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Disassembly Pictures for NexStar GT Azimuth 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 of the bottom of the GT base, we can see the bar that holds the base to the tripod and the nut securing the bottom of the azimuth axis.
After removing the bar and the nut, 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 the base, first you will replace the large washer, then the lock washer and finally the large nut.
This view shows the large gear removed from the top half of the base.  Note the large white nylon washer that provides the bearing surface between the gear and the top of the base.  Also note the 3 white nylon disks that provide the bearing surface between the top and bottom of the base.  They must be replaced in the recesses on the top of the base prior to reassembly.
This view of the top of the base shows the nut securing the top of the azimuth axis.  The top cover of the base is removed by prying up gently at the two openings just above the orange ring (not shown here).
When reassembling the top of the base, 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 bottom nut as much as you like.  This nut simply allows the mount to slip 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 top nut just to the point where the fork arm no longer rocks back and forth.  Too tight on the top 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 top 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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