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machining iso 40 tapers.

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  • machining iso 40 tapers.

    I would like to make a iso 40 to drill arbor. I dont know what the common 13mm chuck taper would be.Maybe b16 ?Anyway there was a practical machinest thread about the mistakes made in calculating the taper. I dont understand the maths when it comes to minutes and seconds.So is there a different way or correct way to do this operation.?

    It is an akward workpiece to hold so I am wondering what the steps would be. Work between centers but dial in an existing arbor.
    I wonder how close ,close is?What percentage out would still be good enough. Would I need to blue the spindle up to see and if I remove it from between centers does it go back a hundred percent true.I have done very little between center work.

  • #2
    My lathe tailstock takes a proprietary (Rivett) taper, which surviving documentation only states should be "to gauge"... and the gauge was thrown into a landfill 50 years ago along with everything else from the factory. I've made a couple of my own tapers to fit it, and I did just as you mentioned, I mounted an existing factory-made taper between centers and set the compound to match it using a test indicator (I don't have a set-over tailstock or a taper attachment, but the compound fortunately has a lot of travel). It worked really well, I began checking the fit by bluing, while I still had plenty of meat left to turn away, that gave me a chance to make very minor tweaks along the way. The fit ended up being really good.

    If you're using a dead center rather than a live center, make sure you're using some good lubrication. I used to use moly grease before discovering Cimcool "center saver" grease, now that's all I use.


    • #3
      I'd blue or felt pen the taper then lightly place the chuck onto it and twist to rub away at the contact zones. That'll rapidly tell you if the taper is the right one or not and the quality of it.

      After that run the arbor between centers and check for runout and finally zero the angle of your compound or tail stock offset. For a short taper such as used for a drill chuck I'd aim for no more than a half a needle's width of total runout.

      Machining the taper is just the start anyway. You want it close but after that you're going to need/want to lightly file and then dress the surface with control and testing with the blue or felt marker and try it in the chuck's taper until it fits as well or better than the original arbor you use as the setup reference.

      I'd suggest that the same would hold true if you opt to send it out for center grinding.
      Chilliwack BC, Canada