Re: 1200GTO servicing project notes


thanks Dale - great info

On Mon, Apr 12, 2021 at 8:58 AM Dale Ghent <daleg@...> wrote:
I recently took over as Observatory Director for my club's observatory and outreach center. With COVID putting a halt on the in-person outreach events that we have done on a monthly basis (and hope to return to once conditions allow), I figured now was the time to do heavy maintainence on the mount, scope, and dome.

The observatory's 1200GTO is a fairly early example and, from what we've been able to determine, has not been heavily serviced during its lifetime which is approaching 20 years old. Yep! It probably still had the original grease! Nonetheless, it has been operating fine for the most part, but it has developed some notable backlash in both axes and could use some attention so it can soldier on into the future with better performance.

The servicing tasks to be done:

1. Dismantle the mount and clean its external surfaces
2. Clean and regrease the RA and dec worm, worm wheel, and motor spur gears
3. Replace RA and Dec clutch delrin plugs
4. Polish out rust spots on CW shaft and weights and give them a nice shine (ooh pretty)
5. General inspection of mount

In addition to servicing the mount, I also wanted to install some upgrades into it for improved operation. It already had a CP4, so that only needed a firmware update. The following upgrades were chosen:

1. 1200 R.A. Motor Bracket with Spring-Loaded Action (12SLBR), Qty. 1
2. Replacement for 900/1200 Dovetail Knob (DOVEKREP), Qty. 2
3. Modified R.A. Clutch Set Screw for 1200 Mount, all models (M12668), Qty. 4

(1) was chosen to replace the original RA motor mounting bracket design with a newer version that addresses backlash better. The new bracket keeps the RA worm meshed better with the worm wheel. From what I undertand this improved bracket was standard on later 1200GTO serial numbers. It would appear that I snagged the last of this bracket at A-P, as it is now listed as out of stock and discontinued.

(2) and (3) were chosen to replace the four RA clutch knobs and two Declination axis dovetail knobs, respectively, with set screws. The 1200GTO's design predates the through-mount cabling feature found on current mount models, so any wiring coming off the scope and down the side of the mount can run the risk of snagging on one of these knobs. I've witnessed this briefly happen with ours, with the power and USB coming off the telescope getting picked up and carried briefly by one of these knobs, but the cable would free itself each time. I don't have to watch for this situation with my finger hovering over the STOP! button with these set screw replacements as the dec axis now lacks such protrusions.

Breakdown of the mount went fine save for unscrewing 1 of 5 screws that fastened the RA motor to the RA motor bracket. Despite all efforts and even a few tries with a #1 and then #2 screw extractor, the screw just would not turn. I decided that the folks at Astro-Pysics would be the best people to deal with this, so I detached the bracket from the mount body and sent the bracket+motor combination to them. Dave and their machinist went to work on it and eventually freed the screw. Upon its return, the RA motor was cleaned, greased up, and mounted on the upgraded bracket with no further issues.

Cleaning the gearing and regreasing using the Astro-Physics grease kit was easy and familiar to me, having done the same with my own Mach1 prior to this. I use flat toothpicks to gently press paper towel into the worm wheel and gear teeth which allows me gently scrape out the gummy black old grease. Cleaning the external surface of the mount was done with microfiber cloths, first with a diluted solution of citrus degreaser to get areas caked-on oil/dirt off of, then a final wipe-down with isopropyl alcohol. A little bit of elbow work got dirt and grime out of the setting circle engravings, returning the numbering and marks to their original white. We don't use them, but it makes the mount look nicer.

Replacing the delrin clutch plugs was a quick and easy. My method for extracting the old ones was to remove the clutch knob and gently tap a #1 screw extractor into the center hole of the old delrin plug, attach a tap wrench, and unscrew it out. The new delrin plugs dropped right back in to the hole.

When all the service and upgrade items were done, the mount was reassembled and the (also cleaned) TOA-150B went back on top of it. The smooth action of the unclutched axes during balancing was great, a clear difference from the sticky balky motion caused by the old delrin clutch plugs that would not fully disengage. With everything balanced and locked in, it was really nice to be greeted with a soft hum of the motors with no backlash. I now await a clear night to re-do the polar alignment using SharpCap Pro. Eventually, I want to get the club to spring for APPC Pro so we can run this with pointing and tracking models.

Throughout this project, I talked quite a bit with George, Dave, and Daleen at Astro-Physics. I can't stress how awesome they are to work with, not just on a person-to-person basis but certainly with Astro-Physics as a company. It's a rare level of service in this hobby/industry these days where things can seem kind of impersonal and faceless, and I shudder to think about what I would have to go through to get a similar level of attention with vendors of cheaper mounts, or if it would even be possible in that reality. I really want to thank them and it's why I've never hesitated in recommening their products.

I have a chronologically-ordered gallery of images from this maintenance. There's a lot of photos, so you may need to click the "Load 22 more images" button once you scroll to the bottom:



Brian Valente

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