Kodiak Cutting Tools® Speeds and Feeds Blog

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

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