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  • AL chip control question?

    I'm puzzled. I was turning some parts, and had some strange chip control issues.
    All of the parts were cut from the same bar of 6061 Aluminum.
    Running at 1000 RPM (my lathe's top speed).
    .035 depth of cut.
    .018 feed per revolution.
    ...but the chips were going from nice, curley-q's on one part.... to long, nasty, stringy torn chips on the next part.
    No consistency. One part easy, the next part nasty.
    Is there such thing as hard-spots in AL?, or differences within the material?
    Photo below is the result of two different parts, out of the same material.
    Chips on the left are nice, steady, breaking chips.
    Chips on the right are nasty stringy, torn chips.
    Strange. Any ideas, what's going on here?

  • #2
    If you were NOT using a coolant I'd suggest that the chips on the right were the result of aluminum caking on the crest of the cutting edge causing the business edge of the cutter to rub rather than cut the material. This happens to me from time to time. The chips on the left look like normal chips coming off of a sharp edge. 6061-T6 aluminum can be cut with no coolant if you don't overdo the speed and feed causing it to cake the material to the edge. Otherwise, I'd say the chips on the right were being cut by a dull tool.

    EDIT: Rub your finger over the top of the cutter and if you feel a bump right at the cutting edge it is aluminum caked to the edge. You can simply scrape it off with another tool bit. I'd avoid stoning to keep from loading my stone with the soft aluminum. Sometimes the buildup will pop off of its own accord during machining, but this is more the exception than the rule. If material buildup IS the cause you can eliminate it by brushing on a little bit of oil during the cutting phase.
    Last edited by DATo; 05-21-2011, 02:45 PM.

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    • #3
      Progressive wear/welding on the tool

      Aluminum is notorious for welding onto the tool at the cutting edge. It changes the geometry of the cutting edge and affects the shear angle on the material being cut as well as the amount of heat generated. Copper does the same, only worse. The welded edge breaks off occasionaly and carries away with the chip and you are back to the original cutting geometry.

      Not much you can do short of using coolant. I keep a pump spray bottle of WD40 to use as coolant when welding onto the tool becomes a problem, especially on the mill.

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      • #4
        AAHHH YES.
        That's what's going on.
        It's nice having a wealth of knowledge at your fingertips.
        Thanks guys.

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        • #5
          Originally posted by Jpfalt
          Aluminum is notorious for welding onto the tool at the cutting edge. It changes the geometry of the cutting edge and affects the shear angle on the material being cut as well as the amount of heat generated. Copper does the same, only worse. The welded edge breaks off occasionaly and carries away with the chip and you are back to the original cutting geometry.

          Not much you can do short of using coolant. I keep a pump spray bottle of WD40 to use as coolant when welding onto the tool becomes a problem, especially on the mill.
          I've noticed a lot of posts here at HSM which mention WD 40 as a cutting fluid. Nothing wrong with that but it can become pricy over time. In my home shop I use a mixture of kerosene and motor oil for aluminum (1 quart motor oil to 1 gallon kerosene). Kerosene isn't as pleasant a smell as WD 40 but it's a lot cheaper.

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          • #6
            I use straight kerosene...

            Works great and doesn't need much. I use WD-40 when boring or drilling simply because I can spray it into the hole. What advantage does the motor oil give mixed with the kerosene? Later.

            Dave

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            • #7
              Originally posted by daved20319
              Works great and doesn't need much. I use WD-40 when boring or drilling simply because I can spray it into the hole. What advantage does the motor oil give mixed with the kerosene? Later.

              Dave
              Hi Dave ! An old timer taught me that recipe (1:4 oil to kerosene) a long time ago. The oil is used to add a bit more lubrication to the mix and makes it more of a universal coolant. Actually I use it on just about everything but I have an exhaust to clear the fumes because the smell does get pretty strong after awhile if you're using a lot of it. Never considered the advantage of the spray WD 40 for boring holes before ... good idea, especially if you use that tube adaptor they give you with the spray can to reach back into those long bores.

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              • #8
                For all the shooters out there -try Ed's Red for turning aluminum. I mix Ed's Red as equal parts of Kerosene, Varsol, and Automatic Transmission fluid. Makes the best gun cleaning mix you will ever use, and leaves a beautiful finish when used for turning aluminum. It is also a great penetrating oil.

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                • #9
                  Although not perhaps strictly useful in this situation, I sometimes rub a candle when milling materials that can form a built up edge (brass, al). The wax melts locally and seems to provide enough lubrication to stop the build up but without the mess of a cutting fluid. This may not work as well for turning but is a handy trick to remember.

                  Michael

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                  • #10
                    Although it doesn't appear this was your problem, I did have a case where I found numerous soft spots on the outside half inch of a 6" bar of 6061. My part looks like it had silver leopard spots.
                    Eric Sanders in Brighton, Michigan
                    www.scope-werks.com
                    www.compufoil.com

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                    • #11
                      What kind of cutter were you using? HSS or carbide? What kind of back rake did you have? Aluminum likes 15 deg, more or less depending, and that helps to cut down on cutter edge build up.

                      .018" feed seems a little high for what you were doing. Did you have a radius on the cutter or was it a sharp point? Using .018" feed, did you have enough side clearance so the side of the cutter didn't rub the work?

                      Aside from using a coolant/lube with aluminum, the shape of the cutter has a lot to do with how well it cuts aluminum.
                      It's only ink and paper

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                      • #12
                        Bit of irony

                        Kerosene was the first expedient coolant for aluminum that I was introduced to in shop.

                        The kerosene and oil mix is a bit ironic as the basic formula for diesel fuel is 6 parts kerosene to 1 part mineral oil.

                        Probably much cheaper to buy a gallon of diesel.

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                        • #13
                          Originally posted by form_change
                          Although not perhaps strictly useful in this situation, I sometimes rub a candle when milling materials that can form a built up edge (brass, al). The wax melts locally and seems to provide enough lubrication to stop the build up but without the mess of a cutting fluid. This may not work as well for turning but is a handy trick to remember.

                          Michael

                          Hi Mike! Interesting that you mentioned wax. I use a special commercial wax to coat the blade of the band saw. I just hold it against both of the flat sides as it is going around under power till I estimate that the entire blade has been coated. Regular wax works well too. I just used it the other day to cut a 26" diameter of 1" thick aluminum out of plate - makes all the difference in the world.

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                          • #14
                            Originally posted by Jpfalt
                            Kerosene was the first expedient coolant for aluminum that I was introduced to in shop.

                            The kerosene and oil mix is a bit ironic as the basic formula for diesel fuel is 6 parts kerosene to 1 part mineral oil.

                            Probably much cheaper to buy a gallon of diesel.
                            That is what I've been using at school for several years. The diesel ,
                            it's cheaper than Kerosene, at least here in Abq.. Apply it with a small
                            brush (keep the bristles out of the way of the cutting edge)
                            All this for Aluminum of course, for steel I use the dark thread cutting
                            oil.
                            ...lew...

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                            • #15
                              I use the fluid out the parts washer if its not flood cooling. That's kerosene with whatever washed off the parts in the last few months.

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