question-of-the-day answered
Rich Littleton
be718 at scn.org
Sat Oct 9 20:15:23 PDT 1999
A most impressive answer. While I think the "plumbob" method is the
easiest, I'm facinated by the other solutions.
Thanks, Kurt
Rich
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On Wed, 6 Oct 1999, Kurt Cockrum wrote:
> Rich said:
> >Solution needed.
> >
> >If I have a styrofoam ball one foot in diameter, how can I find the
> >precise location of the opposing poles?
>
> Suspend the ball from a thread attached to the eye of a needle driven
> into the sphere, and lower it until it touches the ground, plumbob style.
> It will touch at a point more or less antipodal to the point of suspension.
>
> Another thing to try is to make 2 tangent cones that match at their perpendicular
> bases. The sphere will be securely contained within the two joined cones.
> Then a line going from the apex of one cone to the other apex will pierce
> a diameter of the sphere. Try a hot coat-hanger. A CO2 laser bore-sighted
> along the apices would make the work easy. This could also be the basis for
> a drill-press fixture that would hold the sphere for drilling. Rather than the
> cones, an open-air design using tripods that bolt together, caging the sphere,
> might be a workable design.
>
> Lastly, try a tangent equilateral tetrahedron, with the bottom side missing.
> Put it over the sphere. A line from the top vertex to where the sphere touches
> the ground will pass thru the center of the sphere.
> --kurt
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