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  • End mill surface finish

    I ran into something today that I haven't seen before or maybe just didn't notice. I have a Tormach CNC mill and when doing a flat area with a standard end mill I get the usual tool marks and a slight ridge from pass each I thought was due to my mill being slightly out of tram.

    I've been using pretty good quality two flute end mills, (mostly Hertel) that I pick up in the $15 range. I needed some thread mills for another project and ended up at Lakeshore Carbide and they have some interesting three flute end mills, but they were pretty expensive at $48 each, but I thought what the heck, maybe I can cut faster with them.

    They arrived today and I tried one out and before I did any changes to my feeds, I did some test cuts, and I don't understand is why my ridges went away and the milled surface is very smooth. Is it the difference 2 flute vs three? The quality of the tool? I didn't do anything but switch end mills. Before, I could run my finger over the cut and feel the ridges, now there is nothing.

    I'm not associated with any of these vendors in any way, just a hobby machinist who is a little confused at the moment.

  • #2
    Does the three flute have radiused corners?

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    • #3
      No, square end.

      http://www.lakeshorecarbide.com/12sq...uminumzrn.aspx

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      • #4
        What else changed? Feed per tooth? RPM? Were the old cutters worn and no longer sharp? Material?

        Clearly something....

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        • #5
          Did you put the old one back in to make sure the ridges are still there. You may
          have bumped your table into a more "trammed" state.
          John Titor, when are you.

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          • #6
            Since the general consensus seems to be that the cutter cannot be the difference, when I get a moment I'll do a test on a couple identical pieces with a larger flat area.

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            • #7
              Are you cutting mild steel? if so, Nobody knows! Just put those endmills into a special box, with the RPM you used written down on it next to the writing "Magical mild steel endmills, For mild steel use only"

              Otherwise, could your 2 flute endmills be chipped or have material buildup on the tips? 3 flutes also does reduce your feed per teeth slightly, and generally is a little more rigid flute as 3 flutes form a more solid structure that resists bending better then 2 flutes.
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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              • #8
                Don't be too quick to conclude that the cutters are not the difference. Have you examined them under magnification. You would be surprised what a good quality, 10X magnifying glass will show you. Your old milling cutters may not be as sharp as you think.

                http://smile.amazon.com/Bausch-Lomb-...let+magnifiers
                Paul A.

                Make it fit.
                You can't win and there is a penalty for trying!

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                • #9
                  Perhaps the feed rate was too high for the HSS cutter but well within the feed range for the carbide cutter.

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                  • #10
                    Perhaps if you are running at the same feed rate then the three flute catches the bit the two skips over if you see what I mean, I suppose if you increased feed than at some point the pattern will return.
                    Either way carbide does work well.
                    Mark

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                    • #11
                      The other significant thing is that, for the same size and shape, a carbide cutter will be three times as stiff as a steel one.

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                      • #12
                        Almost certainly the cutter is the main difference because of the increased stiffness and sharpness. Unlikely that the machine would have been out of tram and suddenly better, coincidental to getting better quality tooling. I have long advocated that "good tooling doesn't cost, it pays."

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                        • #13
                          If your original cutters were 4-flute there might be one phenomenon occurring. Think about the forces coming into play as the cutter is rotating. As one flute is cutting in the feed direction (12:00) the force of resistance in the material will be pushing the cutter towards 9:00. With a four flute cutter there are teeth at exactly 3:00 and 9:00 that can be cutting if there's any cutter deflection. With a two or three flute cutter this won't occur.
                          .
                          "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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                          • #14
                            The new cutters may have "wiper flats" on the bottom near the edge. A lot of the newer face mill inserts have this. It is a small flat area on the bottom of the cutter that smooths off any ridges left by the previous tooth.

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                            • #15
                              The Lake shore cutters are great, they are my go-to cutters for aluminum. They cut faster with less load, it might be that load that is making a difference, less deflection in the head.

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