When To Use 2-flute, 3-flute And 4-flute End Mills

[jmarkwolf]

Much of my home-shop machining experience has been aluminum (experimental aircraft applications). I'm advancing into the "hard stuff" now (mild steel).

I never paid much attention to how many flutes my end mills had, I just purchased what the local Production Tool Supply had on hand. The aluminum didn't seem to care.

I recently needed to cut a 1 -1/16in diameter counter bore 0.125in deep in some angle iron, to accommodate flush mounting some weld studs I fabricated. The only end mill I had was a 2-flute.

It did the job for me, but it "chattered" to beat the band, even with flooding with oil. It seemed to like a faster feed rate as well.

Can anyone advise "when and why" to use end mills with various numbers of flutes?

 

[CraigB1960]

Much of my home-shop machining experience has been aluminum (experimental aircraft applications). I'm advancing into the "hard stuff" now (mild steel).

I never paid much attention to how many flutes my end mills had, I just purchased what the local Production Tool Supply had on hand. The aluminum didn't seem to care.

I recently needed to cut a 1 -1/16in diameter counter bore 0.125in deep in some angle iron, to accommodate flush mounting some weld studs I fabricated. The only end mill I had was a 2-flute.

It did the job for me, but it "chattered" to beat the band, even with flooding with oil. It seemed to like a faster feed rate as well.

Can anyone advise "when and why" to use end mills with various numbers of flutes?

Sometimes a 2 flute mill just will chatter and a 4 flute does not provide enough chip clearance, so a 3 flute end mill will do the job. In your this example, a 3 flute end mill would of worked better, and since you were just counter boring and not going too deep, a 4 flute might of worked even better.

As a generalization:
2 Flute end mills are used to plunge (drill) and cut slots. Since they have a larger gullet, they provide better chip clearance. If you are using a smaller mill, a 2 flute is a better roughing tool. For finish work or in hard materials, more cutting edges are desired, so a 3 or 4 flute end mill works better.

There are 2 flute roughing end mills...sometimes referred to as Cobb mills. These are especially useful when working with aluminum, but work well on hot rolled steel too. As a note, 2 flute end mills are more versatile, especially if you use a roughing end mill then switch to a normal 2 flute end mill and upping your speed for the finish pass.

Bottom line, need to have an assortment of good high quality end mills available for different materials, speeds and feeds. I prefer to buy good used end mills off of eBay rather than cheap lower quality ones new.