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  • end mill best choice

    Broke my last 1/8 end mill while slotting hot roll shaft 10 th by pass 1.4 IPM, import mill drill.
    What is the best choice 2 ,3 or 4 flutes, stub or regular, hss or carbide

  • #2
    Originally posted by Luke55 View Post
    Broke my last 1/8 end mill while slotting hot roll shaft 10 th by pass 1.4 IPM, import mill drill.
    What is the best choice 2 ,3 or 4 flutes, stub or regular, hss or carbide
    I prefer to use 4 flute carbide regardless of size, but especially at the small diameters. Too much deflection and vibration in hss 2 flute end mills. If your geometry permits use a carbide slitting saw. No chance of breakage at all.

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    • #3
      4 flute, but what rpm are you running?

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      • #4
        Fo slotting a 2-flute will produce a slot much closer to the mill diameter than one with more flutes. And in smaller diameters their extra strength is an advantage. That said a mill/drill has little rigidity, so slow feeds and a small DOC are necessary to avoid breakage.

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        • #5
          Use a 2 or 3 flute for slotting. 4 flute packs in too many chips when slotting because of the shallow gullet. 3 flute is better than 2 for slotting too, 2 flute end mills will cut on both sides of the groove and cause a poor, oversized finish. 3 flute keeps one flute in contact when cutting.

          Use coolant of some kind to flush chips out so you are not recutting them. This even includes air. Packed chips are what causes these small mills to break.

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          • #6
            For slotting, use a 2-flute.
            4-flute endmills will 'pull' to one side when slotting.

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            • #7
              Everyone is assuming he's cutting a slot the same width as the EM. If it's 50% (roughly..) bigger then the EM, I use a 4 flute. If it's DEEP or narrow, 2 flute but either requires the chips to be evacuated by air or whatever. I try to never cut a precision slot the same with as the EM. Worse case, even 10 thou difference is enough to plow the center to depth then clean up both sides.

              We need more info - depth, width, speed, etc..

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              • #8
                thanks for your reply. depht 10 th speed 70 fpm travel 1.4 ipm width 1/8 four flutes hss M42 2inch slot with closed ends. End mill broke when slowly plunging at one end. Table not moving. I'm doing the keyways on the crank on a Paul Breich associated model engine. I had to said that the kit went by a fire 7 years ago. the aluminun parts are melted. The crank seem to be not too hard. a prick punch leave a nice mark.

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                • #9
                  Hi,

                  Plunging is a different thing than milling and a 4 flute 1/8" endmill is a poor tool to plunge. Are you sure you were using a center cutting endmill? 3+ fluted mills aren't necessarily center cutting.

                  I would choose a 2 flute 1/8" endmill for this job because of the plunge cut. I might consider drilling a start hole to ease the plunge with the endmill even with a 2 flute. This would limit possible damage to the cutting edges of such a small tool.

                  dalee
                  If you think you understand what is going on, you haven't been paying attention.

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                  • #10
                    Interesting, conflicting opinions here on cutting oversize, whether 2 or 4 flute cut oversize.

                    What does "10 th" mean for depth?

                    M42, 4 flute, I would jack the rpm up to around 3000 if possible. It appears your chip load was too little at 1.4 ipm, but that wouldn't necessarily cause breakage just dulling from rubbing.

                    Actually, I don't know anything about mill drills, are they rigid?

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                    • #11
                      i always thought a two flute would produce a truer slot, because its cutting on oposing sides at the same time, so deflection woud be less.

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                      • #12
                        You are absolutely right Dian.
                        Keyways and slots should be cut with a 2-Flute end mill, as the flutes oppose each other and keep the cut straight.
                        With a 4-Flute end mill, two flutes will essentially be climb cutting, while the third will be conventional cutting. (the 4th being out of the cut on the backside)
                        So it will pull towards the climb cut side, and drift off center.
                        I found out about this the hard way, and scrapped some shafts while milling keyways.
                        My boss gave me a stern lesson in keyway cutting.

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                        • #13
                          Hi,

                          Outside of milling blind slots, I don't think it really matters much about the number of flutes you might use. Simply because if the size of the slot matters, you should be using an undersized endmill, (all hail the resharp!). And then widening the slot to the proper size for very best accuracy. It's the best way to achieve the best accuracy. Anything else is a crap-shoot for end results.

                          dalee
                          If you think you understand what is going on, you haven't been paying attention.

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                          • #14
                            Originally posted by dalee100 View Post
                            Hi,

                            Outside of milling blind slots, I don't think it really matters much about the number of flutes you might use. Simply because if the size of the slot matters, you should be using an undersized endmill, (all hail the resharp!). And then widening the slot to the proper size for very best accuracy. It's the best way to achieve the best accuracy. Anything else is a crap-shoot for end results.

                            dalee

                            Exactly, especially with home shop grade machines with loose spindles, less rigid tables, collet/holder run out, etc, etc.

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                            • #15
                              well, my idea is to machine the slot in one go and have the keystock fit.

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