Shapes and Types

There are as many different end mill types as there are possible cutting operations: profiling, contouring, slotting, counterboring, drilling,... Here is a short overview of the main ones.

Square end mills are the most common ones and can be used for many milling applications, including slotting, profiling and plunge cutting.

Corner-radius end mills have slightly rounded corners that help distribute cutting forces evenly to prevent damage to the end mill and extend its life. They can create flat-bottomed grooves with slightly rounded inside corners.

Roughing end mills are used to quickly remove large amounts of material during heavy operations. Their design allows for little to no vibration but leaves a rougher finish.

Tapered end mills are centre-cutting tools that can be used for plunging, and are designed to machine angled slots. They are generally used in die-casts and moulds.

Ball end mills have rounded tips and are used to mill 3D shapes or rounded grooves.

T-slot end mills can easily cut accurate keyways and T-slots to create working tables or other similar applications.

Straight flutes end mills have a zero degrees helix.  They work well for materials where the lifting effect of a spiral flute might cause unwanted results, such as wood, plastics and composites. For those materials, the straight flute minimizes the fraying of the edges and provides better surface finishes than helical general purpose end mills.

As your CNC router spins the cutter clockwise, the helical direction of the flutes determines if chips are ejected towards the top or bottom of the workpiece. Upcut end mills are the most conventional ones, pullingthe chips away from the material, which is a very important feature for most milling operations on many different materials. It has a downside if you want to cut laminated materials since it leaves a poorer surface finish on the top of the workpiece. A downcut end mill has the advantage to push chips down, leaving a cleaner cut on top, but then it will also fray the bottom edge.

Combine an upcut and a downcut and you have a compression cutter, where the flutes are carved one way for the bottom half of the flute length and the other way at the top.  That feature makes them a very good candidate to cut plywood, composites, and laminates. Try to use one to cut a sheet of plywood in one pass, and you should obtain cleaner edges on both sides.

Milling Types & Solutions

End mills with less flutes on the cutting edge will provide better chip clearance, while end mills with more flutes will be able to a finer finish and operate with less vibration while being used on harder cutting materials.

Two and three flute end mills have better stock removal than multiple flute end mills but a significantly decreased finish. End mills with five or more flutes are ideal for finishing cuts and cuts in harder materials, but must operate at lower material removal rates due to their poor chip evacuation properties.