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Stubborn Stainless

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  • Stubborn Stainless

    I'm making an adapter to drive 3/4" sockets with my HF electric pipe threader. The part I need looks like a 3/4" cube sitting in the center of a 2 3/4" disk that is 1/4" thick. I took a chance on using a piece of 3" diameter SS bar that I've had hanging around in my shop for years. No idea what type of SS it is & yes, I know, it's better to use known stock, but I'm too cheap to throw out a $100+ piece of stock, and besides, it's a challenge.

    I turned a 1.08" diameter boss .75" long using a carbide cutter. Chips came off blue, but no problem. I parted off using HSS, leaving the 1/4" disc. It didn't like it, but with care I got it done. So far, so good. Now I have to turn the round boss into a 3/4" square. I have a K&T horizontal mill fitted with a Bridgeport M-head. A 1/2" 4-flute HSS milling cutter running at 145 SFPM wouldn't touch it. I realized, like a dummy, that the turning left me with a hard surface.

    So, how to proceed? Can it be annealed or the hard surface ground off? Even so, won't each milling pass leave a new hard surface? Carbide cutter? My maximum shank size is 1/2", and my top 3 speeds give 145, 275, and 510 SFPM with a 1/2" cutter. It's an interrupted cut. Should I trash it and start again with some less stubborn material? Suggestions?

  • #2
    Can you use a fly cutter with a brazed carbide bit?


    • #3
      Didn't think of that. It might work, but I'd be concerned that the carbide would chip because of the interrupted cut.


      • #4
        Best to start with a known material. Cheap 1045 w/home shop heat treat would serve well.
        Got any cutters for the horizontal? Seems a gang cut would make quick work, one index.
        SS needs to cut and not rub so you don't work harden every pass. Blue chips don't necessarily mean you work hardened the turning.
        You are leaving a generous radius at the base, right?


        • #5
          Hacksaw and file, all engineers should have a firm grounding in bench-work! ;-)
          If you benefit from the Dunning-Kruger Effect you may not even know it ;-)


          • #6
            A 1/2" 4-flute HSS milling cutter running at 145 SFPM wouldn't touch it.
            Maybe, just maybe on 303 or 416 that just might work for a short while... On any other "mystery" stainless its not going to work..

            An assumption on the "mystery" metal, since you've already cut it, its probably not some odd ball unobtanium, most likely 304 or something
            that is going to behave in a similar manner...

            35 to 50 sfm, and you should be fine... 250-380 rpms or so.


            • #7
              You are probably not going to cut that with anything but carbide at this point. I will be hard all the way through.
              Kansas City area