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c8 repair – dec fine adjustment June 3, 2009

Posted by aquillam in Astronomy, telescope maintanance.
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This post is one in a series about C8 repair and maintenance.  You should see the introduction and disclaimers before trying anything here.

When mounted on an equatorial wedge, the telescope rotates in right ascension (RA) and declination (dec). The telescope needs to move freely to align it, but once aligned, you don’t want it to move too easily, so there are locks in both directions.  There are also fine motion controls for both directions. Below are instructions for adjusting the dec fine motion control.  You might also want to check out the instructions for opening the base, dec lock, and the RA lock position.

The dec fine adjustment knob is connected to a threaded rod, which moves another rod that is connected to the dec gear at the top of the arm.

The dec fine adjustment knob is connected to a threaded rod, which moves another rod that is connected to the dec gear at the top of the arm.

The fine adjustment knob is on the base, at the bottom of the left hand arm. Turning the knob moves a small arm along a threaded rod.  The small arm connects to the dec gear at the top of the support arm.

General maintenance: clean and oil the threaded rod periodically.  Some lubricants will also work as cleaners (think WD-40, although I recommend something more like a silicone spray, which remains slippery in freezing temperatures.)

The dec fine adjustment rod is too far to the left - the telescope will not move in that direction any more.

The dec fine adjustment rod is too far to the left - the telescope will not move in that direction any more.

If you turn the knob in one direction and the telescope doesn’t move, chances are the rod is all the way to one side. Turning the knob in the other direction should move the rod back toward the center.

Turn the fine adjustment knob to move the rod back toward the center

Turn the fine adjustment knob to move the rod back toward the center

If the knob doesn’t turn the threaded rod, you may have to tighten the set screws in the base of the knob using a small allen wrench.

If the threaded rod turns but the small arm doesn’t move, you may have to take the threaded rod apart. It is held in place by a collar on the left side with a set screw that connects it to the knob, and a pin on the other end held in place by a nut. A really determined observer (especilly students without sfficient supervision) can get the arm to slip onto the pin or bind with the collar. Turn the rod so the set screw is visible,  and remove the knob. Also, loosen the nut on the other end. That should give you enough slack in the rod to get it out if you need to, or to get the small arm back onto it.

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