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Facemilling for smooth aluminum

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  • Facemilling for smooth aluminum

    I'm starting this as a separate thread as I do not wish to hijack BB's thread on face milling.

    I'm going to be doing a project in aluminum that will need to have a nice smooth finish before any profiles get milled into it. The two questions I have center upon the material and best face mill for the job. It is an industrial model with several access doors and vents that will be cut as profiles and shallow pockets.

    I'm thinking of using 6061 aluminum. If there is a better aluminum to use for a better finish, please give me suggestions on that.

    The second part is the face mill. I have two Bridgeport Series II NC machines that have been modified to full CNC with Mach 3. The motors are 4HP 3Ph and the spindle uses NMTB40 tool holders. Any suggestions on a good face mill for this application? I've thought about the GMT FM's but I don't know very much about their quality and durability. I'd like to stay with an American brand if I can. Any suggestions here as well?

    Thanks,
    Terry
    Terry

    There's only one way to find out, might as well get started now!

  • #2
    2024 will give a better finish than 6061. The harder the material the better the finish since it will resist scratching and isn't as prone to generate a built up edge. 7075 is even harder but also harder to find. 2024 is a good compromise and machines easily to a mirror finish given other parameters are in order. Use either kerosene, white spirits or ethyl alcohol for cutting fluid. Note that these cutting fluids are only to be used on non-sparking metals and only need to be used sparingly. You can also use soapy water if you aren't concerned about rust. Water is commonly used as a lubricoolant in industry with the addition of a surface tension reducer (ionic surfactant=soap) and a rust inhibitor. Ethylene glycol (the non toxic anti freeze used in food stuffs) mixed with water is common.
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    • #3
      Originally posted by Evan
      Ethylene glycol (the non toxic anti freeze used in food stuffs) mixed with water is common.
      -Nitpick: Ethylene glycol is the toxic stuff. Propylene glycol is the non-toxic version.

      It'd be more than a nitpick if we were talking a situation where it could be ingested, but there are a few people that use watered-down automotive antifreeze (the toxic kind) as machine coolant, out of concerns for rust or bacteria growth in the sumps of infrequently-used machines.

      I considered it myself for bandsaw coolant, but I have cats that spend time in the shop.

      Doc.
      Doc's Machine. (Probably not what you expect.)

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      • #4
        Terry: I have a lot of the GMT tooling and it is very good. My mill is R8 but I would think the 40 tool holders would be even better. Ask them questions by E mail. They know their business!
        Byron Boucher
        Burnet, TX

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        • #5
          -Nitpick: Ethylene glycol is the toxic stuff. Propylene glycol is the non-toxic version.

          Actually I meant to write polyetheylene glycol. PEG is considered inert and is used in laxatives among many other things.

          Propylene glycol is actually toxic but has a low toxicity rating.

          http://www.inchem.org/documents/pims...cal/pim443.htm
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          • #6
            Any name brand face mill that has square inserts set at 45 degrees, and with same backwards-leaning angle (to give top rake) would work fine.

            I have tried cutting dry, with an air blast, oil, and water soluble coolant, and noticed no difference in the surface finish. I think my inserts are just really good about throwing chips out of the way. Next I will try re-seating the inserts to make them more level, and maybe WD-40.

            Recently I have read that to get a really good finish, you need to get a diamond or PCD insert.

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            • #7
              PCD inserts work very well on brass, bronze and aluminum. I also discovered that it is possible to sharpen them if you chip one. To reshape a chipped PCD you can use a fine grit diamond wheel. It's slow but it works. That is how diamonds are cut and ground for gemstones (not counting recent developments with lasers). PCD inserts are relatively fragile compared to cermets or carbide. They aren't suitable for interrupted cuts.
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              • #8
                Originally posted by Evan
                Propylene glycol is actually toxic but has a low toxicity rating.
                -That's like saying Pepsi is toxic, but has a low toxicity rating.

                But yeah, propylene glycol is used as the fluid carrier in paintballs, the rest being solid fillers like sorbotol or talc, and food coloring. (No "paint", per se'.)

                Doc.
                Doc's Machine. (Probably not what you expect.)

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                • #9
                  Hey Evan & Doc!

                  You're both smart guys with a lot to offer here. It looks to me like there's a p!ssing match developing. Maybe you could work out a way to avoid that?

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                  • #10
                    Not sure it is really that critical.......

                    I have gotten a nice smooth reflective finish with just a shell end mill, and that at a lower than recommended SMM.

                    I don't think ANY cutters will give you a "hardware finish".

                    Depends what you want, really very smooth, or a regular pattern like fine flycutting, or what.

                    This is a part I have made several times for a client's prototypes. The vertical surfaces were done with an ordinary shell end mill. IIRC WD-40 as a cutting fluid.

                    1601

                    Keep eye on ball.
                    Hashim Khan

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                    • #11
                      Facemilling Aluminum

                      The high helix facemills work great, the 2024 is good advice, use Tap Magic or Tap Matic for Aluminum for the cutting fluid. They both have one specific to aluminum. Nothing else works nearly as well. One or two thin lines down the length of the part per pass is all you need. A little bit goes a long way.
                      Kansas City area

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                      • #12
                        I would also recomend a high helix facemill. The big advantage over the 45؛ square insert mills, is that they will mill a shoulder. The 45؛ facemills are only really any good, if you are milling the whole face of your workpiece.

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                        • #13
                          What's a high helix facemill?

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                          • #14
                            BB, I was just going to ask the same question. As well as a definition of a high helix face mill can you guys also recommend who makes a good quality product in this category?

                            Thanks,
                            Terry
                            Terry

                            There's only one way to find out, might as well get started now!

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                            • #15
                              High helix = lots of positive rake. Softer materials like aluminum like it better.

                              The 90's can cut shoulders and are more general purpose, but the 45's leave a better surface finish.

                              BTW, if you start considering varying heights of your inserts, you want them either very close indeed (friend with adjustable on Fadal sets them to a tenth) or actually force ONE insert to stand proud by two or three thou. That one insert will do the finishing job as a flycutter.

                              Cheers,

                              BW
                              ---------------------------------------------------

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