For most operations, CNC machines use end mills that cut laterally (side to side). End mills have cutting surfaces called flutes. The most common end mills have two to four flutes. Generally, fewer flutes evacuate more chips from your material, keeping the bit cool.
What is a CNC Machine?
Milling cutters, or endmills, are used in a CNC machine: Computerised Numeral Controlled.
Specialised software is used to send automated milling instructions or a ‘toolpath’ to the machine which then cuts away a design in your stock material.
The craft market has recently exploded with exciting compact, table top CNC Routers and Mini-milling machines. CNC Routers are now affordable enough to allow DIY enthusiasts access to this high- precision milling tool for carving and engraving.
How Many Flutes?
Flutes are what we call the individual cutting edges or “teeth” that make up the spiral on an end mill.
The number of flutes the endmill has is crucial depending on the material you want to cut and the capabilities of your machine. The most common options are 2, 3, or 4 flutes. Unless you know exactly what you’re doing, you never want to use more than 3 flutes with aluminum. The reason is that aluminum produces very large chips relative to other materials. The flutes provide the path for chips to escape when the endmill is down in a hole or slot. 2 and 3 flute endmills have a lot more chip clearance so they work with aluminum. Using a 4 flute where the chips are confined at all results in jammed chips and a broken cutter in aluminum (End Mills for Aluminum) almost every time.
For most other materials 4 flutes is the norm. You want to use as many flutes as you can because the flutes act sort of like a “spindle multiplier”. For a given spindle speed and chip load, a 4 flute can be fed twice as fast as a 2 flute and it will tend to give a better surface finish. The 3 flute was developed as a nice compromise between using a 2 flute or a 4 flute in aluminum. It has sufficient chip clearance for all but the most gummy aluminums, yet it can be fed about 50% faster than a 2 flute at the same spindle rpm.