideally, the depth for cutting tools should always be less than the flute length, and this should be used as a metric while choosing your end mills.

Choose the Ideal Number of Flutes

Flutes are the deep spiral cutting edges below the shank that are used for chip removal in end mills. The number of flutes on the end mill impacts the chip removal rate, the surface finish of the workpiece, and the feed rate required during the machining. If retaining high chip removal is primary in end mills, or if you are trimming soft metals like aluminum, choosing a lower number of flutes (two or three) yields the best results. On the other hand, more flutes ensure a high-quality surface finish at the cost of a high feed rate throughout the procedure.

Select the Material

Usually, the cutting material must be harder than the workpiece material to be able to handle excess heat generated during the cutting operation. In this regard, end mills come in two different materials: high-speed carbon steel (HSS) and tungsten carbide. Here is a quick comparison between the two materials:

	HSS	Tungsten Carbide
Price	Cheap	Costly
Recommended for	Intermittent cutting application	Continuous cutting application
Cutting speed	Low	High
Composition	Steel (metal)	Tungsten, carbon, and cobalt (ceramic metal)
Wear resistance at high temperatures	Low	High
Finishing	Poor finishing	High-quality finishing

Because of their wear resistance, high-speed steel cutting, and high-quality surface finish capabilities, solid carbide end mills are highly sought-after over HSS cutting tools. Your end mills can be further coated with TiAlN (Titanium aluminum nitride) to increase high-speed steel cutting by up to 25%.

Choose the Right Helical Direction

There are two end mill types depending upon the helical direction; upcut and downcut. Upcut end mills push up the chips but fray the top edge. In the case of downcut end mills, the opposite happens. So, if you want a smooth finish both at the top and bottom, choose a compression cutter, as it is designed to offer a clean cutting edge on both ends for cutting plywood, composites, or laminates.

Your Local Partner for Meeting Tough CNC Requirements With Ease