[Jewelry making - Article 00364] - Re: [Orchid] [Source] Opal cylinder

[John Donivan]

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Hi, Kevin

>     The Dremel could be advanced towards the work by using shims
>     between the tool and the tray). This way would probably be easier
>     to set up than a centreless grinding system and would produce a
>     true cylinder. 

    As Ian points out, turning it is the best and maybe only way, really.
    Centerless grinding is great, but it HAS to be a precision machine,
    and the wheels all have to be precision dressed, etc. That's why
    they're expensive. The problem you're going to have, I think is
    workholding. That's where centerless grinding would be great, but ---
    well, if you can build it economically, good for you. Or if you can
    farm it out...My question to you is, How precise does it really need
    to be? Doesn't it really just need to LOOK like a cylinder?
    Especially since material is at a premium, I'd probably use a core
    drill, which is obvious, and then dop it and spin it carefully in my
    fingers on a fine wheel - even get a piece of sandpaper and twist it
    round in your fingers. Workholding: any sort of lathe, dremel or
    flexshaft arrangement is going to need a tailstock to get any kind of
    precision, and since you can't use center drills and a steel center
    with opal, you'd have to somehow dop both ends on the same center,
    and mount it all, on and on, and then you'll still need a lathe with
    a fine wet grinder and sander. I like the idea of encasing it in
    plastic tubing, myself. We used to encase rocks in cement in a
    similar way for the big slab saws. Personally, I think you will spend
    $1000 to get $200 worth of opal that's more precision than necessary,
    and just spinning the dop in your fingers on a fine wheel very
    carefully would probably give perfectly satisfactory results. Or
    grind off the drill marks, hand sand it, and throw it in a tumbler.
    Now, if you needed 1000 pieces, that would be different. Then talk to
    the marble and granite workers - they have all that kind of equipment
    - rock lathes and such. The problem would be getting that
    comparatively tiny work done by them. 

http://www.donivanandmaggiora.com
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