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  • What a difference !

    Just a hint for our beginners- I was making some small pins for the motionwork of a model steam engine. I grabbed two pieces of 3/8 dia steel bar from the drawer of mixed mystery metal. The first piece turned perfectly, the second, using the same tool, speed, overhang etc, gave me a finish I would not be proud of from the tool. Given what is in the drawer it is likely piece one is 12 L 44 and piece two is 1018. So the motto here would be, do not blame your lathe, or your tool grinding until you have tried using a known material. Regards David Powell.

  • #2
    Blaming your lathe for a poor finish
    is like blaming a fork for making you fat.

    -D
    DZER

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    • #3
      I blame the television---

      Originally posted by Doozer View Post
      Blaming your lathe for a poor finish
      is like blaming a fork for making you fat.

      -D
      The food ads on the TV make me feel hungry--- so I do not watch much TV ! Regards David Powell.

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      • #4
        Actually Doozer is somewhat correct. Cold rolled is harder to turn in the sense that it's more picky when it comes to tool shape and feeds/speeds. Whereas 12l14 doesn't care in the least.

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        • #5
          Originally posted by Doozer View Post
          Blaming your lathe for a poor finish
          is like blaming a fork for making you fat.

          -D
          Except when it is a loosey-goosey old wobbly used machine that chatters if you look at it funny. Or has had the wrong bearings installed by a P.O.
          CNC machines only go through the motions

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          • #6
            If it is that loose
            a real machinist would use a
            box turning tool.
            (or a steady rest,
            done that before)
            -D
            DZER

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            • #7
              Originally posted by David Powell View Post
              I grabbed two pieces of 3/8 dia steel bar from the drawer of mixed mystery metal.
              I no longer have any mystery metal in the workshop, once I recognised how much time can be wasted with the wrong grade of material anything unidentified went in the scrap bin and all new material coming in gets the end stamped to ID it permanently.
              Even expensive grades of steel are cheap when compared to the time which can be lost making scrap parts,

              - Nick
              If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

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              • #8
                I blame the tool- the one wearing the shoes
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  Originally posted by darryl View Post
                  I blame the tool- the one wearing the shoes
                  I think that word is spelled with an F not a T . :-)
                  ...lew...

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                  • #10
                    Different materials require different tools and techniques. Steel is not steel, could be 20ksi yield or could be 100ksi+. JMO but blame lies on the "machinist" either way, no reason not to be able to make good parts whether the material is plastic, a turd, or steel.
                    "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

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                    • #11
                      Well, I know you cannot POLISH a turd.....

                      So the person who tried is being silly. Or the person who instructs him to do it.
                      CNC machines only go through the motions

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                      • #12
                        Originally posted by J Tiers View Post
                        Well, I know you cannot POLISH a turd.....

                        So the person who tried is being silly. Or the person who instructs him to do it.
                        I though the mythbusters showed you could polish a turd.
                        Location: Long Island, N.Y.

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                        • #13
                          Originally posted by RichR View Post
                          I though the mythbusters showed you could polish a turd.
                          Ah but look at the material they used, no ordinary turd, it was a lion turd. Must be like 4140 PH..

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                          • #14
                            Another huge difference one will find when confronted with a choice between using a soft gummy steel and a softer gummy steel is the grind of the tool bit. I find a sharp and very positive rake tool grind can be a lifesaver and will definitely make a huge difference in finish quality. Of course you can't use that same grind to hog off a 1/4" of rust and mill scale, but for finishing passes it can be a project saver. It also allows one the option of using a softer steel that would otherwise be unusable due to poor surface finish.

                            For those that consistently get poor a finish with the combo they're using, get out there and experiment. Make some chips until you are happy with the results. Not saying you'll get a mirror finish out of mild steel, but you will find there are huge gains to be made with the proper tool bit grind along with depth of cut and feed rate technique.
                            Last edited by Willy; 11-05-2016, 11:59 AM.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories​

                            Location: British Columbia

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                            • #15
                              When I am not getting a good finish the first thing I do is inspect the tool with a 10x loupe. Usually I find it needs attention. I have a lot of scrap cold rolled around and usually it will cut OK with a good tool. As will stainless, and O1.

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