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  1. #1
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    Default Turning Double Ended Cones

    In Home Shop Machinist Volume 29, Number 2 (March/ April 2010) Page 28 there is Part 2 of an article about an "Anti-gravity Machine" Attached is a scan (jpeg) of the page. Essentially it is a "double" cone piece of steel on a double rail.

    I can understand how I would cut one end of the cone shape, but I am struggling with how to cut the second half - and make it exactly the same!

    If I had the previous edition ...... I am sure it would have been explained, but I don't!

    Any thoughts on a solution would be welcome.

    Regards,
    Alan.
    HSM V29 No.2 P28.jpg

  2. #2
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    Default

    My guess and I am no expert, it would be turned in one piece in the the center of a piece of stock and parted off each end

  3. #3
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    I'm not quite sure I'm understanding the question correctly, but anyway:

    It's not necessarily one piece - it may be two cones joined together by one means or another. Getting the two halves exactly the same then only requires you to make sure that you turn a straight OD to begin with that is the exact same diameter for both pieces. Then simply turn till you have your point, and part off right at the transition from taper to straight.

    If I had to make it in one piece however, I'd probably use a fixture. First, I'd set the compound to turn a taper that is smaller at the headstock end, and use something like a boring bar whilst running the machine in reverse to cut on the BACK side to create the taper on the tailstock side. Then swap to a regular turning tool, run the spindle forwards and cut the majority of the headstock side taper from the front side. For smaller light versions, you may be able to finish the second taper to a complete point by using a 'reverse centre' (I'm sure there's a name for that) in the tailstock to support the end of the workpiece, but bigger parts will likely fall off before you get a clean taper even with that approach.

    So for a bigger part, once the majority of the second taper is done, I would part off allowing enough length to finish up the point. Then take a piece of round stock considerably larger than the double cone, put it in the mill, and drill and tap 3 holes from the end, close to the OD. Then drill the first half of the holes to a clearance hole. Take this round stock, chuck it up in the lathe with the tapped end facing the headstock, and half of it hanging out, and bore it out using the same compound angle as before, to create a tapered bore that is smaller on the headstock side, and is not significantly larger at the major diameter than the major diameter of your double cone. Then part off the outer half, and flip it so that the parted face now faces the tailstock.

    Insert almost complete cone to tapered bore still in chuck, then slide over the parted off piece and secure it with 3 bolts through the tapped holes, and you now have the double cone clamped concentrically by it's midsection, and can take a cleanup pass to finish the tip with the same procedure you used for the first tapered end you turned.

    Clear as mud? There are of course going to be many other ways to do it, some probably far easier - that's kind of the beauty of this game, working out the setups... It's one of the reasons my projects go slowly - I ponder how to set something up for a couple of days while doing other things, think of a solution, then often think of a better solution a day or two later - until eventually I actually do it.

  4. #4
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    York, North Yorkshire UK
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    Default

    Hi Guys,

    I've seen double ended cones like this one turned out of a single piece of bar ! Admittedly it was on a CNC lathe.

    The first cone was turned and then the second cone machined until the piece just dropped off. The free end was supported in a rotating hollow cone. A bit like an overgrown live centre, while the second cone was being turned.

    Rinse and repeat.
    Best Regards:
    Baron J.

  5. #5
    Join Date
    Oct 2008
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    Cairns, Q
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    Is this my imagination? In the top photo which I enlarged the cones' joining faces appear to be at an angle to their axes, so in the lower side of the cones in the photo is close to a straight line. If this is so, machining the double cone n one set up would be an interesting exercise!

    Frank

  6. #6
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    Default

    Quote Originally Posted by BaronJ View Post
    Hi Guys,

    I've seen double ended cones like this one turned out of a single piece of bar ! Admittedly it was on a CNC lathe.

    The first cone was turned and then the second cone machined until the piece just dropped off. The free end was supported in a rotating hollow cone. A bit like an overgrown live centre, while the second cone was being turned.

    Rinse and repeat.
    No reason you couldn't do the same on a manual lathe using the compound with a female live centre. You could possibly even set up a steady rest of sorts with some V shaped plastic inserts to hold the part captive in the live centre so it doesn't get damaged from falling off.


    Quote Originally Posted by franco View Post
    Is this my imagination? In the top photo which I enlarged the cones' joining faces appear to be at an angle to their axes, so in the lower side of the cones in the photo is close to a straight line. If this is so, machining the double cone n one set up would be an interesting exercise!

    Frank
    Just an optical illusion, but it could be done on a CNC lathe with some fancy programming. Doing it manually would require a taper attachment plus a camshaft lathe or attachment...technically possible, but not my idea of fun.

  7. #7
    Join Date
    May 2010
    Location
    Perth
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    135

    Default

    Those foreverspin tops are made using a custom pot chuck.

    so to make the double cone, I would:
    1) - normal chuck for my rod material and turn up the pointed cone for one end
    2) - leave my compound untouched and chuck up some larger diameter bored stock and turn a tapered bore to match the conical section (would only need to overlap by 25mm or so, not the full length and point)
    3) - mark the #1 jaw position on the piece turned in #2 above
    4) - cut the rod stock with the conical point from #1 off at 3+ mm over length
    5) - put the stock in the pot chuck using some suitable loctite, superglue, etc
    6) - turn the other taper bringing the cones into each other at the OD
    7) - Heat to release the loctite/ superglue
    8) - clean/ Polish the conical thingy

    The foreverspin top makers have their pot chuck so it collapses a little to grip without glue, and it's shaped to mate to one profile of the top, PLUS the first 20% of the second profile so the chuck is gripping the largest diameter. They are running a production environment and using CNC/Profile tools to ensure a repeated profile to match the pot chuck.

    HTH,
    Des



    Quote Originally Posted by A J in WA View Post
    In Home Shop Machinist Volume 29, Number 2 (March/ April 2010) Page 28 there is Part 2 of an article about an "Anti-gravity Machine" Attached is a scan (jpeg) of the page. Essentially it is a "double" cone piece of steel on a double rail.

    I can understand how I would cut one end of the cone shape, but I am struggling with how to cut the second half - and make it exactly the same!

    If I had the previous edition ...... I am sure it would have been explained, but I don't!

    Any thoughts on a solution would be welcome.

    Regards,
    Alan.
    HSM V29 No.2 P28.jpg

  8. #8
    Join Date
    Aug 2008
    Location
    Melbourne
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    34
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    Default

    Quote Originally Posted by desbromilow View Post
    The foreverspin top makers have their pot chuck so it collapses a little to grip without glue, and it's shaped to mate to one profile of the top, PLUS the first 20% of the second profile so the chuck is gripping the largest diameter. They are running a production environment and using CNC/Profile tools to ensure a repeated profile to match the pot chuck.

    HTH,
    Des
    Sounds like a Diecraft chuck. We've got 4 at work (one per lathe and one for the mill) and they're awesome; full surface contact so you can hold delicate/thin-walled parts with even pressure.

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