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Basic milling question

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  • Basic milling question

    I have just purchased one of the mill drill combos. (rong Fu clone). it will be used primarily for some simple slotting, and milling of aluminum, nothing thicker than 1/4" at this time.

    I am really a novice at this so I ahve a couple questions regarding holders for end mills.

    This machine has an R8 spindle. I see there are two kinds of holders for end mills. Collets and a holder that uses a set screw to hold the tool. The holder with the set screw seems pretty self-explanatory. Does the collete holder require any kind of an adapter to work with the machine? Does each kind of holder require different style of end mill or are mills interchangeble between the two?

    I have read that 2 flute is the best for aluminum. is there a certain helix style or profile that is best for aluminum?

    Finally, what is the optimum RPM to mill aluminum (6061) while using a manual feed?

    Thanks for any and all responses in advance.

    Jim Chinn

  • #2
    Request a copy of the free (and mind-boggling) MSC catalog and you'll see hundreds of styles of end mills, some specifically engineered for aluminum. As a practical matter, for home shop use I doubt you'd notice much difference between those and general-pupose end mills...but then again, I've never tried the ones engineered for aluminum.

    The R8 spindle will take (duh!) R8 collets, for which you will need a drawbar, which presumably will come with the machine. You can put an end mill directly into a collet, or you can get an end mill holder (with the setscrew) with an R8 shank to fit the mill spindle. Either way will work. The holder extends the end mill a bit, which is sometimes handy and sometimes inconvenient...depends on the job you're doing. The end mills are the same in either case. Note that you do NOT need a "full set" of collets. Odds are astronomical that you'll never use a 17/64" collet for anything, ever, for instance. 3/16", 3/8", 1/2", 5/8", and 3/4" will likely hold any end mill you'll ever buy. Personallly, I think paying for good collets (Hardinge, Royal, etc.) is worth the extra money.

    2 flute end mills have more chip clearance, and since aluminum (some alloys, at least) cut pretty easily a 2 flute end mill will let you cut faster. 2 flute end mills are also better for cutting slots, although you will find that for most accurate width and best finish you'll need to either do two passes, one with a slightly undersize end mill and a final pass with a to-size end mill, or multiple passes with an undersize end mill, finishing each side of the slot in turn.

    You can whizz an end mill pretty fast in aluminum, although with some alloys a high rpm will cause chips to weld to the end mill and cause no end of problems...some kind of lubrication (WD-40 seems to be a favorite for aluminum) will help that problem a lot.

    Try to make a living, not a killing. -- Utah Phillips
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    • #3
      Jim, I bought most of the normal sizes of end mill holders. I think if I had to do it over I'd buy collets instead except for the 3/4" holder. I use that for some bigger cutters and some of my "Hillbilly Homebrew" gear cutters. I don't know how collets would hold up to the abuse with the bigger size. Someone else could tell you better.
      I just bought a Niagra alu end mill with a bunch of helix. I haven't tried it yet but it is supposed to remove chips better from slots.
      I've found that the other two flute alu end mills I have do a little better job in alu than a 4 flute mill.
      I have tools I don't even know I own...


      • #4

        I bought the full Bison ER-40 collect set + collet chuck, covering 0.120" up to 1.020". My logic is that the collets are used for both milling & drilling.

        I often run 1" carbide or cobalt end mills and the collets grip like death. For tough drilling (hot rolled flat comes to mind) where the drill has a tendency to hang when penetrating the bottom, these collets don't slip.

        If you ever use screw machine drills (which I do) the collets allow you to grip a huge shank without a monster chuck. They also allow gripping on the drill flute which shortens projection and increases hole accuracy.

        The only thing I'd trade my ER-40 set for is a full set of TG-100. The TG's grip tight enough for tapping (if you don't have a tapping head). But it takes 59 TG collets to cover the full range versus 23 of the ER-40.

        Barry Milton
        Barry Milton


        • #5
          Even in my mini-mill, the MT3 collets have a griup like a snapping turtle.


          • #6


            i've always like collets because i think they are more accurate, as mentioned, either will work. I've got a set of R8 hardinges and they are very nice. What does nice mean for a collet? finish & accuracy of course, right level of hardness so it stands up and just the right amount spring so that tools are easily inserted/removed but stay put by friction when you are changing them.

            on speed, there is a theoretical number based upon a linear distance per minute, (ie feet per minute) beyond which bad things happened like shorted tool life ect. This is a theoretical number not always achieved by us home shop types as our machines are usually lighter or older. Here’s one link for you that gives some theory, but don’t get too bogged down with it.


            get a آ½â€‌ end mill, and R8 .500 collet, run the machine at say 1000 rpm (well under theoretical speed ). Pay attention to safety – eye protection, work secured and all that, then have some fun with that machine. In the meantime, a really good starting place is to pick up a grade 11 or 12 high school level text on machining – it’ll give you a ton of the basics and is easily understood.


            • #7
              Your mill probably won,t turn a tool in the collet when cinched down correctly. The emill holders become nescessary when you start doing heavy milling or using cutters and machines which can overpower the grip of the collet. I have used endmills and and collets to do some serious milling on machining centers and never had any trouble. The proper fit between tool and collet should be a close slip fit. If fit is too lose the collet will not close properly and you risk slippage and could possibly ruin the collet. Avoid using drills in your collets unless absolutely nescessary.

              Two flute will work best for slotting but for profiling cuts (any DOC less than 1/3 dia tool) you can use four or more for improved finish. Four flute will give better finish than 2 at equal speed and feed. The helix will probably not effect your situation as much as using lubrication. I like kerosene or WD-40 (aerosol is convenient for appllication). Using fluid will greatly improve the finish and chip evacuation. Aluminum tends to stick to the rake face of HSS and carbide tools fluid helps prevent this.