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Turning Tapers Between Centers

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  • Turning Tapers Between Centers

    After much adieu over nothing I suppose (since at the moment I only have one to do) I decided to turn a tapered mandrel between centers. *The first one turned out pretty good except I screwed up the finish pass(es) and came in under sized. *No I can't just shorten it up.* It looks really good though.* So I still have just one to do. *LOL.

    I picked up one of those little offsettable centers and it worked well enough, except the tip melted. *I kept it lubricated, but it might have just been to high of an rpm for the method. *I can turn it slower, but if I get to do more of these I sure don't want to go slower.

    I have two thoughts:

    I can offset the tail stock and use a ball bearing center.

    I can machine off the melted center, center drill it, and insert a ball bearing between it and the center drill on that end of the stock. *The ball bearing certainly won't melt, and it will more evenly distribute the load from the stock to the center. *It would also have more contact with the drilled out center. *It would also allow me to have a small reservoir of grease behind the bearing.

    I really don't have a strong feeling for which approach will work out better other than I dislike the time spent adjusting my tailstock back in. *I can leave the offset center setup for this taper indefinitely. Ok, maybe I hope the ball bearing method will work out atleast as well.

    The taper is pretty shallow. *.157 over 10 inches.
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  • #2
    Originally posted by Bob La Londe View Post
    After much adieu over nothing I suppose (since at the moment I only have one to do) I decided to turn a tapered mandrel between centers. *The first one turned out pretty good except I screwed up the finish pass(es) and came in under sized. *No I can't just shorten it up.* It looks really good though.* So I still have just one to do. *LOL.

    I picked up one of those little offsettable centers and it worked well enough, except the tip melted. *I kept it lubricated, but it might have just been to high of an rpm for the method. *I can turn it slower, but if I get to do more of these I sure don't want to go slower.

    I have two thoughts:

    I can offset the tail stock and use a ball bearing center.


    I can machine off the melted center, center drill it, and insert a ball bearing between it and the center drill on that end of the stock. *The ball bearing certainly won't melt, and it will more evenly distribute the load from the stock to the center. *It would also have more contact with the drilled out center. *It would also allow me to have a small reservoir of grease behind the bearing.

    I really don't have a strong feeling for which approach will work out better other than I dislike the time spent adjusting my tailstock back in. *I can leave the offset center setup for this taper indefinitely. Ok, maybe I hope the ball bearing method will work out atleast as well.

    The taper is pretty shallow. *.157 over 10 inches.
    Carbide tipped centers are less likely to weld&melt.
    Same goes for ball bearings, carbide or ceramic ball wont weld.
    Location: Helsinki, Finland, Europe

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    • #3
      This is one that I built

      mandrel sizes

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      • #4
        Right off the bat I can help. McMaster has small rare earth magnets. K&J Magnets has them cheaper and better. K&J also has a better selection and they have the ones with the higher heat rating. In addition their dimensions are not all under by .001 like McMaster's. For some things it doesn't matter, but I use magnets pressed into aluminum to hold other parts in place while casting or injecting. I need to know the dimensions. Not have to guess.
        *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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        • #5
          For holding parts for machining I'm thinking that .157" over 10" is a rather steep taper. So it's not a typical mandrel to use for holding pulleys or other parallel hole items.

          Still .157 means an offset of only half of that or .078'ish. And over 10" length that's not all that much for a live center with an offset tail stock. As in roughly 0.45° offset which will double for a final roughly 0.9°. So all in all I'd just offset the tail stock.
          Chilliwack BC, Canada

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          • #6
            I got a 2" mill boring head and put a 3MT shank on it to fit the tailstock. Then got a 1/2" diam. hardened steel dowel pin and made a 3/4" diam. 01 tool steel point with a drilled and reamed to .501 slip fit hole for the dowel pin. A 1/4" steel bearing ball and some grease finished off the live center. The pin goes in the hole of the boring head, the grease and ball goes in the bottom of the hole. The drill point keeps the ball centered, and the grease lubricates everything.

            The graduations on the boring head are in the horizontal plane facing the operator. You can dial the offset you want in thousandths. For steep tapers, I use a tooling ball in a collet and replace the 01 point with one that has a ball instead of a point. Both balls are greased.
            Last edited by Toolguy; 01-08-2018, 12:14 PM.
            Kansas City area

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            • #7
              I have never liked turning tapers by off setting the tail stock center. A few years ago I needed to turn a chimney for a traction engine, not having a taper turning attachment I needed to come up with another trick. The inside also needed boring taper so I could not offset the tail stock center for that.
              I realized that I needed to feed the cross slide in or out at a ratio to the saddle moving up and down the bed of the lathe. I fitted a bobbin to the cross slide feed screw and made some outriggers that clamped to the front sheer of the bed, one at the head stock side and one at the tail stock side, attached to these was fitted a steal cable to the one side with one wrap around the bobbin and with a turn buckle on the other side. Now the cross slide would feed in or out as the saddle was moved up and down. The tool in feed was accomplished by the top slide.

              Worked like a charm.

              Werner

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              • #8
                "Both balls are greased." .... the late great Sir John had a good pic of the boring head method:



                I last used the method to make some polishing mop pigtails for an old motor.

                Paul

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                • #9
                  If you do offset the tailstock and use a live center I am pretty sure you should drill the end of the shaft with a "bell" center drill.

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