[Jewelry making - Article 00036] - Re: [Orchid] Setting - cone shaped hole

[Jack Schmidling]

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>            In order to bead-set a stone however, you need a
>     cone-shaped seat to drop it below the surface of the metal..... 

    I suppose I should gracefully give this one up.  I feel like I am
    telling a Robin how to build a next but let me try one more time. 

    Draw a 90 deg angle on a piece of paper. 

    Next do the same for a 93 deg angle.  This is the included angle for
    a brilliant with a 43 deg culet angle. 

    Now cut this out of the paper and place it into the 90 you drew. 
    You will find that it will only contact the "seat" at two points.  In
    the case a cut stone, it will contact at 16 points. This is true of
    any pair of angles that are not exactly the same as long as you allow
    a hole for the culet to clear. 

    When I hear the word seat, I think of the way valves seat in an
    engine head. They are lapped in to produce identical angles on each
    part. 

    If all of the above simple geometry is true, then there is no
    difference between a drilled straight hole and a "seat" formed by a
    conical bur.  In both cases the stone rests on a circle of points not
    a form fitting seat. 

    I am sure there are good reasons to use a bur but a better seat is
    not one of them. 

    As a point of interest, I received a bunch of burs today from Rio
    and seem to have missed something about using them. 

    I didn't have a collet for my hand piece Dremel so I but it in my
    B&D cordless drill and it seemed to work pretty well.  Made a nice
    neat hole the size of the bur which happened to be the size of the
    stone (8mm) I was playing with.  Couldn't do much else with the bulky
    tool but this much worked. 

    My collets arrived in the mail a little later and I found the Dremel
    totally useless for this tool.  I have a speed control on it but it
    is still too fast and just chatters and screams.  The drill runs
    about 200 RPM so I gather most commercial flex tools can be run very
    slow for this operation. Is this correct?  The ones I see in the
    catalogs don't say anything about speed other than variable. 

js

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