I recently bought a used Celestron CG-5 mount and decided that after verifying basic operation, the next thing to do was to take it apart and do some basic maintenance.
It’s well known that the Celestron mounts made overseas need some rework to get full performance out of them. They frequently contain “lube” that is more like glue, the gears need polishing to remove burrs and many of the plastic rings look they’ve been cut from milk bottles.
I’d done the same maintenance job on my Super Polaris mount which is almost identical to the CG-5 except that the CG-5 has brass gears and ball bearings rather than just sliding plastic rings.
Armed with information from Astroboy I set about disassembling my CG-5. Full pictures of the dis and re-assembly are in the gallery, selected pictures will be included here. I also won’t cover every single step since it’s already been covered by Astroboy.
The first thing to do was to take a series of pictures of the unit so I could make sure everything went back where it came from.
Once I’d removed the various covers and motors I started work on the RA axis. Removing the gear shaft housing showed a little wear. A bit more than I would have expected but perhaps not unusual given that it’s brass moving against aluminum.
To remove the RA shaft from the housing I had to fashion a special tool so I could unscrew the retaining screw.
I’ve got various bit of aluminum from my Holography endeavors and drilled out two holes using my drill press and hammered through a couple of nails.
After removing the set screws (there were three on my mount vs the two mentioned in the Astroboy article) I was able to wiggle the main screw a little but couldn’t unscrew it. I kept looking for a set screw I’d missed and finally just forced it unscrewed. Turns out that it was bound up on the shaft and after forcing it a turn, it unscrewed the rest of the way very smoothly.
After removing the screw I made a pleasant discovery. Rather than the plastic washers that are on my SP mount, this mount has bearings.
The grease used wasn’t all black and goopy but wasn’t as buttery as the marine grease I was planning on using so I forged ahead. Keeping track of where things came from.
And carefully removing washers for cleaning an polishing.
I used 1000grit sandpaper for removing the burrs from the washers as well as from the worm gears. I found that I could feel rough spots on both as I moved my fingers across them.
One disturbing discovery I made was a spot of rust on a bearing and shaft housing.
I gently buffed those spots off and made sure there was an even coating of grease all around when putting them back together.
Another discovery I made was that there was almost no grease on the Dec worm or shaft.
That got taken care of too.
On one part of the Dec axis I did finally find some of that Chinese glue everyone hears about.
I think I could have hung a picture on the wall with that stuff and it definitely took some work to get it all off.
After completing the cleaning and re-greasing of the Dec axis it was just a matter of reversing the dis-assembly and I now have a mount that moves easily and smoothly on both axes.
Now if the clouds would just go away.
More pictures of the process are in the gallery.