Re: Hub for a stick dome



> My current concern is that there would not be enough rigidity, or 
> locking of
> each ball in place during erection and dismantling to make it 
> viable.  It

I've just had an inspiration about how to make the ball end lock into
the hub socket, without the need for a cover plate.  Let me see if I
can draw it.  If I can (my drafting abilities are rather poor) I'll send
a scan of it to Pat.

If not, it involves a design similar to that used to hang a ceiling fan.
The hub socket covers not 180 degrees, but closer to 270.  This
would provide the stability necessary for assembly, and then allow
a "cover plate" to lock everything into place.  Pat's design uses 2
basically identical halves which cover only 180 degrees each, and
which do not provide a locking mechanism individually.

> be pushed into place in the hubs, immediately loosening the whole 
> thing
> again, with the danger of some of the first balls falling out of 
> place.  And
> so on.

The forces involved usually cause the strut ends to pop out -- that
means that they're primarily tensional.  My 270 degree socket would 
address that problem, with nearly no increase in complexity.  In 
essence you would only need to take the full top and bottom of Pat's
hub...glue them together, and saw it apart at the 1/3 point, rather than 
the 1/2 point where it is now.

An alternate design would have strut ends sticking *out* of the hub,
able to pivot freely.  The actual struts could connect to these ends,
perhaps with coarse screw threads, and the entire assembly could
be locked into place with the central set screw.

> this, if it's going to be manufactured and put out for public use, 
> must be
> safe.  I'm not convinced it is.  I shall probably generate a 
> prototype to
> check it out as it is a very neat and pretty design in principle.

HOORAY!  Renderings are one thing...samples and prototypes are
the next logical step.  Thank you!

> Can Pat or anyone else shed any light on whether there is a way of
> determining whether the hub will bear the pressures of assembly and
> disassembly without risk of the balls falling out?

I'm sure there is, though it might be easier with simple prototypes
as a proof of concept.  They don't have to be finely milled, etc...they
just need to prove the concept sufficiently.

     -- Chuck Knight
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