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On Reading Chips..

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  • On Reading Chips..

    Strange thing happened tonite while whittle'n on the lathe. i was turning down some mixed stock (ISO C40 & C45, free machining steel similar [i think] to 1040).. when i came across a piece of "mystery metal"

    i recall picking it up when i bought the lathe (used) and just assumed it was a piece of rusty C40 (the rest of the batch was all C40)

    the diameter was close, so i used it.

    while machining *known* c40, everything was dandy. beautiful chips; good feed, good speed.

    on the mystery metal, i had alot of sparks flying from the insert. SPARKS!
    occasionally the chips got red hot. glowing.
    i dont think it was heat treated.
    turning heattreated steel, as i'm sure you know, is ALOT uglier than what i was seeing tonite.

    nothing changed; same tool, same diam., same feed, same speed. but they mystery stock was throwing off sparks.

    anyone have any idea what kind of metals throw sparks off an insert (carbide)?

    in this vein, i'd like to ask you all a second question: what kind of information do you gather from the chips you cut?
    (lathe, mill, drill, bandsaw, whatever you like)

    ie.. short tight curly shiney chips... long thick blue chips, needle-like flakes (akin to what bronze will give you), etc? what do they tell you?

    i was always told that "blue" was the color to go for. is this correct?

    can fortune tellers read chips?

    -tony

  • #2
    Is the material magnetic? Can you cut it with a file? Can you scratch it with a pocket knife? What do the sparks look like when you touch it to a grinding wheel? These are more or less standard questions to answer quickly. Some kind of measurement of density is good information but is enough trouble to do that you need to answer the first ones above first.

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    • #3
      All kinds of stuff will do what you describe,Ilook for anything that isn't long and stringy,those really suck.

      I once had a piece of steel I know not what kind,but when I turned it the chips broke into little c's and turned the pettiest sky blue color never happened again though.

      Oh,I know,that piece of steel you have could be airhardening,I found a piece at work once,the abrasive saw would not cut it,the blade would get maybe 1/16"into it and glow red and thats it.
      I just need one more tool,just one!

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      • #4
        Tony

        You want your chips to come out as "6's & 9's" for safety reasons. It is a matter of selecting the proper chip breaker on your inserts and using the proper feed and DOC. Long stringy chips are very dangerous because they are difficult to handle and tend to get wrapped up in the work.

        The metal you were trying to cut was most likely a hardenable steel or a super alloy - the sparks are from excessive speed.

        Sparks are common when dry machining super hard alloys with CBN or Cermet inserts (hard turning).

        I dry machine as I don't like the mess suds make. When using the lathe the chips come off white and cool down to a nice blue. Most of the heat is removed in the chips. I rarely use HSS or brazed carbide (just for wierd stuff) and stick to coated carbide inserts.

        [This message has been edited by Thrud (edited 10-10-2003).]

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        • #5
          thrud,
          most of the time i use 3 point (80deg) inserts on a negative rake tool holder.

          it came with this big used lathe.

          the "chips" always come off in big
          long strings... pretty tightly curled.
          some as long as 8' (scouts honor)

          they come off tan and cool to blue.

          i agree that they are dangerous. usually
          they get spun around the chuck pretty fast.

          rarely do i get 6's or 9's.

          what am i doing wrong?

          -tony

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          • #6
            Talk about long stringy chips. I had a customer call wanting me to come repair his DRO on a lathe he had. It seems that he had such a ball of chips going that it grabbed both cables for the DRO scales and ripped them off completely.

            Dan

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            • #7
              Ya want "stringy chips" just try turning nylon. The stuff comes off in a continous thread and it won't break. A freekin PITA.
              Free software for calculating bolt circles and similar: Click Here

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              • #8
                evan,take a knife an score the part over its length when ruffing plastics in the lathe.It will help break a chip.You can do this on stringy cutting steel by advancing he tool .010-.020 and with lathe turning,crank carrage fast the length of cut then back out.Then proceed with your next cut.It will cause a weak spot in the stringy chip giving it a spot to break. Jim

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                • #9
                  I'll try it.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Tony

                    By a 80* triangular insert do you mean a "trigon" insert?

                    I don't like negative inserts except where I have no choice - I use them when I have to cut off the hardened skin on blanks. Ohterwise always use positive inserts as they require less power and deliver a better finish. Crank the speed up, increase DOC, and feed. If the tops of your inserts are "sculpted" then it has a built in chipbreaker. A smaller nose radius requires less power and produces far less chatter. If it is sparking out, then reduce the speed. If this does not work, contact the insert maker for assistance.

                    Normal chip action has the chip curling over and hitting the top of the insert - this is what "breaks" the chip. This normally requires a heavy feed to get a thick chip and greater depth of cut.

                    [This message has been edited by Thrud (edited 10-13-2003).]

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                    • #11
                      thrud,
                      i've been reading the old files and it seems you're one of the resident Insert Experts.

                      in the interest of learning more, i've posted a picture of my inserts (trigon), along with toolholder, and a chip sample.

                      though the shape *is* trigon, i can't make out any significant chipbreaker. the toolholder looks like it carries a pretty hefty 15-deg negative rake. dont know if you can see it in the pic.

                      i got these all out of a sale bin at a local "yard" .. probably about $0.40 an insert ($4/10pack).. they are different colors... gold, black, and silver. have NO idea what the differences are.

                      hope you could shed some light.

                      also, these are the blue chips it puts out on the infamous 1045 steel. these are after they've been mangled round the chuck and cooled down. otherwise they come off in long long curls.

                      here's the link: http://www.photobucket.com/albums/09...op/inserts.jpg

                      thanks,
                      -tony

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                      • #12
                        The way to get chipbreakers to work is to increase the feed rate.

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