Replacement of NexStar 5i/8i Altitude Bearings

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Chad Lamb
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Replacement of NexStar 5i/8i Altitude Bearings March 22, 2011

the altitude bearings are affixed, it became obvious that the

Figure 1 below shows the altitude gear housing and the arrangement of

Figure 1 Altitude Gear Train Load Bearing Removal of the Allen screws

1 Replacement of NexStar 5i/8i Altitude Bearings March 22, 2011 Introduction My (used) NexStar 5i/8i mount began to exhibit excessive altitude backlash. After disassembling and removing the altitude motor/encoder to which the altitude bearings are affixed, it became obvious that the altitude load bearing had failed. Figure 1 below shows the altitude gear housing and the arrangement of the gear train. Figure 1 Altitude Gear Train Load Bearing Removal of the Allen screws securing the adjustment ring and drive gear to the jack shaft permitted removal of the main load bearing. As you can see from Figure 2 below, the bearing had failed and disintegrated. Good bearing Figure 2 Altitude Bearings

Remove the adjacent adjustment ring in a similar manner. 4. Using caution, remove the small retaining ring at the rear of the gear housing (see Figure 3). Figure 3 Shaft Retainer Ring 5.

2 Bearing Removal Steps Replacement of the front and rear altitude bearings is fairly straightforward. I suggest the following process. 1. Remove the Allen set screw from the altitude drive gear and the adjacent adjustment ring. 2. Carefully slide the altitude drive gear off the jack shaft. 3. Remove the adjacent adjustment ring in a similar manner. 4. Using caution, remove the small retaining ring at the rear of the gear housing (see Figure 3). Figure 3 Shaft Retainer Ring 5. Carefully slide the jack shaft back and forth to permit removal of the bearings. This may require carefully tapping the bearings to remove them from the bracket housing. 6. I recommend leaving the angle gear attached to the jack shaft since it does not necessarily require removal to replace the bearings.

3 Bearing Installation 1. Carefully slide the replacement bearings over the jack shaft and seat them in their housings with the bearing retaining flanges pressed against the outside of the gear housing bracket (front and rear). If it is necessary to apply pressure to slide the bearings along the jack shaft, you may either use liquid nitrogen to cool the shaft or use a short piece of ½ wooden dowel with a ¼ long hole drilled in one end lengthwise. Carefully tap the other end of the wooden dowel to move the bearing into position against the gear housing. 2. Once the bearings have been seated against the gear housing, reconnect the rear bearing retaining ring. 3. Slide the adjustment ring onto the jack shaft until it just touches the drive gear bearing. The adjustment ring should be tightened to permit a small amount of horizontal play in the jack shaft. Tighten the adjustment ring Allen set screw. 4. Slide the altitude drive gear on the jack shaft and tighten the Allen set screw. The reassembled gear train should resemble the photograph in Figure 1. Reassemble Mount and Test Reassemble the mount hardware in the reverse order in which it was disassembled. The photographs below are provided as an aid in this effort. Reattach Altitude Motor Bracket to Mount

4 Check for Proper Altitude Gear Mesh Reconnect Altitude Motor/Encoder Cable Assembly to Motor Control Board

Test Proper Mount Operation At this point it is suggested you connect the hand controller, apply mount power and

It may be necessary to loosen the Allen set screw on the angle gear on the jack shaft and gently nudge the gear

Retighten the angle gear Allen set screw after this adjustment has been completed.

5 Test Proper Mount Operation At this point it is suggested you connect the hand controller, apply mount power and test proper mount operation. Pay particular attention to altitude backlash. It may be necessary to loosen the Allen set screw on the angle gear on the jack shaft and gently nudge the gear to just make contact with the mating motor gear to ensure minimum backlash. Retighten the angle gear Allen set screw after this adjustment has been completed. Note: As shown in the photograph above, you may connect the NexStar hand controller to the base AUX jack since this connection is paralleled with the hand controller RJ12 jack inside the mount rear housing cutout.

6 Complete Mount Reassembly Reattach Altitude Gear Backplate Cover Reattach covers and mount OTA

Complete Reassembly and Test with OTA Mounted Carefully

complete backlash adjustments as necessary.

Follow the backlash software adjustment procedure in

7 Complete Reassembly and Test with OTA Mounted Carefully test the altitude and azimuth motor controls and complete backlash adjustments as necessary. Note the mount firmware includes a backlash entry. Follow the backlash software adjustment procedure in the manual. Clear skies Michael Wheeler Haverhill, Massachusetts w1vi@comcast.net

8 Appendix Boca Bearing Replacement Altitude Bearing Specifications

9 Front drive shaft bearing Rear drive shaft bearing Close Up View of Altitude Bearings

How to replace or adjust the altitude clutch of the NexStar N11GPS

Langenbrettach/Germany, February 10 th 2004 Matthias Bopp How to replace or adjust the altitude clutch of the NexStar N11GPS Table of content How to replace or adjust the altitude clutch of the NexStar