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Patrick,

I would glue nuts or similar metal objects with female threads into
holes in your polypropylene board.  Those would not develop loose
threads.

In thinking about a transit, with four screws, first, those don't
rock, as they're bolted to the tripod.  Second the four screws would
let one rotate 90 degrees to level and also flip the telescope.
That's not needed with an artificial horizon.

Fred

On Mar 25, 2011, at 6:10 PM, Patrick Goold wrote:

> A break in the weather allowed me to take a series of sun sights
> with my mirror assembly sitting side by side with my Davis
> artificial horizon.
>
> It took me 15 minutes to level the mirror assembly.  Fred and Bill
> are definitely right that a three-leg arrangement would be
> superior.   With four I repeatedly leveled the base only to find
> that it would rock on two of the legs.  Secondly, there was
> evidence that the polypropylene board was not rigid enough and that
> the bolts were loose in their threads.  Both effects were part of
> the cause of the difficulty of leveling the assemble.   I will be
> rebuilding this with three legs, a thicker base, and levelers more
> carefully machined than bolts from the local hardware store.
>
> Still, against the odds I did manage to get a decent series of
> sights.  Obviously, I could not simultaneously shoot off the mirror
> assembly and off the Davis AH.   I went back and forth between them
> and then plotted the readings against time to see if the lines
> overlapped.  The result (attached), I think, is promising.  The
> approach is feasible but the assembly I have needs to be thoroughly
> reworked to facilitate reliably stable leveling.
>
> Patrick
>
>
> 

   

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