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Old 01-02-2009, 09:09 PM
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erick (Eric)
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Join Date: Dec 2006
Location: Shoalhaven Heads
Posts: 8,481
I have the scope in this article:-

http://www.iceinspace.com.au/63-401-0-0-1-0.html

Look for the part:-

"Next problem: when I depressed the telescope tube from zenith to horizon, the tube shifts 8 mm to one side. I presume the altitude bearing is not perfectly circular. In any event, the end result is that my encoder assembly – attached as it is to the altitude bearing – also moves 8 mm to the side. The photo above illustrates this shift. My solution was, again, to avoid screwing the encoder arm to the rocker box. This is actually the recommended technique for many telescopes, including the Obsession: don’t completely tighten either encoder arm, to account for such minor wiggling, although the 8mm shift noted here was more than most premium scopes would manifest. On the Obsession Yahoo group, I’d heard about not even screwing the altitude encoder arm down at all, but rather letting gravity hold it motionless. This worked great in my case. As the photo displays, a small hook (same as that used to “fence in” the az arm) catches the notch in the alt encoder arm; gravity holds it in one place. As the tube shifts left-to-right, the “floating” encoder arm moves with it (along the hook’s shaft) but not in such a way as to register rotary motion.
You’ll note the small hair-bungee tied to the encoder. I thought this might be needed, but in fact, I don’t use it anymore. It just sits there without anything – other than gravity –holding it against screw-in hook other. I was just too lazy to take a new picture."

The photo shows the encoder arm tied to the pin, but as Scott says and I have found, gravity holds the Alt encoder arm nicely in place. I just drop it in place on the pin when I screw in the encoder each time I set up, and it can slide in and out as much as it wishes without affecting performance to the level I need. I have done some work to reduce that sideways movement, but still do not restrict the arm moving in the direction of the axis of the encoder. Obviously the pin should be as close as possible to being parallel to the encoder axis. If it sloped up or down, that would be a problem. Drill the hole straight, tighten the pin up and eyeball it for being "true" was all that was done in this case.
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