flute count

Why Flute Count Matters

One of the most important considerations when choosing an end mill is determining which flute count is best for the job at hand. Both material and application play an important role in this critical part of the tool selection process. Understanding the effects of flute count on other tool properties, and how a tool will behave in different situations is an essential consideration in the tool selection process. As end mills have become more and more advanced, certain standards have been created for flute counts in certain materials. While there is obvious overlap due to a myriad of factors, proper flute count is critical for machining success and ensuring you are making the most of your end mill and it’s associated MRR.

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Tool Geometry Basics

Generally, tools with more flutes have a larger core and smaller flute valleys than tools with fewer flutes.  More flutes with a larger core can provide both benefits and restrictions depending on the application.  Simply put, a larger core is directly proportional to tool strength; the larger the core, the stronger a tool will be.  In turn, a larger core also reduces the flute depth of a tool, restricting the amount of space for chips to exist.  This can cause issues with chip packing in applications requiring heavy material removal.  However, these considerations only lead us part way when making a decision on which tool to use, and when.

3, 5, and 8 flute end mills and their core sizes in relation to flute valleys

Material Considerations

Traditionally, end mills came in either a 2 flute or 4 flute option.  The widely accepted rule of thumb was to use 2 flutes for machining aluminum and non-ferrous materials, and 4 flutes for machining steel and harder alloys.  As aluminum and non-ferrous alloys are typically much softer than steels, a tool’s strength is less of a concern, a tool can be fed faster, and larger material removal rates (MRR) is facilitated by the large flute valleys of 2 flute tools.

Consequently, ferrous materials are typically much harder, and require the strength of a larger core.  Feed rates are slower, resulting in smaller chips, and allowing for the smaller flute valleys of a larger core tool.  This also allows for more flutes to fit on the tool, which in turn increases productivity.

end mill flute count comparisons

Recently, with more advanced machines and toolpaths, higher flute count tools have become the norm in manufacturing.  Non-ferrous tooling has become largely centered on 3 flute tools. This has created a slight advantage over 2 flute tools by increasing productivity while still affording proper chip evacuation. The softness of non-ferrous materials affords a much deeper flute valley. As previously discussed, this allows the tool to be fed much faster than in ferrous materials. Adding an additional flute increases the productivity of the tool, while still affording machinists faster feed rates.

Ferrous tooling has taken a step further and progressed not only to 5 and 6 flutes, but up to 7 flutes and more in some cases.  With a wider range of hardness, sometimes at the very top of the Rockwell hardness scale, many more flutes have allowed longer tool life, less tool wear, stronger tools, and less deflection.  All of this results in more specialized tools for more specific materials. Material specific tooling combines proper flute counts with coatings that aid in lubricity and heat generation to ensure the most effective end mill possible in the material being machined. The end result is higher MRR and increased productivity across the entire range of ferrous materials that machinists will work with in their shops.

Running Parameters

Just as material considerations will have an impact on the tool you choose, operation type and depth of cut requirements may also have a big impact on the ideal number of flutes for your application.  In roughing applications, lower flute counts may be desirable to evacuate large amounts of chips faster with larger flute valleys.  That said, there is a balance to find, as modern toolpaths such as High Efficiency Milling (HEM) can achieve extreme MRR with a very small step over, and a higher number of flutes.  In a more traditional sense, higher flute counts are great for finishing operations where very small amounts of material are being removed, and greater finish can be achieved with more flutes, not worrying as much about chip evacuation as that phase has already been accomplished during roughing.

helical end mill with lines showcasing the flute valleys

Flute count plays a big role in speeds and feeds calculation as well.  One common rule of thumb is “more flutes, more feed,” but this can be a very detrimental misconception.  Although true in some cases, this is not an infinitely scalable principle.  As stated previously, increasing the number of flutes on a tool limits the size that the flute valleys can be.  While adding a 5th flute to a 4 flute tool theoretically gives you 25% more material removal per revolution with an appropriately increased feed rate, feeding the tool that much faster may overload the tool.  The 25% increase in material removal is more likely closer to 10-15%, given the tool is exactly the same in all other specifications.  Higher flute count tools may require speeds and feeds to be backed off so much in some cases, that a lower flute count may be even more efficient.  Finding the right balance is key in modern milling practices. Consulting a tooling manufacturer’s speeds and feeds will be the perfect starting point, and then machinists can make changes as they see fit to properly accomplish the job at hand.

In all, the importance of flute count identification is critical to continued success at the spindle. Different materials have different strength requirements as well as variability in how much material can be appropriately removed per tooth.

18 replies
    • Jeff Rauseo
      Jeff Rauseo says:

      Hi Rob,

      For wood, you would be looking for a tool with 1-2 flutes as a general rule of thumb. Corian could be a bit trickier, so we would encourage you to call our tech team at 800-645-5609 to talk about what sort of application you would be running. That way we can find the right tool for you!

  1. Shishkin Vladimir
    Shishkin Vladimir says:

    Hello! I work with wood – I make classical guitars. What kind of cutters would you recommend for working with soft wood – spruce, linden, maple? Which cutters are better suited for hard, caustic and resinous rocks – oak, rosewood, ziricot, wenge. When working with cheap Chinese cutters, it is not possible to get a smooth edge and surface without burns. Looking for a better solution.

    • Jill Chergey
      Jill Chergey says:

      Harvey Tool offers Plastic Cutting End Mills which will likely work well for your woodworking jobs. Opt for either the single flute, or two flute version. The key on these is the sharp edge and large flute valley. Also, make sure to keep your RPMs to a minimum with a larger IPT in order to avoid burning.

    • Guy Petrillo
      Guy Petrillo says:

      Our tooling is designed for non-ferrous, ferrous and plastic materials. Unfortunately, we can not recommend using our tooling in skull cutting applications.

  2. Rodger Olds
    Rodger Olds says:

    I’m milling C110 copper. The feeds and speeds from different tool vendors are all over the place. I’ve found that with a 1/2″ square end mill 18,000 RPM, at 30 in/min, 5 in/min lead in/out works best with a cooling fluid. I’m still getting lots of chatter and occasional crashes.


  3. Gage Siebieda
    Gage Siebieda says:

    Good AFternoon,

    What is the best recommendation for a good standard set of short flute EM, long flute EM and ball EMs? We machine primarily 304 and 303 Stainless Steel. We are also in the process of tooling for the machining of 360 Brass. I know the difference of hardness is substantial, but could we tool for the Stainless and it would be fine for the Brass? Also, this is all done on a manual Bridgeport mill. Any and all help is appreciated!

    • Guy Petrillo
      Guy Petrillo says:

      Hello Gage,

      Great question! We would recommend tooling up with the Harvey Tool Miniature End Mill’s. Here is the link to the page . We suggest using our 4 flute tools for the stainless steels and our 2 fluted tools for the brass. Then use the correct coating for each material type, ZrN or uncoated for Brass and AltiN and AlTiN Nano for steels.

  4. Telkom University
    Telkom University says:

    How does flute count impact the performance of end mills, and what are the key considerations when selecting the appropriate flute count for a given machining application?


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