Question:

	How do I make the Sudiball base?

Answer:


First, what may NOT work is a thin walled 'rim' such as the top of a can or bucket or bowl.
 
They are tempting because, vertically, they may be more than strong enough.
However a Sudiball's weight will also exert a horizontal force which may distort
the thin walled rim from round to the point it interferes with smooth motion. 

What has worked;  

Symmetrically rigid rings with bearing surfaces tangent to the point of contact.

Where "rigid" is not limited to just the telescope's static weight,
but considers the dynamic forces of the top of scope as a lever-arm 
with the base ring the fulcrum point. 


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Question: 

	How big should the hole in the base ring be?
 
Answer:

Smaller than the sudiball but larger than the spaces between the edges on the Sudiball.

Smaller rings allow greater access to the sky near the horizon and are more able to tip.
Larger rings can limit access to the horizon and are less able to tip.


For a standard Sudiball, 
three planes tilted @45-degrees intersecting at center (octahedron based)
the largest spaces between the edges are equilateral triangles with the 
length of each side being the square root of the Sudiball diameter,
and half that for radius. (0.707106781)

The "height", center of base to top point of an equilateral triangle is:
half the square root of three (0.866025404)
times the length of a side

0.866025404 * 0.707106781 =  0.612372436

So a  (0.612372436 * Sudiball) inside diameter ring contact   
is guaranteed to be too small a diameter as the base ring bearing surface 
will fit within the edges of the Sudiball.

I have been using  (0.7071 * Sudiball) and rounding to whatever is convenient 
this is approximately 15% larger than absolute minimal possible,
which allows me to use readily available 45-degree router bits 
to chamfer the inside of plywood rings to form the bearing surface (substrate). 
and at some rotations about the optical axis, allows viewing below the horizon.  

I have been using the Sudiball diameter as the outside dimension of the base ring
because it has been radially strong enough, is stable, and looks okay.

A note on the Cloverball styles: 

With a four vane style, at the equator the two points of edge contacts are:
  0.707 * Cloverball-diameter apart.

With a three vane style, at the equator the two points of edge contacts are:
  2*sin(120/2)  which is  (0.866 * Cloverball-diameter) apart.

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Question:

	What should I do for bearing surfaces

Answer: 

That is a good question... (or similar platitude when answer is unknown)
 
For some limited applications (look at the moon with low power) 
unfinished plywood has worked but it is stiff and grabby.
Waxing the bearing surface does wonders but need to be reapplied.


Plastics cut as arcs to wrap into a cone. 

Thin HDPE works great as a bearing surface because nothing sticks to it; 
which leaves the problem of how to fasten it since we cant glue it down.
Pro tip, don't try to form it with heat, it just shrivels up.

ABS is suppose to thermoform well 
but my one attempt with a heat gun is unusable but ugly.
Perhaps a pizza oven that heated it all at once would work better...

Formica/laminate is on my list to try but I am reluctant as it is 
tricky and unforgiving to apply on curved slanted surfaces and difficult to remove.
Beginning opposite the two ends and working symmetrically around
is what I will try. (watch this space)

You may note I am a bit out of my depths with plastics.

Other things I may try include 
  - epoxy or varnish or other paint-on liquid that hardens. 
  - metal sheet, which of course will work, so it is saved for last.

	More research is needed!