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Not getting a good finish when using my craftsman 618

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  • Not getting a good finish when using my craftsman 618

    I'm having a hard time getting a smooth cut on my craftsman 618. I bought a QCTP with indexable inserts from LMS. From what I have read here about carbide tools my first thought is that the lathe doesnt have the RPM for them so I have ordered some HSS bits. Does anyone have any tips and or sugestions?

  • #2
    You may be pushing the limits of the 618. I have one, and I think the machine is just not rigid enough for carbide.

    The only things I can suggest are tight gibs and minimal overhangs. Drive belt slippage may also affect performance.

    I have limited my lathe to HSS.
    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
    ~Practitioner of the Electromechanical Arts~


    • #3
      Carbide is a waste on that machine. It doesn't have the rigidity or power to load the cut like a carbide bit wants. Use sharp HSS with correct rakes and a nicely honed edge and you can get excellent results. I've taken up to .020 cuts in O1 steel on mine without killing the machine, the bit, or me.


      • #4
        I did the same thing on my 618. I get great results with HSS so I bougrt the 3 sided inserts & the 30 pc 1/4" carbides & absolutly hate them. Wasted my money. Stick with HSS. I can peel off a kile long string the dia of a pencil 1/4" between the coils in alum. All I got was little chips with the carbide. Watch the youtube video by the viper on HSS. Thanks! Eric


        • #5
          Chips is what you want. Thats what chip breakers do.

          Try some warner HSS inserts for the holders.


          • #6
            I tried a zero rake brazed carbide tool on my 618. At .018 DOC, 400SFM, .0039 feed on 4140HT I got a beautiful, almost polished finish. So obviously the lathe will do it, but the lathe was clearly struggling. I experimented a little more and concluded that although it can be done, its more of a stunt than a good working practice. I no longer use carbide on that lathe. I believe that Hss will make you happier in the long run.

            If you are having trouble with grinding HSS, check out Watch all of his videos.

            For a great finish using HSS, Google “shear bit”, I use 20°.

            Have fun with it, Mike


            • #7
              When using a small lathe and carbide, make sure you get the inserts that are ground and not the molded kind.

              The ground inserts can have very sharp cutting edges.

              You also need some rake (negative????) to allow it to cut easier.

     has some very nice inserts that are well suited to smaller lathes.

              As pointed out, you don't usually want strings, but instead want a shower of chips. When turning 2011 aluminum I get the most beautiful waterfall of chips when cutting .050 deep on my 7x12 lathe.

              At the end of the project, there is a profound difference between spare parts and extra parts.

              Location: SF East Bay.


              • #8
                Yes, use a nice sharp style of insert on a small lathe and you'll get good results. I use the ground inserts for cutting AL and finishing steel. They work great but often you will be working a DOC that doesn't allow the chip breaker to do it's job.

                They don't last as long as the molded inserts though so they do up the operating cost. I simply suck at grinding bits. I keep trying but I eventually go back to my TCGTs and CCGTs for finishing. That's where it all seems to go wrong for me with HSS. I also have some PVD inserts that do some kick-butt work with steel. Made my whole chuck back plate out of 6" diameter A2 from them and the finish was great even on my dinky G0602.