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2 vs 4 flutes

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  • 2 vs 4 flutes

    Can anyone explain the difference in the way 2 and 4 flute end mills work and under what conditons is each preferred?


  • #2

    In general, the lower the number of flutes the less the HP required. Strength wise, the 2 flute is stronger than a 4 flute. A two or three flute are the best choice for a milled slot. A a four flute can produce a nicer finish than a 2 flute - a good choice for final passes.


    • #3
      A heavier cut can be taken with a two flute, due to the greater strength, and I believe the feed can be increased because of greater chip clearance.

      The four flute will produce a finer finish as stated above.



      • #4
        I was under the understanding that 2 flute (also called slot drill) can be used for plunging. But that being said I have noticed some 3 and 4 flute end-mills with their teeth ground over center on the end like the 2 flute.



        • #5
          When end milling with 4 or more flutes, at least one edge can be cutting all the time. This keeps it from hammering the spindle drive spline.


          If ya wannit done your way ya gotta do it yourself.


          • #6
            Thanks TWise, I knew someone would bring up slot drills. In Tubal Cain's Milling Ops in Lathe, he shows slot drills as having one (end) cutting edge which extends past centerlne. End mills are ground to dead center from both sides, aren't they? Was this longer tooth un-necessary or to no advantage? Or just more complex / expensive than the advantage it may provide?



            • #7
              T Wise, four flutes can be either center cutting or non center cutting. Center cutting end mills have two cutting edges that extend to the mill center and two that are gashed short. Non center cutting mills have four identical tips and usualy have a pilot for a dead center used in grinding.


              • #8
                Not all endmills are ground for center cutting (an thus the ability the plunge the cutter) and yes, some enmills only have a single center cutting edge while the other flutes are recessed back from the center - this is strictly a cost cutting manouver on the part of the tool maker. More expensive center cutting endmills are sharpened like a good split point drill (a must for extreme high speeds).


                • #9
                  I my tool makers school two flute end mills were reserved for aluminum brass and plastic.
                  Four flute for all steels. now I don't know about taking a heavier cut with a two flute compaired to a four flute based on strength.
                  if you take the same feed cut with a two flute compaired to a four flute you will double the chip load(half the flutes = twice the load) making your machine and end mill work twice as hard and therfore negating any added strength. I would put them on equal levels of strength. You just don't use a four flute in soft material that can stick to the end mill or at least use lots of coolant at a high velocity.
                  Rule #1 be 10% smarter then what you\'re working on.
                  Rule #2 see Rule #1


                  • #10
                    I read somewhere that when choosing an endmill for a side cutting operation , there should always be at least one edge in contact with the work at all times,sort of using the same rule when choosing the number of teeth on a saw blade per the thickness of material to be cut


                    • #11
                      Onsrud makes some great endmills for wood & Plastic/composites. From single flute on up. The neat ones are the compression cut mills for wood & plastics - these have both up and down spiral so the wood fibres are compressed when edge milling and there is zero tearout on top and bottom surfaces.


                      In production work a two flute may or may not have any advantage over a 3+ flute mill - but maximum performance in the home worksop is not really a consideration. A two flute's best advantage is strength and reduced horsepower requirements - the home shop wants the durability and low costs, but seldom has more than 5 HP mills.