Kodiak Cutting Tools® Speeds and Feeds Blog

Cutting Tool Talk, Tips and News for Machinist, Metalworkers and Fabricators of All Kinds

question about 2 flute vs. 4 flute carbide end mill for aluminum

A customer was trying to decide whether to use a 2-flute or 4-flute carbide end mill for his job on aluminum. One important question before spending the extra money for a high-performance tool, is how many parts are you making?

 I think one you might look at is our part number 136475. This is 1/4" x 4" long with a 1" length of cut. The number of flutes is a trade-off between better finish and better chip evacuation. Sometimes with softer grades of aluminum the flutes could get clogged up, but as long as that is not an issue for you a 4 flute will give you a better finish and do more work per rotation of the tool. I think a lot of people are using this tool for doing a similar application. There is also a popular one with the gunsmiths that is specifically for aluminum. The part number is 150104 (150027 for uncoated). This is a high-performance tool that is capable of doing long production runs and much high speeds & feeds than the standard tool, but if you are not doing a large quantity it would probably be more than you need. The high performance ones have 3 flutes, a deeper clearance between the flutes for better chip evacuation and an optional ZrN coating specifically for aluminum and other non-ferrous metals. The high-performance also has a 45 degree helix instead of the standard 30 degree. This provides a better finish due to a shearing action of the flutes and also helps get the chips up and out. The main reason carbide end mills fail is when the re-cut a chip from the previous machining, so the chip evacuation is important, but if you are doing a smaller quantity you can try to use air of fluids to keep the cutting area clear from chips.


End Mill Selection

A customer recently asked what end mill to run for a full-slotting application in stainless steel and for some general recommendations about high speed vs. carbide and how many flutes to use. Listen in to our reply:

The 2 flute is usually used when you have a material that produces long stringy chips that get clogged in the flutes. That is usually referred to as 'chip evacuation'. The 2 flute has more room to clear the chips, however it does not leave as good of a finish as the 4 flute. So you can get from 2 to 6 flutes, and as you go up in flutes you get better finish and more work, or cutting action, per rotation of the tool. For example, if you were taking a chip load of .001" per tooth, you would be removing only .002" per rotation of the tool with the 2 flute, as opposed to .004" per revolution with the 4 flute.  The tool is also more engaged with the workpiece when you have more flutes, so you have less chance of chatter and poor surface finish. For tools that produce stringy, chips like aluminum, brass and other mostly non-ferrous materials we offer 2 and 3 flute tools that have a higher degree of helix than the standard 30 degree. These aluminum tools are available in 2 or 3 flute and have a 45 degree helix which creates a shearing action and gives a better finish because of that. We have some high performance tools for stainless that also have a higher helix.

     We would definitely recommend carbide as long and you have a good rigid toolholding and workholding setup. These days high speed steel is usually used on older machines that cannot generate the spindle speed or are not rigid enough for carbide. Carbide used to be more expensive than high speed steel, as usage and volume has shifted to carbide, they have become the less expensive in many cases than the high speed counterparts.  Especially on the smaller diameter tools.

    So depending on the amount you have to do and the capability of you machine, you would have to decide to run a high performance tool or the standard end mill. It also depends on the depth of your slot. For the standard tools you can do full slotting at 1x's the diameter on the tool. If you go with the VI-Pro high performance end mill, you can slot at 2x's the diameter. So with most grades of stainless you should not have a chip evacuation problem, so you should use 4 or more flutes. However, a common reason for end mill failure is caused by 're-cutting' a chip. So it is important to have some means of removing the chips from the workpiece as you go to avoid any re-cutting. The carbide is capable of doing a lot of work, but it is also brittle to some degree. So the chips can get work-hardened from the initial cutting and then if the tool re-cuts a chip it can cause the tool to chip. The only chips you want are from the workpiece. The rule of thumb is to use as short of a flute length as possible, which produces the most rigid setup. However you want to make sure you have enough flute to get the chips up and out of there. Especially in a full-slotting application. We would recommend the ALTiN coating for stainless. Below we have listed the different series of tools that you might consider and a link the reference documents.

These are all stub length. Go for a longer tool if you need one, but start here - these are also the least expensive option.


standard 4 flute stub length for max 1xs diameter slotting per pass http://www.kodiakcuttingtools.com/viewproducts/carbide-end-mills-4-flute-single-end-stub-altin-coated/

standard end mill speeds, feeds and recommendations


you can plug the figures from the above chart into this milling calculator:


Best for higher production and max 2xs diameter slotting per pass:

VI-Pro variable index high performance end mill (less chatter with high speeds and feeds)http://www.kodiakcuttingtools.com/viewproducts/carbide-end-mills-vi-pro-4-flute-stub-altin-coated/

Vi-Pro speeds and feeds


Another option for better chip removal:

3 flute high performance with 45 degree helix (this would give you more chip clearance if that is an issue)


high performance speeds and feeds






End Mills - High Speed Steel vs Carbide

End Mill Selection has Evolved and Materials Have Improved

   It used to be that carbide end mills were much less prevalent than they are today. Some time ago high speed steel and cobalt tools were much more widely used and less expensive. As time has gone on carbide tools have become more competitively priced and have become the preferred end mill by many machinists. The advantages of carbide endmills are numerous. They are much more rigid and produce tighter tolerances for machining precision parts. Carbide is also much more wear resistant. However, although carbide is tough and wear resistant, it can also be brittle. For this reason many older machine setups that are not as rigid prefer to still run high speed steel and cobalt tools for the additional forgiveness they provide.

   At Kodiak cutting tools our solid carbide endmills are made from ultra-micrograin carbide. This means that the structure of the molecules in the carbide are smaller and more consistent than and lesser grades of carbide. This grain structure allows the carbide to wear in a more even pattern and provide better tool life. Other tools, such as carbide burs which are not as precise, may be manufactured with a carbide that has a larger grain size. Some inferior manufacturers of carbide end mills use a lesser grade carbide with a larger grain structure, which makes the tools less expensive, but it also makes them less durable and more difficult to grind to exacting tolerances. That is why, although our tools might cost slightly more, in the long run better quality will save you money and increase your productivity through longer tool life and precision performance.