Dave Bell wrote:
>
> Nice!! So, you have two matching inclined surfaces, one on the pedestle,
>and one on the "carrier".
Actually no, there is only one surface (the big one in front) that *has* to be
inclined. I gave the rear one a similar tilt to catch the pivot point more
securely and prevent the upper table from sliding foward under gravity. But its
angle is not critical.
>
>If you were doing this for a telescope, I guess you'd put two Teflon
>pads on the carrier's surface. For this application, more friction is actually
>beneficial, so that's not necessary.
Good points.
>I've seen Poncet mounts that use a ball/socket for the pivot point. How
>are you suggesting the pivot be made? Maybe a rounded pin into a
>conical hole in a hardwood block? And it looks like the pin would lie in
>an equatorial plane, parallel to the polar end plane...
The pivot can be almost anything -- even a nail through the upper table. Its
angle is nothing special.
>Is there a height alignment requirement for the pivot point, relative to
>the inclined plane? Horizontally, it should be centered, but I have a
> feeling it needs to be placed at the right height on the meridian
>end, as well.
Nope -- the height is not important, nor does it have to be centered. But you
are right that the unit will be more stable this way. If the table tilts too
much, as can happen when star-tracking with a heavy camera or telescope on top,
things can get out of balance and there is a risk of the upper board toppling
off. But this problem shouldn't arise in a sundial with an equation-of-time
correction, and maybe not with a daylight-saving-time correction either.
>Great sketch - I have to get around to learning Sketchup!
I first heard of SketchUp about a year ago, on this list, and I've been having
a BLAST with it!
-- Roger
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