Choosing flute count for end mills

2, 3, 4, 5 or more flutes: what the tool makers recommend for each material and operation.

More flutes = bigger core and less chip room. Drawn to the same diameter.

Harvey's rule of thumb: non-ferrous work usually gets 2 or 3 flutes, and ferrous work uses anywhere from 3 to 14 depending on the operation [1].

Operation (ferrous)	Flutes
Traditional roughing	3, 4 or 5
Slotting	4
Finishing	5 to 14
High-efficiency milling	5 to 7

All rows from [1].

More flutes means a bigger core, which makes the tool stronger and lowers deflection, but leaves less room for chips [2]. For miniature slots, Harvey suggests as many flutes as possible for core strength, with axial steps of only 5-15% of diameter [3].

Open the end mill calculator

Tooling for this job

Carbide end mill sets

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Sources

[1] Harvey Performance, 5 Questions to Ask Before Selecting an End Mill
[2] Harvey Performance, Why Flute Count Matters
[3] Harvey Performance, Optimized Machining With Miniature End Mills