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  • Broken endmill

    I broke a nice 1/4" carbide endmill milling a slot in aluminum. Was about 7/8" deep at the time, and had z & y axes locked down. At the time it broke I wasn't actually advancing, but rather backing out of the slot which was pretty filled with chips. Is that normal? I'd expect that endmill to go thru those chips like, as they say, excrement thru a goose.
    The piece was held firmly in vise, so I don't think there was any slippage.
    Lynn (Huntsville, AL)

  • #2
    Bet it had its cutting edges loaded with alum and was incapable of cutting its way through anymore. Those carbide tools don't like bending much! Apart from the fact that 7/8ths deep is like the Grand Canyon to a 1/4 cutter, I like to use the shop secondary air supply (called lips an lungs) to blow away those pesky chips when doing something that deep.

    Don't think you did anything wrong Lynnl - other than not clear the chips.

    RR

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    • #3
      Yep. The chips need a place to go, and if there isn't any the end mill isn't going to like it much. Keep the chips cleaned out. Aside from reducing the danger of breakage, you'll probably get a better finish.
      ----------
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie

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      • #4
        I was keeping them cleaned out early on, then I guess I got too lax as it got deeper. Well, at least I've learned a lesson. These are the kinds of lessons one tends to remember best.
        Thanks
        Lynn (Huntsville, AL)

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        • #5
          I agree with the other guys. Also, was it a 4 flute or a 2 flute end mill? A 4 flute will clog with chips really easy when milling aluminum.

          Greg
          "The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is." Winston Churchill

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          • #6
            It was a 4-flute.
            Also I noticed after it broke that the business end was coated in shiney AL. ie. it appeared to be bonded to the carbide and would not rub off. This was the second of 2 slots I had to mill. I cleaned out the chips and finished with a HSS mill. At that point I didn't have much more to mill out.

            I prefer using 1/2" endmills, they're a lot sturdier. But I find it tricky to get a good 1/4" slot with them.

            [This message has been edited by lynnl (edited 01-09-2003).]
            Lynn (Huntsville, AL)

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            • #7
              "I prefer using 1/2" endmills, they're a lot sturdier. But I find it tricky to get a good 1/4" slot with them."

              Don't you see: You're getting two, Count Em', two 1/4 inch slots with the 1/2" end mill!!!!

              Greg

              "The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is." Winston Churchill

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              • #8
                By golly you're right Greg. ... and with only half the machining effort at that. 'course one might be a little bit off in its location. And sometimes only one is called for.
                Lynn (Huntsville, AL)

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                • #9
                  In the words of Roseanne Rosanadanna: "Never Mind"
                  "The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is." Winston Churchill

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                  • #10
                    Lynn
                    The chips are deceiving and a problem in high speed machining. This is why through the spindle coolant at 1500PSI is popular in the "wet world" and air jets on "dry land". Blows the little buggers the hell out of the way! If you have ever been beside a VMC with a 2" drill and through spindle coolant you will know what I mean - if not, bring a beach umbrella - unless you LIKE coolant in your hair...wish I had some hair on my head instead of my ass... (its tough to be a gorilla, baby)

                    Geeze I forgot my point...oh yeah, all those chips are just as hard to cut the second time and when you have a bunch of them all screaming "me first, me first" no wonder the end mill packed it in - overloaded.

                    Did I mention I like chocolate milk...

                    [This message has been edited by Thrud (edited 01-11-2003).]

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