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  • material piling up in front of tool

    today i tackled a job turning the shanks of a bunch of 1/2" and smaller drill bits that were all chewed up. using a carbide tool and running at 1200 rpm (the fastest i can go) and taking off 005-010 tho. on some of bits, the material builds up in front of the carbide. im using the slowest feed rate my machine will go as im thinking this will make a better overall finish.

    i've noticed this same problem before and have not really come up with a solution or even a reason for it. sometimes carbide tooling sometimes hss. and not always on drill bits but other stuff i turn down.

    obviously im not very experienced at this so i am asking for input from you wizzards.

    thanks in advance.

    davidh

  • #2
    With carbide run it as hard and fast as you can. If it looks like this then you have it right.

    Free software for calculating bolt circles and similar: Click Here

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    • #3
      Take a look at the "falure mechanism analysis and corrective actions" document on Kennametals website.

      http://kennametal.com/images/pdf/tec...iveActions.pdf

      Your description sounds like "built up edge" which is a common problem in machining. Basically, some of the workpiece material welds itself to the tip of the cutting tool. By increasing the surface speed, you're half-way to solving the problem. Increasing the feed-rate and adding some oil should completely solve your problem.

      Carbide tooling should be used pretty agressively. I've seen a lot of cases where someone reduces the feed-rate and depth-of-cut in hopes of improving the surface-finish, when they really need to increase them instead. Of course, the extent to which you can increase these parameters is limited by the ridgitiy and power of your lathe, so you really just need to find a sweet-spot that gives good results.

      I hope this helps.

      Edit/Addition: When you're cutting steel with carbide, the chips should turn blue from heat. Increase your cutting speed (if possible) until this is obtained. If the steel is VERY hard, it might glow like Evan's picture shows, but you should really make sure that the speed is correct by checking the chips.
      Last edited by b2u44; 06-14-2008, 07:30 PM.

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      • #4
        wow, chips on fire. . . ok, my lathe will run 1350 flat out. its a couple horsepower sheldon 13 inch tool room lathe. i will try the faster cut next time. i though that when the cutter started making sparks it was all over for the cutter. . . thanks for the info. i'll check kennametals site next.
        davidh

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        • #5
          Carbide

          Check the data sheets for carbide and I expect you are outside the operating "window" for the tooling. Carbide needs to be worked, not taking a light skim cut.

          JRW

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          • #6
            Mostly it WON'T take a 'skim cut", because it is by nature "blunt".... it's bits of hard stuff in a softer matrix, so it can't ever take the edge that HSS can.

            If you DO sharpen the edge, it will blunt down fast.

            A blunt edge will cut better if the work spins faster........ but you can't spin fast enough

            So get an HSS bit on there and clean 'em up right.
            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              Agreed

              I agree with JT.

              The shanks of most drills are not "hard" - just (maybe) "tough" - mostly - and as such are prime candidates for machining with HSS.

              HSS by its nature is used less "aggressively" than Carbide and as such is not going to "push" the comparatively long and thin shanks "ahead" or "away" from the cutter.

              "Getting stuck into it with TC" not only requires a rigid machine but also a rigid job - of which small drill shanks are not one of them.

              Take it easy - use low speed and feeds and very good sharp (honed) cutting edges with adequate rakes, clearances and "lead" angles and you will do OK. Cutting oil (including "tapping oil") is highly recommended.

              Unless you really are in a hurry or just like "tear-arsing", go easy on your machine and take your time - "hasten slowly".

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              • #8
                Really should not be getting glowing like that unless you are running CBN or ceramic. Well, at least if you want any insert life that is. With carbide you want nice blue chips.

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                • #9
                  DavidH, what kind of carbide tooling are you using?

                  Some of the cheap triangular insert tooling doesn't perform that well. I can't imagine what you're trying would be a problem for CCMT insert tooling based on my experience with it.

                  There's no question you're a tad low on the rpm's, but that shouldn't be the end of the world.

                  Cheers,

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

                  http://www.cnccookbook.com/index.htm
                  Try G-Wizard Machinist's Calculator for free:
                  http://www.cnccookbook.com/CCGWizard.html

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                  • #10
                    Really should not be getting glowing like that unless you are running CBN or ceramic. Well, at least if you want any insert life that is. With carbide you want nice blue chips.
                    That depends entirely on the grade of carbide. That's C1 carbide which is intended for interrupted cuts in roughing cast iron among other things. It's tough as old boots and very hard to chip. It also takes an edge as fine as HSS.
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      Originally posted by Evan
                      It also takes an edge as fine as HSS.
                      All carbide "TAKES" the edge......

                      The difference is in it KEEPING the edge...... Some ARE in fact better, but NONE will or can "keep" an edge like HSS when used within its "envelope".
                      1601

                      Keep eye on ball.
                      Hashim Khan

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                      • #12
                        Just about all drills have soft shanks, just a little tough. That way you will not ruin a good chuck. Use a regular HSS toolbit!

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                        • #13
                          Originally posted by davidh
                          today i tackled a job turning the shanks of a bunch of 1/2" and smaller drill bits that were all chewed up. using a carbide tool and running at 1200 rpm (the fastest i can go) and taking off 005-010 tho. on some of bits, the material builds up in front of the carbide. im using the slowest feed rate my machine will go as im thinking this will make a better overall finish.

                          i've noticed this same problem before and have not really come up with a solution or even a reason for it. sometimes carbide tooling sometimes hss. and not always on drill bits but other stuff i turn down.

                          obviously im not very experienced at this so i am asking for input from you wizzards.

                          thanks in advance.

                          davidh
                          Slow feed rate is wrong, crank the feed.. you are better off running rapid traverse then slow feed as far as tool life.

                          Some guys dont understand that 12,000 rpm at 110 IPM is not that fast at all. when you crank the rpm you can crank the feed and "GET ER DONE"

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