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Hard turning on a smallish lathe

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  • Hard turning on a smallish lathe

    Got a box of cheap CBN inserts from ebay and made holder for them. Seem to cut hardened 52100 bearing race without complaints on my 11x24 Kerry:


    Seem to cut anything I can throw in the lathe, including nasty intermitted cut to HSS with too low speed:



    Just a heads up in case someone else has been also wondering if its doable on small lathe...

    Also did try to sharpen the CBN inserts and seemed no big deal. Cheapo 3000 grit diamond disk took off 0.1 or 0.2 mm from the CBN edge without drama and the sharpened insert cut hardened steel even better than right out of box.

  • #2
    https://m.ebay.de/itm/5x-SANDVIK-Wen...sAAOSwyjBW7YD0

    In case anyone has urge to try hard turning. I think I paid 30 euros including postage. List price for these is probably 15 times that

    Didn’t have holder for these but making one is super easy. Hole is enough big for M5 12.9 allen screw so that one was also easy..

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    • #3
      Wow, that's impressive. As much as I want to try that, I'm pretty sure I'd end up burning my house down! How fast was the lathe running?

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      • #4
        Originally posted by alanganes View Post
        Wow, that's impressive. As much as I want to try that, I'm pretty sure I'd end up burning my house down! How fast was the lathe running?
        Yeah, normally I would keep the chuck guard down but for demonstration I let the chips fly. Easier to make video without dirty chip shield.

        1500rpm and abouts 80mm diameter so surface speed is ”plenty” fast. 400m/min or abouts 1200 sfpm.

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        • #5
          The lathe didn't seem to complain at all other than the motor loading down. But at 1500 rpm I can see why it would slow down a little. And the 1200 sfpm would certainly explain the fire snakes.... Does it need to run that fast? If you drop down to a lower SFPM does it start to go badly?

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          • #6
            Originally posted by
            And the 1200 sfpm would certainly explain the fire snakes.... Does it need to run that fast? If you drop down to a lower SFPM does it start to go badly?
            Recommended range is 100-200m/min or 300-650sfpm. Same fire snake still at that speed.
            Actually felt like the hyperspeed sfpm was easier cutting, I'm guessing downside is increased insert wear.

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            • #7
              So how many kW motor on that old Kerry?
              1601

              Keep eye on ball.
              Hashim Khan

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              • #8
                Originally posted by J Tiers View Post
                So how many kW motor on that old Kerry?
                The old clunker has 1.1kW motor. And its a 3-phase so it probably has about 2x rated power short-term overload capacity.
                Guessing from the sound (and experience )the cut was taking plenty of power but still reasonably far from stalling the motor.

                edit: power-wise even lot less than 1.1kW would be still usable. I was taking nearly 2mm DOC on the videoed part. 0.2mm DOC wont need much ponies.
                Last edited by MattiJ; 12-05-2017, 05:13 PM.

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                • #9
                  "smallish" is a relative term. Not familiar with Kerry lathes, but it looks like a substantial gear head machine. I don't think I'd try on a Chinese machine of comparable size.

                  My Colchester will do it too.

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                  • #10
                    As funny as it sounds the smaller lathes typically do a better job with hard turning because the increased spindle rotational speed.
                    Hard turning with CBN requires lots of speed. A big 14 plus inch lathe is gonna go maybe 1500 RPM and that's not typical.
                    The little 9 ot 10 inch lathe will have a 3000 RPM spindle and hard turning likes that.

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                    • #11
                      Originally posted by OhioDesperado View Post
                      As funny as it sounds the smaller lathes typically do a better job with hard turning because the increased spindle rotational speed.
                      Hard turning with CBN requires lots of speed. A big 14 plus inch lathe is gonna go maybe 1500 RPM and that's not typical.
                      The little 9 ot 10 inch lathe will have a 3000 RPM spindle and hard turning likes that.
                      Won't do much good if the old flat belt slips due to torque. My 10" will go about 1500, but the 1" belt (rubber composition! ) will slip if a serious cut is attempted. I figure no matter what motor is on it, it is good for about 1/4 HP through the belt on the fast and slow speeds of the cone pulley. a bit over 1/3 HP on middle position. Slip point is about 35-45 lb tension in best position, clean, I measured it.
                      1601

                      Keep eye on ball.
                      Hashim Khan

                      Comment

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