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Disassembly Pictures for NexStar GT Altitude Axis

In chapter 12 of the NexStar User's Guide I describe how to disassemble, reassemble and adjust the NexStar GT mount.  I included as many pictures as was practical for a book, but thought additional pictures would be useful.  Note that the book describes more detail; these pictures are meant to supplement.

Caution! The very real possibility exists during the procedures described here that you may damage something. Also, disassembly may void your warranty and you should consider returning your telescope for warranty work rather than attempting adjustments on your own. After the warranty has expired you should consider the possibility that you will cause costly damage when working on your scope. While I consider the following procedures reasonably safe, not everyone should approach an expensive piece of equipment with a screwdriver in their hand.

Click any of the pictures below for a larger version.

In this view, the tube ring is opened showing the nut that holds the tube ring to the altitude axis.
After removing the nut and tube ring, I have laid out all the parts in order.  Note the red fiber disk.  The surface of this disk, as well as the area of the large gear that the disk mates to, must be free of grease.
When reassembling, first you will replace the large washer, then the lock washer and finally the large nut.

On some models, particularly those with a plastic tube ring, you may find that the large washer has been replaced by a large metal plate like the one shown to the left.  This plate distributes the force of the nut across more of the plastic surface.  The top photo clearly shows the plate while the bottom photo shows the plate in its correct location.

Photos courtesy Larry Stedman and Donna.

This view shows the large gear removed from the fork arm.  Note the large white nylon washer and 3 white nylon disks that provide the bearing surface between the gear and the fork.  The 3 disks must be replaced in the recesses in the fork arm prior to reassembly.
In this view, I have removed the outside cover of the fork arm - it is held in place by two recessed screws.  With the cover removed, you can see the nut securing the outside end of the altitude axis.
When reassembling the outside end of the altitude axis, first you will replace the plastic washer, then the flat washer, then the cone-shaped washer (large side down) and finally the nut.

To correctly adjust the tightness of the nuts, first tighten the nut inside the tube ring as much as you like.  This nut simply allows the optical tube to slip up and down at the point of the red disk, should you need to move the mount by hand (during storage).  In practice, we never move the mount by hand.  Next tighten the nut under the outside fork arm cover just to the point where the tube ring no longer rocks back and forth.  Too tight on the outside nut and the mount may not move freely, tracking will suffer and battery life will be shortened.  Apply power to the mount and ensure free movement for 360 degrees.  Adjust the outside nut again if necessary.

See The NexStar User's Guide for more details on adjustments, cleaning and lubrication of the axis.

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Michael Swanson
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